Identification of clozapine N(+)-glucuronide in the urine of patients treated with clozapine using electrospray mass spectrometry.

Clozapine N(+)-glucuronide was detected in the urine of five patients chronically treated with clozapine. Identification was made on the basis that the material isolated from urine had the same high-performance liquid chromatographic retention time and positive electrospray mass spectra as that of an authentic reference standard of clozapine N(+)-glucuronide. These results indicate that electrospray mass spectrometry is a valuable technique in the analysis of low-molecular-weight biologically derived N(+)-glucuronide metabolites.