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 electrochemical 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 the column and the peak height (0.05–10 pmol/5 μl). During the validation 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 acetylcholine standards which had been stored at 4°C and −20°C before and after cleaning the platinum electrode with ethanol or methanol indicated that the decrease in the peak height of acetylcholine is caused by a decrease in sensitivity of the electrode itself. Results with a second microbore high-performance liquid chromatographic system confirmed these findings. On the basis of these results, we recommend that the platinum electrode is cleaned periodically with ethanol or methanol, and that quantitation is regularly calibrated with external acetylcholine.