Just Published: Microchemical Journal

A new issue of this journal has just been published. To see abstracts of the papers it contains (with links through to the full papers) click here:

Microchemical Journal
http://rss.sciencedirect.com/publication/science/6599

Selected papers from the latest issue:

Determination and speciation of mercury in environmental and biological samples by analytical atomic spectrometry

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Ying Gao, Zeming Shi, Zhou Long, Peng Wu, Chengbin Zheng, Xiandeng Hou
Mercury and its compounds are ubiquitous in the environment. Much concern has been attracted to the determination of mercury and its species due to their high toxicity and biomagnification. The state of the arts of mercury determination and speciation analysis and its applications in environmental and biological sciences since 2008 are reviewed with 133 references. The methodological innovations in sample preparation, preconcentration, instrumentation and speciation analysis are summarized, and the future perspectives are briefly discussed and speculated.

Use of passive biomonitoring to evaluate the environmental impact of emissions from cement industries in Sergipe State, northeast Brazil

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Angélica B. Ferreira, José O. Santos, Sidnei O. Souza, Wilson N.S. Júnior, José do Patrocínio H. Alves
Measurements of trace elements in tree bark were used to investigate pollution caused by emissions from two cement production plants in the vicinity of the cities of Laranjeiras and Nossa Senhora do Socorro (Sergipe State, northeast Brazil). Samples of tree bark were collected across a wide area within the municipalities of Machado, Estivas, and Estivas II, as well as close to the two cement plants. Analyses were carried out by EDXRF to determine the concentrations of Al, Ca, Cu, Fe, K, Mg, S, Sr, and Zn in the tree barks. The resulting data were used to generate distribution maps of element concentrations, which enabled identification of pollution hotspots. The results indicated that emissions from the cement industry affect the region as a whole, as demonstrated by accumulation of trace elements in the tree barks.

Development of carboxylic acid search prefilters for spectral library matching

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Barry K. Lavine, Kadambari Nuguru, Nikhil Mirjankar, Jerome Workman
435 infrared (IR) absorbance spectra of 140 carboxylic acids and 295 noncarboxylic acids which included aldehydes, ketones, esters, amides as well as compounds containing both carbonyls and alcohols were preprocessed using the wavelet packet tree to enhance subtle but important features in the data. Wavelet coefficients that optimized the separation of the spectra by functional group in a plot of the two largest principal components of the data were identified using a genetic algorithm (GA) for pattern recognition analysis. Because principal components maximize variance, the bulk of the information encoded by the wavelet coefficients selected by the pattern recognition GA is characteristic of the carboxylic acid functional group. The carboxylic acid search prefilter developed as part of this study was successfully validated using two external validation sets. The first validation set consisted of 24 carboxylic acids and 61 noncarboxylic acids and the second validation set consisted of 264 carboxylic acids and 72 noncarboxylic acids.

Prediction of mold contamination from microbial volatile organic compound profiles using solid phase microextraction and gas chromatography/mass spectrometry

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Barry K. Lavine, Nikhil Mirjankar, Ryan LeBouf, Alan Rossner
An integrated chemical and microbiological approach was used to develop a new sampling and analytical methodology to characterize the fungal load of a contaminated area or building. A set of microbial volatile organic compound (MVOC) profiles were developed with corresponding bioaerosol measurements as input–output pairs for a discriminant to predict the presence or absence of mold contamination in indoor environments. Spore collection to characterize the indoor air quality of the residences and buildings was performed using an Anderson N6 impactor. Simultaneously, solid phase microextraction was used as a passive sampling device to collect VOCs from the air for GC/MS analysis. The volatile organic signatures that molds emit as reflected by the gas chromatographic profiles were compared to the impactor data collected from each sampling site. By comparing the bioaerosol data to the volatile organic profiles, a discriminant could be trained to classify a residence with potential mold growth based on its MVOCs.

Use of solid phase microextraction (SPME) in the analysis of the reduced sulfur compounds (RSC) and its experimental limitations

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Ehsanul Kabir, Ki-Hyun Kim
In this study, techniques based on solid-phase microextraction (SPME) with gas chromatography (GC)–pulsed flame photometric detection (PFPD) were evaluated for its application toward a list of reduced sulfur compounds (RSCs) such as hydrogen sulfide (H2S), methanethiol (CH3SH), dimethyl sulfide (DMS), carbon disulfide (CS2), and dimethyl disulfide (DMDS). Its performance was tested against direct injection (DI) and thermal desorber (TD) approaches. Although the SPME-based calibration of RSCs showed good linearity (r² >0.9) like other methods, it was more prone to analytical bias for the lighter molecular weight (MW) RSCs (especially H2S) due to distinctively reduced sensitivity relative to the heavier MW compounds. As such, the detections limits (DL) of SPME vary by more than an order of magnitude for the lighter and heavier MW RSCs (DL=16.9ng for H2S and 1.46ng for DMS). Evidence collected from an extended reproducibility test further supports that the experimental reliability of SPME approach is fairly low, especially with respect to H2S. The quality of SPME-based analysis thus needs more cautious validation in the study of odor and air pollution, as the lighter RSCs like H2S (or CH3SH) are often identified as the key components under various settings.

Analysis of vanilla extract by reversed phase liquid chromatography using water rich mobile phases

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Barry K. Lavine, Desire T. Corona, Undugodage Don Nuwan Tharanga Perera
Vanillin is the major constituent of vanilla extract, a flavoring ingredient used in food and beverages. Natural vanilla extract prepared from the bean of the tropical orchid, Vanilla planifolia, is expensive due to the limited supply of the vanilla bean. For this reason, synthetic vanilla extracts are widely used. Synthetic vanilla extracts are less complex and usually contain vanillin, ethyl vanillin, and other related compounds that are prepared from inexpensive starting materials. Several liquid chromatographic methods have been developed to quantitate coumarin, vanillin, and ethyl vanillin in vanilla extract. The use of water rich mobile phases in reversed phase liquid chromatography (RPLC), e.g., 1% butanol in water with 0.2% acetic acid with C18, C8, and cyanopropyl columns, has been investigated as a potential method to characterize the composition of synthetic vanilla extracts. Better resolution is achieved in the separation of vanillin compounds when hydrophobic alcohols are used as organic modifiers. This can be attributed to butanol partitioning into the bonded phase, which provides a more extended ordered surface increasing the contact surface area of the stationary phase and thereby increasing the selectivity of the separation. Using water rich mobile phases, constituents of vanilla extract in 36 commercial products obtained from stores in the local area were identified demonstrating the efficacy of the proposed RPLC method.

A portable photometer based on LED for the determination of aromatic hydrocarbons in water

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Kássio Michell Gomes de Lima
The present work describes a portable photometer based on light-emitting-diodes (LED) for the determination of total aromatic hydrocarbons in water contaminated with gasoline. Two LED were employed as the light source with maximum emission at 1300nm and 1689nm. The radiation of each LED was collected with bundles of 24 silica optical fibers, which were assembled in a single bundle pointed toward the detection cell. An InGaAs photodiode was directly connected to the measuring cell. Software was written in VisualBasic.NET to control the photometer through a USB interface and for data acquisition. The determination of total aromatic hydrocarbons was performed using a silicone-sensing phase (length of 5mm and diameter of 3.2mm), which was employed to extract these compounds from the contaminated water. The extraction (60min under constant stirring) was performed in a 100-mL flask filled with the water sample diluted in 2.0molL⁻¹ NaCl. A repeatability of 1.8% and 1.3% (expressed as the relative standard deviation of 10 measurements) was obtained at 1300nm and 1689nm, respectively. Absorbance values were calculated considering the signal at 1300nm as reference because hydrocarbons do not absorb at this wavelength. Analytical curves up to 200mgL⁻¹ and 400mgL⁻¹ were constructed for benzene and toluene, providing limits of detection of 1.2mgL⁻¹ and 1.7mgL⁻¹, respectively. The sensitivity was similar to those obtained with a FT-NIR Bomem MB 160 spectrophotometer at the same wavelength. The photometer was applied to the determination of total hydrocarbons in water contaminated by gasoline. An analytical curve (50–300mgL⁻¹) was constructed from reference solutions containing benzene and toluene in the ratio of 3:7, which is a ratio commonly found in Brazilian gasoline. The results provided by the photometer were compared with those obtained with the commercial spectrophotometer and did not show significant differences at a confidence level of 95%.

Antimony coordination to humic acid: Nuclear magnetic resonance and X-ray absorption fine structure spectroscopy study

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Tserenpil Sh, Cong-Qiang Liu, Lihua Wang
This current study examined the fate of antimony (Sb) in the soil environment and its association with soil humic acid (HA). It is anticipated that a significant proportion of Sb is retained in soil organic layer; therefore, the oxidation state of Sb is controlled by the soil HA to some extent which influences Sb solubility and ecotoxicity. Parent HA material as well as prepared HA–Sb (III) composites was investigated by determining elemental composition and by performing nuclear magnetic resonance (NMR) and X-ray absorption fine structure (XAFS) spectroscopy study in order to study Sb coordination to natural macro organic ligand. The Sb (III) binding to soil derived HA mainly contributed to its open chains through carboxyl and hydroxyl moieties as revealed by the ¹H and solid state ¹³C NMR spectroscopy. The protons in carboxylic and hydroxylic groups (those proton signals are characteristic of HAs with different origins) disappeared in the HA–Sb composite; and relative changes were observed in aliphatic proton distribution between the HA samples with and without Sb. The overall patterns of ¹³C NMR spectra for the investigated samples were analogous to each other; moreover, it was estimated that the cyclic structure of the HA nucleus remained unchanged during Sb (III) association. Based on the absorption edge energy and coordination numbers, Sb oxidation state in a native soil was interpreted as pentavalent, meanwhile the HA–Sb composite contained both Sb (III) and Sb (V). It was shown that HA catalyzes Sb (III) oxidation to Sb (V) but the process was relatively slow. However, XAFS spectra sensitivity was limited when studying the HA–Sb composite that was prepared from the isolated soil HA fraction, so only data on the first shell Sb–O coordination were interpreted.

Ligand exchange spectrophotometric method for the determination of mole ratio in metal complexes

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Fotouh R. Mansour, Neil D. Danielson
An innovative ligand exchange method involving the displacement of Fe(III) or Cu(II) ion by a ligand such as EDTA from the corresponding metal-salicylate complex has been developed to determine the mole ratio of the metal-ligand complex. The validity of the method is ascertained as the overlay of the plot showing the decrease in the absorbance of 1.0mM Fe(III)-salicylate upon the addition of serial concentrations of EDTA (0.1–0.6mM) with the absorbance calibration curve of Fe(III)-salicylate. At the intersection point of the two lines, the ratio of the two parts of the x-axis to the left and to the right of the intersection point is equal to 1:1, the mole ratio of Fe(III)-EDTA. Two other different concentrations (0.9 and 1.1mM) of Fe(III)-salicylate are used to confirm our method using the same concentration range of EDTA with each. The analysis of variance (ANOVA) is applied to compare the three slopes where no significant difference is observed with confidence limit of 95%. This method for the determination of metal complex mole ratios is compared with the reported methods known as Job, Mole Ratio, Bent-French, Asmus, and Nash. The mole ratios for Fe(III)-citrate, Cu(II)-citrate, and Cu(II)-EDTA complexes are also determined. Application to many transition metals which also complex with salicylate or related aromatic ligands is envisioned.

Evaluation of the effect of six different paint cross section preparation methods on the performances of Fourier Transformed Infrared microscopy in attenuated total reflection mode

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
S. Prati, F. Rosi, G. Sciutto, R. Mazzeo, D. Magrini, S. Sotiropoulou, M. Van Bos
The purpose of the present research was to compare the effect of different embedding and polishing procedures on the performances achievable with Fourier Transformed Infrared (FTIR) microscopy in Attenuated Total Reflection (ATR) mode. The attention was specifically focused on this technique since it is generally considered one of the most appropriate methods to analyze cross sections, thanks to the fact that the recorded spectra are similar to those collected in transmission mode. The research work was structured as a round robin among six different conservation and research laboratories. They were asked to embed fragments derived from the same area of a real sample following each one a different procedure. The performances of FTIR microscopy in ATR mode were evaluated on the different cross sections, considering the cross section morphology and the possible source of contamination. The cross sections were previously observed with optical microscopy, Environmental Scanning Electron Microscope (ESEM) and confocal microscopy. Three procedures were eventually selected, because they provided the best results in terms of both limiting the contamination of the embedding medium and achieving good contact with the ATR crystal. They were: a) embedding in KBr; b) cyclododecane pre-treatment before embedding in an organic resin and cutting of the sample; c) embedding in an organic resin and polishing with argon ion milling. These three procedures were finally compared and the weak points outlined, indicating where improvements could be made for further researches.

A sensitive method for extraction and determination of endocrine-disrupting compounds from wastewater using 10-ethyl-acridone-2-sulfonyl chloride as pre-column labeling reagent by high-performance liquid chromatography with fluorescence detection

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Shijuan Zhang, Jinmao You, Zhiwei Sun, Cuihua Song, Shujing Ning, Changsheng Zhao, Yourui Suo
A sensitive pre-column derivatization method using 10-ethyl-acridone-2-sulfonyl chloride (EASC) as pre-column labeling reagent followed by high-performance liquid chromatography (HPLC) with fluorescence detection has been developed for the determination of eight endocrine-disrupting compounds: 4-octylphenol, 4-nonylphenol, bisphenol A, diethylstilbestrol, estrone, 17α-ethynylestradiol, 17β-estradiol and estriol in wastewater samples. Solid phase extraction (SPE) with ODS C18 cartridges was used for the extraction and purification. Derivatizing parameters including pH value, temperature and concentration of EASC, as well as types of SPE cartridges and eluents were investigated in detail. Under optimal conditions, the quantification limits for the desired compounds ranging from 1.0 to 2.0ngL⁻¹ were obtained. The recoveries were higher than 80.4% with a noticeable improvement for 4-octylphenol and 4-nonylphenol, whose recoveries were usually lower than 50% during the SPE process. The proposed method was successfully applied to the determination of the target compounds in wastewater samples with a much higher sensitivity than traditional HPLC method.

Novel turbidimetric method to study polymer swelling

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Barry K. Lavine, Leah Oxenford, Mariya Kim, Necati Kaval, Marcus Benjamin, W.R. Seitz
The swelling behavior of pH sensitive polymer particles has been investigated by embedding the particles in a polyvinylalcohol (PVA) hydrogel membrane. Changes of one-half of an absorbance unit in the turbidity of the hydrogel membrane were observed as a result of the swelling and shrinking of the polymer particle in response to changes in the pH of the solution in contact with the membrane. The PVA membrane responded to multiple swelling and shrinking cycles without loss of functionality. This approach to studying polymer swelling is not subject to the mechanical problems of delamination and/or cracking associated with polymers immobilized on surfaces as the polymer particles embedded in the hydrogel membrane are free to swell in all directions. The membrane not only serves as a flexible medium to contain the polymer particles but also acts as a filter to protect the swellable polymer from sample components such as suspended particles that are too large to diffuse through the membrane. Because membrane turbidity can be measured at any wavelength, inexpensive instrumentation can be used to study polymer swelling.

Simple mercury speciation analysis by CVG-ICP-MS following TMAH pre-treatment and microwave-assisted digestion

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Yi Wu, Yong-Ill Lee, Li Wu, Xiandeng Hou
A simple method was proposed for mercury cold vapor generation (CVG) in tetramethylammoniumhydroxide (TMAH) solution for speciation analysis of ultratrace inorganic mercury and total mercury in biological samples by inductively coupled plasma mass spectrometry (ICP-MS). Prior to analysis, 100–300mg of the biological sample was accurately weighed into a conical tube. Then, 2mL of 25% (m/v) TMAH solution was added to the sample, incubated at room temperature for several hours (hair, 3h), and diluted to 25mL with water. Finally, inorganic mercury was directly determined by CVG-ICP-MS, while microwave-assisted oxidation with H2O2 was needed for total mercury detection. The concentration of organic mercury, mainly methylmercury, was obtained by difference of total mercury and inorganic mercury. Only one calibration curve against mercury aqueous standards in 2% TMAH medium was needed for both procedures. Optimum conditions for mercury CVG, as well as sample preparation and microwave-assisted digestion were investigated in detail. A limit of detection (LOD, 3σ) of 3ngL⁻¹ was obtained and the linear working range was 0.1–100μgL⁻¹. Validation data were provided based on the analysis of water samples, as well as a CRM human hair sample (GBW 070601). This is a simple, rapid, ultrasensitive and relatively green method for the determination of mercury in water and biological samples.

An analytical approach based on X-ray diffraction, Fourier transform infrared spectroscopy and gas chromatography/mass spectrometry to characterize Egyptian embalming materials

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Jeannette Jacqueline Łucejko, Anna Lluveras-Tenorio, Francesca Modugno, Erika Ribechini, Maria Perla Colombini
An analytical approach based on X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and gas chromatography/mass spectrometry (GC/MS) was used to characterize Egyptian embalming materials from the University of Florence's (Italy) Natural History Museum. FTIR was used as a fast fingerprinting tool due to its ability to characterize inorganic compounds and to highlight different classes of organic materials. GC/MS following alkaline hydrolysis, solvent extraction, and trimethylsilylation was used to determine the molecular nature of organic materials and their degradation products. The results show that the embalming materials consisted of complex mixtures of natural products as well as transformation products due both to natural ageing and human interventions. FTIR analyses, along with evidence of organic materials, enabled us to identify the presence of calcium oxalates, phosphates and carbonates, while XRD patterns confirmed the crystalline nature of both phosphates and oxalates. On the basis of the GC/MS identification of specific profiles of long-chain fatty acids, long-chain alcohols and alkanes, polycyclic terpene hydrocarbons and diterpenes, and triterpenes, we found that the balms of the mummies mainly consisted of beeswax, pine pitch and mastic resin. Ricinoleic acid suggests that castor oil was used as an ingredient in the mummification balm in three of the samples. The combination of results allowed the identification of the organic and inorganic composition of the residue of embalming material sampled from the skulls to be achieved and also permitted us to exclude the presence of possible products used during past restoration cure.

Prediction of mold contamination from microbial volatile organic compound profiles using head space gas chromatography/mass spectrometry

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Barry K. Lavine, Nikhil Mirjankar, Ryan LeBouf, Alan Rossner
A set of volatile organic compound (VOC) profiles was developed with corresponding bioaerosol measurements as input–output pairs for a discriminant to predict mold exposure in indoor environments. Entech Bottle-Vacs were used to collect whole air grab samples while viable spores were collected concurrently using an Andersen impactor in conjunction with malt extract agar and dichloran glycerol 18. By comparing the bioaerosol data to VOC profiles that were obtained using a GC/MS equipped with a cold trap preconcentrator, a discriminant was developed to classify a residence as to potential mold growth based on its microbial volatile organic (MVOC) profile.

Electrochemical immunoassay based on gold nanoparticles and reduced graphene oxide functionalized carbon ionic liquid electrode

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Sheng Yu, Xiaoyu Cao, Meng Yu
In this paper, a gold nanoparticle, reduced graphene oxide (R-GO) and poly(l-Arginine) composite material modified carbon ionic liquid electrode (CILE) was used as the platform for the construction of a new electrochemical carcinoembryonic antigen (CEA) immunosensor. The poly(l-Arginine)/R-GO composite film was used to modify CILE to fabricate Arg/R-GO/CILE through electropolymerization of l-Arginine on R-GO/CILE. Gold nanoparticles (AuNPs) were adsorbed on the modified electrode to immobilize the CEA antibody and to construct the immunosensor. The stepwise assembly process of the immunosensor was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). By combining the specific properties such as the biocompatibility and big surface area of AuNPs, and the excellent electron transfer ability of R-GO and the high conductivity of CILE, the synergistic effects of composite increased the amounts of CEA antibody adsorbed on the electrode surface and then resulted in the great increase of the electrochemical responses. Under the optimal conditions, differential pulse voltammetric responses of [Fe(CN)6]^3−/4− were proportional to CEA concentration in the range from 0.5 to 200ngmL⁻¹ with the detection limit as 0.03ngmL⁻¹ (S/N=3). The proposed immunosensor showed good reproducibility, selectivity, and acceptable stability.

Analytical methods for the determination of 137Cs and 90Sr in ash of fuel pellets used in Italy

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Donatella Desideri, Alba Rongoni, Carla Roselli, Daniela Saetta, Laura Feduzi
In this study the radiological characterization of ashes of 22 different brands of wood pellets coming from different countries and used in the regions of central Italy was carried out. ¹³⁷Cs and ⁹⁰Sr, were found in the samples taken into account, ¹³⁴Cs resulted always below the detection limit. ¹³⁷Cs activity concentration ranges from 30 to 3176Bqkg⁻¹ (the arithmetic mean resulted to 571Bqkg⁻¹); ⁹⁰Sr activity concentration ranges from 154.75Bqkg⁻¹ to 1443.70Bqkg⁻¹ (the arithmetic mean resulted to 684.80Bqkg⁻¹). The ratio of ⁹⁰Sr and ¹³⁷Cs activity concentration ranged from 0.22 to 40.79 showing a high variability. 77.2% of the samples show a ⁹⁰Sr activity concentration higher than that of ¹³⁷Cs. The concentration factors (activity concentration in ash/activity concentration in wood pellets) resulted to 222.8 and 230.0 for ¹³⁷Cs and ⁹⁰Sr respectively; both radionuclides are found completely in the ashes.

Rapid screening of poly(ethylene glycol) polymers by C18 column-flow injection with piezoelectric detection system

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
María R. Plata, Ana M. Contento, Ángel Ríos
A rapid and low cost analytical method for the screening and determination of poly(ethylene glycol)s polymers has been developed. Several initial studies were carried out in order to demonstrate the utility of a piezoelectric quartz crystal as a detection system for the quantification of poly(ethylene glycol)s. The method involves the use of a simple flow injection device connected to a piezoelectric quartz crystal detector. Several parameters associated with the simple flow injection manifold were optimized. Subsequently, this detector was coupled to a C18 column and the best experimental conditions were investigated in order to perform the screening and determination of poly(ethylene glycol)s. The applicability of this method, as an analytical screening tool, was demonstrated by the characterization of samples with different molecular mass polymers without using HPLC and CE techniques to carry out oligomer separations. A standard curve to determine the polymer content was obtained by relating the resonance frequency shift and polymer concentration, which showed good linearity and good regression coefficients. The working range, repeatability, limit of detection and recovery were all acceptable for the analysis of the poly(ethylene glycol)s. Finally, the proposed method was applied to determine these polymers in several samples, such as pharmaceutical products, washing powder, detergents and a body spray.

Instrumental neutron activation analysis of some fish species from Danube River in Romania

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Ana Pantelica, Antoaneta Ene, Iulia I. Georgescu
Instrumental neutron activation analysis (INAA) was applied to determine elemental concentrations in some fish species collected frome the Romanian sector of Danube River at km 1049, near the entrance in Romania (Carassius auratus gibelio, Ctenopharingodon idella, Rutilus rutilus and Silurus glanis) and km 630 (Acipenser ruthenus). Concentration values of 32 elements (Ag, As, Au, Ba, Br, Ca, Ce, Co, Cr, Cs, Eu, Fe, Hf, Hg, K, La, Lu, Na, Ni, Rb, Sb, Sc, Se, Sm, Sr, Ta, Tb, Th, U, W, Zn and Zr) in calcined fish samples were obtained based on long half-life radionuclides. Bioaccumulation factors (BAF) in fresh fish relative to Danube water (km 1049) were assessed and compared with literature data.

Microchemistry and stable isotope systematics of gold mineralization in a gabbro–diorite complex, SE Egypt

11 April 2012, 09:16:24

Publication year: 2012
Source:Microchemical Journal, Volume 103
Basem Ahmed Zoheir
Electron probe micro-analysis (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data of ore minerals from the Um Eleiga deposit (SE Egypt) suggest that primary Au was sequestered within Ni–pyrrhotite and Co–Ni–Fe sulfarsenide, while refined, free-milling gold grains (~93wt.% Au) are associated with late pyrite, or occur along micro-fractures in quartz veins. A magmatic source of gold is most likely, yet endowment by circulating metasomatic fluid was crucial for Au concentration. Sulfur stable isotope values (δ³⁴S) of sulfide minerals disseminated in the quartz veins (pyrite: −0.5 to 1.5‰, chalcopyrite: −0.3 to 0.6‰, and sphalerite: −0.1 to −0.4‰), indicate a generally light sulfur source. Similarly, measured δ¹³C of vein calcite (−3.1 to −1.8, n=9) and calculated fluid δ¹³CCO2 values (−0.6 to 0.6‰, for the temperature range 350–375°C of associated hydrothermal chlorite) cluster around 0‰, consistent with a magmatic source for carbon. Oxygen isotope data for vein calcite (10.3–13‰, n=9) and quartz (11.7–14.3‰, n=10) indicate average fluid δ¹⁸OH2O values of 7.4 and 7.8‰, respectively, which implicate fluids similar to those in intrusion-related systems. 

Reliable method for characterising Polyfluorinated compounds

Exeter Analytical has developed a reliable analytical method for accurately determining the percentage Carbon (C), Hydrogen (H) and Nitrogen (N) content of polyfluorinated compounds (PFCs).

Polyfluorinated compounds are extremely thermally and chemically stable and have soil, water and fat-repellent properties. They are nearly non-biodegradable and accumulate in the environment and the food chain. Due to their specific technical characteristics - polyfluorinated compounds are used in quite a number of products such as in textiles, carpets, cosmetics, paper, packaging materials as well as in general in the chemical synthesis, metallation, photo and semi-conductor industries.

Generally compounds containing fluorine can be successfully analysed for percentage CHN content on an elemental microanalysis system under standard operating conditions. The magnesium oxide in the combustion tube reagent packing absorbs fluorine as HF, and releases the hydrogen. However, polyfluorinated samples, which are often difficult to combust, can give incorrect low carbon and high nitrogen data.

For these highly fluorinated compounds, Exeter Analytical have developed a new reliable analytical method based upon their Model 440 Elemental Analyser that is described in Application Note 217.

For a copy of application note 217 please visit www.exeteranalytical.co.uk/ce440_notes.htm or contact Exeter Analytical on +44-2476-323223 / +1-978-251-1411 or email info@exeteranalytical.co.uk / sales@eai1.com. 

Just Published: Journal of Chromatography A

A new issue of this journal has just been published. To see abstracts of the papers it contains (with links through to the full papers) click here:

Journal of Chromatography A http://rss.sciencedirect.com/publication/science/5248

Selected papers from the latest issue:

Stir bar sorptive extraction and high performance liquid chromatographic determination of carvedilol in human serum using two different polymeric phases and an ionic liquid as desorption solvent

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Zahra Talebpour, Maryam Taraji, Nuoshin Adib
This article presents a method employing stir bar coated with a film of poly (methyl methacrylate/ethyleneglycol dimethacrylate) (PA-EG) and polydimethylsiloxane (PDMS) in combination with liquid desorption (LD) using ionic liquid, followed by high performance liquid chromatography (HPLC) equipped with ultraviolet (UV) detection for the determination of carvedilol in human serum samples. Stir bar sorptive extraction (SBSE) variables, such as desorption and extraction time and temperature, desorption solvent and pH of the matrix were optimized, in order to achieve suitable analytical sensitivity in a short period of time. Also, the concentration effect of 1-methyl-3-octylimidazolium tetrafluoroborate [Omim][BF4] ionic liquid on the efficiency of LD was investigated. A comparison between PA-EG/SBSE and PDMS/SBSE was made by calculating the experimental recovery and partition coefficient (K), where PA-EG phase demonstrated to be an excellent alternative for the enrichment of the carvedilol from serum samples. The effect of [Omim][BF4] on carryover was studied and no carryover was observed. Under optimized experimental conditions, the analytical performance showed excellent linear dynamic range, with correlation coefficients higher than 0.999 and limits of detection and quantification of 0.3 and 1.0ngmL⁻¹, respectively. Intra- and inter-day recovery ranged from 94 to 103% and the coefficients of variations were less than 3.2%. The proposed method was shown to be simple, highly sensitive and suitable for the measurement of trace concentration levels of carvedilol in biological fluid media.

Recovery of crocins from saffron stigmas (Crocus sativus) in aqueous two-phase systems

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Bertha Montalvo-Hernández, Marco Rito-Palomares, Jorge Benavides
Crocins are carotenoid derivates that have recently attracted the interest of the scientific community due to their nutraceutical properties. Saffron (dry Crocus sativus stigmas) is one of the main known sources of crocins. In this study the potential use of aqueous two-phase system (ATPS) for the extraction of crocins from C. sativus stigmas was evaluated. The partitioning behavior of crocins in different types of ATPS (polymer–polymer, polymer–salt, alcohol–salt and ionic liquid–salt) was evaluated. Ethanol–potassium phosphate ATPS were selected based on their high top phase recovery yield and low cost of system constituents. The evaluation and optimization of system parameters rendered conditions (V R =3.2, ethanol 19.8% (w/w), potassium phosphate 16.5% (w/w), TLL of 25% (w/w), 0.1M NaCl and 2% (w/w) of sample load) under which more than 75% of total crocins were recovered in the top (ethanol rich) phase, whereas the wasted stigmas accumulated in the bottom phase. Lastly, a comparison between an optimized solid–liquid extraction using ethanol:water as solvent and ATPS was conducted demonstrating that similar yields are achieved with both strategies (76.89±1.8% and 79.27±1.6%, respectively). However, ATPS rendered a higher extraction selectivity of 1.3±0.04mg of crocins for each mg of phenolic compound, whereas ethanolic extraction showed a selectivity of 0.87±0.01. The results reported herein demonstrate the potential application of ATPS, particularly ethanol–potassium phosphate systems, for the recovery of crocins from C. sativus stigmas.

Liquid chromatography–flame ionisation detection using a nebuliser/spray chamber interface. Part 1. Design and testing

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Erepamowei Young, Roger M. Smith, Barry L. Sharp, Joanne R. Bone
A nebuliser and spray chamber have been used to link a flow injection analyser to a flame ionisation detector, with the potential for the combination to be used as a universal detector for liquid chromatography. The hydrogen and air flows were adjusted to achieve a stable system. The detector responded to both volatile and involatile analytes and to compounds with and without chromophores, including alkanes, alkanols, aromatic amides and acids, phenols, amino-acids and carbohydrates and gave a linear response for many analytes. However, for involatile polar analytes it was necessary to add traces of acid or salt to the carrier stream to obtain a linear response.

Liquid chromatography-flame ionisation detection using a nebuliser/spray chamber interface. Part 2. Comparison of functional group responses

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Erepamowei Young, Roger M. Smith, Barry L. Sharp, Joanne R. Bone
The application of a LC-nebuliser/spray chamber interface-flame ionisation detection has been demonstrated for the superheated water liquid chromatography of a wide range of aliphatic and aromatic analytes. The linearity and sensitivity of the response of volatile and involatile analytes have been compared. The response of the detector toward different analytes is similar to that in GC-FID and for volatile analytes was comparable to UV detection. However, the responses from involatile analytes, such as amino acids and carbohydrates, were poor and often lower than for a refractive index detector.

Comparison of the fast gradient performance of new prototype silica monolithic columns and columns packed with fully porous and core–shell particles

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Fabrice Gritti, Nobuo Tanaka, Georges Guiochon
The gradient elution performance of narrow-bore 2.3mm×50mm (N733) and wider bore 3.2mm×50mm (N648 and N655) prototype silica monolithic columns was investigated and compared to the performance of commercially available columns packed with sub-2μm fully porous particles (2.1mm×50mm, 1.7μm BEH-C18, Waters) and sub-3μm superficially porous particles (2.1mm×50mm, 2.7μm Halo-ES-Peptide-C18 (AMT), 1.7 and 2.6μm Kinetex-C18, Phenomenex). Results show that the two wide monolithic columns show peak capacities similar to the one measured for the Kinetex column. In contrast, the narrow-bore monolithic column delivers a lower performance (−30%) than the BEH, the Halo and the Kinetex columns. This work stresses out the importance of reducing the extra-column band broadening contribution of HPLC instruments when short 2.1mm I.D. columns are used. The part of the instrument contribution originating downstream the column is important for all compounds; the one originating upstream the column is significant only for weakly retained compounds.

Preparation and characterization of bonded silica hydride intermediate from triethoxysilane and dimethylmethoxysilane using supercritical carbon dioxide and dioxane as reaction medium

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Benjamin A. Ashu-Arrah, Jeremy D. Glennon, Klaus Albert
This research examines bonding methodology, surface coverage and silanol conversion efficiencies on the preparation of silica hydride (SiH) intermediate from triethoxysilane (TES) and dimethylmethoxysilane (DMMS) using sc-CO2 and dioxane as reaction solvent. Under sc-CO2 reaction conditions (at temperature and pressure of 100°C, 414bar, respectively and 3h reaction time), the surface coverages of SiH (evaluated from %C obtained from elemental analysis) prepared with DMMS (3.39μmol/m²) and TES (4.46μmol/m²) increased by 2- and 4-folds respectively, when compared to reaction performed in dioxane (2.66μmol/m², SiH, DMMS and 0.69μmol/m², SiH, TES). The relatively higher surface coverage of SiH from TES over DMMS generated in sc-CO2 is due to the inherent trialkoxy moiety of the TES that favours siloxane crosslinkage, forming polymeric surface attachments to yield a higher ligand density than the monomeric DMMS ligand. A conversion efficiency of ∼84.4% of SiH prepared from TES in sc-CO2 estimated from ²⁹Si CP/MAS NMR analysis is comparable to TES silanization in dioxane or toluene. Moreover, silica hydride (SiH) conversion efficiency of ca. 42.4% achieved for the hydride intermediate prepared from DMMS in sc-CO2 is more superior to 33.3% efficiency obtained in dioxane. The differences in conversion efficiencies is attributed to the ability of sc-CO2 being able to access silica pores that are inaccessible in organic solvents. Bonded silica hydride from TES, DMMS prepared in sc-CO2 were characterized using elemental analysis, thermogravimetric analysis (TGA), BET surface area, Fourier transform infrared (FI-IR) and solid state NMR spectroscopy. Silica hydride technology/chemical functionalization of silica in sc-CO2 avoid extended purification steps (i.e. filtration and washing), generation of waste organic solvent and the need of costly or energy consuming drying processing with improved modification efficiency.

Multiple, simultaneous, independent gradients for versatile multidimensional liquid chromatography. Part I: Theory

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Allen G. Hirsh, Latchezar I. Tsonev
The general method for constructing coupled dual gradients in liquid chromatography (LC) is to begin by filling a reservoir A with a solution of one mobile phase (MP) component at concentration [c 1(A)] and a second MP component at concentration [c 2(A)], followed by filling a reservoir B with a solution containing MP component one at concentration [c 1(B)] and the second MP component at concentration [c 2(B)]. In another scenario the reservoirs A and B are filled with solutions of only one MP component at different concentrations [c 1(A)] and [c 1(B)] and the two solutions are titrated to a different pH value: pH (A) for the reservoir A and pH (B) for the reservoir B respectively. In either case, mixing of flows from the two reservoirs varies the concentrations of the two MP components (MP solutes) or the concentration of one MP component and pH along a particular compositional curve producing an eluent with two compositionally coupled gradients. This is a kind of a two dimensional LC utilizing dual simultaneous dependent gradients (DSDGs) wherein two parameters affecting the binding free energy of an analyte to a stationary phase (SP) are being altered simultaneously. Such a DSDG suffers from a significant limitation in that the gradient concentration of the two solutes or the concentration of one MP component and the pH cannot be varied independently. The only way to attain an optimal multigradient LC system, that promises a remarkable increase in chromatographic resolution of complex analyte mixtures, is to uncouple the multiple (dual) gradients, making each independent of the other(s). In this paper the theory of uncoupling of n such gradients, n ≥2 is developed. It is shown that for n solutes 2 ⁿ reservoirs are required in concert with an LC eluent delivery system capable of freely apportioning the flows among the reservoirs according to equations we develop here. We go on to predict a substantial increase in chromatographic resolution when applying dual simultaneous independent gradients (DSIGs) of salt and pH to fractionate difficult to separate proteins. This prediction is naturally explained by the electrostatic interaction theory of protein binding to an ion exchanger. In subsequent experimental papers it will be shown that the algorithms presented here properly instruct a quad pump HPLC system to produce well controlled independent simultaneous gradients of pH and non-buffering solutes with attendant significant gain in chromatographic resolution of complex mixtures of protein isoforms.

Kinetic optimisation of the reversed phase liquid chromatographic separation of proanthocyanidins on sub-2μm and superficially porous phases

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Kathithileni M. Kalili, Deirdre Cabooter, Gert Desmet, André de Villiers
Phenolic compounds, and proanthocyanidins in particular, are important natural molecules which are of significant importance due to their sensory and biological activities. The analysis of proanthocyanidins in natural products is very challenging due to their complex nature. In this study, the kinetic performance of a range of recently developed C18 columns, including sub-2μm fully porous and 2.6μm superficially porous particle-packed columns, was evaluated for improved proanthocyanidin analysis. The kinetic plot method was employed to compare the ultimate performance limits of each column in terms of efficiency and speed for different maximum pressures and temperatures using representative proanthocyanidins comprising a range of molecular weights and functionalities as test analytes. By combining plate height data with relevant parameters such as column permeability and mobile phase viscosity, plots of practically attainable efficiencies as a function of analysis time for specific experimental configurations were obtained and performance limits for all investigated supports could accurately be compared. Both fully- and superficially porous particles provided significant speed and/or efficiency gains compared to conventional 5μm particle packed columns. Analyte properties, particle size and packing quality as well as analysis temperature were all found to have a significant influence on the performance of the presently investigated chromatographic supports. For smaller compounds, higher optimal linear velocities and better performance in the low-efficiency range were observed, while the lower diffusion coefficients of larger procyanidins resulted in lower optimal linear velocities and better performance in the high-efficiency regime. Faster analyses become possible at higher temperatures due to decreased eluent viscosity and faster mass transfer, which was especially beneficial for larger compounds and resulted in dramatic improvement in efficiency. A possible explanation of the abnormal behaviour of oligomeric procyanidins is presented. Our findings indicate that new column formats, when used under optimal conditions, significantly improve the speed and/or efficiency of reversed phase liquid chromatographic analyses of proanthocyanidins.

Quantifying injection solvent effects in reversed-phase liquid chromatography

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Bradley J. VanMiddlesworth, John G. Dorsey
Peak distortion due to the injection was measured as a function of injection solvent strength, volume, mass, retention factor, and column selectivity. The concept of a method's sensitivity (s) to injection solvent strength was mathematically defined as a vector of theoretical plate counts compared to an ideal vector that does not change with injection solvent strength. Near ideal sensitivity (s >0.90) was measured on all columns with all analytes in low volume injections of 1.25μL. Increasing the injection volume reduces the measured sensitivity from ideality to a greater extent than increasing the injection mass, with differing values for each column. Using column parameters measured from the hydrophobic-subtraction model and fitting parameters from the acetonitrile excess adsorption isotherm, differences among the columns studied are explained. Decreased ligand density and increased silanol activity provide a consistent peak shape with changes in injection volume or solvent strength. For method development, a quick test is suggested with the ratio of hydrophobic-subtraction column parameters, H/A, to predict the injection solvent sensitivity of a column. As H/A decreases, the sensitivity to injection solvent worsens. Sensitivity to organic modifiers other than acetonitrile are predicted with cited sorbed layer thickness, such that MeOH>EtOH>IPA≈THF≈MeCN, i.e., a strong MeOH diluent is more ideal (better) than a strong MeCN diluent.

Purification of a PEGylated single chain Fv

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Anna Moosmann, Elke Gerlach, Robert Lindner, Heiner Böttinger
In this manuscript we describe the two-step purification of a mono-PEGylated anti-epidermal growth factor receptor (EGFR) single-chain Fv. A weak cation exchanger was used for capture. Elution using arginine suppressed protein aggregation and allowed a very good resolution with purity and product-recovery was above 90%. Free PEG was removed completely. The use of hydrophobic interaction chromatography (HIC) increased purity to 98%. Increasing the size of PEG from 5 to 30kDa increased retention on HIC and reduced it on cation exchangers. Bioactivity of PEGylated scFv was confirmed by ¹²⁵I based cell tests. Proteins modified with 5kDa PEG showed higher bioactivity than proteins modified with larger PEGs. The combination of cation exchange and HIC provides a rational and effective basis for PEGylated scFv purification.

Simultaneous determination of fluoxetine and norfluoxetine enantiomers using isotope discrimination mass spectroscopy solution method and its application in the CYP2C9-mediated stereoselective interactions

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Lushan Yu, Shengjia Wang, Huidi Jiang, Hui Zhou, Su Zeng
In this study, we developed an LC–MS/MS method based on an isotope discrimination mass spectroscopy solution (IDMSS) technology to simultaneously quantify enantiomers of fluoxetine (FLX) and norfluoxetine (NFLX) in a CYP2C9 incubation mixture. S-FLX and S-NFLX were labeled to form S-FLX-d5 and S-NFLX-d5. The method has several advantages over conventional chiral separation methods, in terms of the analysis period, resolution, and lower limit of quantification. The primary advantage of the method is that the two enantiomers can always be simultaneously determined by mass spectroscopy regardless if they are separated on column or not, owing to which it has high throughput and high sensitivity. The lower limit of quantification (amount on column) is 12.5 and 1.25pg for FLX and NFLX, respectively. The retention time of FLX, NFLX, and the internal standard is only 1.9min. The calibration curves were linear over the concentration range of 0.1–100ng/ml for NFLX and 1–1000ng/ml for FLX with an accepted reproducible (RSD<10%) and accurate (CV<10%). No significant kinetic isotope effect was found in the metabolism of S-FLX-d5 catalyzed by CYP2C9*1 and CYP2C9*2. The half-maximal inhibitory concentration values between R-FLX and S-FLX catalyzed by CYP2C9*1 and CYP2C9*2 were determined in this study. The inhibitory effects of R- to S-FLX were stronger than those of S- to R-FLX in both CYP2C9*1 and CYP2C9*2. The IDMSS technology is useful for stereoselective study of chiral compound in vitro.

Kinetic performance of narrow-bore columns on a micro-system for high performance liquid chromatography

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Fabrice Gritti, Georges Guiochon
The kinetic performance of 0.5mm×50mm columns packed with 2.7μm Halo-C18 core–shell particles and 3μm EP-120-C18 fully porous particles fitted on an Eksigent LC-Express Ultra μHPLC system were measured. The instrument contribution to band broadening was obtained by directly connecting the injection valve and the detector cell with a short, narrow PEEKSIL tube. The connections between the column and the connecting tubes, the column endfittings and its frits contribute to band spreading and are responsible for a significant rear peak tailing, even for retained compounds, resulting in a significant loss of efficiency. Our results show that the μHPLC system could outperform the current VHPLC systems using 2.1mm I.D. columns packed with 1.7μm particles if it were using 0.5mm I.D. columns packed with 1μm particles, if it could operate at a few kbar pressure drop, and if the sum of the contributions of the instrument, column endfittings and the column frits to band dispersion were three times smaller than it is at present.

Ion-exchange centrifugal partition chromatography: A methodological approach for peptide separation

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Leslie Boudesocque, Pedro Lameiras, Nassima Amarouche, Matthieu Giraud, Francesca Quattrini, John Mc Garrity, Jean-Marc Nuzillard, Jean-Hugues Renault
This article presents the scope and optimization strategies employed in ion-exchange centrifugal partition chromatography (IXCPC). Both the weak and the strong modes were used to separate the constituents of a model mixture of dipeptides. Thus, the combined use of the quaternary biphasic solvent system, methyl-tert-butylether/acetonitrile/n-butanol/water (2:1:2:5, v/v) in the descending mode, of the lipophilic di(2-ethylhexyl)phosphoric acid (DEHPA) cation-exchanger, and of two displacers: calcium chloride and hydrochloric acid, has proven to be efficient for the preparative separation of the model mixture of five dipeptides (GG, GY, AY, LV and LY, in the order they were collected). The separation was optimized by splitting the stationary phase into two sections that differed by their triethylamine concentration. Moreover, the chemical nature of the exchanger/analyte entities that were involved in the chromatographic process was determined by ³¹P and ¹H DOSY NMR experiments.

Simulated moving bed enantioseparation of amino acids employing memory effect-constrained chromatography columns

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Markus Fuereder, Sven Panke, Matthias Bechtold
Teicoplanin aglycone-based chromatography columns (Chirobiotic TAG) enable amino acid enantioseparation with aqueous mobile phases, which perfectly accommodates the distinct hydrophilicity of most amino acids. Therefore, this stationary phase constitutes a promising option in particular for preparative-scale separations that require high feed concentrations for economic operation. However, detailed studies revealed a solute-related memory effect when this column is subjected to high loadings of amino acids, conditions that prevail in SMB operation. High loadings yield an activation of the column as indicated by increased retention times when comparing finite injection chromatograms obtained before and after the column had been subjected to a concentrated amino acid feed. This effect can be slowly reversed by flushing the column with solvent devoid of amino acid. Obviously, the activation of the stationary phase needs to be accounted for in the determination of adsorption isotherms that are used for SMB design. In this work we introduce a perturbation method adapted specifically to capture the stationary phase behaviour at SMB-like conditions. The adsorption isotherms obtained from this method indeed allowed for accurate SMB design of a methionine enantioseparation as judged by the very good agreement of experimentally obtained and model-predicted purities. Furthermore, SMB operation over 3 days with constant purities (besides deviations originating from a dip in temperature) was accomplished indicating that the adsorption behaviour in the activated state is indeed time invariant and stable long-term SMB operation with these columns is principally feasible.

Bioactivity-guided fractionation of the volatile oil of Angelica sinensis radix designed to preserve the synergistic effects of the mixture followed by identification of the active principles

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Ju-Ching Yeh, Ian J. Garrard, Chin-Wen Chantal Cho, S.W. Annie Bligh, Guang-hua Lu, Tai-Ping Fan, Derek Fisher
In natural product research, it is a common experience that fractionation of biologically-active crude extracts can lead to the loss of their original activity. This is attributed to synergistic effects, where two or more components are required to be present together for full activity of the sample. Our previous study showed that a volatile oil of Angelica sinensis radix (VOAS) inhibited endothelial cell proliferation in culture. Here we have used a bioactivity-guided fractionation method to preserve any synergistic effects of VOAS combining countercurrent chromatography (CCC), the MTS cell viability assay and gas chromatography (GC). Using a two-phase CCC solvent system (heptane–ethyl acetate–methanol–water at a volume ratio of 27:23:27:23%), forty-five fractions were isolated, nine of which exhibited anti-endothelial properties. GC analysis showed two bioactive alkylphthalides, Z-ligustilide and n-butylidenephthalide (BP) were the major compounds detected in the bioactive fractions, and were absent in non-bioactive fractions. Our results indicate that Z-ligustilide and BP are the main constituents responsible for the anti-endothelial properties of VOAS. This rapid and reliable approach in preserving sample activity while isolating and identifying its active compounds suggests that this protocol can be a powerful tool for drug discovery from natural products.

CHROM2—A method to enhance the dynamic binding capacity, yield and productivity of a chromatographic column

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Mayuratheepan Puthirasigamany, Peter van Beijeren, Peter Kreis
Therapeutic proteins are biotechnological products with a fast-growing market. Despite the rapid development of available process technologies, a bottleneck in production capacities is still present due to limitations in the associated downstream process, particularly within chromatographic purification steps. Membrane chromatography has been introduced as a promising alternative for conventional chromatography because it allows for higher throughputs but it does not deliver comparable dynamic binding capacities. To combine the strengths of the two technologies, the so-called “CHROM² concepts” are introduced, which merge conventional chromatography with membrane adsorption. The serial connection of a large conventional chromatographic column followed by a small membrane chromatography unit enables to combine the strength of both the individual technologies. The larger column delivers the required high binding capacity, whereas the rapid binding kinetics of membrane chromatography sharpens the breakthrough curve. Furthermore applied higher velocities do not result in poor breakthrough performance since the membrane chromatography is able to compensate for the poor column breakthrough performance. In comparison to column chromatography, the CHROM² setup exploits the full column capacity and delivers higher productivities and yields.

Sequential determination of anionic-type detergents by complexation with methylene blue using dual high speed counter-current chromatography

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Eiichi Kitazume, Saki Koikawa, Lu Hui, Syou Sannohe, Yanjun Yang, Yonosuke Maki, Yoichiro Ito
A new dual high-speed counter-current chromatographic system using organic extraction phase and aqueous mobile phase containing methylene blue was applied to the analysis of anionic-type detergents. After selecting appropriate conditions such as flow rate of each mobile phase and sample volume, the new system was successfully applied to the analysis of anionic detergent in river water. As all the analytical procedures can be made in a closed system, the method has no health hazard. The present method is safe, precise, and highly sensitive, and can be applied for sequential determination of multiple samples in a short analysis time.

On the chromatographic efficiency of analytical scale column format porous polymer monoliths: Interplay of morphology and nanoscale gel porosity

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Ivo Nischang
Porous monolithic poly(styrene-co-divinylbenzene) stationary phases in 4.6mm I.D. analytical-scale column format with varying porosity, globule scale polymer morphology and flow-through pore structure have been investigated with respect to their transport properties toward small retained solutes in isocratic elution, reversed-phase liquid chromatography. The current study was performed under kinetically and thermodynamically relevant conditions comprising retention factors from close to zero up to the order of 50–100 under most extreme conditions, while a linear chromatographic flow velocity up to 4mm/s, in some instances up to 7mm/s, was realized. Carefully designed experiments aimed at resolving issues associated with the monoliths performance, while a particular focus is given on gel porosity, chromatographic retention and band dispersion. Elucidation of three important metric properties gave orthogonal insight. These are: (i) the columns dry-state morphology and surface area, (ii) the gel porosity with tetrahydrofuran as solvent determined by size exclusion chromatography using a range of small subnanometer-sized molecules and polystyrene standards, as well as (iii) the isocratic reversed-phase performance of small molecules at varying binary acetonitrile/water mobile phase solvent compositions, modulating gel porosity. Consistently throughout the study, the adjustable and general retention-factor-dependence of the performance of these monolithic materials is shown. It can also be correlated to the analytes molecular weight and consequently size. Isocratic performance strongly depends on the amount of gel porosity of the scaffold, which can be changed by varying the percentage of organic modifier in the mobile phase and indicates the adjustable chromatographic nature of porous polymer monoliths. This gel porosity which is absent in the dry-state of the polymer monoliths and is characterized by sub-nanometer to nanometer-sized pore space induces, additionally to permanent porosity, stagnant mass transfer zones. The displayed major reason for mass transfer resistance implied by the use of polymeric monolithic columns determines dispersion behavior of small molecules and its varying importance with respect to morphology and size of the globular features containing stagnant mass transfer zones is addressed. This leads to the conclusion, that a reduction in polymer feature size and increase in number of flow-through pores per unit cross-section of the monolith with an improved homogeneity may be an interesting option of tailoring column performance. It is further concluded that dry-state methods (such as nitrogen adsorption analysis and scanning electron microscopy) or solvated-state methods (such as size-exclusion chromatography in tetrahydrofuran) by itself are insufficient measures to explain the adjustable chromatographic performance of porous polymer monoliths.

Development of anion-exchange/reversed-phase high performance liquid chromatography–inductively coupled plasma-mass spectrometry methods for the speciation of bio-available iodine and bromine from edible seaweed

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Vanessa Romarís-Hortas, Pilar Bermejo-Barrera, Antonio Moreda-Piñeiro
Anion exchange high performance liquid chromatography hyphenated with inductively coupled plasma-mass spectrometry has been novelly applied to assess inorganic (iodide and iodate) and organic (3-iodotyrosine – MIT, and 3,5-diiodotyrosine – DIT) iodine species in a single chromatographic run. The optimized operating conditions (Dionex IonPac AS7, gradient elution with 175mM ammonium nitrate plus 15% (v/v) methanol, pH 3.8, as a mobile phase and flow rates within the 0.5–1.5mLmin⁻¹ range) have also been used to perform inorganic bromine speciation analysis (bromide and bromate). The developed method has been applied for determining the bio-available contents of iodine and bromine species in dialyzates from edible seaweed. Reverse phase high performance liquid chromatography (Zorbax Eclipse XDB-C8, gradient elution with 0.2% (m/m) acetic acid, and 0.2% (m/m) acetic acid in methanol, as mobile phases, and a constant flow rate of 0.75mLmin⁻¹) also hyphenated with inductively coupled plasma-mass spectrometry was used to confirm the presence of organic iodine species (MIT and DIT) in the dialyzates. The verification of the presence of iodinated amino acids (MIT and DIT) in the extracts was also performed by reverse phase high performance liquid chromatography–electrospray ionization-mass spectrometry (LTQ Orbitrap). The developed methods have provided good repeatability (RSD values lower than 10% for both anion exchange and reverse phase separations) and analytical recoveries within the 90–105% range for all cases. The in vitro bio-availability method consisted of a simulated gastric and an intestinal digestion/dialysis (10kDa molecular weight cut-off – MWCO) two-stage procedure. Iodide and MIT were the main bio-available species quantified, whereas bromide was the major bromine species found in the extracts.

Evaluation of a new wide pore core–shell material (Aeris™ WIDEPORE) and comparison with other existing stationary phases for the analysis of intact proteins

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Szabolcs Fekete, Róbert Berky, Jenő Fekete, Jean-Luc Veuthey, Davy Guillarme
The separation of large biomolecules such as proteins or monoclonal antibodies (mAbs) by RPLC can be drastically enhanced thanks to the use of columns packed with wide-pore porous sub-2μm particles or shell particles. In this context, a new wide-pore core–shell material has been recently released under the trademark Aeris WIDEPORE. It is made of a 3.2μm solid inner core surrounded by a 0.2μm porous layer (total particle size of 3.6μm). The aim of this study was to evaluate the performance of this new material, compare it to other recently developed and older conventional wide-pore columns and demonstrate its applicability to real-life separations of proteins and mAbs. At first, the traditional h min values of the Aeris WIDEPORE column were determined for small model compounds. The h min values were equal to 1.7–1.8 and 1.4 for the 2.1 and 4.6mm I.D. columns, respectively, which are in agreement with the values reported for other core–shell materials. In the case of a small protein Insulin (5.7kDa), the achievable lowest h value was below 2 and this impressive result confirms that the Aeris WIDEPORE material should be dedicated to protein analysis. This column was then compared with five other commercially available wide-pore and medium-pore stationary phases, in the gradient elution mode, using various flow rates, gradient steepness and model proteins of MW=5.7–66.8kDa. The Aeris WIDEPORE material often provided the best performance, in terms of peak capacity, peak capacity per time and pressure unit (PPT) and also based on the gradient kinetic plot representation. Finally, real separations of filgrastim (18.8kDa) and its oxidized and reduced forms were performed on the different columns and the Aeris WIDEPORE material provided the most impressive performance (peak capacity>100 for t grad <6min). Last but not least, this new material was also evaluated on digested and reduced mAb and powerful, high-throughput separations were also attained.

Comparison of indirect and direct quantification of esters of monochloropropanediol in vegetable oil

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Mathieu Dubois, Adrienne Tarres, Till Goldmann, Anna Maria Empl, Alfred Donaubauer, Walburga Seefelder
The presence of fatty acid esters of monochloropropanediol (MEs) in food is a recent concern raised due to the carcinogenicity of their hydrolysable moieties 2- and 3-monochloropropanediol (2- and 3-MCPD). Several indirect methods for the quantification of MEs have been developed and are commonly in use until today, however significant discrepancies among analytical results obtained are challenging their reliability. The aim of the present study was therefore to test the trueness of an indirect method by comparing it to a newly developed direct method using palm oil and palm olein as examples. The indirect method was based on ester cleavage under acidic conditions, derivatization of the liberated 2- and 3-MCPD with heptafluorobutyryl imidazole and GC–MS determination. The direct method was comprised of two extraction procedures targeting 2-and 3-MCPD mono esters (co-extracting as well glycidyl esters) by the use of double solid phase extraction (SPE), and 2- and 3-MCPD di-esters by the use of silica gel column, respectively. Detection was carried out by liquid chromatography coupled to time of flight mass spectrometry (LC–ToF-MS). Accurate quantification of the intact compounds was assured by means of matrix matched standard addition on extracts. Analysis of 22 palm oil and 7 palm olein samples (2- plus 3-MCPD contamination ranged from 0.3 to 8.8μg/g) by both methods revealed no significant bias. Both methods were therefore considered as comparable in terms of results; however the indirect method was shown to require less analytical standards, being less tedious and furthermore applicable to all type of different vegetable oils and hence recommended for routine application.

Micellar electrokinetic chromatography of aromatic anions and non-ionic aromatic compounds with stepwise changes of the concentration of cetyltrimethylammonium chloride

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Yukihiro Esaka, Miki Kobayashi, Hiroya Murakami, Bunji Uno
Micellar electrokinetic chromatography in which the concentration of cetyltrimetylammmonium chloride (CTAC) was sequentially changed in the separation system was investigated using 10 aromatic anions and 11 non-ionic aromatic compounds as model analytes. All separations were performed in the absence of electroosmotic flow (EOF), and thus, analytes were detected in the order of their strength of interaction with micelles in the system. In isocratic elutions without EOF, the model analytes could be separated better with lower concentrations of CTAC but migration times of the analytes possessing relatively higher polarities increased markedly, and thus, long analysis times were required. Therefore, we attempted to increase the concentration of CTAC during a single measurement to reduce the analysis time without hindering the resultant separation of analytes obtained with lower concentrations. Briefly, the present surfactant stepwise elution can be performed by a sequential increase in CTAC concentrations of the running solution in the anodic reservoir from 30 to 50mM for the anions and from 20 to 50mM for the non-ionic compounds. Additionally, to perform expected gradient separations with good reproducibility, each running solution with a different CTAC concentration was treated with tetraethylammmonium chloride as an additive to adjust electric conductivities of each running solution to be equal. Under this condition, CTAC micelles of each zone of different CTAC concentrations would migrate with practically the same velocity. Consequently, by the present stepwise method, both the 10 anionic analytes and the 11 non-ionic analytes were well separated within reasonable periods which corresponded approximately to two-third and less than half of those by the isocratic elutions, respectively.

Study of chemical selectivity of molecular binary mixed micelles of sodium 10-undecenyl sulfate and sodium N-undecenyl leucinate using linear solvation energy relationships model

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1236
Hamid H. Ahmed, David M. Ahlstrom, Hakan Arslan, Mustafa Guzel, Cevdet Akbay
Poly(sodium 10-undecenyl sulfate) (poly-SUS), poly(sodium N-undecenyl leucinate) (poly-SUL) and their five molecular binary mixed micelles with varied SUS:SUL composition were prepared and used as pseudostationary phases in micellar electrokinetic chromatography (MEKC). Linear solvation energy relationships (LSERs) model and free energy of transfer studies were used to characterize the retention behavior and the selectivity differences among the seven surfactant systems. System constant differences and regression models for varied benzene derivative compounds are used to establish the selectivity differences of the seven pseudostationary phases. The cavity formation and dispersion interaction (the v system constant) and the hydrogen-bonding acidity (the b system constant) of the surfactant systems were found to have the most significant influence on selectivity and MEKC retention. The molecular micelle with sulfate head group, poly-SUS, was found to be more hydrogen-bond acidic than the molecular micelle with leucinate head group, poly-SUL. The other system constants (a, s and e) have modest effect on the retention and selectivity of the benzene derivatives. The model intercept coefficients (c system constants), which are negative for all surfactant systems have unusually large values. The free energy changes of transfer for the functional groups studied have all negative values except phenol and benzyl alcohol. Selectivity differences between pseudostationary phases were also compared by plotting the log k values against each other and were found to agree well with LSER results.

Low-density solvent based ultrasound-assisted emulsification microextraction and on-column derivatization combined with gas chromatography–mass spectrometry for the determination of carbamate pesticides in environmental water samples

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1235
Liang Guo, Hian Kee Lee
A fast and efficient method for the determination of trace level of carbamate pesticides using a lower-density-than-water solvent for ultrasound-assisted emulsification microextraction coupled to on-column derivatization and analysis by GC–MS has been developed and studied. In this approach, a soft plastic Pasteur pipette was employed as a convenient extraction device. Fifty microliters of extraction solvent, of lower density than water, was injected into the sample solution held in the pipette. The latter was immediately immersed in an ultrasound water bath to form an emulsion. After 2min extraction, the emulsion was fractionated into two layers by centrifugation. The upper layer (organic extract) could be collected conveniently by squeezing the bulb of the pipette, now held upside down, to move it into the narrow stem of the device, facilitating its retrieval for analysis. The extract was then combined with trimethylphenylammonium hydroxide and directly injected into a gas chromatography–mass spectrometry (GC–MS) system for on-column derivatization and analysis. The on-column derivatization provided an added convenience (since a separate step was not necessary). Parameters affecting the derivatization and extraction were investigated. Under the most favorable conditions, the method demonstrated high extraction efficiency with low limits of detection of between 0.01 and 0.1μg/L, good linearity in the range of 0.05–50μg/L, to 0.5–100μg/L, and good repeatability (RSD below 9.2%, n =5). The proposed method was evaluated by determining carbamate pesticides in river water samples.

Smart polymer mediated purification and recovery of active proteins from inclusion bodies

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1235
Saurabh Gautam, Priyanka Dubey, Pranveer Singh, S. Kesavardhana, Raghavan Varadarajan, Munishwar N. Gupta
Obtaining correctly folded proteins from inclusion bodies of recombinant proteins expressed in bacterial hosts requires solubilization with denaturants and a refolding step. Aggregation competes with the second step. Refolding of eight different proteins was carried out by precipitation with smart polymers. These proteins have different molecular weights, different number of disulfide bridges and some of these are known to be highly prone to aggregation. A high throughput refolding screen based upon fluorescence emission maximum around 340nm (for correctly folded proteins) was developed to identify the suitable smart polymer. The proteins could be dissociated and recovered after the refolding step. The refolding could be scaled up and high refolding yields in the range of 8mgL⁻¹ (for CD4D12, the first two domains of human CD4) to 58mgL⁻¹ (for malETrx, thioredoxin fused with signal peptide of maltose binding protein) were obtained. Dynamic light scattering (DLS) showed that polymer if chosen correctly acted as a pseudochaperonin and bound to the proteins. It also showed that the time for maximum binding was about 50min which coincided with the time required for incubation (with the polymer) before precipitation for maximum recovery of folded proteins. The refolded proteins were characterized by fluorescence emission spectra, circular dichroism (CD) spectroscopy, melting temperature (T m), and surface hydrophobicity measurement by ANS (8-anilino1-naphthalene sulfonic acid) fluorescence. Biological activity assay for thioredoxin and fluorescence based assay in case of maltose binding protein (MBP) were also carried out to confirm correct refolding.

One step solvent bar microextraction and derivatization followed by gas chromatography–mass spectrometry for the determination of pharmaceutically active compounds in drain water samples

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1235
Liang Guo, Hian Kee Lee
For the first time, a simple and novel one-step combined solvent bar microextraction with derivatization with GC–MS analysis, was developed for the determination of pharmaceutically active compounds (PhACs) in water samples. In the procedure, the derivatization reagent was added in the extraction solvent (solvent bar), so that the analytes could be extracted from the aqueous sample and simultaneously derivatized in the solvent bar to enhance their volatility and improve chromatographic performance. After extraction, the derivatized analytes in the extract were directly injected into a GC–MS system for analysis. Six PhACs including naproxen, ibuprofen, ketoprofen, propranolol, diclofenac, and alprenolol were used here to develop and evaluate the method. The parameters affecting the derivatization and extraction efficiency including derivatization time and temperature, the proportion of derivatization reagent, the type of organic solvent, extraction time, extraction temperature, pH of sample solution, effect of ionic strength, and sample agitation speed, were investigated in detail. Under the most favorable conditions, the method provided good limits of detection ranging from 0.006 to 0.022μg/L, linearity (from 0.1–50 to 0.2–50μg/L, depending on analytes) and repeatability of extractions (RSDs below 9.5%, n =5). The proposed method was compared to hollow fiber protected liquid-phase microextraction and solid-phase microextraction, and showed higher extraction efficiency and/or shorter extraction time. The proposed method was applied to the determination of six PhACs in drain water, and was demonstrated to be simple, fast and efficient.

Application of step-wise gradient high-performance counter-current chromatography for rapid preparative separation and purification of diterpene components from Pseudolarix kaempferi Gordon

10 April 2012, 09:29:39

Publication year: 2012
Source:Journal of Chromatography A, Volume 1235
Shichao He, Shucai Li, Jianhong Yang, Haoyu Ye, Shijie Zhong, Hang Song, Yongkui Zhang, Cheng Peng, Aihua Peng, Lijuan Chen
In general, simultaneously separation and purification of components with a broad polarity range from traditional Chinese medicine (TCM) is a challenge by an ordinary high-speed counter-current chromatography (HSCCC) method. In this paper, we describes a rapid and efficient separation method of combining three-step gradient elution and two-step flow-rate gradient elution using high-performance counter-current chromatography (HPCCC) to separate 8 diterpene compounds simultaneously within 80min in a single run from the alcohol extract of Pseudolarix kaempferi Gordon. This separation process produced 166mg pseudolaric acid B O-β-d-glucopyranoside (PABGly), 152mg pseudolaric acid C (PAC), 8mg deacetylpseudolaric acid A (deacetylPAA), 5mg pseudolaric acid A O-β-d-glucopyranoside (PAAGly), 484mg pseudolaric acid B (PAB), 33mg pseudolaric acid B methyl ester (PAB methyl ester), 10mg pseudolaric acid A (PAA) and 18mg pseudolaric acid H (PAH) from 1.0g crude sample with purities of 98.6%, 99.6%, 92.3%, 92.2%, 99.2%, 99.4%, 98.3%, 91.0%, respectively. Our study indicates that the suitable combination of step-wise gradient elution and flow-rate gradient elution using HPCCC is an effective strategy to separate complex components from natural products. 

StarDrop 5.2 Adds New FieldAlign Plug-in Module

Optibrium, developer of software solutions for drug discovery, today announces a new version of its StarDrop™ platform. StarDrop 5.2 features a new plug-in module that provides users with access to Cresset’s FieldAlign™ technology, which offers a unique, 3-dimensional insight into the biological activity of their compounds. This new development is the first result of the technology exchange between Optibrium and Cresset announced earlier this year, and adds another powerful tool to StarDrop that will enable chemists to understand the 3D structure activity relationship (SAR) of their chemistry in order to optimise their compounds.
Achieving a combination of potency with appropriate ADME and safety properties is essential to the discovery of high quality drug candidates. Optibrium’s StarDrop platform helps to identify compounds with a good balance of properties by integrating in silico and experimentally measured data using a unique multi-parameter optimisation approach, chemical space visualisation and intuitive data analysis. StarDrop’s interactive designer with Glowing Molecule™ visualisation guides the exploration of compound design strategies with instant feedback on the impact of changes on a compound’s predicted properties. These core features can be extended with plug-in modules to predict key ADME properties and P450 metabolism, build and validate robust QSAR models of in-house compounds and data, and automatically generate new, relevant compound ideas. The new FieldAlign module in StarDrop adds a powerful 3D view of compound interactions that will complement StarDrop’s existing 2D QSAR models.
FieldAlign provides a unique insight into the biological activity, properties and interactions of molecules. Using fields, biologically meaningful comparisons can be made that are not limited by two-dimensional structure. FieldAlign is a powerful molecular design and 3D SAR tool that allows the molecular fields of multiple compounds to be compared in their bioactive conformations. By highlighting both similarities and differences between molecules, FieldAlign shows where and how lead molecules bind to their protein target. This enables regions of active molecules that can be replaced, to be quickly identified, to perfect the design of a new lead compound. Furthermore, given the 3D structure of an active molecule and a series of 2D compound structures, FieldAlign will generate the best 3D alignment for the compounds, scored and ranked according to their field similarities with the known active. With this information, small compound libraries can be screened to look for novel series with greater structural diversity, and the design of focused libraries can be optimised for synthesis or initial screening.
Version 5.2 also introduces new enhancements of StarDrop’s core capabilities, in particular a flexible tool for performing automatic R-group analysis. This new feature analyses a chemical series to interactively visualise the impact of variations to R-groups, linkers, atoms or fragments on compound properties to help chemists to further understand the SAR of their chemistry and identify new optimisation strategies.  StarDrop can also enumerate the full, combinatorial library to explore the properties of compounds that have not yet been synthesised and identify potential missed opportunities.
Matt Segall, CEO of Optibrium, commented “We are excited to be able to provide a great range of new features to our users, continuing to extend StarDrop’s seamlessly integrated environment that helps to guide the efficient identification of high quality compounds. We are particularly pleased that our new collaboration with Cresset has so quickly yielded an important new capability for the StarDrop platform and look forward to continuing to work with Cresset on further joint projects.”

Extensive Range of Bromodomain Protein Domains & Profiling Kits

AMSBIO provides an extensive portfolio of bromodomains and kits suitable for bromodomain profiling, inhibitor screening assays, and drug discovery.

Bromodomains (BRDs) are 110 amino acid long domains that are found in many chromatin associated proteins. Bromodomains can interact specifically with acetylated lysine.

The ability of bromodomain regulators to alter chromatin status and control gene expression is important in the development of certain human cancers, adipogenesis, energy metabolism and inflammation. Bromodomains are emerging as a new class of targets, alongside HATs and HDACs, which will be important in drug discovery. There are over 50 proteins containing one or more BRDs. Better understanding of bromodomains will also lead to better design of epigenetically-directed therapeutics.

For further information please visit www.amsbio.com/search-results.aspx?value=bromodomain or contact AMSBIO on tel. +44-1235-828200 or email info@amsbio.com.

Heat Sealer reproducibly seals microplates of all types & sizes

The new MiniSeal Plus heat sealer from Porvair Sciences operates with a very high force thereby ensuring high integrity sealing of deep well or even irregularly shaped microplates.

Building upon the proven track record of Porvair's trusted MiniSeal semi-automatic microplate sealer - MiniSeal Plus offers users even greater comfort and safety in use, together with unmatched reproducibility in sealing microplates of all types and sizes.

Designed for ease-of-use and installation the compact MiniSeal Plus just requires plugging into a single electrical outlet to operate.  Unlike larger and more expensive automated sealers the MiniSeal Plus does not require a compressed air supply to operate.  Controlled through a splash-proof keyboard a MiniSeal Plus can be installed, up to temperature and sealing plates within minutes of unpacking. The compact footprint, about the size of a sheet of A4 paper, means that MiniSeal Plus will fit just about anywhere - on your lab bench or inside a fumehood if required.

Rapid heat-up time, a real-time display of the sealing head temperature, automatic plate head detection and pre-cut sealing films combine to simplify your microplate sealing.  Drawer loading of microplates into the MiniSeal Plus is both quiet and eliminates the health and safety risks found with some heat sealing systems. In addition to accommodating regular microplates the MiniSeal Plus comes as standard with 2 plate adapters that also enable sealing of deep well and PCR plates.
The MiniSeal Plus is capable of producing an accurate and tight seal on any standard, deep well or PCR microplate from 3 to 48mm in height. Offering adjustable temperature heat-sealing from 50C up to 200C - MiniSeal is able to operate optimally with most foil and film seals.

Established in 1992, Porvair Sciences Ltd. expertise in microplate technology and manufacturing covers scientific fields including Life Sciences, Drug Discovery, Combinatorial Chemistry, Solid Phase Extraction, Protein Purification, High Throughput Screening, Proteomics and Genomics.  Porvair Sciences Ltd. is a wholly owned subsidiary of Porvair plc.

For further information on the MiniSeal Plus heat sealer please contact Porvair Sciences on telephone +44-1372-824290, email int.sales@porvair-sciences.com or visit the website at www.porvair-sciences.com