Determination of trace level gamma-aminobutyric acid using an improved OPA pre-column derivatization and on-column...

An improved pre-column derivatization with o-phthalaldehyde/tert-butylthiol and on-column preconcentration are used with packed capillary liquid chromatography and electrochemical detection to obtain low concentration detection limits for gamma-aminobutyric acid (GABA). Using derivatization procedures from the literature, it was found that the detection limits for GABA were 380 amol in 50 microns i.d. packed capillaries, which is over 10-fold worse than the detection limit possible with the instrumentation. The higher detection limit was directly the result of electroactive interferences generated by the derivatization chemistry. Derivatization was improved by scavenging excess reagents with excess amine and iodoacetamide. With these improvements, the interfering peaks were eliminated and the detection limit was improved to 50 amol. With injection volumes of 0.5 microL, under conditions that permitted on-column preconcentration, the concentration detection limit, that is the concentration at which analytes could be derivatized and detected, was 100 pM. The technique was applied to determination of GABA release from islets of Langerhans.