Hydrophobic labeling of amino acids: Transient trapping-capillary/microchip electrophoresis

Development of transient trapping micellar electrokinetic chromatography coupled with mass spectrometry for steroids analysis

An on-line sample preconcentration technique based on transient trapping (tr-trapping) in micellar electrokinetic chromatography (MEKC) was applied for steroid detection with UV (tr-trapping-UV) and electrospray ionization mass spectrometry detection (tr-trapping-ESI-MS). ESI-MS was used to improve the sensitivity in MEKC. The MEKC separation was carried out using volatile ammonium formate as a background solution to facilitate the coupling with ESI-MS. The partial introduction of a sodium dodecyl sulfate (SDS) micellar solution before the introduction of a sample solution to the capillary provided the effective preconcentration of analytes. At the same time, the SDS micelle would not enter the ESI-MS system, so its interference in ESI-MS detection was suppressed under the optimal condition, then five steroids can be separated by the developed method. In tr-trapping-ESI-MS, an acidic condition of pH 3.5 was employed to suppress the electroosmotic flow, which can avoid micellar solution migrating to the MS instrument. The developed method showed that the micellar solution requires a twofold slower time than the sample to migrate along the column, which can prohibit the cause of the problem with the MS instrument and interference signal of SDS in the steroid's detection. The tr-trapping-ESI-MS protocol showed up to 540-fold enhancements of the peak intensity and 50-fold improvement of the limit of detection compared with capillary zone electrophoresis using androsterone as a model sample.

Sensitive analysis of reduced glutathione in bacteria and HaCaT cells by capillary electrophoresis via online pre-concentration of transient trapping combined with the dynamic pH junction mode

A new method of capillary electrophoresis was developed for the sensitive determination of glutathione in biological samples.

Recent advances in capillary electrophoretic migration techniques for pharmaceutical analysis

Since the introduction about 30 years ago, CE techniques have gained a significant impact in pharmaceutical analysis. The present review covers recent advances and applications of CE for the analysis of pharmaceuticals. Both small molecules and biomolecules such as proteins are considered. The applications range from the determination of drug-related substances to the analysis of counterions and the determination of physicochemical parameters. Furthermore, general considerations of CE methods in pharmaceutical analysis are described.

Hydrophilic interaction electrokinetic chromatography using bio-based nanofillers

Hydrophilic interaction (HI)-based separation like HILIC is effective for analyzing hydrophilic biological samples such as carbohydrates, peptides, and metabolites. To overcome the drawbacks of conventional HILIC such as large consumption of organic solvents and easy deterioration of the separation column, we developed HI electrokinetic chromatography (EKC) by employing bio-based nanomaterials as the hydrophilic pseudostationary phase. By mechanical/chemical treatments, cellulose, chitin, and chitosan were processed to 10-nm wide nanofibers/nanowhiskers (NFs/NWs), which are longer/shorter than 1000/200 nm, respectively. In HI-EKC of oligosaccharides using 0.001% uncharged cellulose NFs, strong interaction was observed for the large-size oligosaccharides with the retention factors (k) of up to 1.56, indicating a HILIC-mode interaction. In HI-EKC with 0.1% positively charged chitosan NFs, benzenedisulfonic acid, benzenesulfonic acid (BS), and p-hydroxy BS (HBS) had k values of 0.036, 0.018, and 0.018, respectively, suggesting that the ion-exchange interaction mainly occurred via sulfonate groups. Finally, HI-EKC was demonstrated using 0.05% chitin or chitosan NWs. In both cases using chitin and chitosan NWs, HBS showed much stronger interaction with k > 0.192 compared with BS with k < 0.070. It indicated structural difference between NFs and NWs affected the HI behavior in terms of both the ion-exchange and HILIC modes.

Toward 10,000-fold sensitivity improvement of oligosaccharides in capillary electrophoresis using large-volume sample stacking with an electroosmotic flow pump combined with field-amplified sample injection

A combination of two online sample concentration techniques, large-volume sample stacking with an electroosmotic flow pump (LVSEP) and field-amplified sample injection (FASI), was investigated in CE to achieve highly sensitive oligosaccharide analysis. In CE with LVSEP-FASI, analytes injected throughout the capillary were concentrated on the basis of LVSEP, followed by an electrokinetic introduction of concentrated analytes from the inlet vial by the FASI mechanism. After switching the inlet vial solution from the sample to running buffer, the concentrated analytes were then separated by CZE. In the present LVSEP-FASI-CZE, pressure was applied to the capillary inlet until the inlet vial solution was exchanged. The applied pressure generated a counterflow against the EOF. It kept the stacked sample zone within the capillary, minimizing loss of concentrated analytes. Fluorescein was first analyzed by LVSEP-FASI-CZE to optimize preconcentration condition. Up to 110 000-fold sensitivity increase was obtained with 200 μL of sample, compared to normal CZE with sample injection of 0.3 psi for 3 s (ca. 1.7 nL). From the results, the pressure application improved the efficiency of the FASI-mode concentration significantly at total concentration time longer than 10 min. In the analysis of maltoheptaose, a 10 000-fold sensitivity increase was achieved, which is the highest concentration efficiency ever reported in CE of oligosaccharides. The relative standard deviations of the detection time and peak height were 2.4 and 11%, respectively. In the analysis of glucose oligomer, up to 8600-fold sensitivity increases were achieved without reducing the separation performance of conventional CZE.

Electrophoretic analysis of cations using large-volume sample stacking with an electroosmotic flow pump using capillaries coated with neutral and cationic polymers

To realize the high-performance and simple-operation analysis of cationic compounds in capillary electrophoresis, we investigated large-volume sample stacking with an electroosmotic flow pump (LVSEP) using capillaries with hydrophilic and weakly cationic inner surface. Three capillary modification methods were employed: thermally passivated physical coating with polymer mixture of poly(vinyl alcohol) and poly(allylamine); covalent modification with random copolymer of acryl amide and 3-(methacryloylamino)propyltrimethylammonium chloride; easily preparable physical coating with dimethyldioctadecylammonium bromide and polyoxyethylene stearate. In these capillaries, the electroosmotic flow (EOF) was well suppressed in the high ionic strength (I) electrolyte under the acidic and basic pH, whereas the EOF was enhanced in the low I electrolyte, indicating a suitable EOF property for the rapid LVSEP and following separation. In the LVSEP-capillary zone electrophoresis (CZE) analyses of benzylamine and 1-naphthylethylamine, up to 550-fold sensitivity increases were successfully obtained in the three capillaries without significantly reducing the repeatability and resolution. LVSEP-cyclodextrin-modified CZE of chlorpheniramine and brompheniramine was also carried out, resulting in up to 380-fold sensitivity enhancement with keeping the baseline separation for the enantiomers. Finally, we performed the LVSEP-CZE analysis of basic proteins, where up to 100-fold sensitivity increases were achieved, but a peak broadening was observed due to the sample adsorption in the low I sample matrix.

Recent progress of on-line sample preconcentration techniques in microchip electrophoresis

This review highlights recent developments and applications of on-line sample preconcentration techniques to enhance the detection sensitivity in microchip electrophoresis (MCE); references are mainly from 2008 and later. Among various developed techniques, we focus on the sample preconcentration based on the changes in the migration velocity of analytes in two or three discontinuous solutions system, since they can provide the sensitivity enhancement with relatively easy experimental procedures and short analysis times. The characteristic features of the on-line sample preconcentration applied to microchip electrophoresis (MCE) are presented, categorized on the basis of "field strength-" or "chemically" induced changes in the migration velocity. The preconcentration techniques utilizing field strength-induced changes in the velocity include field-amplified sample stacking, isotachophoresis and transient-isotachophoresis, whereas those based on chemically induced changes in the velocity are sweeping, transient-trapping and dynamic pH junction.

Review of recent developments of on-line sample stacking techniques and their application in capillary electrophoresis

Capillary electrophoresis (CE) has become one of the most useful tools in separation science because of its high separation efficiency, low cost, versatility, ease of sample preparation and automation. However, some limitations of CE, such as poor concentration sensitivity due to its lower sample loading and shorter optical path length, limits its further applications in separation science. In order to solve this problem, various on-line sample preconcentration techniques such as transient isotachophoresis preconcentration, field-enhanced sample stacking, micelle to solvent stacking, micelle collapse, dynamic pH junction, sweeping, solid phase extraction, single drop microextraction and liquid phase microextraction have been combined with CE. Recent developments, applications and some variants together with different combinations of these techniques integrating in CE are reviewed here and our discussions will be confined to the past three years (2008–2011).

Recent advances in amino acid analysis by capillary electrophoresis

This paper describes the most important articles that have been published on amino acid analysis using CE during the period from June 2009 to May 2011 and follows the format of the previous articles of Smith (Electrophoresis 1999, 20, 3078-3083), Prata et al. (Electrophoresis 2001, 22, 4129-4138) and Poinsot et al. (Electrophoresis 2003, 24, 4047-4062; Electrophoresis 2006, 27, 176-194; Electrophoresis 2008, 29, 207-223; Electrophoresis 2010, 31, 105-121). We present new developments in amino acid analysis with CE, which are reported describing the use of lasers or light emitting diodes for fluorescence detection, conductimetry electrochemiluminescence detectors, mass spectrometry applications, and lab-on-a-chip applications using CE. In addition, we describe articles concerning clinical studies and neurochemical applications of these techniques.