Abstract
Assays that combine liquid chromatography and tandem mass spectrometry (LC-MS/MS) for measurement of drug and metabolite concentrations in physiological specimens have proliferated dramatically in recent years. The popularity of LC-MS/MS for these applications is primarily due to the sensitivity and versatility offered by electrospray and atmospheric pressure chemical ionization and the specificity provided by tandem mass spectrometry. However, during the development and application of LC-MS/MS methods we have encountered a number of problems that adversely affected the precision and accuracy of the assays. These include: 1) electrospray formation of dimers which can cause nonlinear calibration curves when a co-eluting internal standard is used; 2) interference from unsuspected metabolites; 3) ion suppression causing a reduction in sensitivity; 4) “charging” of components of the mass analyzer which also can cause a reduction in sensitivity; and 5) difficulties in converting an assay from one matrix to another. Procedures for overcoming each of these problems are discussed in this report.
