Rapid and sensitive ion-exchange fluorometric measurement of γ-aminobutyric acid in physiological fluids

Improvements of the ion-exchange/fluorometric method for measuring γ-aminobutyric acid (GABA) have resulted in an automatic three-column analyzer which produces an analysis every 15 min using 200-μl samples to a sensitivity of 1 pmol. This high-performance liquid chromatographic procedure utilizes three stainless-steel microbore columns containing cation-exchange resin. GABA is eluted using a lithium citrate buffer and then detected in the flow stream after reaction with the fluorogenic reagent orthophthalaldehyde. Each column utilizes a timer-controlled, pneumatically actuated two-way 10-port valve containing a 200-μl loop for sample injection and a 1-ml loop for regeneration. Similar 4-port valves sequentially direct the output from one of the columns to the reaction manifold. Measurement of GABA levels in sequential aliquets of the first 20 ml of human lumbar cerebrospinal fluid revealed an increasing gradient of GABA level in cerebrospinal fluid from six patients and no gradient in a seventh patient, the mean rate of increase being 2% per milliliter.