Bioequivalence and Bioavailability Forum

Dear Ohlbe!

❝ My worry is not really with UV or fluo detection, rather with MS.

OK, but UV and fluorescence spectra change just a little by common phase-1 metabolic pathways (e.g. demethylation, hydroxylation, …).
Unless you check peak purity (DAD) of ‘unknown samples’ you probably simply don’t get the interference.

❝ Many labs just forget that LC/MS/MS starts with LC and go for very short run times with a reduced sample preparation.

Yes this is a major problem. The first-shot-approach of protein-precipitation-and-inject IMHO is just b……shit (sorry).
Many analysts were caught in this pitfall set by vendors of LC/MS-MS systems.
In my experience LC/MS-MS calls for more sophisticiated sample preparation (getting ‘cleaner’ extracts) – not less.

❝ If you don't separate your metabolite chromatographically you may end with real trouble,...

Sure, but still the metabolite(s) may either not be available commercially, or even worse not possible to synthetize. At least if the drug is excreted renally, extraction form urine may be an option…