Imipramine is a tricyclic antidepressant drug that is not a Drug Enforcement Administration controlled substance but has been classified by the Association of Racing Commissioners International Inc. as a class two drug in horses. Desipramine is a major metabolite of imipramine. These two analytes were analyzed on-line by LC–PDA MS/MS from extracts of horse urine. The urine sample was first treated with b-glucuronidase to hydrolyze glucuronide conjugates of imipramine and desipramine. This was followed by solid phase extraction. The concentration of imipramine and desipramine in the sample was determined by the internal standard method using the peak area ratio and linear regression analysis.

This application note presents a rapid method for quantitation of imipramine and desipramine in horse urine. It illustrates the advantages of MS/MS detection in terms of specificity, sensitivity and unambiguous identification, for the analysis of drugs and their metabolites.