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The use of CE with contactless conductivity detection was evaluated for monitoring enzymatic reactions. The nonionic species ethanol, glucose, ethyl acetate, and ethyl butyrate were made accessible for analysis by CE via charged products or by-products obtained in enzymatic conversions using hexokinase, glucose oxidase, alcohol dehydrogenase, and esterase. Two of the reactions, namely the conversion of glucose with glucose oxidase and that of ethylacetate with esterase, were also successfully demonstrated on a microchip device. Quantification for ethyl acetate, taken as an example, was found possible with a detection limit of approximately 7 microM.

The hydrolysis of acetylcholine and acetylthiocholine as catalyzed by the enzyme acetylcholinesterase was monitored by CE with contactless conductivity detection by determining the acetate produced in the reaction. This approach eliminates the need for a color forming derivatization procedure. The effects of the three inhibitors galanthamine, hyperzine A and paraoxon on the enzyme kinetics could also be investigated by the new procedure and the IC(50) values were determined. The contactless conductivity detection was also found to be compatible with the electrophoretically mediated microanalyis approach, in which the enzymatic reaction is carried out directly inside the capillary prior to separation and quantification.

The progress of the enzymatic hydrolysis of racemic mixtures of the enantiomers of the methyl esters of serine and threonine was monitored. This was possible in a reaction vessel of 1.5 mL by direct sampling of volumes in the nanoliter-range directly into an electrophoresis capillary. Contactless conductivity detection was used for quantification as the analytes are not accessible by UV-detection in capillary electrophoresis. Porcine pancreatic lipase and wheat germ lipase both showed a preference for the L-enantiomers of both amino acid esters. The selectivity of the porcine lipase between the two L-esters of the two amino acids was also studied and it was found that the production of L-threonine had priority over L-serine. Chirality 22:331-335, 2010. V V C 2009 Wiley-Liss, Inc.