[Quantitative fluorometric determination of 4-aminobutyric acid in cerebrospinal fluid using an amino acid analyzer]

A rapid and simple procedure is described for the determination of 4-aminobutyric acid in human CSF. The o-phthaldialdehyde derivative of 4-aminobutyric acid is analysed with a slightly modified commercially available Amino Acid Analyser. We investigated the sample preparation with special emphasis on the sulphosalicylic acid-induced hydrolysis of 4-aminobutyric acid containing compounds in human liquor. Our experiments demonstrate that the amount of estimated 4-aminobutyric acid depends considerably on the sulphosalicylic acid concentration used for protein precipitation. Application of ultrafiltration instead of sulphosalicylic acid precipitation resulted in markedly decreased 4-aminobutyric acid values. By first using ultrafiltration and by minimizing the time between lumbar puncture and analysis, it was shown that protein precipitation with a concentration of sulphosalicylic acid as low as 5 g/l gives 4-aminobutyric acid values in CSF that are essentially correct.