Enzymes adsorbed on an ion exchanger as a post-column reactor: application to acetylcholine measurement

Enzymes can be used in high-performance liquid chromatography post-column reactors to improve sensitivity and specificity of detection for some compounds by converting the compounds to easily detectable products. The enzymes can be covalently bound to a post-column reactor, but a simpler approach is to bind them by adsorption to an ion exchanger or a hydrophobic interaction support. This technique has been applied to electrochemical detection of acetylcholine by using adsorption of choline oxidase and cholinesterase to a 3-cm long commercially available weak anion-exchange cartridge. Conversion of acetylcholine to peroxide is quantitative during the 10-sec residence time in the cartridge. Enzyme elution from the cartridge is negligible when low ionic strength mobile phases are used. Fresh enzyme needs to be added to the cartridge at only 1-2 week intervals.