Determination of acetylcholine and choline with platinum-black ultramicroarray electrodes using liquid chromatography with a post-column enzyme reactor

A method for the highly sensitive determination of acetylcholine (ACh) and choline (Ch) was developed using platinum (Pt) black microarray electrodes as detectors in a microbore liquid chromatography (LC) with a post column enzyme reactor. The electrodes were prepared by plating a gold (Au) film electrode with sub-mu m Pt-black particles. Since hydrogen peroxide generated by the enzymatic reaction of ACh and Ch was oxidized only at the Pt-black microarray electrode, each Pt-black particle (typically 0.1-0.2 mu m in size) operated as an ultramicroelectrode. A high signal-to-noise ratio was achieved because of the high current density at the Pt-black microarray electrodes and because the Au film has a much lower baseline noise than the Pt. Detection limits of 5.7 (ACh) and 6.0 (Ch) fmol were obtained, with a wide linear range. The ACh and Ch signals with an Au film electrode modified with Pt-black particles retained more than 70% of their initial value after 5 days with continuous potential application. This is better stability than for a bare platinum electrode which retained only 40% of its initial response under comparable conditions.