In gastric aspirate from a case of severe chlorprothixene poisoning, large amounts (approximately 30% of the chlorprothixene) of a previously unrecognized compound were found and identified tentatively as 2-chlorothioxanthen-9-one by combined GLC-low-resolution mass spectrometry and high-resolution mass spectrometry. The identity of the unknown compound was verified after synthesis of 2-chlorothioxan-then-9-one by two procedures. Only negligible amounts of 2-chlorothioxanthen-9-one were formed when chlorprothixene, dissolved in acids, bases, chloroform-isopropanol, methanol, or gastric fluid, was stored in the dark. However, large amounts of the drug were converted to 2-chlorothioxanthen-9-one upon exposure to UV light. Moreover, considerable quantities of unidentified degradation products were formed when chlorprothixene was exposed to lamp light as well as to UV light. Therefore, samples from cases of acute drug poisoning should be protected from light until analysis.
