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Aqueous two-phase systems for protein separation: Phase separation and applications
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Juan A. Asenjo, Barbara A. Andrews
Aqueous two-phase systems (ATPS) that are formed by mixing a polymer (usually polyethylene glycol, PEG) and a salt (e.g. phosphate, sulphate or citrate) or two polymers, and water can be effectively used for the separation and purification of proteins. The partitioning between both phases is dependent on the surface properties of the proteins and on the composition of the two phase system as has been recently reviewed by Asenjo and Andrews [1]. This paper analyses and reviews some elements that are important for implementation of these processes which are related to phase separation and continuous processing of ATPS. Phase separation for ATPS formed by PEG and salts has been studied and has been found to depend on which of the phases is continuous. Profiles of dispersion heights can be represented as a fraction of the initial height and are independent of the dimensions of the separator. This is important for the design of large scale aqueous two-phase separations. The kinetics of phase separation has been investigated as a function of the physical properties of the system. The settling rate is a crucial parameter for equipment design and it has been studied as a function of viscosity and density of the phases as well as the interfacial tension between them. Correlations that describe the rate of phase separation have been developed. Working in a continuous bottom-phase region is advantageous to ensure fast separation. A mathematical model to describe the continuous, study state operation of these systems has been investigated. Two simulations to show the effect of phase ratio on purification have been carried out which clearly show the effectivity of using such models. The practical application of ATPS has been demonstrated in many cases including a number of industrial applications with excellent levels of purity and yield. Examples include the purification of α-amylase and the large scale “in situ” purification of IGF-1 carried out by Genentech. The production scale purification of chymosin from recombinant Aspergillus supernatant is the most successful industrial application of this technology. Other applications include the separation and purification of human α-antitrypsin from transgenic sheep milk, the purification of monoclonal antibodies, tPA from CHO supernatant and recombinant VLPs (virus like particles) from yeast cells.
Source:Journal of Chromatography A, Volume 1238
Juan A. Asenjo, Barbara A. Andrews
Aqueous two-phase systems (ATPS) that are formed by mixing a polymer (usually polyethylene glycol, PEG) and a salt (e.g. phosphate, sulphate or citrate) or two polymers, and water can be effectively used for the separation and purification of proteins. The partitioning between both phases is dependent on the surface properties of the proteins and on the composition of the two phase system as has been recently reviewed by Asenjo and Andrews [1]. This paper analyses and reviews some elements that are important for implementation of these processes which are related to phase separation and continuous processing of ATPS. Phase separation for ATPS formed by PEG and salts has been studied and has been found to depend on which of the phases is continuous. Profiles of dispersion heights can be represented as a fraction of the initial height and are independent of the dimensions of the separator. This is important for the design of large scale aqueous two-phase separations. The kinetics of phase separation has been investigated as a function of the physical properties of the system. The settling rate is a crucial parameter for equipment design and it has been studied as a function of viscosity and density of the phases as well as the interfacial tension between them. Correlations that describe the rate of phase separation have been developed. Working in a continuous bottom-phase region is advantageous to ensure fast separation. A mathematical model to describe the continuous, study state operation of these systems has been investigated. Two simulations to show the effect of phase ratio on purification have been carried out which clearly show the effectivity of using such models. The practical application of ATPS has been demonstrated in many cases including a number of industrial applications with excellent levels of purity and yield. Examples include the purification of α-amylase and the large scale “in situ” purification of IGF-1 carried out by Genentech. The production scale purification of chymosin from recombinant Aspergillus supernatant is the most successful industrial application of this technology. Other applications include the separation and purification of human α-antitrypsin from transgenic sheep milk, the purification of monoclonal antibodies, tPA from CHO supernatant and recombinant VLPs (virus like particles) from yeast cells.
Selective transport of single protein molecules inside gold nanotubes
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Changbei Ma, Rui Han, Shengda Qi, Edward S. Yeung
Diffusion of single protein molecules inside gold nanotubes was investigated. 3-dimensional imaging was employed to locate the individual molecules inside the nanotubes as a function of time. As expected, larger proteins and smaller pore sizes resulted in smaller diffusion coefficients. Diffusion within PEG-coated gold nanotubes was found to be two orders of magnitude faster than in previously reported, similar sized untreated polycarbonate membrane pores, showing that adsorption was serious in the latter case. We further demonstrate chromatographic selectivity during transport by modifying the inner surface of the gold nanotubes with self-assembled monolayers of derivatized alkyl thiols. These results should be useful for designing membrane separations.
Source:Journal of Chromatography A, Volume 1238
Changbei Ma, Rui Han, Shengda Qi, Edward S. Yeung
Diffusion of single protein molecules inside gold nanotubes was investigated. 3-dimensional imaging was employed to locate the individual molecules inside the nanotubes as a function of time. As expected, larger proteins and smaller pore sizes resulted in smaller diffusion coefficients. Diffusion within PEG-coated gold nanotubes was found to be two orders of magnitude faster than in previously reported, similar sized untreated polycarbonate membrane pores, showing that adsorption was serious in the latter case. We further demonstrate chromatographic selectivity during transport by modifying the inner surface of the gold nanotubes with self-assembled monolayers of derivatized alkyl thiols. These results should be useful for designing membrane separations.
Simultaneous analysis of 10 trihalomethanes at nanogram per liter levels in water using solid-phase microextraction and gas chromatography mass-spectrometry
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Sebastien Allard, Jeffrey W.A. Charrois, Cynthia A. Joll, Anna Heitz
Trihalomethanes are predominantly formed during disinfection of water via reactions of the oxidant with natural organic matter. Even though chlorinated and brominated trihalomethanes are the most widespread organic contaminants in drinking water, when iodide is present in raw water iodinated trihalomethanes can also be formed. The formation of iodinated trihalomethanes can lead to taste and odor problems and is a potential health concern since they have been reported to be more toxic than their brominated or chlorinated analogs. Currently, there is no published standard analytical method for I-THMs in water. The analysis of 10 trihalomethanes in water samples in a single run is challenging because the iodinated trihalomethanes are found at very low concentrations (ng/L range), while the regulated chlorinated and brominated trihalomethanes are present at much higher concentrations (above μg/L). An automated headspace solid-phase microextraction technique, with a programmed temperature vaporizer inlet coupled with gas chromatography-mass spectrometry, was developed for routine analysis of 10 trihalomethanes i.e. bromo-, chloro- and iodo-trihalomethanes in water samples. The carboxen/polydimethylsiloxane/divinylbenzene fiber was found to be the most suitable. The optimization, linearity range, accuracy and precision of the method are discussed. The limits of detection range from 1ng/L to 20ng/L for iodoform and chloroform, respectively. Matrix effects in treated groundwater, surfacewater, seawater, and secondary wastewater were investigated and it was shown that the method is suitable for the analysis of trace levels of iodinated trihalomethanes in a wide range of waters. The method developed in the present study has the advantage of being rapid, simple and sensitive. A survey conducted throughout various process stages in an advanced water recycling plant showed the presence of iodinated trihalomethanes at ng/L levels.
Source:Journal of Chromatography A, Volume 1238
Sebastien Allard, Jeffrey W.A. Charrois, Cynthia A. Joll, Anna Heitz
Trihalomethanes are predominantly formed during disinfection of water via reactions of the oxidant with natural organic matter. Even though chlorinated and brominated trihalomethanes are the most widespread organic contaminants in drinking water, when iodide is present in raw water iodinated trihalomethanes can also be formed. The formation of iodinated trihalomethanes can lead to taste and odor problems and is a potential health concern since they have been reported to be more toxic than their brominated or chlorinated analogs. Currently, there is no published standard analytical method for I-THMs in water. The analysis of 10 trihalomethanes in water samples in a single run is challenging because the iodinated trihalomethanes are found at very low concentrations (ng/L range), while the regulated chlorinated and brominated trihalomethanes are present at much higher concentrations (above μg/L). An automated headspace solid-phase microextraction technique, with a programmed temperature vaporizer inlet coupled with gas chromatography-mass spectrometry, was developed for routine analysis of 10 trihalomethanes i.e. bromo-, chloro- and iodo-trihalomethanes in water samples. The carboxen/polydimethylsiloxane/divinylbenzene fiber was found to be the most suitable. The optimization, linearity range, accuracy and precision of the method are discussed. The limits of detection range from 1ng/L to 20ng/L for iodoform and chloroform, respectively. Matrix effects in treated groundwater, surfacewater, seawater, and secondary wastewater were investigated and it was shown that the method is suitable for the analysis of trace levels of iodinated trihalomethanes in a wide range of waters. The method developed in the present study has the advantage of being rapid, simple and sensitive. A survey conducted throughout various process stages in an advanced water recycling plant showed the presence of iodinated trihalomethanes at ng/L levels.
Aniline–silica nanocomposite as a novel solid phase microextraction fiber coating
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Habib Bagheri, Ali Roostaie
A new unbreakable solid phase microextraction (SPME) fiber coating based on aniline–silica nanocomposite was electrodeposited on a stainless steel wire. The electropolymerization process was carried out at a constant deposition potential, applied to the corresponding aqueous electrolyte containing aniline and silica nanoparticles. The scanning electron microscopy (SEM) images showed the non-smooth and the porous surface structure of the prepared nanocomposite. The applicability of the new fiber coating was examined by headspace-solid phase microextraction (HS-SPME) of some environmentally important polycyclic aromatic hydrocarbons (PAHs), as model compounds, from aqueous samples. Subsequently, the extracted analytes were transferred into a gas chromatography (GC) by thermal desorption. Parameters affecting the synthesizing and extraction processes including the voltage of power supply, the weight ratio of components, the time of electrodeposition, extraction time and temperature, the ionic strength, and desorption temperature and time were optimized. Eventually, the developed method was validated by gas chromatography–mass spectrometry (GC–MS). At the optimum conditions, the relative standard deviation (%RSD) values for a double distilled water spiked with the selected PAHs at 40ngL−1 were 6–13% (n =3) while the limit of detection (LOD) results were between 1 and 3ngL−1. The calibration graphs were linear in the concentration range from 20 to 4000ngL−1 (R 2 >0.995). Finally the developed method was applied to the analysis of Kalan dam, rain and tap water samples and the relative recovery values were found to be in the range of 76–109%, under optimized conditions. In addition, the synthesis of the nanocomposite coating was carried out conveniently while it is rather inexpensive, easy, simple, rapid and highly durable and can be used frequently.
Source:Journal of Chromatography A, Volume 1238
Habib Bagheri, Ali Roostaie
A new unbreakable solid phase microextraction (SPME) fiber coating based on aniline–silica nanocomposite was electrodeposited on a stainless steel wire. The electropolymerization process was carried out at a constant deposition potential, applied to the corresponding aqueous electrolyte containing aniline and silica nanoparticles. The scanning electron microscopy (SEM) images showed the non-smooth and the porous surface structure of the prepared nanocomposite. The applicability of the new fiber coating was examined by headspace-solid phase microextraction (HS-SPME) of some environmentally important polycyclic aromatic hydrocarbons (PAHs), as model compounds, from aqueous samples. Subsequently, the extracted analytes were transferred into a gas chromatography (GC) by thermal desorption. Parameters affecting the synthesizing and extraction processes including the voltage of power supply, the weight ratio of components, the time of electrodeposition, extraction time and temperature, the ionic strength, and desorption temperature and time were optimized. Eventually, the developed method was validated by gas chromatography–mass spectrometry (GC–MS). At the optimum conditions, the relative standard deviation (%RSD) values for a double distilled water spiked with the selected PAHs at 40ngL−1 were 6–13% (n =3) while the limit of detection (LOD) results were between 1 and 3ngL−1. The calibration graphs were linear in the concentration range from 20 to 4000ngL−1 (R 2 >0.995). Finally the developed method was applied to the analysis of Kalan dam, rain and tap water samples and the relative recovery values were found to be in the range of 76–109%, under optimized conditions. In addition, the synthesis of the nanocomposite coating was carried out conveniently while it is rather inexpensive, easy, simple, rapid and highly durable and can be used frequently.
Enhanced pressurized liquid extraction technique capable of analyzing polychlorodibenzo-p-dioxins, polychlorodibenzofurans, and polychlorobiphenyls in fish tissue
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Bikram Subedi, Sascha Usenko
A high-throughput enhanced pressurized liquid extraction technique was developed by incorporating pressurized liquid extraction and multiple cleanup techniques. USEPA methods of polychlorodibenzo-p-dioxins, polychlorodibenzofurans (PCDD/Fs) and dioxin-like polychlorobiphenyls (dl-PCBs) analysis in fish tissue include independent silica gel, florisil, alumina, and carbopack/celite column cleanup techniques following extraction. Under the improved method, fish composites (∼10g) were extracted and cleaned simultaneously using alumina (∼10g), florisil (∼10g), silica gel (∼5g), celite (∼5g), and carbopack (∼0.5g). Clean extracts were concentrated and then analyzed by high resolution gas chromatography coupled with electron capture negative ionization mass spectrometry. Carbopack/celite within the extraction cell provided the analytical separation of dl-PCBs from PCDD/Fs, reducing potential molecular interferences. The average recoveries (n =3) of dl-PCBs in dichloromethane:hexane (1:1, v/v) extracts were 93±2.4% and PCDD/Fs in toluene extracts were 85±3.0%. The developed method was applied to measure the PCDD/Fs and dl-PCBs in catfish from San Jacinto River Waste Pits, a Superfund site in Houston, TX. The dl-PCBs were measured at 5.0–17,000pgg−1 ww. Sample preparation time and solvents were reduced as much as 95% and 65%, respectively, as compared to USEPA method 1613.
Source:Journal of Chromatography A, Volume 1238
Bikram Subedi, Sascha Usenko
A high-throughput enhanced pressurized liquid extraction technique was developed by incorporating pressurized liquid extraction and multiple cleanup techniques. USEPA methods of polychlorodibenzo-p-dioxins, polychlorodibenzofurans (PCDD/Fs) and dioxin-like polychlorobiphenyls (dl-PCBs) analysis in fish tissue include independent silica gel, florisil, alumina, and carbopack/celite column cleanup techniques following extraction. Under the improved method, fish composites (∼10g) were extracted and cleaned simultaneously using alumina (∼10g), florisil (∼10g), silica gel (∼5g), celite (∼5g), and carbopack (∼0.5g). Clean extracts were concentrated and then analyzed by high resolution gas chromatography coupled with electron capture negative ionization mass spectrometry. Carbopack/celite within the extraction cell provided the analytical separation of dl-PCBs from PCDD/Fs, reducing potential molecular interferences. The average recoveries (n =3) of dl-PCBs in dichloromethane:hexane (1:1, v/v) extracts were 93±2.4% and PCDD/Fs in toluene extracts were 85±3.0%. The developed method was applied to measure the PCDD/Fs and dl-PCBs in catfish from San Jacinto River Waste Pits, a Superfund site in Houston, TX. The dl-PCBs were measured at 5.0–17,000pgg−1 ww. Sample preparation time and solvents were reduced as much as 95% and 65%, respectively, as compared to USEPA method 1613.
Biocompatible phosphatidylcholine bilayer coated on magnetic nanoparticles and their application in the extraction of several polycyclic aromatic hydrocarbons from environmental water and milk samples
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Shengxiao Zhang, Hongyun Niu, Yuanyuan Zhang, Junshen Liu, Yali Shi, Xiaole Zhang, Yaqi Cai
In this work, phosphatidylcholine (PC) was coated on magnetic nanoparticles to form lipid bilayer as solid-phase extraction (SPE) sorbents for the enrichment of polycyclic aromatic hydrocarbons (PAHs) from environmental water and milk samples. The lipid bilayer was coated on Fe3O4 nanoparticles using a modified dry lipid film hydration method. The resulted Fe3O4/PC could be readily isolated from solution with a magnet, and exhibited excellent adsorption performance to organic pollutants. Only 0.1g of sorbents was enough to extract PAHs from 500mL aqueous solution, and 6mL of acetonitrile was required to desorb them. The method was fast and relied on 10min extraction time and 5min magnetic separation. The proposed method was successfully applied to determine PAHs in some environmental water and milk samples. The detection limit was in the range of 0.2–0.6ngL−1. The recoveries of the spiked water samples ranged from 89% to 115% with relative standard deviations (RSD) varying from 1% to 8%. For spiked milk samples, RSD was satisfactory (1–9%), but the recoveries were relatively low (42–62%). We show the potentials of Fe3O4/PC sorbents in environmental water and biological sample analyses.
Source:Journal of Chromatography A, Volume 1238
Shengxiao Zhang, Hongyun Niu, Yuanyuan Zhang, Junshen Liu, Yali Shi, Xiaole Zhang, Yaqi Cai
In this work, phosphatidylcholine (PC) was coated on magnetic nanoparticles to form lipid bilayer as solid-phase extraction (SPE) sorbents for the enrichment of polycyclic aromatic hydrocarbons (PAHs) from environmental water and milk samples. The lipid bilayer was coated on Fe3O4 nanoparticles using a modified dry lipid film hydration method. The resulted Fe3O4/PC could be readily isolated from solution with a magnet, and exhibited excellent adsorption performance to organic pollutants. Only 0.1g of sorbents was enough to extract PAHs from 500mL aqueous solution, and 6mL of acetonitrile was required to desorb them. The method was fast and relied on 10min extraction time and 5min magnetic separation. The proposed method was successfully applied to determine PAHs in some environmental water and milk samples. The detection limit was in the range of 0.2–0.6ngL−1. The recoveries of the spiked water samples ranged from 89% to 115% with relative standard deviations (RSD) varying from 1% to 8%. For spiked milk samples, RSD was satisfactory (1–9%), but the recoveries were relatively low (42–62%). We show the potentials of Fe3O4/PC sorbents in environmental water and biological sample analyses.
Bifunctional ultrasound assisted extraction and determination of Elettaria cardamomum Maton essential oil
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Hassan Sereshti, Ahmad Rohanifar, Sadjad Bakhtiari, Soheila Samadi
A new hyphenated extraction method composed of ultrasound assisted extraction (UAE)-optimized ultrasound assisted emulsification microextraction (USAEME) was developed for the extraction and preconcentration of the essential oil of Elettaria cardamomum Maton. The essential oil was analyzed by gas chromatography–mass spectrometry (GC–MS) and optimization was performed using gas chromatography-flame ionization detection (GC-FID). Ultrasound played two different roles in the extraction of the essential oil. First, as a source of sufficient energy to break the oil-containing glands in order to release the oil, and second as an emulsifier to disperse the organic phase within water. The effective parameters (factors) of USAEME including volume of extraction solvent (C2H4Cl2), extraction temperature and ultrasonic time were optimized by using a central composite design (CCD). The optimal conditions were 120μL for extraction solvent volume, 32.5°C for temperature and 10.5min for ultrasonic time. The linear dynamic ranges (LDRs) were 0.01–50mgL−1 with the determination coefficients in the range of 0.9990–0.9999. The limits of detection (LODs) and the relative standard deviations (RSDs) were 0.001–0.007mgL−1 and 3.6–6.3%, respectively. The enrichment factors were 93–98. The main components of the extracted essential oil were α-terpenyl acetate (46.0%), 1,8-cineole (27.7%), linalool (5.3%), α-terpineol (4.0%), linalyl acetate (3.5%).
Source:Journal of Chromatography A, Volume 1238
Hassan Sereshti, Ahmad Rohanifar, Sadjad Bakhtiari, Soheila Samadi
A new hyphenated extraction method composed of ultrasound assisted extraction (UAE)-optimized ultrasound assisted emulsification microextraction (USAEME) was developed for the extraction and preconcentration of the essential oil of Elettaria cardamomum Maton. The essential oil was analyzed by gas chromatography–mass spectrometry (GC–MS) and optimization was performed using gas chromatography-flame ionization detection (GC-FID). Ultrasound played two different roles in the extraction of the essential oil. First, as a source of sufficient energy to break the oil-containing glands in order to release the oil, and second as an emulsifier to disperse the organic phase within water. The effective parameters (factors) of USAEME including volume of extraction solvent (C2H4Cl2), extraction temperature and ultrasonic time were optimized by using a central composite design (CCD). The optimal conditions were 120μL for extraction solvent volume, 32.5°C for temperature and 10.5min for ultrasonic time. The linear dynamic ranges (LDRs) were 0.01–50mgL−1 with the determination coefficients in the range of 0.9990–0.9999. The limits of detection (LODs) and the relative standard deviations (RSDs) were 0.001–0.007mgL−1 and 3.6–6.3%, respectively. The enrichment factors were 93–98. The main components of the extracted essential oil were α-terpenyl acetate (46.0%), 1,8-cineole (27.7%), linalool (5.3%), α-terpineol (4.0%), linalyl acetate (3.5%).
Rapid whole protein quantitation of staphylococcal enterotoxins A and B by liquid chromatography/mass spectrometry
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Isabel Sospedra, Carla Soler, Jordi Mañes, José Miguel Soriano
Staphylococcus aureus is an important pathogen and has been indicated as the fifth causative agent of food-borne human illness throughout the world. Staphylococcal enterotoxins (SEs) are toxic compounds excreted mainly by strains of S. aureus. Among these toxins, enterotoxins A (SEA) and B (SEB) are both of the most prevalent compounds in staphylococcal food poisoning. In this work, reverse phase liquid chromatography coupled to ESI mass spectrometry (LC–ESI/MS) has been applied for its rapid identification and quantification. Limit of detection (LOD) values were 0.5 and 0.2ng for SEA and SEB, respectively and limit of quantification (LOQ) value was 1ng for both enterotoxins. SEA and SEB have been analyzed as intact proteins in milk and fruit juices. Analytical methods are essential for routine monitoring purposes and safeguard public health and the proposed technique can detect and quantify successfully SEA and SEB in food samples.
Source:Journal of Chromatography A, Volume 1238
Isabel Sospedra, Carla Soler, Jordi Mañes, José Miguel Soriano
Staphylococcus aureus is an important pathogen and has been indicated as the fifth causative agent of food-borne human illness throughout the world. Staphylococcal enterotoxins (SEs) are toxic compounds excreted mainly by strains of S. aureus. Among these toxins, enterotoxins A (SEA) and B (SEB) are both of the most prevalent compounds in staphylococcal food poisoning. In this work, reverse phase liquid chromatography coupled to ESI mass spectrometry (LC–ESI/MS) has been applied for its rapid identification and quantification. Limit of detection (LOD) values were 0.5 and 0.2ng for SEA and SEB, respectively and limit of quantification (LOQ) value was 1ng for both enterotoxins. SEA and SEB have been analyzed as intact proteins in milk and fruit juices. Analytical methods are essential for routine monitoring purposes and safeguard public health and the proposed technique can detect and quantify successfully SEA and SEB in food samples.
A novel hydroquinidine imprinted microsphere using a chirality-matching N-Acryloyl-l-phenylalanine monomer for recognition of cinchona alkaloids
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Qi Zhou, Jing He, Youwen Tang, Zhiguang Xu, He Li, Chengcheng Kang, Jiabing Jiang
Using a combination of molecular imprinting technology and traditional chiral stationary phases, the synergistic effect between chiral monomer and chiral cavity of molecularly imprinted polymers in stereoselective recognition was investigated. We designed and synthesized an amino acid derivative to be used as a novel chiral functional monomer. Monodisperse molecularly imprinted core–shell microspheres using surface imprinting method on silica gel were prepared with hydroquinidine as the pseudo-template molecule for the resolution of cinchona alkaloids. The results showed a significant synergistic effect in stereoselective recognition, confirming our initial hypothesis. Furthermore, our computational simulation and experiments intensively support the hypothetical chiral recognition mechanism for the imprinted microspheres.
Source:Journal of Chromatography A, Volume 1238
Qi Zhou, Jing He, Youwen Tang, Zhiguang Xu, He Li, Chengcheng Kang, Jiabing Jiang
Using a combination of molecular imprinting technology and traditional chiral stationary phases, the synergistic effect between chiral monomer and chiral cavity of molecularly imprinted polymers in stereoselective recognition was investigated. We designed and synthesized an amino acid derivative to be used as a novel chiral functional monomer. Monodisperse molecularly imprinted core–shell microspheres using surface imprinting method on silica gel were prepared with hydroquinidine as the pseudo-template molecule for the resolution of cinchona alkaloids. The results showed a significant synergistic effect in stereoselective recognition, confirming our initial hypothesis. Furthermore, our computational simulation and experiments intensively support the hypothetical chiral recognition mechanism for the imprinted microspheres.
A priori selection of the mobile and stationary phase in centrifugal partition chromatography and counter-current chromatography
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Elisabeth Hopmann, Andreas Frey, Mirjana Minceva
The selection of the mobile and the stationary phase in support-free liquid–liquid chromatography (centrifugal partition chromatography and counter-current chromatography) is equivalent to a selection of a biphasic liquid system and its global composition. There is an immense number of choices of biphasic liquid systems. On one hand what makes this technique extremely versatile, on the other hand turns the selection of the appropriate system for a particular separation problem into a challenging and demanding task. In this work a systematic procedure for the selection of biphasic liquid systems for preparative scale separations is presented. The procedure is adaptable to the production scale requirements including production cost and safety. The experimental effort of different stages of the selection procedure is minimized by using a fully predictive method, the conductor-like screening model for real solvents (COSMO-RS). The COSMO-RS is used to assess properties relevant for the selection of a biphasic liquid system, such as the solute solubility and the partition coefficient.
Source:Journal of Chromatography A, Volume 1238
Elisabeth Hopmann, Andreas Frey, Mirjana Minceva
The selection of the mobile and the stationary phase in support-free liquid–liquid chromatography (centrifugal partition chromatography and counter-current chromatography) is equivalent to a selection of a biphasic liquid system and its global composition. There is an immense number of choices of biphasic liquid systems. On one hand what makes this technique extremely versatile, on the other hand turns the selection of the appropriate system for a particular separation problem into a challenging and demanding task. In this work a systematic procedure for the selection of biphasic liquid systems for preparative scale separations is presented. The procedure is adaptable to the production scale requirements including production cost and safety. The experimental effort of different stages of the selection procedure is minimized by using a fully predictive method, the conductor-like screening model for real solvents (COSMO-RS). The COSMO-RS is used to assess properties relevant for the selection of a biphasic liquid system, such as the solute solubility and the partition coefficient.
Band broadening in fast gradient high-performance liquid chromatography: Application to the second generation of 4.6mm I.D. silica monolithic columns
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Fabrice Gritti, Georges Guiochon
The sources of band broadening in fast gradient elution chromatography include the contributions of the tubings placed upstream the column, the isocratic migration of the sample that takes place in the column until the moment when the front of the gradient catches up with it, dispersion and mass transfer resistance during band migration under gradient elution to the column outlet, and dispersion in the tubings downstream the column to the detector. The measurements of all these contributions is meticulously described, analyzed, and applied to assess the kinetic performance of monolithic columns of the second generation (KGaA Merck) in gradient elution, at the highest possible speed at which they can be operated (t 0=25s at P =200bar). These results are compared to those provided by several 4.6mm × 100mm columns packed with sub-3μm core–shell particles (Kinetex, Phenomenex and Halo, Advanced Material Technologies) and by a 2.1mm × 100mm column packed with fully porous 1.7μm BEH particles (Waters). A RPLC checkout sample (Agilent) containing nine alkanophenones (molecular weights between 120 and 204g/mol) was used for this purpose. The mobile phase was a mixture of acetonitrile and water and the instrument, an optimized version of the 1290 Infinity HPLC system (Agilent). The results show that the overall peak capacity provided by this second generation of monolithic columns is nearly 30% smaller than that provided by commercial columns packed with sub-3 μm core–shell particles and 20% smaller than that provided by a narrow-bore column packed with sub-2μm fully porous particles. After isolating the sole band broadening contribution due to the gradient migration of the analytes along the columns, the BEH column proved to provide the highest resolution power (apparent average plate height, of 2μm), followed by the 2.6μm Kinetex particles (3.0μm), the Halo particles (3.2μm), and the second generation of 4.6mm I.D. monolithic columns (6.5μm). This work demonstrates that analysts have an urgent need for very high pressure liquid chromatographs having smaller dwell and extra-column volumes that those of the currently available instruments. The gradient elution peak capacity provided by the modern, narrow-diameter columns, which are short and highly efficient (plate heights of 3–4μm), is barely half what the column alone could produce if it were fitted to a perfect instrument. The other half of the peak capacity is just wasted by the instrument.
Source:Journal of Chromatography A, Volume 1238
Fabrice Gritti, Georges Guiochon
The sources of band broadening in fast gradient elution chromatography include the contributions of the tubings placed upstream the column, the isocratic migration of the sample that takes place in the column until the moment when the front of the gradient catches up with it, dispersion and mass transfer resistance during band migration under gradient elution to the column outlet, and dispersion in the tubings downstream the column to the detector. The measurements of all these contributions is meticulously described, analyzed, and applied to assess the kinetic performance of monolithic columns of the second generation (KGaA Merck) in gradient elution, at the highest possible speed at which they can be operated (t 0=25s at P =200bar). These results are compared to those provided by several 4.6mm × 100mm columns packed with sub-3μm core–shell particles (Kinetex, Phenomenex and Halo, Advanced Material Technologies) and by a 2.1mm × 100mm column packed with fully porous 1.7μm BEH particles (Waters). A RPLC checkout sample (Agilent) containing nine alkanophenones (molecular weights between 120 and 204g/mol) was used for this purpose. The mobile phase was a mixture of acetonitrile and water and the instrument, an optimized version of the 1290 Infinity HPLC system (Agilent). The results show that the overall peak capacity provided by this second generation of monolithic columns is nearly 30% smaller than that provided by commercial columns packed with sub-3 μm core–shell particles and 20% smaller than that provided by a narrow-bore column packed with sub-2μm fully porous particles. After isolating the sole band broadening contribution due to the gradient migration of the analytes along the columns, the BEH column proved to provide the highest resolution power (apparent average plate height, of 2μm), followed by the 2.6μm Kinetex particles (3.0μm), the Halo particles (3.2μm), and the second generation of 4.6mm I.D. monolithic columns (6.5μm). This work demonstrates that analysts have an urgent need for very high pressure liquid chromatographs having smaller dwell and extra-column volumes that those of the currently available instruments. The gradient elution peak capacity provided by the modern, narrow-diameter columns, which are short and highly efficient (plate heights of 3–4μm), is barely half what the column alone could produce if it were fitted to a perfect instrument. The other half of the peak capacity is just wasted by the instrument.
Computer assisted optimization of liquid chromatographic separations of small molecules using mixed-mode stationary phases
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Edgar Y. Ordoñez, José Benito Quintana, Rosario Rodil, Rafael Cela
Mixed-mode stationary phases are gaining adepts in liquid chromatography (LC) as more and more applications are published and new commercial columns appear in the market ought to their ability to retain and separate analytes with multiple functionalities. The increased number of adjustable variables gives these columns an enhanced value for the chromatographer, but, on the other hand, it complicates the process of developing satisfactory separations when complex samples must be analyzed. Thus, the availability of computer assisted methods development (CAMD) tools is highly desirable in this field. Therefore, the first specific tool for the CAMD of LC separations in mixed-mode columns is presented. The tool consists in two processes. The first one develops a retention model for peaks in a predefined experimental domain of pH and buffer concentration. In this domain, the retention as a function of the proportion of organic modifier is modeled using a two-stage re-calibration process departing from isocratic retention data and then, from gradient elutions. With this two-stage approach, reliability is gained. In the second process, the model is finally interpolated and used for the unattended optimization of the different possible elution modes available in these columns. This optimization process is driven by an evolutionary algorithm. The development and application of this new chemometrics tool is demonstrated by the optimization of a mixture of neutral and ionizable compounds. Hence, several different types of gradients were generated, showing a good agreement between simulated and experimental data, with retention time errors lower than 5% in most cases. On the other hand, classical CAMD tools, such as design of experiments, were unable to efficiently deal with mixed-mode optimizations, rendering errors above 30% for several compounds.
Source:Journal of Chromatography A, Volume 1238
Edgar Y. Ordoñez, José Benito Quintana, Rosario Rodil, Rafael Cela
Mixed-mode stationary phases are gaining adepts in liquid chromatography (LC) as more and more applications are published and new commercial columns appear in the market ought to their ability to retain and separate analytes with multiple functionalities. The increased number of adjustable variables gives these columns an enhanced value for the chromatographer, but, on the other hand, it complicates the process of developing satisfactory separations when complex samples must be analyzed. Thus, the availability of computer assisted methods development (CAMD) tools is highly desirable in this field. Therefore, the first specific tool for the CAMD of LC separations in mixed-mode columns is presented. The tool consists in two processes. The first one develops a retention model for peaks in a predefined experimental domain of pH and buffer concentration. In this domain, the retention as a function of the proportion of organic modifier is modeled using a two-stage re-calibration process departing from isocratic retention data and then, from gradient elutions. With this two-stage approach, reliability is gained. In the second process, the model is finally interpolated and used for the unattended optimization of the different possible elution modes available in these columns. This optimization process is driven by an evolutionary algorithm. The development and application of this new chemometrics tool is demonstrated by the optimization of a mixture of neutral and ionizable compounds. Hence, several different types of gradients were generated, showing a good agreement between simulated and experimental data, with retention time errors lower than 5% in most cases. On the other hand, classical CAMD tools, such as design of experiments, were unable to efficiently deal with mixed-mode optimizations, rendering errors above 30% for several compounds.
Comparison of various ternary simulated moving bed separation schemes by multi-objective optimization
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Gaurav Agrawal, Yoshiaki Kawajiri
Over the past decade, many modifications have been proposed in simulated moving bed (SMB) chromatography in order to effectively separate a binary mixture. However, the separation of multi-component mixtures using SMB is still one of the major challenges. In addition, the performance of SMB system highly depends on its operating conditions. Our study address this issue by formulating a multi-objective optimization problem that maximizes the productivity and purity of intermediate eluting component at the same time. A number of optimized isocractic ternary SMB operating schemes are compared both in terms of productivity and amount of desorbent to feed ratio. Furthermore, we propose a generalized full cycle (GFC) formulation based on superstructure formulation encompassing numerous operating schemes proposed in the literature. We also demonstrate that this approach has a potential to find the best ternary separation strategy among various alternatives.
Source:Journal of Chromatography A, Volume 1238
Gaurav Agrawal, Yoshiaki Kawajiri
Over the past decade, many modifications have been proposed in simulated moving bed (SMB) chromatography in order to effectively separate a binary mixture. However, the separation of multi-component mixtures using SMB is still one of the major challenges. In addition, the performance of SMB system highly depends on its operating conditions. Our study address this issue by formulating a multi-objective optimization problem that maximizes the productivity and purity of intermediate eluting component at the same time. A number of optimized isocractic ternary SMB operating schemes are compared both in terms of productivity and amount of desorbent to feed ratio. Furthermore, we propose a generalized full cycle (GFC) formulation based on superstructure formulation encompassing numerous operating schemes proposed in the literature. We also demonstrate that this approach has a potential to find the best ternary separation strategy among various alternatives.
Development of analysis of volatile polyfluorinated alkyl substances in indoor air using thermal desorption-gas chromatography–mass spectrometry
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Yaoxing Wu, Victor W.-C. Chang
The study attempts to utilize thermal desorption (TD) coupled with gas chromatography–mass spectrometry (GC–MS) for determination of indoor airborne volatile polyfluorinated alkyl substances (PFASs), including four fluorinated alcohols (FTOHs), two fluorooctane sulfonamides (FOSAs), and two fluorooctane sulfonamidoethanols (FOSEs). Standard stainless steel tubes of Tenax/Carbograph 1 TD were employed for low-volume sampling and exhibited minimal breakthrough of target analytes in sample collection. The method recoveries were in the range of 88–119% for FTOHs, 86–138% for FOSAs, exhibiting significant improvement compared with other existing air sampling methods. However, the widely reported high method recoveries of FOSEs were also observed (139–210%), which was probably due to the structural differences between FOSEs and internal standards. Method detection limit, repeatability, linearity, and accuracy were reported as well. The approach has been successfully applied to routine quantification of targeted PFASs in indoor environment of Singapore. The significantly shorter sampling time enabled the observation of variations of concentrations of targeted PFASs within different periods of a day, with higher concentration levels at night while ventilation systems were shut off. This indicated the existence of indoor sources and the importance of building ventilation and air conditioning system.
Source:Journal of Chromatography A, Volume 1238
Yaoxing Wu, Victor W.-C. Chang
The study attempts to utilize thermal desorption (TD) coupled with gas chromatography–mass spectrometry (GC–MS) for determination of indoor airborne volatile polyfluorinated alkyl substances (PFASs), including four fluorinated alcohols (FTOHs), two fluorooctane sulfonamides (FOSAs), and two fluorooctane sulfonamidoethanols (FOSEs). Standard stainless steel tubes of Tenax/Carbograph 1 TD were employed for low-volume sampling and exhibited minimal breakthrough of target analytes in sample collection. The method recoveries were in the range of 88–119% for FTOHs, 86–138% for FOSAs, exhibiting significant improvement compared with other existing air sampling methods. However, the widely reported high method recoveries of FOSEs were also observed (139–210%), which was probably due to the structural differences between FOSEs and internal standards. Method detection limit, repeatability, linearity, and accuracy were reported as well. The approach has been successfully applied to routine quantification of targeted PFASs in indoor environment of Singapore. The significantly shorter sampling time enabled the observation of variations of concentrations of targeted PFASs within different periods of a day, with higher concentration levels at night while ventilation systems were shut off. This indicated the existence of indoor sources and the importance of building ventilation and air conditioning system.
Chemometric analysis of gas chromatography with flame ionisation detection chromatograms: A novel method for classification of petroleum products
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
N.J. Nielsen, D. Ballabio, G. Tomasi, R. Todeschini, J.H. Christensen
Most oil characterisation procedures are time consuming, labour intensive and utilise only part of the acquired chemical information. Oil spill fingerprinting with multivariate data processing represents a fast and objective evaluation procedure, where the entire chromatographic profile is used. Methods for oil classification should be robust towards changes imposed on the spill fingerprint by short-term weathering, i.e. dissolution and evaporation processes in the hours following a spill. We propose a methodology for the classification of petroleum products. The method consists of: chemical analysis; data clean-up by baseline removal, retention time alignment and normalisation; recognition of oil type by classification followed by initial source characterisation. A classification model based on principal components and quadratic discrimination robust towards the effect of short-term weathering was established. The method was tested successfully on real spill and source samples.
Source:Journal of Chromatography A, Volume 1238
N.J. Nielsen, D. Ballabio, G. Tomasi, R. Todeschini, J.H. Christensen
Most oil characterisation procedures are time consuming, labour intensive and utilise only part of the acquired chemical information. Oil spill fingerprinting with multivariate data processing represents a fast and objective evaluation procedure, where the entire chromatographic profile is used. Methods for oil classification should be robust towards changes imposed on the spill fingerprint by short-term weathering, i.e. dissolution and evaporation processes in the hours following a spill. We propose a methodology for the classification of petroleum products. The method consists of: chemical analysis; data clean-up by baseline removal, retention time alignment and normalisation; recognition of oil type by classification followed by initial source characterisation. A classification model based on principal components and quadratic discrimination robust towards the effect of short-term weathering was established. The method was tested successfully on real spill and source samples.
A novel headspace gas chromatographic method for in situ monitoring of monomer conversion during polymerization in an emulsion environment
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Xin-Sheng Chai, Jin-Feng Zhong, Hui-Chao Hu
This paper describes a novel multiple-headspace extraction/gas chromatographic (MHE-GC) technique for monitoring monomer conversion during a polymerization reaction in a water-based emulsion environment. The polymerization reaction of methyl methacrylate (MMA) in an aqueous emulsion is used as an example. The reaction was performed in a closed headspace sample vial (as a mini-reactor), with pentane as a tracer. In situ monitoring of the vapor concentration of the tracer, employing a multiple headspace extraction (sampling) scheme, coupled to a GC, makes it possible to quantitatively follow the conversion of MMA during the early stages of polymerization. Data on the integrated amount of the tracer vapor released from the monomer droplet phase during the polymerization is described by a mathematic equation from which the monomer conversion can be calculated. The present method is simple, automated and economical, and provides an efficient tool in the investigation of the reaction kinetics and effects of the reaction conditions on the early stage of polymerization.
Source:Journal of Chromatography A, Volume 1238
Xin-Sheng Chai, Jin-Feng Zhong, Hui-Chao Hu
This paper describes a novel multiple-headspace extraction/gas chromatographic (MHE-GC) technique for monitoring monomer conversion during a polymerization reaction in a water-based emulsion environment. The polymerization reaction of methyl methacrylate (MMA) in an aqueous emulsion is used as an example. The reaction was performed in a closed headspace sample vial (as a mini-reactor), with pentane as a tracer. In situ monitoring of the vapor concentration of the tracer, employing a multiple headspace extraction (sampling) scheme, coupled to a GC, makes it possible to quantitatively follow the conversion of MMA during the early stages of polymerization. Data on the integrated amount of the tracer vapor released from the monomer droplet phase during the polymerization is described by a mathematic equation from which the monomer conversion can be calculated. The present method is simple, automated and economical, and provides an efficient tool in the investigation of the reaction kinetics and effects of the reaction conditions on the early stage of polymerization.
Use of the isopycnic plots in designing operations of supercritical fluid chromatography: IV. Pressure and density drops along columns
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Abhijit Tarafder, Krzysztof Kaczmarski, Megan Ranger, Donald P. Poe, Georges Guiochon
The pressure- and the density-drops along a chromatographic column eluted with supercritical fluid carbon dioxide were mapped as a function of the outlet column pressure and the temperature on the P–T diagram of neat CO2. At low densities, the viscosity of CO2 is low, which is expected to result into a low pressure drop along the column. However, at these low densities, the volumetric flow rates of the mobile phase at constant mass flow rates are high, which might result into a high pressure drop along the column. These conflicting effects of an adjustment in the mobile phase density on the pressure drop of the mobile phase along the column makes it nearly impossible to develop a simple intuitive understanding of the relationships between the net pressure drops and the operating temperatures and pressures. The development of a similar understanding of their relationships with the density drop along the column is even more complex, because this density drop depends also on the compressibility of the mobile phase, itself a function of the operating pressures and temperatures. Numerical calculations of the pressure and density drops along columns packed with particles of different sizes, under different operating conditions (temperature, outlet pressure, and flow rate), provide important insights regarding the extent of the pressure and density drops under these operating conditions.
Source:Journal of Chromatography A, Volume 1238
Abhijit Tarafder, Krzysztof Kaczmarski, Megan Ranger, Donald P. Poe, Georges Guiochon
The pressure- and the density-drops along a chromatographic column eluted with supercritical fluid carbon dioxide were mapped as a function of the outlet column pressure and the temperature on the P–T diagram of neat CO2. At low densities, the viscosity of CO2 is low, which is expected to result into a low pressure drop along the column. However, at these low densities, the volumetric flow rates of the mobile phase at constant mass flow rates are high, which might result into a high pressure drop along the column. These conflicting effects of an adjustment in the mobile phase density on the pressure drop of the mobile phase along the column makes it nearly impossible to develop a simple intuitive understanding of the relationships between the net pressure drops and the operating temperatures and pressures. The development of a similar understanding of their relationships with the density drop along the column is even more complex, because this density drop depends also on the compressibility of the mobile phase, itself a function of the operating pressures and temperatures. Numerical calculations of the pressure and density drops along columns packed with particles of different sizes, under different operating conditions (temperature, outlet pressure, and flow rate), provide important insights regarding the extent of the pressure and density drops under these operating conditions.
Improved capillary electrophoresis frontal analysis by dynamically coating the capillary with polyelectrolyte multilayers
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Chao Liu, Jingwu Kang
An improved CE-FA method using a polyelectrolyte multilayer (PEML) coated capillary is described. The coating was simply created by alternatively flushing the capillary with positively charged polyelectrolyte polybrene (HDB) and negatively charged polyelectrolyte dextran sulfate (DS). Human serum albumin (HSA) and 6 drugs were selected as an experimental model to evaluate such an improvement. The PEML coating was demonstrated to effectively reduce the protein adsorption on the capillary wall. Compared with the uncoated capillary, the repeatability (RSD%) of the EOF mobility and the plateau height of free drug were improved significantly from 3.7% to 0.51% and from 0.61% to 0.34%, respectively. No interference of the coating on the measurement of protein–drug binding parameters was observed.
Source:Journal of Chromatography A, Volume 1238
Chao Liu, Jingwu Kang
An improved CE-FA method using a polyelectrolyte multilayer (PEML) coated capillary is described. The coating was simply created by alternatively flushing the capillary with positively charged polyelectrolyte polybrene (HDB) and negatively charged polyelectrolyte dextran sulfate (DS). Human serum albumin (HSA) and 6 drugs were selected as an experimental model to evaluate such an improvement. The PEML coating was demonstrated to effectively reduce the protein adsorption on the capillary wall. Compared with the uncoated capillary, the repeatability (RSD%) of the EOF mobility and the plateau height of free drug were improved significantly from 3.7% to 0.51% and from 0.61% to 0.34%, respectively. No interference of the coating on the measurement of protein–drug binding parameters was observed.
High resolution separation by pressure-driven liquid chromatography in meander extended nanochannels
23 April 2012,
10:43:35
Publication year:
2012
Source:Journal of Chromatography A, Volume 1238
Ryo Ishibashi, Kazuma Mawatari, Takehiko Kitamori
The rapidly developing interest in nanofluidics, which is used to examine liquids on an order that ranges from an attoliter to a femtoliter, correlates with the recent interest in decreased sample amounts, such as in the field of single-cell analysis. In this paper, we have succeeded in the normal phase separation of a 101 fL sample with a high number of theoretical plates (103 plates), and a fast separation (4s), using a pressure-driven flow in extended nanochannels. A meander separation channel 1μm wide was introduced and showed no band broadening at the turns, unlike microchannels (101–102 μm wide), which is an important aspect in order to lengthen the channel in a space-limited micro/nanofluidic chip. Our device enables the fast separation of an ultra-small volume of sample with a high number of theoretical plates, and will serve as a general platform for the separation of aL to fL volumes of samples.
Source:Journal of Chromatography A, Volume 1238
Ryo Ishibashi, Kazuma Mawatari, Takehiko Kitamori
The rapidly developing interest in nanofluidics, which is used to examine liquids on an order that ranges from an attoliter to a femtoliter, correlates with the recent interest in decreased sample amounts, such as in the field of single-cell analysis. In this paper, we have succeeded in the normal phase separation of a 101 fL sample with a high number of theoretical plates (103 plates), and a fast separation (4s), using a pressure-driven flow in extended nanochannels. A meander separation channel 1μm wide was introduced and showed no band broadening at the turns, unlike microchannels (101–102 μm wide), which is an important aspect in order to lengthen the channel in a space-limited micro/nanofluidic chip. Our device enables the fast separation of an ultra-small volume of sample with a high number of theoretical plates, and will serve as a general platform for the separation of aL to fL volumes of samples.
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