Capillary electrophoresis and electrochemical detection of underivatized oligo- and polysaccharides with surfactant-controlled electroosmotic flow

Current landscape of protein glycosylation analysis and recent progress toward a novel paradigm of glycoscience research

This review covers the basics and some applications of methodologies for the analysis of glycoprotein glycans. Analytical techniques used for glycoprotein glycans, including liquid chromatography (LC), capillary electrophoresis (CE), mass spectrometry (MS), and high-throughput analytical methods based on microfluidics, were described to supply the essentials about biopharmaceutical and biomarker glycoproteins. We will also describe the MS analysis of glycoproteins and glycopeptides as well as the chemical and enzymatic releasing methods of glycans from glycoproteins and the chemical reactions used for the derivatization of glycans. We hope the techniques have accommodated most of the requests from glycoproteomics researchers.

Use of Capillary Electrophoresis for Polysaccharide Studies and Applications

CE applications to charged polysaccharides are briefly reported. A simple procedure is presented to determine the esterification degree of a hyaluronan derivative. In this case the degree of substitution was as low as 14 %.The molecular weight distribution of mannuronic oligosaccharides mixture produced by hydrolysis of native polymannuronic is readily calculated from peak area of the species resolved by CE on the basis of a specific degree of polymerization.The influence of the applied electric field strength on the free solution mobility of hyaluronan samples is briefly addressed for molar masses of the order of 10(5) and 10(6) g/mol. The data are compared with the results obtained for a 50 % galactose substituted HA.Mobility data obtained as a function of buffer pH for a native HA sample as well as for two galactose-amide HA derivatives, having slightly different degrees of substitution, are presented and discussed in terms of the polymer charge density parameters ξ.In most cases, more questions than answers arise from the application of CE to charged polysaccharides. However, perspectives are disclosed for a further understanding of the reliability of CE applied for the structural elucidation of such macromolecules.

Use of capillary electrophoresis for polysaccharide studies and applications

Capillary electrophoresis (CE) applications to charged polysaccharides are briefly reported. A simple procedure is presented to determine the esterification degree of a hyaluronan derivative. In this case, the degree of substitution was as low as 14%. The molecular weight distribution of mannuronic oligosaccharides mixture produced by hydrolysis of native polymannuronic is readily calculated from peak area of the species resolved by CE on the basis of a specific degree of polymerization. The influence of the applied electric field strength on the free solution mobility of hyaluronan samples is briefly addressed for molar masses of the order of 10(5) and 10(6) g/mol. The data are compared with the results obtained for a 50% galactose-substituted hyaluronic acid (HA). Mobility data obtained as a function of buffer pH for a native HA sample as well as for two galactose-amide HA derivatives, having slightly different degrees of substitution, are presented and discussed in terms of the polymer charge density parameters xi. In most cases, more questions than answers arise from the application of CE to charged polysaccharides. However, perspectives are disclosed for a further understanding of the reliability of CE applied for the structural elucidation of such macromolecules.

Analysis of alkyl polyglucosides in industrial products by capillary electrophoresis with pulsed amperometric detection

Pulsed amperometric detection following micellar electrokinetic chromatography has been applied successfully to the direct detection of alkyl polyglucosides (APGs) in shampoos and other industrial products without prior conversion to highly absorbing or fluorescing derivatives. For electrochemical detection, it is necessary to dissociate the hydroxyl groups of the APGs. Thus, we used 0.1 M NaOH in the outlet vial to dissociate the APGs. The main problems associated with the combination of electrochemical detection and capillary electrophoresis are the need to isolate the detector from the electric field used in the capillary electrophoresis separation and the difficulty of aligning the working electrode with the end of the capillary. To overcome these problems, a simple capillary-electrode holder was constructed. This holder automatically aligns the capillary and the electrode in a wall-jet configuration without the aid of micropositioners and facilitates the replacement of electrodes and capillaries without reconstruction of the entire capillary/electrode setup. Special microcylindrical gold electrodes have been produced by sealing 300-microm-diameter gold wire into borosilicate-glass capillaries.

Direct electrochemical detection of glucose in human plasma on capillary electrophoresis microchips

We developed an electrochemical detector on a hybrid chip for the determination of glucose in human plasma. The microchip system described in this paper consists of a poly(dimethylsiloxane) (PDMS) layer containing separation and injection channels and an electrode plate. The copper microelectrode is fabricated by selective electroless deposition. The fabrication of the decoupler is performed by platinum electrochemical deposition on the metal film formed by electroless deposition. Factors influencing the performance, including detection potential, separation field strength, and buffer concentration, were studied. The electrodes exhibited good stability and durability in the analytical procedures. Under optimized detection conditions, glucose responded linearly from 10 microM to 1 mM. Finally, glucose in human plasma from three healthy individuals and two diabetics was successfully determined, giving a good prospect for a new clinical diagnostic instrument.

High-performance capillary electrophoresis with indirect UV detection for determination of alpha-galactosides in Leguminosae and Brassicaceae

A rapid, easy, and reproducible capillary electrophoresis method for determination of raffinose family oligosaccharides (alpha-galactosides) was developed. Sucrose, raffinose, stachyose, verbascose, and ajugose were determined with indirect UV detection at moderate alkaline pH 9.2, using pyridine-2,6-dicarboxylic acid as background electrolyte in a sodium tetraborate buffer with added cetyltrimethylammonium bromide. The separation efficiency measured by the number of theoretical plates (N) ranged from 1.4 x 10(5) to 2.3 x 10(5). The precision of the method, measured by the relative standard deviation (RSD), was less than 0.53% for the migration times and better than 3.4% for normalized areas (NA), considering all sugars except verbascose (RSD(NA) = 11.8%). Detection limits were about 110 microg/mL, corresponding to 150-320 microM. Relative response factors (RRF) were calculated on the basis of linearity studies and used for quantification of alpha-galactosides in a lupine sample (Lupinus angustifolius).

Determination of the composition of Chinese ligustrum lucidum polysaccharide by capillary zone electrophoresis with amperometric detection

In this paper, capillary zone electrophoresis with amperometric detection was firstly applied to indirectly determine the composition of Chinese ligustrum lucidum polysaccharide (LLPS) by analyzing its hydrolyzates: fucose, glucose, arabinose and rhamnose. Under the selected optimum conditions, the four monosaccharides could be perfectly separated within 30 min and showed significant current responses at the copper electrode. The linear ranges of fucose, glucose and arabinose were all from 5.0 x 10(-6) to 1.0 x 10(-4) mol l(-1) and that of rhamnose was from 1.0 x 10(-5) to 1.0 x 10(-4) mol l(-1), and their detection limits were lower or near 1.0 x 10(-6) mol l(-1) (S/N=3). Experiments showed that the mole ratio of fucose, glucose, arabinose and rhamnose in Chinese LLPS was 1.80:4.58:2.55:1.91, and the purity of this polysaccharide leached by the introduced leaching method was 93.3%. Analyzing polysaccharide by this method has some merits of quickness, low-volume sampling, simple instrument, high sensitivity and high reproducibility.

Determination of the compositions of polysaccharides from Chinese herbs by capillary zone electrophoresis with amperometric detection

In this paper, capillary zone electrophoresis with amperometric detection (CZE-AD) was applied to determine the compositions of hetero-polysaccharides from Chinese herbs, Angelica sinensis and flax by analyzing their hydrolyzed monosaccharides: fucose, galactose, glucose, arabinose, rhamnose and xylose. Under the selected optimum conditions, the six monosaccharides could be perfectly separated within 25 min and showed significant current responses at copper electrodes. The linear ranges of the six monosaccharides were all from 5.0 x 10(-6) to 2.0 x 10(-4) mol L(-1) and their detection limits were lower or near 1.0 x 10(-6) mol L(-1) (S/N = 3). Experiments showed that the Angelica sinensis polysaccharide was composed of fucose, galactose, glucose, arabinose, rhamnose and xylose (mole ratio 1.0:13.6:15.0:8.7:21.3:3.7), and the flax polysaccharide was composed of galactose, glucose and arabinose (mole ratio 1.0:4.98:1.1). The purity of these polysaccharides leached by the introduced leaching method was 98.3 and 97.6%, respectively. Analyzing polysaccharides by this method has some merits of speed, simple instrumentation and operation, high sensitivity and high reproducibility.

Applications of capillary electrophoresis with electrochemical detection in pharmaceutical and biomedical analyses

As a high efficiency separation technique, capillary electrophoresis has been widely used in various fields of analytical science. This review discusses the applications of electrochemical detection systems combined with capillary electrophoresis in pharmaceutical and biomedical analysis. These detection methods mainly involve amperometric detection but also include conductivity detection and potentiometric detection. Its applications in the field are divided into six parts, including catechol compounds, thiols, amino acids and peptides, carbohydrates, general pharmaceuticals, and other related compounds. A relatively detailed discussion is described for each compound under the current studied. On this basis, we have suggested several conceivable directions for capillary electrophoresis with electrochemical detection in the future.

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).

Determination of beta1,4-galactosyltransferase enzymatic activity by capillary electrophoresis and laser-induced fluorescence detection

We have developed a nonradioactive method to assay UDP-Gal:beta-d-GlcNAcbeta1,4-galactosyltransferase (beta4GalT-I) enzymatic activity. Capillary electrophoresis combined with laser-induced fluorescence detection (CE-LIF) was employed to provide a baseline separation of FITC-conjugated O-GlcNAc-containing substrate peptides and galactose-capped product peptides, while at the same time allowing a level of detection in the low attomole range (10(-18)). The addition of 2 mM hexamethylene diamine to the borate-based capillary electrophoretic buffer modulated the electroosmotic flow, resulting in optimum separation of the glycopeptide product from reactant. beta4GalT-I activity was dependent upon the addition of both manganese and UDP-galactose. Using this assay, we show that two beta4GalT-I constructs, predicted to localize to different intracellular compartments, are enzymatically active when expressed in vitro using a rabbit reticulocyte transcription-translation system. The high sensitivity of product detection by CE-LIF in combination with in vitro transcription-translation is applicable to the facile determination of the enzymatic activity of other newly cloned glycosyltransferases.

Electrochemical determination of carbohydrates: enzyme electrodes and amperometric detection in liquid chromatography and capillary electrophoresis

In recent years, electrochemical detection (EC) methods have become increasingly important for the determination of carbohydrate compounds in a variety of biological and pharmaceutical samples. In this work, recent advances in the design and application of EC approaches are reviewed, with the goal of providing the non-electrochemist with a basic understanding of the most important EC approaches to carbohydrate detection and an overview of their current applications. Two specific EC detection strategies are considered in detail: enzyme electrodes and electrodes used for HPLC or capillary electrophoresis detection.

Postcolumn reaction detection with dual-electrode capillary electrophoresis-electrochemistry and electrogenerated bromine

This is the first report of postcolumn amperometric reaction detection for capillary electrophoresis and dual-electrode detection. Bromide present in the run buffer is oxidized to bromine at the first electrode and subsequently detected at a second electrode downstream. Analytes that react with bromine cause a decrease in signal at the downstream electrode that is proportional to analyte concentration. Bromine is known to react with a variety of compounds, including thiols, thioethers, disulfides, amines, and unsaturated organic compounds. In this paper, the development of a new wire--wire on-capillary dual electrode that is well suited to bromine-based post-column reaction detection is described. System performance was evaluated using glutathione, cysteine, and methionine as test analytes. The final optimized system could be operated continuously for 24 h and was stable for day-to-day use for at least two weeks. The response for cysteine was linear from 0.5 to 20 microM with a limit of detection of approximately 80 nM.

A tabulated review of capillary electrophoresis of carbohydrates

This review summarizes publications on capillary electrophoresis (CE) of carbohydrates, covering almost all hitherto published papers on this topic. It is designed to be a convenient tool for the literature search by providing a comprehensive table. Since CE analysis of carbohydrates is generally complicated due to the structural diversity of carbohydrate species, an attempt is made in this table to supply detailed information on the analyzed form (underivatized or derivatized, type of derivative) and analytical conditions (capillary size, state of the inner wall, composition of the electrophoretic solution, applied voltage, detection method, etc.), for each combination of carbohydrate species to be analyzed. In addition, a brief overview is presented to help in the literature search.

The electroanalysis of mannitol, xylose and lactulose at copper electrodes: voltammetric studies and bioanalysis in human urine by means of HPLC with electrochemical detection

The electrochemical behavior of mannitol, xylose and lactulose has been investigated at a copper working electrode. A sensitive, accurate and precise method employing HPLC with electrochemical detection in the d.c. amperometric mode, has been developed and validated for the determination of mannitol and lactulose in human urine. The ratio of these probe carbohydrates is altered in conditions that cause damage to the intestinal mucosal barrier. Systematic studies employing cyclic voltammetry indicate that the electrode reaction involves an electrocatalytic oxidation of each carbohydrate in a process yielding a single irreversible anodic wave that is dependent on the ionic strength of the sodium hydroxide supporting electrolyte solution. High performance liquid chromatography with electrochemical detection was performed using a thin-layer cell housing a custom manufactured copper working electrode. The optimized HPLC method can detect 72, 57 and 419 pg of mannitol, xylose and lactulose injected on column, respectively. The corresponding linear calibration ranges are 359 pg-2.24 microgram, 57.4 pg-896 ng and 419 pg-262 ng, respectively. Solid-phase extraction of human urine on polar sorbents, and direct injection after simple 1 + 99 dilution in 0.025 M NaOH were compared for bioanalysis. Direct injection was selected for further method developed as the technique proved robust and simple. The optimized method was validated for the determination of mannitol and lactulose in human urine over the concentration ranges predicted when assessing intestinal permeability (0.25-2.5 mg ml-1 mannitol and 0.05-1.0 mg ml-1 lactulose). Over these ranges intra- and inter-assay bias is < +/- 6.5%, and imprecision (coefficient of variation) is < 9% for each carbohydrate. The validated method provides a useful alternative to HPLC with pulsed-amperometric detection at gold electrodes.

Recent developments in capillary electrophoresis of carbohydrate species

Carbohydrates are ubiquitous species involved in many life processes. Because of the multilateral roles of carbohydrates, their analysis has come to have increasing importance. As shown in this review, capillary electrophoresis in its various modes of operation has proved very useful in the analysis of carbohydrate species including mono- and oligosaccharides, glycoproteins, glycopeptides and glycosaminoglycans. Advances in separation approaches and applications as well as advances in detection including sensitive and selective pre-column derivatization are described. In summary, this comprehensive review is a supplement to previous reviews and covers the published work in 1996 and the first half of 1997.

Electrochemical detection in capillary electrophoresis

Recent advances in the design and application of electrochemical detection (EC) systems in capillary electrophoresis (CE) are reviewed, with the objective of providing the non-electrochemist with a state-of-the-art picture of CEEC instrumentation and an overview of the primary analytes and samples for which the technique is best suited. In particular, instrument innovations designed to aid in decoupling the CE and EC systems electrically and in aligning them physically are described in detail. In addition, CEEC applications are summarized for four specific analyte groups: catecholamines, thiols and disulfides, amino acids, and carbohydrates. On this basis, it is clear that EC techniques have reached a stage where they are already having a significant impact on CE usage in selected areas of analysis. Continued developments with respect to new electrode materials and electrode configurations promise to broaden this impact further.

Fast separation of underivatized carbohydrates by coelectroosmotic capillary electrophoresis

A method for the rapid quantitative analysis of underivatized acidic sugars, monosaccharides and disaccharides using coelectroosmotic capillary electrophoresis was developed. Indirect UV detection at 254 nm using sorbate as background electrolyte was employed for monitoring the analytes. A highly alkaline pH value of the electrolyte system was chosen in order to achieve an electrophoretic mobility of the saccharides towards the anode. A dynamic reversal of the electroosmotic flow and, by this means, a codirectional movement of the negatively charged analytes and the electroosmotic flow is accomplished by employing a polycationic surfactant (hexadimethrine bromide), which is added to the background electrolyte. To further improve the resolution of specific carbohydrates, acetone is used as organic modifier. A practical application of the developed method for the fast determination of fructose, glucose, and sucrose in various soft drinks is provided.