A tabulated review of capillary electrophoresis of carbohydrates

Derivatization trends in capillary electrophoresis

This survey gives an overview of recent derivatization protocols, starting from 1996, in combination with capillary electrophoresis (CE). Derivatization is mainly used for enhancing the detection sensitivity of CE, especially in combination with laser-induced fluorescence. Derivatization procedures are classified in tables in pre-, on- and postcapillary arrangements and, more specifically, arranged into functional groups being derivatized. The amine and reducing ends of saccharides are reported most frequently, but examples are also given for derivatization of thiols, hydroxyl, carboxylic, and carbonyl groups, and inorganic ions. Other reasons for derivatization concern indirect chiral separations, enhancing electrospray characteristics, or incorporation of a suitable charge into the analytes. Special attention is paid to the increasing field of research using on-line precapillary derivatization with CE and microdialysis for in vivo monitoring of neurotransmitter concentrations. The on-capillary derivatization can be divided in several approaches, such as the at-inlet, zone-passing and throughout method. The postcapillary mode is represented by gap designs, and membrane reactors, but especially the combination of separation, derivatization and detection on a chip is a new emerging field of research. This review, which can be seen as a sequel to our earlier reported review covering the years 1991-1995, gives an impression of current derivatization applications and highlights new developments in this field.

Use of borate complexation for the separation of non-UV-absorbing calystegines by capillary electrophoresis

A capillary zone electrophoresis method was developed for the simultaneous analysis of seven closely related polyhydroxyalkaloids called calystegines. Successful results were obtained with a fused-silica capillary, 80 mM sodium tetraborate at pH 9.2 and temperature of 50 degrees C. Detection of non-UV-absorbing calystegines was achieved through in-situ complexation with borate ions. To further improve method sensitivity, a capillary with a bubble cell was used and detection performed at low wavelength (191 nm). Effects of buffer concentration, pH and temperature on migration times and efficiency are discussed. Migration behavior of selected compounds was significantly affected by their chemical structure (i.e., number and position of hydroxy groups). Under optimized conditions, baseline separation of the selected compounds was achieved in less than 12 min. Precision was evaluated by measuring repeatability and intermediate precision of migration times and corrected peak areas. Finally, the method was applied to the qualitative analysis of calystegines in plant extracts and results were confirmed by GC-MS.

Ultramicroanalysis of reducing carbohydrates by capillary electrophoresis with laser-induced fluorescence detection as 7-nitro-2,1,3-benzoxadiazole-tagged N-methylglycamine derivatives

A method for ultramicroanalysis of carbohydrates using capillary electrophoresis with laser-induced fluorescence detection was developed, based on precapillary conversion to 7-nitro-2,1, 3-benzoxadiazole (NBD)-tagged N-methylglycamines. Although the derivatization involves two-step reactions, i.e., reductive N-methylamination followed by condensation with NBD-F, they can be carried out in a one-pot fashion and proceed quantitatively within ca. 50 min in total. Since the reaction conditions are mild, it does not cause desialylation. The derivatives can be well separated by capillary electrophoresis and sensitively detected by argon laser-induced fluorescence. It allowed detection of monosaccharides of down to nanomolar concentrations for analytical sample solution, which correspond to the attomole injected amounts, and good linearity was observed over a wide range. It was also successfully applied to analysis of N-glycans in a microgram quantity of a glycoprotein. Studies on the cleanup of derivatized product are also described in relation to N-glycan analysis.

Effects of amine modifiers on the separation of tetramethylrhodamine-labeled mono- and oligosaccharides by capillary zone electrophoresis

In this work, nine tetramethylrhodamine (TMR) labeled isomeric oligosaccharide derivatives of betaGal(1 --> 4) betaGlcNAc-O-TMR were separated by capillary zone electrophoresis coupled with laser-induced fluorescence detection. Charged species were created in situ by complexation with borate and phenylborate. Micellar separation was achieved by addition of 10 mM sodium dodecylsulfate to the running buffer. We have investigated the effects of adding a homologous series of monoamine modifiers on the separation efficiency of these oligosaccharides. The separation was significantly improved in the presence of the organic modifiers methyl- and ethylamines, but worsened in the presence of propyl- and butylamines. Possible mechanisms of the amine additives are discussed.

Analysis of glycosaminoglycan monosaccharides by capillary electrophoresis using indirect laser-induced fluorescence detection

Two methods for monosaccharide analysis by capillary electrophoresis (CE) using counterelectroosmotic and coelectroosmotic modes with indirect laser-induced fluorescence detection were optimised and compared. A mixture of seven glycosaminoglycan-derived hexoses was separated in alkaline fluorescein-based electrolytes and detected in both counterelectroosmotic and coelectroosmotic conditions. The fluorescein concentration and pH of the background electrolyte, and the influence of the reversal of electroosmotic flow by addition of hexadimethrine bromide on the separation were studied. Coelectroosmotic CE conditions provided better resolution and limits of detection. A 10(-6) M fluorescein solution at pH 12.25 containing 0.0005% (w/v) hexadimethrine bromide was used as background electrolyte. Quality parameters such as run-to-run, day-to-day precision and limits of detection were calculated, and better figures of merit were obtained for the coelectrooosmotic conditions than for the counterelectroosmotic mode. The coelectroosmotic method was applied to the quantitation of the hexosamine contents in glycosaminoglycans after acid hydrolysis. The method proved to be suitable for the determination of dermatan sulfate in heparin down to 2% (w/w).

Preparative electrochromatography of proteins in various types of porous media

The performance of commercial and enzymatically modified size-exclusion (SE) gels in electrochromatography was compared for preparative protein separations. Dextran and agarose-based SE gels were subjected to enzymatic digestion under mild conditions. This treatment partially hydrolyzed the gel matrix modifying its pore size distribution. Enzymatic treatment of agarose-based SE gels was found to increase the resolution of the separation. Successful separation of preparative amounts of the A and B forms of beta-lactoglobulin (difference in electrophoretic mobility of 8.5%) was achieved with a high degree of purity using agarose-based SE gels. The four major whey proteins, beta-lactoglobulin, alpha-lactalbumin, BSA and immunoglobulins, were purified from an acid whey preparation. The degree of retention of a protein in electrochromatography followed their free-solution electrophoretic mobility (mu) when the protein was able to enter the gel pores and the ratio of diffusion/mu when the protein was excluded.

Comparative studies on the analysis of glycosylation heterogeneity of sialic acid-containing glycoproteins using capillary electrophoresis

Comparative studies concerning glycoform analysis of sialoglycoproteins by capillary electrophoresis were performed using a few separation modes hitherto reported. Glycoprotein samples examined in the present study were successfully separated to their respective glycoforms using surface-modified capillaries commercially available for capillary gas chromatography in the running buffer near their isoelectric points. The analysis times were less than 50 min and reproducibilities in migration times were excellent (less than 2.0% RSD for both run-to-run and day-to-day analyses). We present a method for the glycoform analysis of alpha1-acid glycoprotein in sera by simple pre-treatment as an application. The present technique will become one of the general methods for the evaluation of glycosylation heterogeneity of commercially available glycoprotein drugs.

Quantification of hyaluronan in pharmaceutical formulations using high performance capillary electrophoresis and the modified uronic acid carbazole reaction

The amount of hyaluronan (HA) in pharmaceutical formulations was determined by high-performance capillary electrophoresis (HPCE) and the results were compared with the carbazole reaction established by Bitter and Muir (T. Bitter, H.M. Muir, Anal. Biochem. 4 (1962) 330-334), HA analysis was performed in less than 10 min by using an untreated fused silica capillary with bubble detection cell. The influence of several buffers and pH values was examined. Calibration curve shows good linearity from 0.01 to 5.0 mg/ml. The lower limit of detection by monitoring the absorbance at 195 nm was 10 microg/ml at a signal to noise ratio of 5.

Recent developments in capillary electrophoresis and capillary electrochromatography of carbohydrate species

This review article is concerned with the recent developments in capillary electrophoresis (CE) and capillary electrochromatography (CEC) of carbohydrates. The literature shows that CE possesses impressive potential in the analysis of carbohydrates. On the other hand, CEC has just started to show promise in the analysis of carbohydrates. Advances in separation and detection approaches of derivatized and underivatized carbohydrates are discussed based on the available literature. In addition, important applications are illustrated.