Chromatography Forum

I am developing an LC-MS/MS method for bisacodyl and metabolite, bisacodyl diphenol in urine. In 3 colleagues' urine, I see bisacodyl and/or bisacodyl diphenol peaks. The response is as high as e6 or e7 with matched RT. I measure 2 mass transitions for each. They are: bisacodyl -362_184, 362_167; bisacodyl diphenol - 278_184, 278_167. Since bisacodyl is a synethetic laxative and all three healthy colleagues (one of whom is myself) claim they have not taken any.

Is there any possibility that it is contaminant?

I have changed the LC gradient and tested one extract and the analytes are still there with matched RT. Seems not a carryover issue as samples before and after are clean.

Anyone please kindly advise? Thanks.

what is the content and the solvent composition of the "samples before and after" and the urine samples? I am thinking of some carry-over, released by a different sample solvent...

The samples before and after are in the same solvent, i.e. 50% ACN with 1 mM ammonium formate and 0.1% formic acid, as the positive sample.