A capillary liquid chromatographic/tandem mass spectrometric method for the quantification of γ-aminobutyric acid in human plasma and cerebrospinal fluid

A sensitive and reliable method for the determination of γ-aminobutyric acid (GABA), a major inhibitory neurotransmitter, in human plasma and cerebrospinal fluid (CSF) has been developed. The method is based on capillary liquid chromatography (LC)/tandem mass spectrometry (MS/MS) using deuterium-labeled GABA (γ-aminobutyric acid-2,2-D2, GABA-d2) as internal standard. Pre-column derivatization with 7-fluoro-4-nitrobenzoxadiazole (NBD-F) was deployed, allowing both effective in-line pre-concentration and sensitive tandem MS detection of the analyte. An extraction column (10 mm × 0.25 mm, 7 μm, C18) was used for preconcentrating and stacking the sample. Separation was carried out on an analytical column (50 mm × 0.25 mm, 5 μm, C18). Characteristic precursor-to-product ion transitions, m/z 267 → 249 (for NBD-GABA) and m/z 269 → 251 (for NBD-GABA-d2) were monitered for the quantification. A linear calibration curve from 10 to 250 ng/mL GABA with an r2 value of 0.9994 was obtained. Detection limit was estimated to be 5.00 ng/mL GABA (S/N = 3). Human plasma and CSF samples were analyzed. The concentrations of GABA were found to be 98.6 ± 33.9 ng/mL (mean ± S.D., n = 12), and 44.3 ± 10.0 ng/mL (n = 6) in plasma and CSF, respectively.