MICROBORE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC METHOD FOR MEASURING ACETYLCHOLINE IN MICRODIALYSIS SAMPLES - OPTIMIZING PERFORMANCE OF PLATINUM-ELECTRODES

A microbore high-performance liquid chromatographic method with electr ochemical detection was applied to the measurement of acetylcholine in microdialysis samples. There was an excellent linear relationship (r = 0.99998) between the concentration of acetylcholine injected onto th e column and the peak height (0.05-10 pmol/5 mu l). During the validat ion of this method, we noticed that the peak height for acetylcholine decreased over time, coupled with the appearance of a brown coating on the surface of the platinum electrode. Repeated measurement of acetyl choline standards which had been stored at 4 degrees C and -20 degrees C before and after cleaning the platinum electrode with ethanol or me thanol indicated that the decrease in the peak height of acetylcholine is caused by a decrease in sensitivity of the electrode itself Result s with a second microbore high-performance liquid chromatographic syst em confirmed these findings. On the basis of these results, we recomme nd that the platinum electrode is cleaned periodically with ethanol or methanol, and that quantitation is regularly calibrated with external acetylcholine.