Determination of phenelzine in human plasma with gas chromatography-mass spectrometry using an isotope labeled internal standard.

A quantitative gas chromatographic-mass spectrometric assay was developed for the determination of phenelzine in human plasma. Phenelzine, in aqueous solution or in plasma reacts at room temperature with pentafluorobenzaldehyde to form quantitatively a hydrazone derivative. The derivative has good gas chromatographic characteristics. The assay utilizes selected ion monitoring in a gas chromatographic effluent, the molecular ion generated by electron impact ionization of phenelzine derivative. Phenelzine-d, was synthesized and used as an internal standard. The assay can measure 2 ng/ml of the drug with about 10% precision. The method was used for the determination of steady state levels of phenelzine in the plasma of patients taking a therapeutic dose of the drug.