Urinary neurotransmitter metabolites in drug-free chronic schizophrenic patients measured by gas chromatography selected positive ion monitoring

The free urinary metabolites, homovanillic, indoleacetic and 5-hydroxyindoleacetic acid were measured in 24 h urines obtained from seven highly selected drug-free chronic schizophrenic patients and seven mentally normal control subjects on a low amine diet. Gas chromatography selected ion monitoring of silylated extracts was used to assay each metabolite using its own deuterated form as an internal standard. In the electron impact mode the positive ion fragments used to quantitate the amount of each metabolite in the urine were, respectively, m/z 209/211 for homovanillic acid, 319/321 for indoleacetic acid and 290/292 for 5-hydroxyindoleacetic acid. It was found essential that each compound be assayed using its own deuterated derivative as the internal standard. When expressed per mg creatinine, the homovanillic and 5-hydroxyindoleacetic acid levels of the chronic schizophrenic patients were in the normal range, but indoleacetic acid was slightly and statistically significantly higher, p = 0.01.