Enhanced measurement stability and selectivity for choline and acetylcholine by capillary electrophoresis with electrochemical detection at a covalently linked enzyme-modified electrode.

Enzyme-modified microelectrodes were developed for the indirect amperometric detection of acetylcholine and choline following separation by capillary electrophoresis. Electrodes were prepared by first sequentially electrodepositing polypyrrole and polytyramine from the monomers on a 200-microm platinum electrode. The polymer bilayer provides enhanced selectivity and pendant amino groups for covalent coupling of acetylcholinesterase (AChE) and choline oxidase (ChO) by their reaction with glutaraldehyde. The AChE/ChO-modified electrode was then employed as an end-column detector to determine acetylcholine and choline with and without the internal standard butyrylcholine. Excellent operational stability during 2 days of continuous use was observed, with detection limits of 2 microM or 50 fmol for both acetylcholine and choline. The response from potential interferences, such as dopamine, catechol, and norepinephrine, were significantly reduced in comparison to a bare platinum electrode. The utility of this approach was demonstrated by monitoring the uptake of choline into synaptosomes.