HIGH-SENSITIVITY HPLC ASSAY FOR GABA IN BRAIN DIALYSIS STUDIES

The measurement of GABA in brain dialysis experiments involves precolumn derivatization of the amino acid with omicron-phthaldehyde (OPA) in the presence of a thiol and subsequent high-pressure liquid chromatography with electrochemical detection. A method is described which employs an internal standard and coulometric preoxidation (+0.2 V) to eliminate unconjugated OPA/thiol prior to final oxidation (+ 0.4 V) of the derivatized sample. This allows for more efficient separation, providing a retention time for GABA of 9-10 min, a detection sensitivity of 2 to 5 x 10(-14) mol/sample and chromatographic stability for at least 2 weeks of daily use.