Capillary zone electrophoresis of p-aminobenzoic acid derivatives of aldoses, ketoses and uronic acids

The Pre- and Post-Column Derivatization on Monosaccharide Composition Analysis, a Review

Polysaccharides, as common metabolic products in organisms, play a crucial role in the growth and development of living organisms. For humans, polysaccharides represent a class of compounds with diverse applications, particularly in the medical field. Therefore, the exploration of the monosaccharide composition and structural characteristics of polysaccharides holds significant importance in understanding their biological functions. This review provides a comprehensive overview of extraction methods and hydrolysis strategies for polysaccharides. It systematically analyzes strategies and technologies for determining polysaccharide composition and discusses common derivatization reagents employed in further polysaccharide studies. Derivatization is considered a fundamental strategy for determining monosaccharides, as it not only enhances the detectability of analytes but also increases detection sensitivity, especially in liquid chromatography (LC), capillary electrophoresis (CE), and gas chromatography (GC) techniques. The review meticulously examines pre-column and post-column derivatization techniques for monosaccharide analysis, categorizing them based on diverse detection methodologies. It delves into the principles and distinctive features of various derivatization reagents, offering a comparative analysis of their strengths and limitations. Ultimately, the aim is to provide guidance for selecting the most suitable derivatization approach, taking into account the structural nuances, biological functions, and reaction dynamics of polysaccharides.

Liquid Chromatography-Tandem Mass Spectrometry Approach for Determining Glycosidic Linkages

The structural analysis of carbohydrates remains challenging mainly due to the lack of rapid analytical methods able to determine and quantitate glycosidic linkages between the diverse monosaccharides found in natural oligosaccharides and polysaccharides. In this research, we present the first liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based method for the rapid and simultaneous relative quantitation of glycosidic linkages for oligosaccharide and polysaccharide characterization. The method developed employs ultrahigh-performance liquid chromatography coupled with triple quadrupole mass spectrometry (UHPLC/QqQ-MS) analysis performed in multiple reaction monitoring (MRM) mode. A library of 22 glycosidic linkages was built using commercial oligosaccharide standards. Permethylation and hydrolysis conditions along with LC-MS/MS parameters were optimized resulting in a workflow requiring only 50 μg of substrate for the analysis. Samples were homogenized, permethylated, hydrolyzed, and then derivatized with 1-phenyl-3-methyl-5-pyrazolone (PMP) prior to analysis by UHPLC/MRM-MS. Separation by C18 reversed-phase UHPLC along with the simultaneous monitoring of derivatized terminal, linear, bisecting, and trisecting monosaccharide linkages by mass spectrometry is achieved within a 15 min run time. Reproducibility, efficacy, and robustness of the method was demonstrated with galactan ( Lupin) and polysaccharides within food such as whole carrots. The speed and specificity of the method enables its application toward the rapid glycosidic linkage analysis of oligosaccharides and polysaccharides.

Revisiting monosaccharide analysis - quantitation of a comprehensive set of monosaccharides using dynamic multiple reaction monitoring

A rapid method for the quantitation of sixteen neutral and acidic monosaccharides, from both animal and plant sources was developed using ultra-high performance liquid chromatography triple quadrupole mass spectrometry (UHPLC/QqQ-MS) in dynamic multiple reaction monitoring (dMRM) mode. Monosaccharides including three pentoses (ribose, xylose, arabinose), two deoxyhexoses (rhamnose, fucose), five hexoses (fructose, mannose, allose, glucose, galactose), two hexuronic acids (glucuronic acid, galacturonic acid), and two N-acetyl-hexosamines (GlcNAc, GalNAc), were derivatized with 1-phenyl-3-methyl-5-pyrazolone (PMP), while underivatized sialic acids, Neu5Ac and Neu5Gc, were simultaneously analyzed with a 10-minute run. With the optimized UHPLC conditions, baseline separations of the isomers were achieved. The sensitivity and calibration ranges of this method were determined. The limits of detection were between femtomoles and attomoles with linear ranges spanning four to six orders of magnitude and coefficients of variation (CVs) ≤7.2%. Spiking experiments performed on a pooled fecal sample demonstrated the high accuracy of this method even when applied to samples with complicated matrices. The validated method was applied to fecal samples from an infant transitioning from breast milk to weaning foods. Major milk monosaccharides including galactose, fucose, glucose, GlcNAc, and Neu5Ac were found to be the most abundant components in the feces of milk-fed infants. PMP-derivatives of nine other monosaccharides including apiose, lyxose, altrose, talose, gulose, glucosamine, galactosamine, mannosamine, and N-acetylmannosamine (ManNAc) were also tested and could be added to the quantitation method depending on the need. The speed and sensitivity of the method makes it readily adaptable to rapid throughput analysis of monosaccharides in biological samples.

Sialic acid speciation using capillary electrophoresis: optimization of analyte derivatization and separation

Capillary electrophoresis with laser induced fluorescence detection (CE-LIF) was employed for rapid sialic acid speciation, facilitating the quantitative determination of N-glycolylneuraminic acid (Neu5Gc) and N-acetylneuraminic acid (Neu5Ac) on glycoproteins. Derivatization of the sialic acids with 2-aminoacridone (2-AMAC), using classical reductive amination in a nonaqueous solvent, led to the spontaneous decarboxylation of the sialic acid residues as determined by CE-LIF and offline mass spectrometric analysis. Modification of both the labeling conditions, to drive the decarboxylation reaction to completion and the CE-LIF parameters to separate the neutral species by complexation with a neutral coated capillary and borate reversed polarity, led to a robust platform for the rapid, sensitive, and quantitative speciation of sialic acids. The method can readily be used for quality control of recombinant biopharmaceuticals.

Optimized conditions for 2-aminobenzamide labeling and high-performance liquid chromatography analysis of N-acylated monosaccharides

The monosaccharides GlcNAc (N-acetylglucosamine) and the home-made GlcNC(16) (N-palmitoyl-D-glucosamine) were labeled with 2-AB (2-aminobenzamide) by reductive amination of the sugar. The aldehyde group of the monosaccharide reacts with the amino group of 2-AB, forming a Schiff base. In the second step, the Schiff base is reduced with sodium cyanoborohydride to yield a stable secondary amine. We describe here a simple and fast procedure. Previous studies reported the same labeling at high concentration (10(-1) M) during 30 h with further purification steps. In the present paper all operations were carried out in an Eppendorf tube and the reaction medium was directly analyzed without purification. Using the described protocol, the whole procedure can be accomplished in less than 6 h at 65 degrees C at very low concentration (10(-4) M). For both GlcNC(16) and GlcNAc, the 2-AB labeling conditions were optimized and, in addition, new conditions of high-performance liquid chromatography analysis were developed. These N-alkylated sugars were analyzed on reversed-phase HPLC with fluorimetric detection at excitation and emission wavelengths of 340 and 400 nm, respectively. The separation was achieved on a C(18) column with a gradient mobile phase composed of water (0.1% formic acid)-methanol (volume varying) in less than 19 min with 12.5 and 18.3 min retention times for GlcNAc and GlcNC16, respectively. Positive-ion electrospray ionization mass spectrometry (ESI-MS) analysis enabled their structural determination.

Electrospray ionization quadrupole time-of-flight tandem mass spectrometric analysis of hexamethylenediamine-modified maltodextrin and dextran

A combined methodology for obtaining at the preparative scale and characterization by nanoelectrospray ionization (nanoESI) quadrupole time-of-flight (QTOF) mass spectrometry (MS) and tandem MS (MS/MS) of linear polysaccharides modified at the reducing end is presented. Two polydisperse maltodextrins (1000 and 3000 Da) and a high molecular weight polydisperse dextran (6000 Da) were coupled with hexamethylenediamine (HMD). The coupling products were analyzed by nanoESI-QTOF-MS in the positive ion mode and MS/MS using collision-induced dissociation (CID) at low energies. In the HMD-M1000 mixture, the polysaccharide chains containing from 2 to 8 Glc residues were detected, while in HMD-M3000 we identified a complete series of chains containing from 8 to 21 Glc moieties. The employed ESI conditions enhanced the detection of chains with up to 46 Glc residues in the HMD-D6000 sample. By optimized MS/MS, HMD-modified polysaccharides of 3, 4, 5, 12 and 46 degrees of polymerization yielded product ion spectra exhibiting the whole set of Y- and B-fragment ions. The MS structural data were obtained within a few minutes of signal acquisition, with a sample consumption situating the analysis sensitivity in the picomolar range.

Analysis of reducing carbohydrates by reductive tryptamine derivatization prior to micellar electrokinetic capillary chromatography

A micellar electrokinetic capillary chromatography method for determination of low molecular weight carbohydrates (dp 1-2) with an unbound carbonyl group as in aldoses or other reducing carbohydrates has been developed. Reductive amination of aldoses on the carbonyl group using tryptamine introduced a chromophor system to the carbohydrates enabling their sensitive UV detection at 220 nm and identification based on the indole group using diode array detection. Twelve carbohydrates including pentoses (d-ribose, l-arabinose, and d-xylose), hexoses (d-glucose, d-mannose, and d-galactose), deoxy sugars (l-rhamnose and l-fucose), uronic acids (d-glucuronic acid and d-galacturonic acid), and disaccharides (cellobiose and melibiose) are included in the study, using d-thyminose (2-deoxy-d-ribose) as the internal standard. Detection of all 12 carbohydrates is performed within 30 min. Linearity with correlation coefficients from 0.9864 to 0.9992 was found in the concentration range of 25-2500 micromol/L for all carbohydrates; the relative standard deviation on the migration times was between 0.27 and 0.80 min, and limits of quantification and limits of determination were in the picomole range.

Determination of carbohydrates as their 3-aminophthalhydrazide derivatives by capillary zone electrophoresis with on-line chemiluminescence detection

A method based on pre-capillary derivatization with luminol (3-aminophthalhydrazide) for carbohydrate analysis using capillary electrophoresis with on-line chemiluminescence (CL) detection was developed. The derivatives of seven monosaccharides were separated and detected by using 200 mM borate buffer containing 100 mM hydrogen peroxide at pH 10.0 as separation electrolyte and 25 mM hexacyanoferrate in 3 M sodium hydroxide solution as post-capillary chemiluminescence reagent with separation efficiencies ranging from 160,000 to 231,000 plates per metre. The minimum amount of carbohydrate derivatized was 2 pmol (corresponding to the concentration of 2 microM). The method also provided a linear response for glucose in the concentration range of 0.1-250 microM with a mass detection limit of 420 amol or a concentration detection limit of 0.1 microM. Preliminary work using the CE-CL format to determine glucose in a rat brain microdialysis sample is presented as a typical case.

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.

Analysis of carbohydrates as 1-phenyl-3-methyl-5-pyrazolone derivatives by capillary/microchip electrophoresis and capillary electrochromatography

The 1-phenyl-3-methyl-5-pyrazolone (PMP) method has many advantages over hitherto reported methods based on reductive amination and hydrazone formation. This short review summarizes the various aspects of the PMP method, including the principle of derivatization, the simplicity of derivatization procedure, the high sensitivities to UV monitoring and ESI-MS, and the diversity of separation modes in capillary electrophoresis, and presents a number of application data for carbohydrate analysis in biological samples by this method. It also describes successful automation of carbohydrate analysis by in-capillary derivatization with PMP and miniaturization to microchip electrophoresis with whole channel UV detection allowing rapid (within 1 min) analysis of small amounts of PMP derivatives of carbohydrates. Furthermore, it discusses the possibility of capillary electrochromatography in carbohydrate analysis as PMP derivatives, and proposes an in-capillary modification strategy for improving column efficiency and elution time 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.

Fluorescent labeling of pectic oligosaccharides with 2-aminobenzamide and enzyme assay for pectin

Oligogalacturonides [oligomers composed of (1-->4)-linked alpha-D-galactosyluronic acid residues] with degrees of polymerization (DP) from 1 to 10, and a tri-, penta-, and heptasaccharide generated from the backbone of rhamnogalacturonan I (RG-I) were labeled at their reducing ends using aqueous 2-aminobenzamide (2AB) in the presence of sodium cyanoborohydride in over 90% yield. These derivatives were analyzed by high-performance anion-exchange chromatography (HPAEC) and structurally characterized by electrospray-ionization mass spectrometry (ESIMS) and by 1H and 13C NMR spectroscopy. The 2AB-labeled oligogalacturonides and RG-I oligomers are fragmented by endo- and exo-polygalacturonase and by Driselase, respectively. 2AB-labeled oligogalacturonide is an exogenous acceptor for galacturonosyltransferase of transferring galacturonic acid from UDP-GalA. Thus, the 2AB-labeled oligogalacturonides and RG-I oligomers are useful for studying enzymes involved in pectin degradation and biosynthesis and may be of value in determining the biological functions of pectic fragments in plants.

High-performance liquid chromatographic profiling of fluorescent labelled N-glycans on glycoproteins

Monitoring protein glycosylation is becoming increasingly important as novel recombinant glycoprotein therapeutics, such as glycoprotein hormones, cytokines and clotting factors, are introduced into clinical use. In this report, we describe an HPLC strategy and an improved and simplified pre-column derivatization procedure to profile N-linked glycans obtained from a variety of commercially available glycoproteins as examples. N-Glycans were first released by peptide:N-glycosidase F and labelled with the fluorescent label, 4-aminobenzoic acid by reductive amination. The labelled N-Glycans were then resolved by normal-phase HPLC and the N-glycan profile could be further improved by separating the N-glycans first according to charge by anion-exchange HPLC prior to the normal-phase HPLC. If required, identification of the fractionated derivatized oligosaccharides can be determined by mass spectrometry. The whole profiling process is simple and can be implemented in most laboratories. Because of the high sensitivity, batch glycan-analysis of low-yield recombinant glycoproteins such as samples in ampoules or obtained in the early stage of production development is possible.

Capillary electrophoresis for the analysis of glycosaminoglycans and glycosaminoglycan-derived oligosaccharides

Glycosaminoglycans are a family of polydisperse, highly sulfated complex mixtures of linear polysaccharides that are involved in many life processes. Defining the structure of glycosaminoglycans is an important factor in elucidating their structure-activity relationship. Capillary electrophoresis has emerged as a highly promising technique consuming an extremely small amount of sample and capable of rapid, high-resolution separation, characterization and quantitation of analytes. Numerous capillary electrophoresis methods for analysis of intact glycosaminoglycans and glycosaminoglycan-derived oligosaccharides have been developed. These methods allow for both qualitative and quantitative analysis with a high level of sensitivity. This review is concerned with separation methods of capillary electrophoresis, detection methods and applications to several aspects of research into glycosaminoglycans and glycosaminoglycan-derived oligosaccharides. The importance of capillary electrophoresis in biological and pharmaceutical samples in glycobiology and carbohydrate biochemistry and its possible applications in disease diagnosis and monitoring chemical synthesis are described.

Ion-pair RP-HPLC determination of sugars, amino sugars, and uronic acids after derivatization with p-aminobenzoic acid

A new, selective, and sensitive ion-pair RP-HPLC method for the simultaneous determination of three classes of natural organic compounds, i.e., carbohydrates, amino sugars, and uronic acids, in environmental samples is presented. p-Aminobenzoic acid is used for precolumn derivatization of the analytes, enabling fluorescence (lambda(ex) 313 nm, lambda(em) 358 nm) or photometric detection (303 nm). The dependence of the derivatization yield on the reaction conditions is examined. Derivatives of lactose, galactose, glucose, mannose, xylose, arabinose, galacturonic acid, glucuronic acid, N-acetylglucosamine, and glycerinealdehyde were separated on a RP-C18 column with hydrophilic end capping within 35 min, applying TBAHSO4 as the ion-pair reagent. The concentration detection limits range between 20 and 30 microg L(-1) ((1-2) x 10(-7) M) for fluorescence detection and between 30 and 75 microg L(-1) for UV detection. A good linearity is achieved in the concentration range from 50 microg L(-1) to 100 mg L(-1) (r2 > 0.99). The described method has been applied for the determination of mono-/disaccharides, uronic acids, and amino sugars in soil solutions and in landfill leachates.

Determination of carbohydrates as their p-sulfophenylhydrazones by capillary zone electrophoresis

p-Hydrazinobenzenesulfonic acid was explored as an ultraviolet labeling reagent for capillary electrophoresis of mono-, di- and trisaccharides. The labeling reaction that produces p-sulfophenylhydrazines took less than 8 min, and introduced both chromphore and charged groups into the carbohydrate molecules. The derivatives of nine mono- and disaccharides were completely separated in 9 min using a 100 mM borate buffer at pH 10.24. On-column UV detection at 200 nm allowed the detection of glucose with a mass detection limit of 17.6 fmol or a concentration limit of 3.6 microM. Reproducible quantification of carbohydrates was achieved in the concentration range of 0.1-9.1 mM in reaction solution. The method was applied successfully to determine the monosaccharide composition of laminaran.

Analysis of sialo-N-glycans in glycoproteins as 1-phenyl-3-methyl-5-pyrazolone derivatives by capillary electrophoresis

A method for the analysis of the sialo-N-glycans in glycoproteins was established by the electrokinetic chromatography mode of capillary electrophoresis (CE) in sodium dodecyl sulfate (SDS) micelles as 1-phenyl-3-methyl-5-pyrazolone (PMP) derivatives, using sialo-N-glycans in fetuin as a model. Six major and some minor peaks were observed for the N-glycans in fetuin, which were well separated from each other using 50 mM phosphate buffer, pH 6.0, containing SDS to a concentration of 30 mM in an uncoated fused-silica capillary, and these peaks were assigned to sialo-N-glycans having either of the biantennary or beta1-3/beta1-4 linked galactose-containing complex type triantennary N-glycans as the basic structures, by an indirect method based on the assignment of the peaks in high-performance liquid chromatography separated in parallel with CE and peak collation between these two separation methods. The attaching position of the sialic acid residue was determined using the linkage preference of neuraminidase isozymes. The established system is considered to be useful for routine analysis of microheterogeneity of the carbohydrate moiety of this model glycoprotein from the following reasons: (1) the derivatization with PMP proceeds quantitatively under mild conditions without causing release of the sialic acid residue, (2) the derivatives can be sensitively detected by UV absorption, (3) the procedure is simple, rapid and reproducible. Preliminary results of N-glycan analysis for several other glycoproteins under these conditions are also presented.

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.

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).

Separation of disaccharides by affinity capillary electrophoresis in lectin-containing electrophoretic solutions

Separation of the 1-phenyl-3-methyl-5-pyrazolone (PMP) derivatives of simple disaccharides (maltose, cellobiose, gentiobiose, lactose, and melibiose) by affinity capillary electrophoresis was investigated using lectin-containing neutral phosphate buffers, filled in a linear polyacrylamide-coated capillary. When Lens culinaris agglutinin (LCA) was added, the derivatives of glucobioses were retarded with varying magnitudes depending on the amount of LCA and were well separated from each other and from galactosyl glucose under optimized conditions. Addition of Ricinus communis 60 kDa agglutinin (RCA60) to the phosphate buffer gave a different migration profile, in which the derivatives of galactosyl glucoses were more retarded than those of glucobioses. However, addition of either lectin did not accomplish complete separation of the derivatives of all these disaccharides even under optimum conditions. The addition of two kinds of lectins in appropriate proportions improved separation. Thus, the binary system composed of LCA and RCA60, as well as LCA and soybean agglutinin from Glycine max (SBA), gave better separation of these derivatives, giving peak tops for all derivatives.

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.

Derivatization in capillary electrophoresis

In recent years capillary electrophoresis (CE) has been developed into a versatile separation technique, next to gas and liquid chromatography (LC), well suited for the determination of a wide variety of e.g., pharmaceutical, biomedical and environmental samples. The main advantages of CE over chromatographic separation techniques are its simplicity and efficiency. It is well recognized, however, that the sensitivity and selectivity of the detection are relatively weak points of CE. One way to overcome these limitations is the conversion (derivatization) of the analytes into product(s) with more favourable detection characteristics. Although, in principle, almost any detection mode can be combined with a derivatization procedure, in practice, fluorescence monitoring is favoured in most cases. This paper aims to give a short overview on the various reagents that can be used for pre-, post- and on-column derivatization in CE. First, a short introduction is given on CE as an analytical technique, followed by a discussion of the pros and cons of the various modes of derivatization, a comparison of derivatizations in CE with derivatizations in LC, the principles of fluorescence and prerequisites for a good fluorophore and the potential of using diode lasers in combination with a labelling procedure. With respect to the derivatization reagents the emphasis is on the labelling of amino, aldehyde, keto, carboxyl, hydroxyl and sulfhydryl groups.

Pre-, on- and post-column derivatization in capillary electrophoresis

This survey gives a short overview of the various reagents and procedures that can be used for pre-, post- and on-column derivatization in capillary electrophoresis. First there is an introduction about capillary electrophoresis as an analytical technique; this is followed by a discussion of the pros and cons of the various modes of derivatization and a comparison with liquid chromatography. In the following paragraphs the reagents for a number of functional groups are discussed. The emphasis is on derivatization of the amino group. Most of the information on the reagents and derivatization procedures is listed in tables together with information on the detection mode, analytes, sensitivity and samples. In addition to the amino group, information is given on labeling of aldehyde, keto, carboxyl, hydroxyl and sulfhydryl groups.

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.

Capillary zone electrophoresis of oligosaccharides derivatized with N-(4-aminobenzoyl)-L-glutamic acid for ultraviolet absorbance detection

A charged and strongly UV-absorbing tag, N-(4-aminobenzoyl)-L-glutamic acid) (ABG), was coupled to oligosaccharides by reductive amination under mild conditions. The effectiveness of ABG as a derivatization agent is shown through the separation of isomaltooligosaccharides from a dextran hydrolysate. The minimum detectable quantities in the subpicomole range are demonstrated.

Efficient capillary zone electrophoretic separation of wood-derived neutral and acidic mono- and oligosaccharides

Neutral and acidic monosaccharides, commonly present as structural units in wood-derived hemicelluloses, were derivatized by reductive amination using 6-aminoquinoline (6-AQ) and subsequently separated as their borate complexes by capillary zone electrophoresis. By using a quite concentrated (420 mmol 1(-1) alkaline borate buffer, a fused-silica capillary column with a small inner diameter (30 microns nominal I.D.) and a constant power of 1200 mW (corresponding to an applied voltage of approximately 21 kV), optimal separation was achieved. Under these conditions, the monosaccharides investigated were separated with a resolution, Rs, of 1.0-1.2 or greater. On-column UV detection at 245 nm was found to provide highly sensitive detection of the 6-AQ-derivatized monosaccharides. The minimum detectable concentrations were on the order of 10(-6) mol 1(-1) (corresponding to an estimated limit of detection of a few fmol). The linear calibration range of the method, including the 6-AQ derivatization step, was found to be about two orders of magnitude. Several neutral beta (1-4)-D-xylooligomers and acidic oligosaccharides containing 4-O-methyl-D-glucuronic acid units, which are common structural elements in hemicelluloses such as birch and spruce xylan, were also efficiently separated as 6-AQ derivatives, using the same buffer system. Finally, the usefulness of this analytical method has been demonstrated using a spruce wood xylan sample subjected to chemical and enzymatic hydrolysis.

Determination of carbohydrates by high-performance capillary electrophoresis with indirect absorbance detection

High-performance capillary electrophoresis (HPCE) methods with indirect absorbance detection (IAD) have been developed for the determination of carbohydrates, e.g. glucose, fructose, rhamnose, ribose, maltose, lactose, sucrose and gluconic acid. The suitability and performance of six background electrolytes (BGEs), i.e., 1-naphthylacetic acid (NAA), 2-naphthalenesulfonic acid, 1,3-dihydroxynaphthalene, phenylacetic acid, p-cresol and sorbic acid, for the IAD method were investigated. The effects of the concentration of the BGE, pH and temperature on the CE separation of these analytes were evaluated. NAA was found to be best suited as the carrier buffer and background absorbance provider for the detection at 222 nm. The optimal CE performance was found when employing 2 mM NAA, pH 12.2, at 25 degrees C. In comparison with the previous method that used sorbate as the BGE, the present method utilizing NAA shows a 3-6 fold increase in the separation efficiency and a 2-5 fold improvement in the detection limit. The calculated number of theoretical plates is in the range of 1.0-3.0 x 10(5). The precision of the present method for most sugar analytes, measured by the coefficient of variation (C.V.), typically, is less than 1% for the migration time and better than 3% for the peak height and peak area (n = 6). The detection limit is about 0.1 mM for all analytes, except for ribose for which it is about 0.2 mM. This new method is fast, accurate and can be readily applied to real biological samples for quantitative determination of selected carbohydrates.

Separation of neutral carbohydrates by capillary electrophoresis

The basic strategies for analysis of neutral carbohydrates by capillary electrophoresis are summarized. Neutral carbohydrates are dissociated in strong alkali to give anions, hence they can be separated directly by zone electrophoresis based on the difference between their dissociation constants. However, neutral carbohydrates are not electrically charged under normal conditions. Therefore, they should be converted to ions prior to or during analysis. Precapillary introduction of a basic or an acidic group to a neutral carbohydrate gives the derivative positive (in acidic media) or negative (in alkaline media) charge, respectively. The derivatives thus obtained can be separated by zone electrophoresis. Analysis of carbohydrates in a carrier containing an oxyacid salt (such as sodium borate) or an alkaline metal salt (such as calcium acetate) causes in situ conversion to anionic or cationic complexes, respectively, which are separated by zone electrophoresis. The effective uses of electrokinetic chromatography in sodium dodecyl sulfate micelles for hydrophobic derivatives (such as 1-phenyl-3-methyl-5-pyrazolone derivatives) and size-exclusion electrophoresis in gel-packed capillaries for size-different oligosaccharides are also discussed. Each separation mode has its inherent method(s) for detection, which are also described here.