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:

Low density supercritical fluids precipitation of 9-cis and all trans-β-carotenes enriched particulates from Dunaliella salina

27 June 2013, 15:00:01

Publication date: 19 July 2013
Source:Journal of Chromatography A, Volume 1299
Author(s): Jian-Ren Chen , Jia-Jiuan Wu , Justin Chun-Te Lin , Yuan-Chuen Wang , Chiu-Chung Young , Chwen-Jen Shieh , Shih-Lan Hsu , Cheih-Ming J. Chang
In this study, supercritical anti-solvent (SAS) pulverization coupled with reverse phase elution chromatography was employed to isolate 9-cis and trans-β-carotenes from Dunaliella salina. Total concentration of 9-cis (134.7mg/g) and trans-β-carotene (204.2mg/g) was increased from 338.9mg/g of the ultrasonic extract to 859.7mg/g (338.9 for 9-cis and 520.8 for trans) of the elution fraction. The SAS pulverization of the collected fraction further produced submicron-sized particulates containing 932.1mg/g (355.6 for 9-cis and 576.5 for trans) of total β-carotenes with a recovery of 86.3% (83.9% for cis and 87.8% for trans). Effects of two SAS operational conditions on the purity, recovery of total β-carotenes, mean size and morphology of the precipitates were obtained from an experimentally designed method. Generation of micronized particulates enriched with 9-cis and trans-β-carotenes by low-density SAS was proved to be feasible and environmental benign.

Facile fabrication of reduced graphene oxide-encapsulated silica: A sorbent for solid-phase extraction

27 June 2013, 15:00:01

Publication date: 19 July 2013
Source:Journal of Chromatography A, Volume 1299
Author(s): Yan-Bo Luo , Gang-Tian Zhu , Xiao-Shui Li , Bi-Feng Yuan , Yu-Qi Feng
In this study, a facile hydrothermal reduction strategy was developed for the preparation of reduced graphene oxide-encapsulated silica (SiO2@rGO). Compared with other conventional methods for the synthesis of SiO2@rGO, the proposed strategy endowed the obtained SiO2@rGO with larger amount of immobilized rGO. The prepared functionalized silica shows remarkable adsorption capacity toward chlorophenols (CPs) and peptides. When it was used as solid-phase extraction (SPE) sorbent, a superior recovery could be obtained compared to commercial sorbents, such as C18 silica, graphitized carbon black and carbon nanotubes. Based on these, the prepared material was used as SPE sorbent for the enrichment of CPs, and a method for the analysis of CPs in water samples was established by coupling SPE with high performance liquid chromatography–ultra violet detection (SPE-HPLC/UV). In addition, the obtained SiO2@rGO was further successfully extended to the enrichment of peptides in bovine serum albumin (BSA) digests.

Application of a strong anion exchange material in electrostatic repulsion–hydrophilic interaction chromatography for selective enrichment of glycopeptides

27 June 2013, 15:00:01

Publication date: 19 July 2013
Source:Journal of Chromatography A, Volume 1299
Author(s): Liwei Cao , Long Yu , Zhimou Guo , Xiuling Li , Xinya Xue , Xinmiao Liang
Glycoproteins are involved in various cellular activities, including inter- and extracellular signaling. However, glycopeptide signals are significantly suppressed by coeluting non-glycosylated peptides in mass spectrometry-based analysis. For detailed elucidation of the biological functions of glycoproteins, selective enrichment of glycopeptides from non-glycosylated peptides is crucial. In the present study, a SAX material, XCharge SAX, was used in a column in the ERLIC mode with the aim of specifically enriching glycopeptides. Enrichment conditions were initially optimized, and selectivity, glycosylation heterogeneity coverage and detection sensitivity of XCharge SAX were subsequently assessed. In the selectivity assessment, glycopeptides were effectively isolated from a peptide mixture (human serum immunoglobulin G (IgG) and human serum albumin digests) and a tryptic digest of human serum using XCharge SAX. In the evaluation of glycosylation heterogeneity coverage, five glycosites and eleven glycopeptides from horseradish peroxidase were identified after enrichment with XCharge SAX. In detection sensitivity assessment, glycopeptides within four orders of magnitude were identified after enrichment with XCharge SAX. In addition, volatile solvents were used in the loading and eluting buffers so that desalting was not necessary for ERLIC fractions. Our results collectively support the utility of XCharge SAX as a suitable chromatographic material for global glycosylation site analysis.

Determination of anionic surface active agents using silica coated magnetite nanoparticles modified with cationic surfactant aggregates

27 June 2013, 15:00:01

Publication date: 19 July 2013
Source:Journal of Chromatography A, Volume 1299
Author(s): Francisco Pena-Pereira , Regina M.B.O. Duarte , Tito Trindade , Armando C. Duarte
The development of a novel methodology for extraction and preconcentration of the most commonly used anionic surface active agents (SAAs), linear alkylbenzene sulfonates (LAS), is presented herein. The present method, based on the use of silica–magnetite nanoparticles modified with cationic surfactant aggregates, was developed for determination of C10–C13 LAS homologues. The proposed methodology allowed quantitative recoveries of C10–C13 LAS homologues by using a reduced amount of magnetic nanoparticles. Limits of detection were in the range 0.8–1.9μgL⁻¹ for C10–C13 LAS homologues, while the repeatability, expressed as relative standard deviation (RSD), ranged from 2.0 to 3.9% (N =6). Finally, the proposed method was successfully applied to the analysis of a variety of natural water samples.

Supported liquid membrane extraction coupled in-line to commercial capillary electrophoresis for rapid determination of formate in undiluted blood samples

27 June 2013, 15:00:01

Publication date: 19 July 2013
Source:Journal of Chromatography A, Volume 1299
Author(s): Pavla Pantůčková , Pavel Kubáň , Petr Boček
A cheap, disposable sample pretreatment device with planar supported liquid membrane (SLM) was proposed, assembled and placed into an autosampler carousel of a commercial capillary electrophoresis (CE) instrument for automated pretreatment and analysis of formate in undiluted whole blood and serum samples. All analytical procedures except for filling the pretreatment device with donor and acceptor solutions, i.e., extraction across SLM, injection of the extracted sample and CE-UV determination of formate, were performed fully automatically. The pretreatment device required only μL volumes of blood sample and organic solvent per extraction and was disposed off after each extraction. Good repeatability of peak areas (≤7.7%) and migration times (≤1.5%), linear relationship (r ² =0.998–0.999) and limits of detection (≤35μM) were achieved. The overall analytical process including blood withdrawal, filling the SLM device with respective solutions, extraction of blood sample, injection into separation capillary and CE separation of formate from other anions took less than 4min. The method was proved useful by direct determination of elevated formate concentrations in undiluted serum samples of a methanol intoxicated patient. Due to its compatibility with currently commercially available CE instrumentation, disposability of extraction devices, minimum sample handling/consumption, and short extraction/analysis times, the developed method might be attractive for rapid diagnosis of methanol poisoning in clinical and toxicological laboratories.

Polyethersulfone solid-phase microextraction followed by liquid chromatography quadrupole time-of-flight mass spectrometry for benzotriazoles determination in water samples

27 June 2013, 15:00:01

Publication date: 19 July 2013
Source:Journal of Chromatography A, Volume 1299
Author(s): J. Casado , I. Rodríguez , M. Ramil , R. Cela
A microextraction method for the determination of 1H-benzotriazole (BTri), and four polar derivatives (4 and 5-methyl-1H-benzotriazole, 4-TTri and 5-TTri; 5,6-dimethyl-1H-benzotriazole, XTri; and 5-chloro-1H-benzotriazole, 5-ClBTri), in surface and wastewater samples is presented. Analytes were pre-concentrated using a disposable, low cost polyethersulfone (PES) sorbent and further analysed by liquid chromatography quadrupole time-of-flight mass spectrometry (LC–QTOF-MS). Parameters affecting the efficiency of sample preparation (extraction conditions and desorption solvent) and those controlling the performance of LC–MS determination were investigated. Analytes were extracted from 15mL water samples, containing a 30% (w/v) of sodium chloride (4.5g) and adjusted at pH 4.5, using a tubular PES sorbent (5cm length×0.7mm o.d., sorbent volume 42μL). After methanol desorption and solvent exchange, benzotriazoles were determined by LC–MS, with chromatograms extracted using a mass window of 20ppm, centred in their [M+H]⁺ ions. The identity of chromatographic peaks was confirmed with accurate ion product scan (MS/MS) spectra. The method provided limits of quantification (LOQs) between 0.005 and 0.100μgL⁻¹, and relative recoveries from 81% to 124% (except for XTri in sewage samples, ca. 60%) with associated standard deviations between 2% and 9%. When compared with polydimethylsiloxane covered stir-bars (coating volume 24μL), the PES polymer achieved significant higher responses (5–20-fold) for these polar pollutants. BTri and tolyltriazoles (4-TTri and 5-TTri) were found in urban sewage and river water samples, affected by wastewater discharges, with the maximum concentration (5.9μgL⁻¹) corresponding to BTri in raw wastewater.

Development of a solid-phase extraction liquid chromatography tandem mass spectrometry method for benzotriazoles and benzothiazoles in wastewater and recycled water

27 June 2013, 15:00:01

Publication date: 19 July 2013
Source:Journal of Chromatography A, Volume 1299
Author(s): Clara H. Loi , Francesco Busetti , Kathryn L. Linge , Cynthia A. Joll
Two methods employing solid-phase extraction and liquid chromatography tandem mass spectrometry were developed for the analysis of benzotriazoles (BTs) and benzothiazoles (BThs), compounds which are commonly found in a large variety of commercial and household products. The first method was able to detect 7 BTs and 7 BThs, the largest suite of BTs and BThs analysed in a single method to-date, but could not distinguish between the isomers, 4-methylbenzotriazole (4-MeBT) and 5-methylbenzotriazole (5-MeBT). Therefore, a second method was developed to achieve the chromatographic separation of 4-MeBT and 5-MeBT. The methods were validated for ultrapure water and secondary wastewater, and method limits of detection (MLD) for BTs and BThs (for the primary method) ranged from 0.1 to 58ngL⁻¹ for ultrapure water, and 2 to 322ngL⁻¹ for secondary wastewater. For the secondary method, MLDs for 4- and 5-MeBT ranged from 8 to 12ngL⁻¹ for ultrapure water, and 388 to 406ngL⁻¹ for secondary wastewater. Analysis of secondary wastewater and reverse osmosis (RO) treated water from an advanced water recycling plant in Australia is presented, and represents the first reported data from the analysis of BTs and BThs in recycled water. Some of these compounds were found to persist through wastewater treatment and incompletely removed by RO treatment. Benzotriazole (BT), 4-MeBT, 5-MeBT and 2-(methylthio)benzothiazole were detected in secondary wastewater, however the latter compound was not quantifiable. Concentrations of BT and tolyltriazoles (TTs, i.e. sum of 4- and 5-MeBT, detected with the primary method) in secondary wastewater were 3.3 (±0.02) and 2.8 (±0.04)μgL⁻¹, respectively. These same compounds were also detected in the post-RO water samples at concentrations of 974 (±28)ngL⁻¹ for BT and 416(±34)ngL⁻¹ for TTs. 2-Hydroxybenzothiazole was also detected in the post-RO water samples, however it was not quantifiable. Removal efficiencies for RO treatment were calculated to be between 70% and 85% for BT and TTs.

Relative importance of column and adsorption parameters on the productivity in preparative liquid chromatography. I: Investigation of a chiral separation system

27 June 2013, 15:00:01

Publication date: 19 July 2013
Source:Journal of Chromatography A, Volume 1299
Author(s): Patrik Forssén , Jörgen Samuelsson , Torgny Fornstedt
Starting out from an experimental chiral separation system we have used computer simulations for a systematic investigation on how the maximum productivity depends on changes in column length, packing particle size, column efficiency, back pressure, sample concentration/solubility, selectivity, retention factor of the first eluting component and monolayer saturation capacity. The study was performed by changing these parameters, one at a time, and then calculating the corresponding change in maximum productivity. The three most important parameters for maximum production rate was found to be (i) the selectivity (ii) the retention factor of the first eluting component and (iii) the column length. Surprisingly, the column efficiency and sample concentration/solubility were of minor importance. These findings can be used as rough guidelines for column selection, e.g. a low-efficiency column are more likely perform better, in terms of productivity, than a high-efficiency column that have higher retention factor for the first eluting component. 

Diluting and Proportional Fluid Control with ±1% Precision for Medical & Analytical Instrumentation

The STH and STQ Duplex metering pumps from Fluid Metering, Inc. are ideal for precision mixing, diluting, and proportional metering for OEM medical, analytical, and industrial instrumentation.

FMI’s OEM Duplex Metering Pumps consist of two FMI valveless pump heads direct coupled to a single variable stepper motor drive. The displacement of each pump head is independently adjustable, and a variety of pump head sizes can be used in combinations to achieve dispensing ratios from 1:1 up to 500:1.
Fluid Metering’s OEM Duplex Metering Pumps feature FMI’s patented CeramPump® valveless piston pumping technology and are the valveless-syringe alternative to conventional syringe pumps. The CeramPump® has only one moving part in the fluid path, a sapphire-hard ceramic piston, which accomplishes both pumping and valving functions, without valves.

The result is a unique valveless pump design which eliminates multiple syringes, valves, actuators, and drivers required by conventional syringe pumps for continuous fluid dispensing and metering. By eliminating valves and utilizing ceramic internals, FMI OEM Duplex Pumps will dispense millions of maintenance-free cycles at ±1% precision without recalibration.

In addition, the FMI pump has unidirectional continuous flow, utilizing two separate ports for input and output. Throughput of the FMI CeramPump® is significantly increased over syringe designs which both fill and dispense through the same single port.

For over 50 years FMI pumps have been used medical diagnostic and analytical instrumentation, laboratory R&D, chemical process, pharmaceutical packaging, water treatment, environmental monitoring, food processing and much more.

For additional information, Call toll free 1-800-223-3388 or 1-516-922-6050, FAX 1-516-624-8261, email: pumps@fmipump.com or visit our website at www.fmipump.com which now features “Live Help”, an online direct connection to FMI’s application experts.

Calypso Succeeds in ABRF-MIRG Study

Wyatt Technology is pleased to report the success of the CalypsoÒ composition-gradient multi-angle light scattering (CG-MALS) system in a study conducting by the Molecular Interactions Research Group (MIRG) of the Association of Biomolecular Research Facilities (ABRF). The conclusions of the 2012 MIRG study were announced at the ABRF 2013 annual meeting in Palm Springs earlier this month.
In the study, a pair of unknown proteins, prepared and characterized by the ABRF, was sent out to multiple labs to determine binding affinity and stoichiometry. In a single afternoon consisting of 2 CG-MALS runs, the Wyatt Calypso system correctly determined that Protein Y (26.3 kDa) contains two binding sites for Protein X (11.9 kDa).
The first X binds with KD of 10 nM and the second X binds with 14 μM. This analysis agreed perfectly with extensive analytical ultracentrifugation (AUC) and isothermal titration calorimetry (ITC) measurements performed by ABRF prior to distributing the samples.
CG-MALS was the only solution-based technique utilized among the participating labs. Other participants used surface plasmon resonance (SPR) instruments which require immobilization of one of the binding partners. Interestingly, the affinities determined by SPR were significantly weaker than those found by any of the solution-based measurements (AUC, ITC, CG-MALS), possibly indicating that immobilization modifies this interaction.
For further details see these two documents:
http://www.abrf.org/ResearchGroups/MolecularInteractions/Studies/ABRF2013-MIRGsession1-Yamniuk.pdf

http://www.abrf.org/ResearchGroups/MolecularInteractions/Studies/ABRF2013-MIRGsession2-Yadav.pdf

Just Published: Biosensors & Bioelectronics

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:

Biosensors & Bioelectronics
http://rss.sciencedirect.com/publication/science/5223

Selected papers from the latest issue:

Electrochemical affinity biosensors for detection of mycotoxins: A review

26 June 2013, 04:25:43

Publication date: 15 November 2013
Source:Biosensors and Bioelectronics, Volume 49
Author(s): Juan C. Vidal , Laura Bonel , Alba Ezquerra , Susana Hernández , Juan R. Bertolín , Carlota Cubel , Juan R. Castillo
This review discusses the current state of electrochemical biosensors in the determination of mycotoxins in foods. Mycotoxins are highly toxic secondary metabolites produced by molds. The acute toxicity of these results in serious human and animal health problems, although it has been only since early 1960s when the first studied aflatoxins were found to be carcinogenic. Mycotoxins affect a broad range of agricultural products, most important cereals and cereal-based foods. A majority of countries, mentioning especially the European Union, have established preventive programs to control contamination and strict laws of the permitted levels in foods. Official methods of analysis of mycotoxins normally requires sophisticated instrumentation, e.g. liquid chromatography with fluorescence or mass detectors, combined with extraction procedures for sample preparation. For about sixteen years, the use of simpler and faster analytical procedures based on affinity biosensors has emerged in scientific literature as a very promising alternative, particularly electrochemical (i.e., amperometric, impedance, potentiometric or conductimetric) affinity biosensors due to their simplicity and sensitivity. Typically, electrochemical biosensors for mycotoxins use specific antibodies or aptamers as affinity ligands, although recombinant antibodies, artificial receptors and molecular imprinted polymers show potential utility. This article deals with recent advances in electrochemical affinity biosensors for mycotoxins and covers complete literature from the first reports about sixteen years ago.

Dielectric spectroscopy as a viable biosensing tool for cell and tissue characterization and analysis

26 June 2013, 04:25:43

Publication date: 15 November 2013
Source:Biosensors and Bioelectronics, Volume 49
Author(s): Khalil Heileman , Jamal Daoud , Maryam Tabrizian
The use of dielectric spectroscopy to carry out real time observations of cells and to extract a wealth of information about their physiological properties has expanded in recent years. This popularity is due to the simple, easy to use, non-invasive and real time nature of dielectric spectroscopy. The ease of integrating dielectric spectroscopy with microfluidic devices has allowed the technology to further expand into biomedical research. Dielectric spectra are obtained by applying an electrical signal to cells, which is swept over a frequency range. This review covers the different methods of interpreting dielectric spectra and progress made in applications of impedance spectroscopy for cell observations. First, methods of obtaining specific electrical properties of cells (cell membrane capacitance and cytoplasm conductivity) are discussed. These electrical properties are obtained by fitting the dielectric spectra to different models and equations. Integrating models to reduce the effects of the electrical double layer are subsequently covered. Impedance platforms are then discussed including electrical cell substrate impedance sensing (ECIS). Categories of ECIS systems are divided into microelectrode arrays, interdigitated electrodes and those that allow differential ECIS measurements. Platforms that allow single cell and sub-single cell measurements are then discussed. Finally, applications of impedance spectroscopy in a range of cell observations are elaborated. These applications include observing cell differentiation, mitosis and the cell cycle and cytotoxicity/cell death. Future applications such as drug screening and in point of care applications are then covered.

Graphical abstract

Fe3O4 magnetic nanoparticles/reduced graphene oxide nanosheets as a novel electrochemical and bioeletrochemical sensing platform

26 June 2013, 04:25:43

Publication date: 15 November 2013
Source:Biosensors and Bioelectronics, Volume 49
Author(s): Hazhir Teymourian , Abdollah Salimi , Somayeh Khezrian
We have developed Fe3O4 magnetic nanoparticles/reduced graphene oxide nanosheets modified glassy carbon (Fe3O4/r-GO/GC) electrode as a novel system for the preparation of electrochemical sensing platform. Decorating Fe3O4 nanoparticles on graphene sheets was performed via a facile one-step chemical reaction strategy, where the reduction of GO and the in-situ generation of Fe3O4 nanoparticles occurred simultaneously. Characterization of as-made nanocomposite using X-ray diffraction (XRD), transmission electron microscopy (TEM) and alternative gradient force magnetometry (AGFM) clearly demonstrate the successful attachment of monodisperse Fe3O4 nanoparticles to graphene sheets. Electrochemical studies revealed that the Fe3O4/r-GO/GC electrode possess excellent electrocatalytic activities toward the low potential oxidation of NADH (0.05V vs. Ag/AgCl) as well as the catalytic reduction of O2 and H2O2 at reduced overpotentials. Via immobilization of lactate dehydrogenase (LDH) as a model dehydrogenase enzyme onto the Fe3O4/r-GO/GC electrode surface, the ability of modified electrode for biosensing lactate was demonstrated. In addition, using differential pulse voltammetry (DPV) to investigate the electrochemical oxidation behavior of ascorbic acid (AA), dopamine (DA) and uric acid (UA) at Fe3O4/r-GO/GC electrode, the high electrocatalytic activity of the modified electrode toward simultaneous detection of these compounds was indicated. Finally, based on the strong electrocatalytic action of Fe3O4/r-GO/GC electrode toward both oxidation and reduction of nitrite, a sensitive amperometric sensor for nitrite determination was proposed. The Fe3O4/r-GO hybrid presented here showing favorable electrochemical features may hold great promise to the development of electrochemical sensors, molecular bioelectronic devices, biosensors and biofuel cells.

A cardiomyocyte-based biosensor for antiarrhythmic drug evaluation by simultaneously monitoring cell growth and beating

26 June 2013, 04:25:43

Publication date: 15 November 2013
Source:Biosensors and Bioelectronics, Volume 49
Author(s): Tianxing Wang , Ning Hu , Jiayue Cao , Jieying Wu , Kaiqi Su , Ping Wang
Drug-induced cardiotoxicity greatly endangers the human health and results in resource waste. Also, it is a leading attribution to drug withdrawal and late-stage attrition in pharmaceutical industry. In the study, a dual function cardiomyocyte-based biosensor was introduced for rapid drug evaluation with xCELLigence RTCA Cardio system. The cardiomyocyte-based biosensor can monitor the cardiomyocyte growth and beating status simultaneously under the drug effects. Two typical cardiovascular drug, verapamil and flecainide were selected as treatment agents to test the performance of this biosensor. The experiment results showed that the performance of cardiomyocyte-based biosensor verified the basic drug effects by beating status and also tested the drug cytotoxicity by the cell index curves of cardiomyocyte growth. Based on the advanced sensor detection technology and cell culture technology, this cardiomyocyte-based biosensor will be a utility platform for the drug preclinical assessment.

A silver–palladium alloy nanoparticle-based electrochemical biosensor for simultaneous detection of ractopamine, clenbuterol and salbutamol

26 June 2013, 04:25:43

Publication date: 15 November 2013
Source:Biosensors and Bioelectronics, Volume 49
Author(s): Huan Wang , Yong Zhang , He Li , Bin Du , Hongmin Ma , Dan Wu , Qin Wei
A multiplexed electrochemical biosensor has been developed for fast and sensitive detection of ractopamine (RAC), salbutamol (SAL) and clenbuterol (CLB) based on reduced graphene oxide (rGO) and silver–palladium alloy nanoparticles (AgPd NPs). In this paper, rGO with high conductivity was used as an electrode material to immobilize artificial antigens and amplify electrochemical signal. AgPd NPs are used to label antibodies and generate a strong electrochemical signal in phosphate buffered saline (PBS) without any other substrates. Screen-printed carbon electrode (SPCE) and competition strategy were adopted to achieve simultaneous detection of RAC, SAL and CLB without cross-talk between adjacent electrodes. This method can simultaneously detect RAC, SAL and CLB ranging from 0.01 to 100ngmL⁻¹ with detection limits of 1.52pgmL⁻¹, 1.44pgmL⁻¹ and 1.38pgmL⁻¹, respectively. Satisfactory results are achieved in pork sample analysis. The designed strategy provides a promising potential in determination of other biological samples.

Acetylcholinesterase biosensor based on SnO2 nanoparticles–carboxylic graphene–nafion modified electrode for detection of pesticides

26 June 2013, 04:25:43

Publication date: 15 November 2013
Source:Biosensors and Bioelectronics, Volume 49
Author(s): Qing Zhou , Long Yang , Guangcan Wang , Yun Yang
A sensitive amperometric acetylcholinesterase (AChE) biosensor, based on SnO2 nanoparticles (SnO2 NPs), carboxylic graphene (CGR) and nafion (NF) modified glassy carbon electrode (GCE) for the detection of methyl parathion and carbofuran has been developed. The nanocomposites of SnO2 NPs and CGR was synthesized and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. Chitosan (CS) was used to immobilize AChE on SnO2 NPs–CGR–NF/GCE and to improve electronic transmission between AChE and SnO2 NPs–CGR–NF/GCE. NF was used as the protective membrane for the AChE biosensor. The SnO2 NPs–CGR–NF nanocomposites with excellent conductivity, catalysis and biocompatibility offered an extremely hydrophilic surface for AChE adhesion. The AChE biosensor showed favorable affinity to acetylthiocholine chloride (ATCl) and could catalyze the hydrolysis of ATCl with an apparent Michaelis–Menten constant value of 131μM. The biosensor detected methyl parathion in the linear range from 10⁻¹³ to 10⁻¹⁰ M and from 10⁻¹⁰ to 10⁻⁸ M. The biosensor detected carbofuran in the linear range from 10⁻¹² to 10⁻¹⁰ M and from 10⁻¹⁰ to 10⁻⁸ M. The detection limits of methyl parathion and carbofuran were 5×10⁻¹⁴ M and 5×10⁻¹³ M, respectively. The biosensor exhibited low applied potential, high sensitivity and acceptable stability, thus providing a promising tool for analysis of pesticides.

Electrochemical impedimetric immunosensor for the detection of measles-specific IgG antibodies after measles infections

26 June 2013, 04:25:43

Publication date: 15 November 2013
Source:Biosensors and Bioelectronics, Volume 49
Author(s): Philani Mashazi , Phumlani Tetyana , Sibulelo Vilakazi , Tebello Nyokong
The detection of measles-specific primary antibodies (IgG) using electrochemical impedimetric immunosensors is reported. The optimum conditions for electrode saturation were reached after 40min for 1μgml⁻¹ antibody concentrations. Surface roughness using AFM increased with each immobilization or antigen-antibody reaction step clearly confirming the surface modification and recognition between antigen and antibody. The human serum (HS) and new-born calf serum (NCS) spiked with antigen-specific antibody were studied to mimic the real sample analysis. The HS and NCS sera containing antibodies due to measles exhibited correlation between the increasing antibody serum concentrations and the charge-transfer resistance (electrochemically measured). This work clearly showed the potential use of impedance as the preferred electrochemical method for detecting measles-antibodies in label-free manner.

Ultrasensitive electrochemical immunoassay for DNA methyltransferase activity and inhibitor screening based on methyl binding domain protein of MeCP2 and enzymatic signal amplification

26 June 2013, 04:25:43

Publication date: 15 November 2013
Source:Biosensors and Bioelectronics, Volume 49
Author(s): Huanshun Yin , Yunlei Zhou , Zhenning Xu , Mo Wang , Shiyun Ai
In this work, we fabricated a novel electrochemical immunosensor for detection of DNA methylation, analysis of DNA MTase activity and screening of MTase inhibitor. The immunosensor was on the basis of methyl binding domain protein of MeCP2 as DNA CpG methylation recognization unit, anti-His tag antibody as “immuno-bridge” and horseradish peroxidase labeled immuneglobulin G functionalized gold nanoparticles (AuNPs–IgG–HRP) as signal amplification unit. In the presence of M. SssI MTase, the symmetrical sequence of 5′-CCGG-3′ was methylated and then recognized by MeCP2 protein. By the immunoreactions, anti-His tag antibody and AuNPs–IgG–HRP was captured on the electrode surface successively. Under the catalysis effect of HRP towards hydroquinone oxidized by H2O2, the electrochemical reduction signal of benzoquinone was used to analyze M. SssI MTase activity. The electrochemical reduction signal demonstrated a wide linear relationship with M. SssI concentration ranging from 0.05unit/mL to 90unit/mL, achieving a detection limit of 0.017unit/mL (S/N=3). The most important advantages of this method were its high sensitivity and good selectivity, which enabled the detection of even one-base mismatched sequence. In addition, we also verified that the developed method could be applied for screening the inhibitors of DNA MTase and for developing new anticancer drugs.

Graphical abstract

A label-free electrochemiluminescence cytosensors for specific detection of early apoptosis

26 June 2013, 04:25:43

Publication date: 15 November 2013
Source:Biosensors and Bioelectronics, Volume 49
Author(s): Lin Zhang , Jin-Huan Jiang , Jian-Jun Luo , Lu Zhang , Ji-Ye Cai , Jiu-Wei Teng , Pei-Hui Yang
A novel electrochemiluminescence (ECL) cytosensors was developed for the detection of early apoptotic cells by the specific interaction between Annexin V and phosphatidylserine(PS) based on ECL signal of CdS-QDs. Immobilization of Annexin V on a L-cysteine-capped CdS-QDs/Polyaniline nanofibers (PANI-NF) resulted in the stable and high loading of Annexin V on the sensor surface and the possibility of sensitivity enhancement. Early apoptotic cells showed an increased exposure of PS on the cell membrane caused by physiological and pathological response reactions, leading to a strong interaction between the apoptotic cells and the sensor surface, which could be probed by the ECL. Using a real of early apoptotic HepG2 cell induced by resveratrol (RVL), the proposed novel strategy has demonstrated its simplicity, high sensitivity, good selectivity and high reproducibility and label-free capability which might hold a great potential for rapid detection of cell apoptosis and drug screening. The results from this approach have showed good agreement with those obtained using inverted microscope, flow cytometry(FCM) and Atomic force microscopy(AFM). The linear range for early apoptotic cells detection ranged from 500 to 1.0×10⁶ cellsmL⁻¹ with a detection limit of 500 cellsmL⁻¹. The reported strategy has provided a promising platform for highly sensitive cytosensing and convenient screening of some clinically anticancer drugs. 

The London Centre for Nanotechnology has installed an Oxford Instruments PlasmaPro NGP80 system for nanotechnology research

Oxford Instruments, a leader in plasma etch and deposition equipment and processes, has recently installed and commissioned a PlasmaPro NGP80 RIE etch system in the London Centre for Nanotechnology (LCN) for use in their research.

The PlasmaPro NGP80 is a compact, small footprint system that is easy to site and operate, without compromising on process quality. It can process from the smallest wafer pieces to 200mm wafers, while the open load design allows fast wafer loading and unloading, ideal for the research being undertaken at LCN.

Steve Etienne, Cleanroom Manager of the LCN commented, “The LCN is a multidisciplinary enterprise operating at the forefront of science and technology, whose purpose is to solve global problems in information processing, healthcare, energy and environment through the application of nanoscience and nanotechnology. We chose the Oxford Instruments tool for our research programme as the excellent technical specification suited our requirements, and in addition, the well founded reputation of their processing tools is backed up by expert specialist support.”

“We are very excited that our systems are being used in medical research at the LCN“, commented Mark Vosloo, Sales, CS and Marketing Director for Oxford Instruments Plasma Technology, “Oxford Instruments’ large Process Applications and Technology teams constantly research to innovate and offer new processes on our portfolio of advanced plasma etch and deposition processes and techniques. Through focusing on our customers’ current and future needs, Oxford Instruments is able to provide leading process solutions, maintained through our excellent global support network.”

Just Published: Analytica Chimica Acta

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:

Analytica Chimica Acta
http://rss.sciencedirect.com/publication/science/5216

Selected papers from the latest issue:

A potential tool for high-resolution monitoring of ocean acidification

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Aron Hakonen , Leif G. Anderson , Johan Engelbrektsson , Stefan Hulth , Bengt Karlson
Current anthropogenic carbon dioxide emissions generate besides global warming unprecedented acidification rates of the oceans. Recent evidence indicates the possibility that ocean acidification and low oceanic pH may be a major reason for several mass extinctions in the past. However, a major bottleneck for research on ocean acidification is long-term monitoring and the collection of consistent high-resolution pH measurements. This study presents a low-power (<1W) small sample volume (25μL) semiconductor based fluorescence method for real-time ship-board pH measurements at high temporal and spatial resolution (approximately 15s and 100m between samples). A 405nm light emitting diode and the blue and green channels from a digital camera was used for swift detection of fluorescence from the pH sensitive dye 6,8-Dihydroxypyrene-1,3-disulfonic acid in real-time. Main principles were demonstrated by automated continuous measurements of pH in the surface water across the Baltic Sea and the Kattegat region with a large range in salinity (∼3–30) and temperature (∼0–25°C). Ship-board precision of salinity and temperature adjusted pH measurements were estimated as low as 0.0001 pH units.

Graphical abstract

Liquid phase microextraction strategies combined with total reflection X-ray spectrometry for the determination of low amounts of inorganic antimony species in waters

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Eva Marguí , Marta Sagué , Ignasi Queralt , Manuela Hidalgo
In the present study, and taking into account the microanalytical capability of total reflection X-ray spectrometry (TXRF), we explored the possibilities of hollow fibre liquid-phase microextraction (HF-LPME) and dispersive liquid–liquid microextraction (DLLME) combined with TXRF for the determination of low amounts of inorganic Sb species in waters. For each of the LPME configurations aforementioned, experimental parameters affecting Sb extraction but specially the proper sample preparation process (deposition volume on the reflective carrier and drying mode) and measurement conditions for subsequent TXRF analysis have been carefully evaluated. The best analytical strategy for the determination of Sb(III) and Sb(V) in the low μgL⁻¹ range was found to be the application of the DLLME mode before TXRF analysis. The developed methodology was successfully applied to the determination of inorganic Sb speciation in different types of spiked water samples.

Graphical abstract

Electrochemical sensor based on chlorohemin modified molecularly imprinted microgel for determination of 2,4-dichlorophenol

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Jin Zhang , Jianping Lei , Huangxian Ju , Chaoying Wang
A newly designed molecularly imprinted polymer (MIP) was synthesized and successfully utilized as a recognition element of an amperometric sensor for 2,4-dichlorophenol (2,4-DCP) detection. The MIP with a well-defined structure could imitate the dehalogenative function of the natural enzyme chloroperoxidase for 2,4-DCP. Imprinted sensor was fabricated in situ on a glassy carbon electrode surface by drop-coating the 2,4-DCP imprinted microgel suspension and chitosan/Nafion mixture. Under optimized conditions, the sensor showed a linear response in the range of 5.0–100μmolL⁻¹ with a detection limit of 1.6μmolL⁻¹. Additionally, the imprinted sensor demonstrated higher affinity to target 2,4-DCP over competitive chlorophenolic compounds than non-imprinted sensor. It also exhibited good stability and acceptable repeatability. The proposed sensor could be used for the determination of 2,4-DCP in water samples with the recoveries of 96.2–111.8%, showing a promising potential in practical application.

Graphical abstract

Determination of aminothiols by liquid chromatography with amperometric detection at a silver electrode: Application to white wines

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Ahmad Sarakbi , Zeynep Aydogmus , Angela Dago , Dominique Mertens , Jean-Yves Dewert , Jean-Michel Kauffmann
Liquid chromatography coupled to a silver electrode based flow-through amperometric detector (LC-EC-Ag) was developed for the determination of aminothiols in white wines. The C18 reversed phase LC system operated in the isocratic mode at 0.7mLmin⁻¹ and used an acidic mobile phase composed of formic acid, EDTA, sodium nitrate, sodium hydroxide, and methanol 1% (v/v) at pH 4.5. The working electrode operated at 0.08V vs Ag/AgCl, 3M KCl and its manual cleaning was realized once a month by smoothing on a polishing cloth. The analyzed aminothiols were resolved and eluted within 4min, and all standard curves were linear in the range 2×10⁻⁷–2×10⁻⁵ M. The analyzed wine samples needed no preparation other than dilution with the mobile phase. The concentration of cysteine (CYS), homocysteine (HCYS), glutathione (GSH) and N-acetylcysteine (NAC) in bottled white wines, determined by the method of standard addition, was found to be in the low μM range (0.2–2mgL⁻¹) depending on the wine type and its age.

Graphical abstract

Comparative studies on zirconia and graphene composites obtained by one-step and stepwise electrodeposition for deoxyribonucleic acid sensing

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Tao Yang , Xiuhong Guo , Qianqian Kong , Ruirui Yang , Qianhe Li , Kui Jiao
In this paper, the comparison of two kinds of electrochemically reduced graphene oxide (ERGNO) and zirconia composites, obtained by one-step (ZrO2–ERGNO) and stepwise (ZrO2/ERGNO) electrodeposition for DNA sensing, is systematically studied. The resulting composites were characterized by scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry. The results indicated that the ZrO2–ERGNO presented fine globular nanostructure. However, ZrO2/ERGNO presented agglomerate massive microstructure due to the absence of the oxygen-containing groups of graphene oxide, confirming the oxygen-containing groups provided a better affinity for the deposition of ZrO2. Due to the strong binding of the phosphate groups of DNA with the zirconia film, DNA probes were attached on the ZrO2-based composites. ZrO2–ERGNO/Au owning fine nanostructure presented larger surface area than microstructured ZrO2/ERGNO/Au. Moreover, compared with microstructured ZrO2/ERGNO, the nanostructured ZrO2–ERGNO provided more accessible space for immobilized DNA probe hybridization with target sequence, which consequently resulted in higher hybridization efficiency. Therefore, the ZrO2–ERGNO was chosen for fabricating DNA sensor with a limit of detection 1.21×10⁻¹⁴ molL⁻¹.

Graphical abstract

An ultrasensitive iron(III)-complex based hydrogen peroxide electrochemical sensor based on a nonelectrocatalytic mechanism

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Pan Li , Yu Ding , Zhaoyang Lu , Yu Chen , Yiming Zhou , Yawen Tang , Chenxin Cai , Tianhong Lu
In this communication, the first nonelectrocatalysis-type hydrogen peroxide electrochemical sensor is reported. The electroactive iron(III) diethylenetriaminepentaacetic acid (DTPA-Fe^III) complex is immobilized on the cysteamine (cys) modified nanoporous gold (NPG) films by covalent method. The immobilized DTPA-Fe^III complex quickly communicates an electron with the electrode. Upon addition of hydrogen peroxide, however, hydrogen peroxide inhibits the direct electron transfer of the DTPA-Fe^III complex due to the generation of nonelectroactive DTPA-Fe^III–H2O2 complex. Based on quenching mechanism, the first hydrogen peroxide electrochemical sensor based on a nonelectrocatalytic mechanism is developed. The novel hydrogen peroxide electrochemical sensor has the ultralow detection limit (1.0×10^–14 M) and wide linear range (1.0×10^–13 to 1.0×10^–8 M) with excellent reproducibility and stability.

Graphical abstract

Application of hot platinum microelectrodes for determination of flavonoids in flow injection analysis and capillary electrophoresis

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Jolanta Magnuszewska , Tadeusz Krogulec
The determination of quercetin and rutin by flow injection analysis (FIA) and capillary electrophoresis (CE) using electrochemical detection was described. These flavonoids were determined at normal (unheated) and hot platinum microelectrodes using cyclic voltammetry. When quercetin or rutin is reaching the platinum electrode, a change of the current in the region of the platinum oxide formation is observed. Integration of the current changes in this in this region creates analytical signals in the form of peaks. An increase of temperature to about 76̊C in a small zone adjacent to the microelectrode causes an increase of the analytical signal by more than 6 times under FIA conditions. This method enables the use of hot microelectrodes as detectors in HPLC or CE. In CE the improvement of the analytical signal at hot microelectrodes is smaller than in FIA and increase only 1.3–3.4 times. Heated microelectrodes were used for analysis of the flavonoids in natural samples of the plant (extract of sea buckthorn) and a pharmaceutical preparation (Cerutin).

Graphical abstract

Microwave-assisted extraction combined with gel permeation chromatography and silica gel cleanup followed by gas chromatography–mass spectrometry for the determination of organophosphorus flame retardants and plasticizers in biological samples

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Yongqing Ma , Kunyan Cui , Feng Zeng , Jiaxin Wen , Hong Liu , Fang Zhu , Gangfeng Ouyang , Tiangang Luan , Zunxiang Zeng
An analytical method for the determination of 14 organophosphorus flame retardants (OPFRs), including halogenated OPFRs, non-halogenated OPFRs and triphenyl phosphine oxide (TPPO) in biological samples was developed using gas chromatography–mass spectrometry (GC/MS). Biological samples were extracted using microwave-assisted extraction (MAE) with hexane/acetone (1:1, v/v) as the solvent; then, a two-step clean-up technique, gel permeation chromatography (GPC) combined with solid phase extraction (SPE), was carried out before GC/MS analysis. Experimental results showed that the developed method efficiently removed the lipid compounds and co-extract interferences. Moreover, using the relatively “narrow” column (with an i.d. of 10mm) significantly decreased the elution volume and, therefore, prevented the loss of the most volatile OPFRs, especially trimethyl phosphate (TMP) and triethyl phosphate (TEP). The method detection limits (MDLs) for OPFRs in the biological samples ranged from 0.006 to 0.021ngg⁻¹ lw, and the recoveries were in the range of 70.3–111%, except for TMP (38.9–55.6%), with relative standard deviations (RSDs) of less than 14.1%. The developed method was applied to determine the amount of the target OPFRs in biological samples (i.e., fish and domestic birds) that were collected from the Pearl River Delta (PRD) region in southern China. Of the 14 OPFRs, tri-n-butyl phosphate (TnBP), tris(2-chloroethyl) phosphate (TCEP), tris(chloropropyl) phosphate (TCPP) and tributoxyethyl phosphate (TBEP) were present in all of the biological samples that were analyzed, and dominated by TnBP, TCEP and TBEP. The concentrations of OPFRs in the biological samples that were collected from the PRD region were higher than those reported in other locations.

Graphical abstract

Analysis of heterocyclic amines in hair by on-line in-tube solid-phase microextraction coupled with liquid chromatography−tandem mass spectrometry

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Hiroyuki Kataoka , Tsutomu Inoue , Keita Saito , Hisato Kato , Kazufumi Masuda
Mutagenic and carcinogenic heterocyclic amines (HCAs) are formed during heating of various proteinaceous foods, but human exposure to HCAs has not yet been elucidated in detail. To assess long-term exposure to HCAs, we developed a simple and sensitive method for measuring HCAs in hair by automated on-line in-tube solid-phase microextraction (SPME) coupled with liquid chromatography–tandem mass spectrometry (LC–MS/MS). Using a Zorbax Eclipse XDB-C8 column, 16 HCAs were analyzed within 15min. The optimum in-tube SPME conditions were 20 draw/eject cycles of 40μL sample at a flow rate of 200μLmin⁻¹ using a Supel-Q PLOT capillary column as an extraction device. The extracted HCAs were easily desorbed from the column by passage of the mobile phase, with no carryover observed. This in-tube SPME LC–MS/MS method showed good linearity for HCAs in the range of 10–2000pgmL⁻¹, with correlation coefficients above 0.9989 (n =18), using stable isotope-labeled HCA internal standards. The detection limits (S/N=3) of 14 HCAs except for MeAαC and Glu-P-1 were 0.10–0.79pgmL⁻¹. This method was successfully utilized to analyze 14 HCAs in hair samples without any interference peaks, with quantitative limits (S/N=10) of about 0.17–1.32pgmg⁻¹ hair. Using this method, we evaluated the exposure to HCAs in cigarette smoke and the suitability of using hair HCAs as exposure biomarkers.

Graphical abstract

Evaluation and optimization of solid adsorbents for the sampling of gaseous methylated mercury species

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Pascale A. Baya , Jenny Leigh Hollinsworth , Holger Hintelmann
This study evaluates the suitability of commercially available adsorbents for the measurement of gaseous organic mercury species namely monomethylmercury (MMHg) and dimethylmercury (DMHg). Bond Elut ENV (BE), a new generation of divinylbenzene (DVB), is evaluated the first time for simultaneous sampling and quantification of ultra-trace levels of MMHg and DMHg in air and its performance compared against Carbotrap^® B (CB) and Tenax^® TA (TA), two commonly used adsorbents for mercury solid phase adsorption. The suitability of TA as an absorbent for MMHg (recovery 100±8.1%) but less so for DMHg (recovery 64±17.3%) was confirmed while the reverse was observed for CB with an average recovery of 100±0.3% for DMHg but only 61±32.5% for MMHg. BE is the only adsorbent that showed excellent performance for trapping both Hg species with recoveries of 98±9.2% and 95±8.1% for MMHg and DMHg, respectively. Furthermore, BE exhibited much higher sampling capacities (>100L at 4°C) and preservation of sample integrity (>1 month at −20°C in the dark). Overall, BE proves to be the most suitable adsorbent for simultaneous trapping of organic Hg species with high sampling capacity and sample stability but also very good chromatographic properties which are desirable characteristics for both collection traps and analytical traps. Bond Elut ENV is proposed as an alternative to both Tenax^® TA and Carbotrap^® B with additional advantages of offering more versatility and sampling options.

Graphical abstract

Determination of acetaldehyde in saliva by gas-diffusion flow injection analysis

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Adlin N. Ramdzan , Patrick J. Mornane , Michael J. McCullough , Waldemar Mazurek , Spas D. Kolev
The consumption of ethanol is known to increase the likelihood of oral cancer. In addition, there has been a growing concern about possible association between long term use of ethanol-containing mouthwashes and oral cancer. Acetaldehyde, known to be a carcinogen, is the first metabolite of ethanol and it can be produced in the oral cavity after consumption or exposure to ethanol. This paper reports on the development of a gas-diffusion flow injection method for the online determination of salivary acetaldehyde by its colour reaction with 3-methyl-2-benzothiazolinone hydrazone (MBTH) and ferric chloride. Acetaldehyde samples and standards (80μL) were injected into the donor stream containing NaCl from which acetaldehyde diffused through the hydrophobic Teflon membrane of the gas-diffusion cell into the acceptor stream containing the two reagents mentioned above. The resultant intense green coloured dye was monitored spectrophotometrically at 600nm. Under the optimum working conditions the method is characterized by a sampling rate of 9h⁻¹, a linear calibration range of 0.5–15mgL⁻¹ (absorbance=5.40×10⁻² [acetaldehyde, mgL⁻¹], R ² =0.998), a relative standard deviation (RSD) of 1.90% (n =10, acetaldehyde concentration of 2.5mgL⁻¹), and a limit of detection (LOD) of 12.3μgL⁻¹. The LOD and sampling rate of the proposed method are superior to those of the conventional gas chromatographic (GC) method (LOD=93.0μgL⁻¹ and sampling rate=4h⁻¹). The reliability of the proposed method was illustrated by the fact that spiked with acetaldehyde saliva samples yielded excellent recoveries (96.6–101.9%), comparable to those obtained by GC (96.4–102.3%) and there was no statistically significant difference at the 95% confidence level between the two methods when non-spiked saliva samples were analysed.

Graphical abstract

Sequential injection immunoassay for human bone morphogenic protein-7 using an immunoreactor immobilized with anti-human bone morphogenic protein-7 antibody–CdSe/ZnS quantum dot conjugates

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Chun-Kwang Kim , Hong Dinh Duong , Jong Il Rhee
The detection of human bone morphogenic protein-7 (BMP-7) was achieved using a sequential injection immunoassay (SIIA) system. The SIIA system is based on the binding between BMP-7 and anti-human BMP-7 (AbBMP7)–CdSe/ZnS quantum dot (QD) conjugates immobilized onto a glass disk or an optical fiber, using fluorescence detection at excitation and emission wavelengths of 470nm and 580nm, respectively. The AbBMP7–QD conjugates were prepared by conjugating anti-human BMP-7 antibody (AbBMP7) to hydrophilic CdSe/ZnS core/shell quantum dots (QDs). The SIIA system was fully automated using software written in the LabVIEW™ development environment. The analytical performance of the SIIA system was characterized with a number of variables such as carrier flow rate and elution buffer. Under partially optimized operating conditions, the SIIA system had a linear calibration graph at up to 10.0ngmL⁻¹ BMP-7 (R ² ≥0.975) and a sample frequency of two samples per hour. The SIIA system with an optical fiber immunosensor was used to detect and quantify BMP-7 in spiked real samples obtained from a biological process with recoveries in the range of 95–102%.

Graphical abstract

Compressed matrix thin film (CMTF)-assisted laser desorption ionization mass spectrometric analysis

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Lulu Huang , Xiao Xiao , Yinping Xie , Hubert Kageruka , Youe Zhou , Fengjiao Deng , Hongying Zhong
The inhomogeneous re-crystallization process of matrix materials is the major concerns associated with matrix assisted laser desorption/ionization (MALDI) analysis. We describe here the approach termed compressed matrix thin film (CMTF) in order to make a uniform matrix deposition. In this approach, solid matrix particles are compressed under 10MPa of pressure by a compressor that is regularly used in infrared spectroscopic analysis. Then aqueous samples can be deposited on the surface of the matrix film. Major advantages of the CMTF approach are summarized as follows. (1) Reproducible sample preparation procedure. Size and thickness of matrix thin films can be controlled by using a fixed mold.force and known amount of matrix materials. (2) Significantly decreased shot-to-shot variations and enhanced reproducibility. (3) Tolerance for in situ salt washing. Because matrix materials are hydrophobic, salts can be washed away while proteins or peptides are retained on the surface of matrix thin films through hydrophobic interactions. (4) Improved sensitivity. The hydrophobic coating of MALDI sample plate by matrix thin films prevents the spreading of samples across the plate and confines analytes to a small area, leading to increased local concentration. (5) A new means for tissue analysis. Tissue sections can be directly transferred to the uniform surface of matrix materials for reproducible and quantitative comparison of different molecules in different localization. The proposed CMTF should be an enabling technique for mass spectrometric analysis with improved correlations between signal intensities and sample quantities.

Graphical abstract

Compound-specific stable carbon isotope ratios of phenols and nitrophenols derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Satoshi Irei , Jochen Rudolph , Lin Huang
We developed an analytical method for measuring compound-specific stable carbon isotope ratios (δ¹³C) of phenols and nitrophenols in filter samples of particulate organic matter. The method was tested on 13 phenols derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA), together with four nonphenolic compounds. The data obtained by our method required two specific corrections for the determination of valid δ¹³C values: (1) for nitro compounds, the routine correction with use of m/z 46 for the contribution of ¹²C¹⁷O¹⁶O molecules) to m/z 45 was modified due to impact of NO2 on the m/z 46 trace, and (2) for the derivatized phenols, measured δ¹³C values were corrected for the shift in δ¹³C due to the addition of carbon atoms from the BSTFA moiety. Analysis of standard-spiked filters showed that overall there was a small compound-dependent bias in the δ¹³C values: the average bias±the standard error of the mean of −0.21±0.1‰ for the standard compounds tested, except 3-methylcatechol, methylhydroquinone, 4-methyl-2-nitrophenol, and 2,6-dimethyl-4-nitrophenol, whereas the average biases±the standard errors of the mean for those were +1.2±0.3‰, +1.2±0.2‰, −1.2±0.2‰, and −1.4±0.5‰, respectively, when the injected mass of a derivatized compound exceeded 15ngC. In situations where such small biases and uncertainties are acceptable, the method described here could be used to obtain valuable information about δ¹³C values. We also analyzed a real filter sample to demonstrate the practical applicability of the method.

Graphical abstract

A matrix-assisted laser desorption/ionization tandem mass spectrometry method for direct screening of small molecule mixtures against an aminoglycoside kinase

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Anne Marie E. Smith , Emelia Awuah , Alfredo Capretta , John D. Brennan
Aminoglycoside phosphotransferase 3′IIIa (APH3′IIIa) is a bacterial enzyme involved in antibiotic resistance through phosphorylation of aminoglycosides, which can potentially be overcome by co-administration of an APH3′IIIa inhibitor with the antibiotic. Current assay methods for discovery of APH3′IIIa inhibitors suffer from low specificity and high false positive/negative hit rates. Here, we describe a method for screening APH3′IIIa inhibitors based on direct detection of kanamycin A phosphorylation using MALDI-MS/MS, which is more rapid than conventional assays and does not require secondary assays or sample cleanup. The MALDI-MS/MS assay operates at an ionic strength of 45mM and co-factors can be utilized at near-physiological levels for optimal enzyme activity. Detection via MALDI-MS/MS allowed for improved reproducibility when compared to ESI-MS/MS. Furthermore, the use of MS/MS provided better signal-to-noise ratios relative to MS alone on the MALDI instrument. The assay was validated via generation of Z′-factors, with values of 0.78 and 0.56 in the absence and presence of 0.2% DMSO, respectively. The assay was used to screen a kinase directed library of >200 compounds, assayed as 21 mixtures of 10 compounds each. Five novel synthetic inhibitors were identified following mixture deconvolution. Inhibition constants were obtained for the aforementioned inhibitors using the MALDI-MS/MS assay, revealing several low to mid micromolar “hits”, and highlighting the quantitative nature of the assay.

Graphical abstract

Fluorescence detection of glutathione reductase activity based on deoxyribonucleic acid-templated silver nanoclusters

25 June 2013, 05:34:56

Publication date: 5 July 2013
Source:Analytica Chimica Acta, Volume 786
Author(s): Shuyun Zhu , Xian-en Zhao , Wei Zhang , Zhongyuan Liu , Wenjing Qi , Saima Anjum , Guobao Xu
Fluorescent silver nanoclusters stabilized by DNA (DNA-AgNCs) exhibit distinct response rates to thiol and disulfide. Glutathione reductase can catalyze the reduction of the oxidized glutathione (GSSG) quickly to reduced glutathione (GSH) in the presence of β-nicotinamide adenine dinucleotide 2′-phosphate reduced tetrasodium salt hydrate (NADPH). Consequently, DNA-AgNCs can serve as a new fluorescent platform for assaying the glutathione reductase (GR) activity. This newly proposed assay has a high sensitivity and a good selectivity toward GR. The GR activity can be detected in the range of 0.2–2.0mUmL⁻¹ with a minimum detectable concentration of 0.2mUmL⁻¹. Pepsin, lysozyme, trypsin, avidin, thrombin, myoglobin, and BSA have little effect on the fluorescence intensity of DNA-AgNCs. The GR activity assay is successfully used to monitor the inhibition of GR activity by a typical inhibitor 1,3-bis(2-chloroethyl)-1-nitrosourea.

Graphical abstract