DETERMINATION OF GAMMA-AMINOBUTYRIC-ACID IN MICRODIALYSIS SAMPLES BY MICROBORE COLUMN LIQUID-CHROMATOGRAPHY AND FLUORESCENCE DETECTION

A method for the determination of gamma-aminobutyric acid (GABA) at co ncentrations as low as 1.5 nM in microdialysis samples is described. A high-performance liquid chromatography (HPLC) autosampler was used fo r precolumn derivatizations of samples with phthalaldehyde-2-mercaptoe thanol reagent, as well as for automated injections of acetonitrile to wash the microbore column between injections. This permitted the use of only one isocratic pump and reduced the run-to-run analysis time to below 20 min, without any risk for late-eluting peaks. Three differen t microbore columns were evaluated. The optimal column was a 150x1 mm I.D., C-18 reversed-phase silica column with a particle size of 3 mu m , operated at a flow-rate of 50 mu l/min. The mobile phase was 0.1 M s odium acetate buffer, pH 5.4, containing 20% acetonitrile. Under these conditions, the column exhibits a low back-pressure of about 11.1 MPa and is usable for at least 1000 injections. Good correlation was foun d between fluorescence and electrochemical detector responses for o-ph thaldialdehyde-GABA derivatives, although the latter detector type gen erally required more skill and maintenance for routine use. Microdialy sis samples of 10-20 mu l, recovered from various rat brain nuclei, we re assayed using the described method. (C) 1998 Elsevier Science B.V.