Abstract
High-performance liquid chromatography (HPLC) coupled with atmospheric pressure ionization (API) tandem mass spectrometry (LC-MS/MS) has become the technique of choice for quantification of small-molecule drugs and metabolites in biological matrices such as plasma, serum, blood, urine, and in vitro biological samples. To achieve enhanced sensitivity and selectivity (specificity), the LC-MS/MS acquisition is conducted via selected reaction monitoring (SRM), simultaneously obtaining the SRM transitions of the analyte and its internal standard. In spite of the great specificity provided by the SRM-based LC-MS/MS analysis, the use of this technique for quantification of drugs in post-dose (incurred) biological samples could be hampered by interferences arising from the presence of some metabolites, which originate from the in vivo biotransformation of the administered drug. In this chapter, two kinds of potential sources of interference and approaches to overcome their untoward consequences are discussed. The first kind is due to inadequate chromatographic or mass resolution between a drug and its metabolite. The second type is due to instability of the metabolite during the multiple sample handling and cleanup steps involved prior to the LC-MS/MS analysis, thereby generating the drug due to degradation of the metabolite.
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