High-performance liquid chromatographic separation of some mono- and disaccharides with detection by a post-column enzyme reactor and a chemically modified electrode

High-performance liquid chromatography of lactose with evaporative light scattering detection, applied to determine fine particle dose of carrier in dry powder inhalation products

A method for quantification of the fine particle dose of lactose is described, using a hydrophilic interaction chromatography (HILIC) method and evaporative light scattering detection. The HILIC method used an aminopropyl column and a mobile phase consisting of acetonitril/water (80/20, v/v) for isocratic elution. Sensitive chromatography was obtained using a low concentration of water in the extraction solvent. The detection limit (RSD<10%) at an injection volume of 10 microL is 10 microg/mL. Linearity was obtained in the range of 10-80 microg/mL (R(2)>0.99). A relative standard deviation (RSD) of 0.5% (N=6) demonstrated good precision of the optimized method.

Enzyme-based sensor arrays for rapid characterization of complex disaccharide solutions

An enzyme-based sensor array has been developed to detect multiple disaccharides in aqueous solutions. Porous agarose beads, derivatized with enzymes for assaying disaccharides, are localized within wells etched into a silicon chip in a regular 5 x 7 array. Each well is individually addressable and acts as a microanalysis chamber where sample solution passes through the agarose matrix and is exposed to the enzymes. Detection is achieved by observing the increase in absorbance of a quinoneimine dye produced during the reaction. This technique is used to quantify the disaccharides lactose, sucrose, and maltose and the monosaccharide glucose. Preexisting glucose in the sample complicates multicomponent sensing but can be accounted for by including a glucose sensor in the array. This detection strategy is applied to the simultaneous analysis of these sugars in several beverages.

Cleanup and analysis of sugar phosphates in biological extracts by using solid-phase extraction and anion-exchange chromatography with pulsed amperometric detection

A cleanup method based on anion-exchange solid-phase extraction (SPE) was developed to render biological extracts suitable for the analysis of hexose phosphates with a modified anion-exchange chromatography method and pulsed amperometric detection. The method was applied to cell extracts of Saccharomyces cerevisiae obtained by using cold methanol as quenching agent and chloroform as extraction solvent. It was shown that pretreatment of the cell extract with SPE markedly improved the quality of the liquid chromatography analysis with recoveries of the sugar phosphates close to 100%. Furthermore, the method allowed for sample enrichment and the original extraction procedure could be simplified by implementing SPE early in the extraction protocol.

Optimization of enzyme ratios in a coimmobilized enzyme reactor for the analysis of D-xylose and D-xylulose in a flow system

A coupled enzyme system for the detection of D-xylose and D-xylulose is presented. The system is based on three consecutive enzymatic steps. The enzymes xylose isomerase (XI), mutarotase (MT), and glucose dehydrogenase (GDH) are coimmobilized on controlled pore glass and packed in a bed reactor. The relative amount of enzymes, i.e., enzyme ratio, plays a critical role in driving the overall reaction, resulting in a system with linear response characteristics and an operational range of several orders of magnitude. Three different enzyme ratios are assayed to achieve maximum conversion efficiencies for xylose and xylulose. The highest enzyme unit ratio assayed, 13.4 of GDH to XI, gave the highest apparent pseudo-first-order rate constant showing the importance of the last enzymatic reaction in the coupled system to make the overall reaction thermodynamically favorable. A pH of 7.0 was found to be an optimum compromise for the multienzyme system. Sensitivity was dependent on NAD+ concentration. The study was carried out in a flow injection system. The optimized reactor has been applied for the catalytic detection of pentoses in flow injection analysis (FIA) and liquid chromatography (LC).

Post-column reactors for sensitive and selective detection in high-performance liquid chromatography: categorization and applications

The increasing interest in the rapid trace analysis of large series of biomedical samples using column liquid chromatographic techniques requires the use of well balanced combinations of sample pretreatment, separation and detection techniques. In such work, selectivity, sensitivity and reproducibility are the key parameters. The application of automated or semi-automated on-line pre-column technology and/or post-column reaction detection are excellent ways to meet these requirements. A critical review is presented of the theoretical background of on-line post-column reactors with emphasis on their categorization, viz., open-tubular, packed-bed, segmented-stream and hollow-fibre membrane reactors. The evaluation of these reactor systems is performed by discussing selected applications of, for instance, systems based on electrochemical and redox, hydrolytic, photochemical, ion-pairing, true chemical derivatization, peroxyoxalate chemiluminescence and solid-phase reactions. As automation is becoming even more important, a number of labelling procedures, which can be performed in an on-line pre-column mode, are briefly discussed and a comparison is made between the potential of on-line pre- and post-column procedures.