A liquid chromatography-mass spectrometry study on the spirocyclization of ninhydrin with the aminothiols

Ninhydrin reacts with some aminothiols to form spiranes adducts whose optical and chromatographic properties have proved to be useful for chiral recognition. Liquid chromatography-mass spectrometry data along with spectroscopic analysis reveal that under certain conditions, in addition to the known single-spirane configuration, the spirothiazolidinic complexes can exist also as double- and mixed double-spiranes. The reaction was exploited to check the enantiomeric purity of two commercially available dosage form of D-penicillamine and to measure the aminothiol concentration in the urine sample from a subject under treatment with the drug. Separation of diastereoisomers was achieved on a C18 column in isocratic mode by using a mixture of an aqueous solution of formic acid (30 mmol/L)/acetonitrile (90:10, v/v) as a mobile phase. Diastereoisomers were detected by a fluorescence detector and mass spectrometer in short times and with a good resolution. Intra- and inter-assay reproducibility were under 4% with an average recovery of 98%. At a LOD of 0.01%, no evidence of the toxic distomer (l-enantiomer) was found in the biological sample and drugs.