Showing papers in "Journal of Separation Science in 2002"
TL;DR: A review of the use of adsorbents containing cyclodextrins in the field of separation techniques can be found in this paper, where the main goal is to provide a summary of the information concerning the synthesis of materials containing CDs and to give a general overview of the different possible applications of CDs as sorbents.
Abstract: Cyclodextrins (CDs), which possess a hydrophobic cavity, have a remarkable capacity to form inclusion complexes with various molecules through host-guest interactions It is well known that the usefulness of CDs is due to the combination of the inclusion properties and structural features of these molecules CDs are used extensively in separation science because CD-complexation phenomena offer a procedure of choice for separation of compounds and extraction processes, and provide a useful and versatile tool for protecting the environment The present review shows the advantages accruing from the use of adsorbents containing cyclodextrins, in particular in chromatographic separations and in waste water treatment The main goal of this review is to provide a summary of the information concerning the synthesis of materials containing CDs and to give a general overview of the different possible applications of CDs as sorbents in the field of separation techniques Recent and continuing interest in these adsorbents is evident from the number of papers that appear each year in the literature
316 citations
TL;DR: A nanoscale capillary column switching HPLC-ESI/MS (n) system intended for routine operation with 50 pm ID packed, fused silica columns, which provides maximum flexibility for a wide array of applications.
Abstract: We describe a nanoscale capillary column switching HPLC-ESI/MS (n) system in detail. It is intended for routine operation with 50 pm ID packed, fused silica columns. The system accepts large injection volumes (typically 10 μL) and uses a trapping column for fast sample loading. Analytes are transferred and then separated on an analytical column at a flow rate of 100-125 nL/min. The design of the system focuses on both robustness for unattended operation and minimization of extracolumn dead volumes. Although the flow direction is controlled by switching valves, the analytes do not pass through any of these valves except the injection valve. A standard, highpressure-mixing binary pump (not necessarily designed for nanoscale applications) is used, while the columns, splitter restrictors and electrospray emitters are home made. This provides maximum flexibility for a wide array of applications. Examples of protein and peptide identification at a concentration level of 100 amol/μL are given, including on-column derivatization. In addition, a minor modification of the setup provides the permanent option of using peak parking for interactive data acquisition (e. g. Ms (n) experiments during analyte elution).
268 citations
TL;DR: In this paper, the influence of modulator temperature, modulation frequency, temperature programming rate, and carrier gas velocity on the performance of comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOF MS) was studied.
Abstract: The influence of modulator temperature, modulation frequency, temperature programming rate, and carrier gas velocity on the performance of comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC–TOF MS) was studied. The system was characterized with respect to the repeatability of peak areas and retention times of selected analytes, their detection limits, and the linearity of their calibration plots. The system was found to be linear in the 0.01–3 ng range, and detection limits for the pesticides were between 5 and 23 pg. The performance of the system was compared with that of conventional one-dimensional (1D) GC–TOF MS, the advantages of TOF MS for identification and deconvolution are discussed, and several approaches for the processing of GC×GC–TOF MS data are explained with the emphasis on (semi)-automated data processing and the differences with 1D-GC–TOF MS.
153 citations
TL;DR: In this article, solid phase extraction with silica cartridges is applied as sole sample preparation step, and a 250-mg sample of oil in n-hexane is loaded onto a 5 g silica cartridge and the PAH fraction is eluted with 8 mL of nhexane/dichloromethane 70/30. After solvent evaporation, the volume was adjusted to 100 μL and injected into a HPLC equipped with a C18 reverse phase column and a spectrofluorometric detector.
Abstract: Despite the carcinogenic properties of some PAHs, and although edible oils are particularly prone to PAH contamination, no international legal limits for PAH in edible oils have been yet established. However, a number of methods for such analyses have been published, most of which are time consuming and unsuitable for routine analysis, as they do not permit analysis of a large number of samples per day. Since sample preparation is the most time-consuming part of analysis, research to find fast sample preparation methods is of topical interest. In this paper, solid phase extraction with silica cartridges is applied as sole sample preparation step. A 250-mg sample of oil in n-hexane is loaded onto a 5 g silica cartridge and the PAH fraction is eluted with 8 mL of n-hexane/dichloromethane 70/30. After solvent evaporation, the volume was adjusted to 100 μL and injected into a HPLC equipped with a C18 reverse phase column and a spectrofluorometric detector. Results show a relatively low recovery for the more volatile PAHs (Na and Ac) and good recovery for heavy PAHs. Repeatability is quite satisfactory, as coefficients of variation range between 5.0 and 13.0%.
127 citations
TL;DR: In this article, the US Food and Drug Administration (US FDA) and Canadian Pest Management Regulatory Agency (ACetonitrile extraction) methods for pesticides were subjected to cleanup with solid phase extraction (SPE) columns.
Abstract: Sample extracts of various commodities, obtained using the US Food and Drug Administration (acetone extraction) and Canadian Pest Management Regulatory Agency (acetonitrile extraction) methods for pesticides were subjected to cleanup with solid phase extraction (SPE) columns. Graphitized carbon black (GCB), octadecylsilyl (C-18), strong anion exchange (SAX), aminopropyl (-NH 2 ), and primary secondary amine (PSA) SPE columns were evaluated. The relative sample cleanup provided by these SPE columns was evaluated using gas chromatography with electron capture, flame photometric, and mass spectrometric detection. The -NH 2 and PSA columns were found to provide the most effective cleanup, removing the greatest number of sample matrix interferences. The GCB columns removed most of the visible plant pigment in the extracts, but did little to eliminate the fatty acid matrix interferences seen by the detectors. Likewise, the C-18 and SAX columns did little to eliminate matrix interferences. Using an acetone extraction followed by a PSA cleanup, both polar and nonpolar pesticides present in samples at 1.0 ng/g could be recovered.
111 citations
TL;DR: In this paper, an automated on-line method for the analysis of endocrine disruptors related to plastics was developed using in-tube solid-phase microextraction coupled with high performance liquid chromatography (in-tube SPME/HPLC).
Abstract: An automated on-line method for the analysis of endocrine disruptors related to plastics was developed using in-tube solid-phase microextraction coupled with high performance liquid chromatography (in-tube SPME/HPLC). In-tube SPME is an extraction technique for organic compounds in aqueous samples, in which analytes are extracted from the sample directly into an open tubular capillary by repeated draw/eject cycles of sample solution. Suspected endocrine disrupting compounds, bisphenol A, two alkylphenols, and nine phthalate esters, tested in this study were well separated with a Hypersil ODS column with diode array detection using acetonitrile/water as a mobile phase. In order to optimize the extraction of these compounds, several in-tube SPME parameters were examined. The optimum extraction conditions were 20 draw/eject cycles of 40 μL of sample using a Supel-Q PLOT capillary column. The extracted compounds were easily desorbed from the capillary by mobile phase flow, and carryover was not observed. Using in-tube SPME/HPLC method, the calibration curves of these compounds were linear in the range from 1 to 500 ng/mL, with correlation coefficient above 0.991 (n = 18), and the detection limits (S/N = 3) were 0.1–4.0 ng/mL. This method was successfully applied to the migration test from plastics and the analysis of food samples.
98 citations
TL;DR: In this article, a method has been developed for continuous monitoring of the emission of volatiles from biological sources with high time resolution using an automatically operated, miniaturised gas chromatographic system equipped with a pre-concentration unit (zNoseTM).
Abstract: A method has been developed for continuous monitoring of the emission of volatiles from biological sources with high time resolution. High time resolution (up to 3 min) is achieved by an automatically operated, miniaturised gas chromatographic system equipped with a pre-concentration unit (zNoseTM). After calibration, the zNoseTM provides reliable quantitative data for individual compounds and allows their emission kinetics to be followed over longer periods of time without supervision. While the results of the zNoseTM provide information about actual composition of aromas during sampling, the analysis of simultaneously trapped volatiles supplies information about the total amount of emitted compounds and permits further spectroscopic analyses (Isotope-Ratio-MS, GC-MS, etc.). Both methods, analysis by the zNoseTM and sampling on charcoal traps, lead to comparable results. The new analytical system has been successfully used to study the kinetics of volatile emission from elicitor-treated Lima bean leaves (Phaseolus lunatus), aphid-damaged paprika plants (Capsicum annuum), and to follow the volatile emission from blossoms of the cactus Rebutia fabrisii over several days. The instrument is portable and can be used in the field.
87 citations
TL;DR: In this article, the formation of particular pseudo-molecular ions depends on ion affinity and molecular structure of the analyte as well as the solvent/buffer conditions used, and the pK a and surface activity of analytes and the pH, concentration, and type of the solvent system strongly affect the ions formed.
Abstract: This study focuses on pseudo-molecular ion formation in electrospray ionization mass spectrometry (ESI-MS) of six anti-inflammatory pharmaceuticals with similar functionality. The formation of particular pseudo-molecular ions depends on ion affinity and molecular structure of the analyte as well as the solvent/buffer conditions used. Six common anti-inflammatory agents are mixed 1:1 with six different acetonitrile/aqueous buffer solutions at varying concentrations. The analytes are ibuprofen, carprofen, naproxen, ketoprofen, flurbiprofen, and fenoprofen. The pK a and surface activity of the analytes and the pH, concentration, and type of the solvent system strongly affect the ions formed [1,2]. The additives are common liquid chromatography (LC) mobile phase modifiers. The spectral intensities of three major pseudo-molecular ions were measured by flow injection analysis ESI-MS. The ions studied correspond to the deprotonated molecular ion ([M - H] - ), a deprotonated dimer ion ([2M - H] - ), and a deprotonated dimer ion pair with sodium ([2M - 2H+Na] - ). These ions were chosen due to their high relative abundance in a majority of the spectra. The pKa of the analytes studied range from 4.1 to 4.4, due to their aromatic acetic acid moiety. The common carboxylic acid group facilitates ESI of the compounds in the negative ionization mode. The changes in molecular structure of these model compounds allows for a wide variety of solution interactions. Some analytes are effectively declustered under the set conditions creating an intense [M - H] - peak, whereas others prefer to form dimers or complexes with sodium.
80 citations
TL;DR: In this article, a capillary gas chromatography method was developed for the quantitative analysis of caffeine in Brazilian guarana as seed powder, dried crude ethanol extracts, and lyophilized water extracts with the addition of 7β-Hydroxyethyltheophylline as the internal standard.
Abstract: The aim of the present study was to develop a capillary gas chromatography method for the quantitative analysis of caffeine in Brazilian guarana as seed powder, dried crude ethanol extracts, and lyophilized water extracts with the addition of 7β-Hydroxyethyltheophylline as the internal standard. The experimental protocol, the conditions, the analytical instrumentation, the recovery studies, as well as the analysis of seven different commercial batches of guarana, are presented and discussed.
75 citations
TL;DR: A stationary phase with hydrophilic endcapping was used for the separation of seven quercetin (Q) glycosides by high-performance liquid chromatography in this paper.
Abstract: A stationary phase with hydrophilic endcapping was used for the separation of seven quercetin (Q) glycosides by high-performance liquid chromatography. The elution order was established as Q 3-rutinoside, Q 3-galactoside, Q 3-glucoside, Q 3-xyloside, Q 3-arabinopyranoside, Q 3-arabinofuranoside, and Q 3-rhamnoside. Since a recent study had revealed that a commercially available reference compound (Q 3-arap) was erroneously labeled as avicularin (Q 3-araf), standards of the two isomers of Q 3-ara were characterized by 1 D and 2D NMR spectroscopy, and by optical rotation. The predominant Q glycosides detected in apple pomace were Q 3-gal, Q 3-araf, Q 3-rha and Q 3-xyl, whereas considerably lower amounts of Q 3-glc and Q 3-arap were found. Total content of Q glycosides was approximately 900 mg/kg on a dry matter basis, indicating that apple pomace is a good source of natural antioxidants.
64 citations
TL;DR: The amount of glycyrrhizin extracted by PLE with methanol as solvent for Glycyr rhizin in medicinal plants was found to be comparable or higher compared to multiple step ultrasonic extraction using a mixture of methnol/ water (70:30).
Abstract: Glycyrrhizin in Radix glycyrrhizae or liquorice was determined using a laboratory made dynamic pressurized liquid extraction (PLE) system coupled with capillary zone electrophoresis (CZE). The amount of glycyrrhizin was determined using CZE with an aqueous buffer of 10 mM of sodium tetraborate at pH 9.25 with UV detection at 254 nm. The effects of pH, buffer concentration, and the applied voltage on the electrophoretic separation were investigated. Temperature was found to be the important parameter in PLE as it was observed that the amount of thermally labile components such as glycyrrhizin extracted from medicinal plants decreased with increasing temperature from 100 to 160°C. The amount of glycyrrhizin extracted by PLE with methanol as solvent for glycyrrhizin in medicinal plants was found to be comparable or higher compared to multiple step ultrasonic extraction using a mixture of methanol/ water (70:30). The overall method precision was found to vary from 6.9 to 8.1% (RSD) for glycyrrhizin in medicinal plants. The specificity of the method was checked using standard addition experiments.
TL;DR: In this article, an inexpensive and disposable hollow fibre based device for liquid-phase microextraction (LPME) where ionic analytes typically are extracted from 1-4 mL aqueous samples (such as plasma and urine) through an organic solvent immobilized in the pores of a polypropylene hollow fibre and into a 10-25 μL volume of acceptor phase present inside the hollow fibre.
Abstract: Recently, we introduced an inexpensive and disposable hollow fibre based device for liquid-phase microextraction (LPME) where ionic analytes typically are extracted from 1-4 mL aqueous samples (such as plasma and urine) through an organic solvent immobilized in the pores of a polypropylene hollow fibre and into a 10-25 μL volume of acceptor phase present inside the hollow fibre. Because of the substantial volume ratio of the sample relative to the acceptor phase, ionic analytes may be preconcentrated considerably during LPME (typical preconcentration factors of 50 to 150). In addition, during LPME from biological samples such as plasma and urine, the majority of matrix components are not extracted into the acceptor phase resulting in excellent sample clean-up. For the extraction of basic drugs, dilute solutions of HCI or acidic phosphate buffers have been utilized as acceptor phase without further optimization. In the present work therefore, systematic studies have been performed to explore new acidic acceptor phase possibilities in combination with dihexyl ether as a standard organic solvent in the pores of the hollow fibre. In general, 10 mM solutions of HCI, H 2 SO 4 , and phosphate pH 3.3 were found to provide the highest extraction recoveries. pH was found to play a major role in adjusting the selectivity of LPME, whereas minor selectivity alterations were observed on changing the type of acid in the acceptor phase. For weakly basic drugs, an increased level of HCI in the acceptor phase may provide higher recovery, and for certain drugs, addition of ethanol to the acceptor phase may improve the extractability.
TL;DR: A chiral stationary phase (CSP) prepared by bonding (+)-(18crown-6)-2,3,11,12-tetracarboxylic acid to silica gel was used for the direct resolution of β-amino acids as discussed by the authors.
Abstract: A chiral stationary phase (CSP) prepared by bonding (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid to silica gel was used for the direct resolution of β-amino acids. To determine the optimum mobile phase composition, two β-amino acids were selected and their resolutions on the CSP were performed with variation of the types and contents of organic and acidic modifiers in the aqueous mobile phase. The chromatographic resolution behaviors were found to be dependent on the types and contents of organic and acidic modifiers in the aqueous mobile phase. From the results of these experiments, a possible optimum mobile phase composition was proposed to be a mixed solvent of 50% methanol in water containing acetic acid (10 mM). The chromatographic resolution behaviors were also found to be dependent on the column temperature, the retention (k1) and the separation factors (α) being greater at lower temperatures. At the optimum mobile phase composition, all β-amino acids tested in this study were resolved quite well on the CSP with baseline separation.
TL;DR: In this article, the authors explore the use of CEC as a potential alternative to conventional HPLC, μ-HPLC, and CE, both theoretical and experimental, and discuss the practical aspects of applying CEC in various modes of separation.
Abstract: CEC is a technique that has attracted increased interest in recent years. It combines the advantages of high efficiency of electrophoretic separation methods with the greater selectivity characteristic of HPLC. In this paper we explore the use of CEC as a potential alternative to conventional HPLC, μ-HPLC, and CE. Recent developments, both theoretical and experimental, are reviewed. The practical aspects of application of CEC in various modes of separation are also discussed.
TL;DR: In this article, the potential of fast temperature-programmed gas chromatography (GC) was studied by combining a resistively heated gas chromatograph and a quadrupole mass spectrometer (MS).
Abstract: The potential of fast temperature-programmed gas chromatography (GC) was studied by combining a resistively heated gas chromatograph and a quadrupole mass spectrometer (MS). An EZ Flash GC was used, which generates temperature ramps up to 1200 /min and cools down from 300 to 50°C in some 30 s; samples were injected via a conventional split/splitless injector in both injection modes. The combination of a short narrow-bore column (5 m x 0.1 mm ID), a high gas flow rate, and fast temperature programs typically decreased conventional analysis times of 30 min to about 3 min. The scan speed of the quadrupole mass spectrometer (16 spectra/s in the range m/z 50-310) was found to be sufficient for a proper reconstruction of the chromatographic peaks, and good-quality mass spectra could be obtained. Six scans across a peak were sufficient for peak integration. The system was linear in the range of 0.01-3 ng injected mass and detection limits for pesticides were in the range of 1-25 pg in the full-scan and 0.1-5 pg in the selected ion monitoring mode. Series of apple and mole liver extracts were analyzed to demonstrate the high sample throughput and suitability of EZ Flash GC for fast screening.
TL;DR: In this paper, the authors proposed a method for stereospecifically evaluating the enantiomers of a drug in quality control of enantiomerically pure drugs, e.g. the determination of the Enantiomeric Excess (EE).
Abstract: The chiral nature of living systems has strong implications for biologically active compounds interacting with them. Consequently, the stereoisomers of drugs can differ in both pharmacodynamic and pharmacokinetic actions. Regulatory authorities encourage the pharmaceutical industry to develop single isomers of chiral drugs. Thus, methods are required which are suitable for stereospecifically evaluating the enantiomers of a drug in quality control of enantiomerically pure drugs, e.g. the determination of the enantiomeric excess (ee). Beside the major methods, chiral HPLC and NMR spectroscopy, cyclodextrin-modified capillary electrophoresis is enjoying increasing popularity in both academic and industrial laboratories. In order to obtain a baseline separation of mixture of a minor and a major isomer which is appropriate for determining the ee, the following parameters have to be optimised: the nature and concentration of the cyclodextrin derivative, the composition of the background electrolyte, the pH value, the organic modifier, and the kind and conditioning of the capillary. In addition, the sensitivity of detection has to be taken into consideration, because a limit of detection of 0.1 percent is necessary to fulfil the requirements of the ICH guidelines. Strategies of method development will be discussed using currently reported examples.
TL;DR: A porous chemically modified photopolymerized sol-gel (PSG) monolith enhanced the capillary electrochromatographic separations of two test mixtures, one containing eight alkyl phenyl ketones and the other containing thiourea and three polyaromatic hydrocarbons.
Abstract: A porous chemically modified photopolymerized sol-gel (PSG) monolith enhanced the capillary electrochromatographic separations of two test mixtures, one containing eight alkyl phenyl ketones and the other containing thiourea and three polyaromatic hydrocarbons. Derivatization of the PSG surface with silane coupling reagents resulted in bonded phases of pentafluorophenylpropyldimethyl, pentafluorophenyl, 3,3,3-trifluoropropyl, n-octadimethyl, perfluorohexyl, and aminopropyl. The fabrication of the bonded-phase PSG column is easy to do with the silanization reaction proceeding at room temperature for not longer than 60 minutes. The hydrophobicity of the PSG was altered without degrading its chromatographic performance. The bonded-phase PSG monoliths have higher stability at pH values below 4 as compared to the parent (underivatized) PSG. Separations of different mixtures containing nucleosides, positively charged peptides, and taxol derivatives illustrate the potential of bonded-phase PSG columns for the analyses of biologically and pharmaceutically important compounds. We report column efficiencies of up to 180 000 plates/meter and retention factors as large as 28.6 for decanophenone.
TL;DR: This reversed phase HPLC/electrospray ionization mass spectrometry system shows good chromatographic resolution for phosphatidylcholine molecular species and allows unequivocal assignment of the positions of the acyl chains on the glycerol backbone in mixture of POPC and OPPC and in mixtures of POPE and OPPE.
Abstract: Since phospholipids are used as excipients in many pharmaceutical products, there is a need for validated strategies to characterize the phospholipid constituents. We describe a reversed phase HPLC/electrospray ionization mass spectrometry method that is an alternative to the laborious phospholipase A2 treatment commonly used to determine the acyl chain positions in phospholipids. This reversed phase HPLC/electrospray mass spectrometry system (a) shows good chromatographic resolution for phosphatidylcholine molecular species, (b) allows determination of the composition of complex mixtures of phosphatidylcholines, and, most important, (c) allows unequivocal assignment of the positions of the acyl chains on the glycerol backbone in mixtures of POPC and OPPC and in mixtures of POPE and OPPE.
TL;DR: In this article, the authors investigated the efficiency of microfabricated COMOSS columns with varying dimensions and found that the efficiency depends on the geometry of the resulting channels, and that an increase of distance between channel intersections (or decrease of trans-channel coupling frequency) leads to a considerable decrease in efficiency.
Abstract: Twenty microfabricated COMOSS columns with varying dimensions were investigated in this work. Columns with different channel depth (1.6–10 μm) and width (2–4 μm) were studied; the size of collocated particles was also varied, including diamonds (5×5–11×11 μm) and their elongated and extended versions: hexagonal structures allowing greater distances between mixing nodes. Comparisons were made by plotting plate height-voltage curves for each type of column geometry using rhodamine 110, fluorescein, or small peptides as standard compounds. It was demonstrated that the efficiency of separation strongly depends on the geometry of resulting channels. An increase of distance between channel intersections (or decrease of trans-channel coupling frequency) was shown to unavoidably lead to a considerable decrease in efficiency of the microfabricated column. It was also found that low aspect ratio structures produced from positive photoresist masters were more efficient than their high aspect ratio equivalents. The highest efficiency of 620000 plates per meter was obtained with 10 μm deep channels and particles of 5.2×5.2 μm (diamonds).
TL;DR: In this paper, a method of generating a retention index base for comprehensive two-dimensional gas chromatography (GC×GC) has been developed for the first and second axes of the two dimensional analysis space.
Abstract: A method of generating a retention index base for comprehensive two-dimensional gas chromatography (GC×GC) has been developed for the first and second axes of the two dimensional analysis space. The approach is described for an alkane base, and also with 2-methyl ketone and fatty acid methyl ester standards. The method involves repetitive, timed, sequential injections of the reference compound standard mixtures, and from the resultant data developing a retention correlation map. The first dimension generates linear temperature programmed indices, whilst the second dimension may be interpreted on the basis of ‘pseudo isothermal’ retention indices. From this map, retention information should be obtainable for any solute eluting within the allowed analysis region. It is proposed that this procedure will allow prediction of comprehensive two-dimensional gas chromatography (GC×GC) retention data or positions for compounds in the 2D separation space, andwill also support development and understanding of rational column choices for GC×GC. The second dimension cannot be easily interpreted based on an alkane retention series, and so a more polar retention index base will be required.
TL;DR: In this paper, a double-cross injection system has been developed which uses electrokinetic focusing to achieve variable-volume injection of the sample plug, which uses a unique sequence of loading steps with different electric potential distributions and potential magnitudes within the various channels to effectuate a virtual valve.
Abstract: This paper adopts a physical model and a numerical simulation approach to study electrokinetic focusing injection on microfluidic chips. The model reflects the principal material transport mechanisms such as electrokinetic migration, ionic concentration, fluid flow, and diffusion. The current study also involves the design and testing of various injection systems used to deliver a sample plug. A novel double-cross injection system has been developed which uses electrokinetic focusing to achieve variable-volume injection of the sample plug. The injection technique uses a unique sequence of loading steps with different electric potential distributions and potential magnitudes within the various channels to effectuate a virtual valve. The proposed design combines several functions of traditional sample plug injection systems on a single microfluidic chip.
TL;DR: In this paper, the effects of pH (7.40 and 8.25) and buffer (various sulfonic acid buffers, Tricine, and phosphate) on the electrophoretic mobilities and sizes of unilamellar liposomes were investigated by capillary electrophoresis, light scattering, and monolayer penetration techniques.
Abstract: Unilamellar liposomes were investigated by capillary electrophoresis, light scattering, and monolayer penetration techniques. Zwitterionic liposomes with and without cholesterol were compared and the effects of pH (7.40 and 8.25) and buffer (various sulfonic acid buffers, Tricine, and phosphate) on the electrophoretic mobilities and sizes of the liposomes were studied. Anionic liposomes containing phosphatidylserine with and without various amounts of cholesterol were used as dispersed phase in electrokinetic capillary chromatography in the separation of six steroidal hormones, with a focus on selectivity differences with increasing amounts of cholesterol in the liposomes. The results were confirmed by monolayer penetration measurements.
TL;DR: The use of at-, on-, and in-line preconcentration procedures in combination with CE in the analysis of biological fluids and the advantages and drawbacks of the techniques are examined.
Abstract: “On-Line” preconcentration in capillary electrophoresis (CE) is a good strategy to overcome the low concentration sensitivity of the technique, which is the main limitation when trace-level compounds are to be determined in complex matrices such as biological samples. Here we discuss the use of at-, on-, and in-line preconcentration procedures in combination with CE in the analysis of biological fluids. The preconcentration strategies discussed are classified into two groups depending on the mechanism involved: chromatographic or electrophoretic techniques. Recent applications are included and the advantages and drawbacks of the techniques are examined.
TL;DR: In this article, a comprehensive two-dimensional gas chromatograph with dual secondary columns (GC × 2 GC) was used to characterize gaseous mixtures of volatile organic compounds (VOCs).
Abstract: A comprehensive two-dimensional gas chromatograph with dual secondary columns (GC × 2 GC) was used to characterize gaseous mixtures of volatile organic compounds (VOCs). Samples were collected on multi-layer sorbent tubes and introduced into the gas chromatograph using a thermal desorption apparatus. Differential flow modulation was used to couple the primary column to the secondary columns. Each GC × 2 GC analysis produced a pair of two-dimensional gas chromatograms. The chromatograms provided complementary information due to the unique selectivities of the secondary columns. The additional information was especially useful in separating and identifying oxygenated and aromatic compounds. Samples of outdoor air, indoor air, and exhaled breath were analyzed with the GC x 2GC system. More than 100 volatile organic compounds could be separated in less than 10 minutes. The identities of approximately 50 peaks were determined for each sample.
TL;DR: In this paper, a photopolymerized sol-gel (PSG) monolith was synthesized in the separation channel of a borosilicate glass chip via UV irradiation (5 min) of a mixture of 3-methacryloxypropyltrimethoxysilane, an acid catalyst, a porogen, and a photoinitiator.
Abstract: A porous photopolymerized sol-gel (PSG) monolith was synthesized in the separation channel of a borosilicate glass chip via UV irradiation (5 min) of a mixture of 3-methacryloxypropyltrimethoxysilane, an acid catalyst, a porogen, and a photoinitiator. The PSG monolith adhered strongly to the chemically untreated channel walls. The chip was fabricated using standard lithography procedures to give channels that are 35-μm deep and 90-μm wide. Masking the other channels defined the 4.7-cm PSG section in the separation channel. Two dyes Coumarin 314 and 510 were successfully separated within baseline resolution in 225 s when fluorescent detection occurred immediately after the PSG section. The separation time was reduced to 80 s with little loss in resolution by detecting the dyes 1.2 cm from the front of the PSG monolith.
TL;DR: In this article, the authors describe the design, fabrication, and analytical performance of a PMMA microchip for isotachophoresis and capillary electrophoresis, which can be used for a wide field of applications.
Abstract: The design, the fabrication, and the analytical performance of a PMMA microchip for isotachophoresis and capillary electrophoresis are described. The microchip offers the possibility of on-line coupling of an isotachophoretic preconcentration step prior to the capillary electrophoretic separation. Conductivity detection with thin film platinum electrodes is used for monitoring of the enrichment and of the separation on the microchip. With the preceding ITP step an enrichment factor of about 80 can be achieved. The seleno amino acids selenomethionine, selenoethionine, and selenocystine can be separated down to a concentration range of just a few micromoles/L. With suitable selection and combination of electrolytes the microchip can be used for a wide field of applications.
TL;DR: In this first application, hollow fiber flow field-flow fractionation is used to fractionate bacteria of biotechnological interest such as deactivated Vibrio cholerae, which are employed for whole-bacteria vaccine production.
Abstract: Interest in low-cost, analytical-scale, highly efficient, and sensitive separation methods for cells and bacteria has recently been increasing. Field-flow fractionation is well suited to the separation of different types of cells, including bacteria. High performance hollow fiber flow field-flow fractionation of such samples is demonstrated here for the first time with potentially disposable channels and high-sensitivity UV/Vis detectors. In this first application, hollow fiber flow field-flow fractionation is used to fractionate bacteria of biotechnological interest such as deactivated Vibrio cholerae, which are employed for whole-bacteria vaccine production. Quite short analysis times, high reproducibility, and low limits of detection are found. Retention of Vibrio cholerae is shown to depend on the mobile phase composition. Two serologically different Vibrio cholerae strains are partly distinguished by their fractogram profiles.
TL;DR: In this paper, the enantiomer migration order of the chiral anaesthetic drug ketamine [RS-2-(2-chlorophenyl)-2-(methylamino)cyclohexanone] was studied by using various cyclodextrins as chiral selectors.
Abstract: The enantiomer migration order of the chiral anaesthetic drug ketamine [RS-2-(2-chlorophenyl)-2-(methylamino)cyclohexanone] was studied by capillary electrophoresis using various cyclodextrins as chiral selectors. The opposite migration order of the enantiomers of ketamine was observed when native α- and β-cyclodextrins were used as chiral selectors in capillary electrophoresis. The possible mechanisms of the opposite enantiomer migration order were investigated by employing electrospray ionization mass spectrometry, 1 H-NMR spectrometry, one dimensional rotating frame nuclear Overhauser and exchange spectroscopy, X-ray crystallography, and molecular modeling techniques. As this study indicates, capillary electrophoresis can be used as a reliable experimental technique for examination of the correctness of the results of molecular modeling calculations. In addition, based on X-ray crystallographic analysis it was confirmed that (-)-ketamine as a free base possesses S configuration.
TL;DR: A method using simultaneous pulsed flame photometric (PFPD) and micro-electron capture detection (lECD) in gas chromatography (GC) was developed and validated for the analysis of 23 organophosphorus (OP) and 17 organochlorine (OC) pesticides in animal fat.
Abstract: A method using simultaneous pulsed flame photometric (PFPD) and micro-electron capture detection (lECD) in gas chromatography (GC) was developed and validated for the analysis of 23 organophosphorus (OP) and 17 organochlorine (OC) pesticides in animal fat. The method entailed the extraction of animal tissue (mixed with twice the sample weight of sodium sulfate) with 7 mL ethyl acetate per 1 g tissue. After the blending step, the extract was centrifuged and 3 mL cyclopentane was added to a 7 mL portion of the extract. A 2.5 mL portion was injected into a 2 cm ID622.5 cm Biobeads S-X3 gel permeation chromatography column (4.5 mL/min flow rate of 70/ 30 ethyl acetate/cyclopentane). A 36 mL fraction (from 8 to 16 min) was collected, evaporated, and solvent-exchanged to 1 mL final volume in iso-octane. The GC/ PFPD+lECD system used a single injector and column, but the flow was split after the chromatographic separation to the two detectors. The final extract was injected (2 lL) into the GC/PFPD + lECD system for simultaneous analysis of the OP and OC analytes. The PFPD was used in the phosphorus-only mode to detect OPs and the lECD mainly detected halogenated pesticides but a few N-containing OPs could be sensitively detected with it as well. Recoveries were 60 ‐ 70% for the bulk majority of pesticides except for methamidophos, acephate, and omethoate which are more difficult in GC analysis due to their more polar nature. Fenthion and phorate also gave more variable recoveries, presumably due to their degradation to sulfones and sulfoxides. In fortification recovery experiments at several different concentrations over multiple days, reproducibilities of 10 ‐ 20% relative standard deviation were achieved, and limits of quantitation were typically 10 ‐ 20 ng/g.
TL;DR: In this paper, a dynamic pressurized liquid extraction (PLE) method was developed to extract ginsenosides in Panax ginseng, American Ginseng and health supplement products with methanol.
Abstract: A method using dynamic pressurized liquid extraction (PLE) was developed to extract ginsenosides in Panax ginseng, American ginseng, and health supplement products with methanol. The extraction efficiency of PLE was comparable to that obtained by Soxhlet extraction. The method precision (RSD) was found to vary from 1.5 to 13.0% for the various ginsenosides, higher RSD values were observed for lower level ginsenosides present in the medicinal plants or health supplement products. Separation of ginsenosides in the methanolic extracts was achieved with a water-acetonitrile gradient system using a C-18 reversed phase column.