LC-MS analysis of serotonergic drugs

Separating drugs which are both polar and basic has long been difficult because of the limited operating pH range of conventional HPLC columns. This paper describes a liquid chromatographic method capable of being used with either diode-array or mass spectrometric detection for the identification and quantitation of 10 antidepressant and 2 antipsychotic drugs, all of which have serotonergic activity. In developing the method, the effects of varying buffers and mobile phase pH and of adding modifying agents on resolution and capacity factors were investigated. The organic buffers ammonia, glycine, and triethylamine were each used in a mobile phase made up of 32.5% buffer/67.5% methanol (v/v) at a pH of 10.0. Additionally, four different concentrations each of tetrahydrofuran and acetonitrile were added to investigate the effect of a modifying agent on resolution and retention. In general, decreasing mobile phase pH reduced retention times and decreased resolution. Adding tetrahydrofuran in place of the same amount of methanol tended to decrease retention times, and adding acetonitrile tended to slightly increase retention times. However, addition of both marginally improved resolution. This method has been used to satisfactorily analyze brain, blood, liver, urine, vitreous fluid, and stomach contents in subjects known to have used these drugs.