Selection of the appropriate matrix for standard curve is critical for an accurate and sensitive biomarker method. Slope of a standard curve is the key factor for parallelism assessment between tested matrix and authentic matrix for LC-MS/MS assays. Here the authors have established slope criteria using a generic equation and endogenous level criteria for achieving assay sensitivity. The slope difference criterion is from -13.0 to +17.6% for LC-MS assays with ± 15% bias criteria. When the ratio of endogenous concentration in the tested matrix to the lower limit of quantitation is <4.0, the lower limit of quantitation is achievable. If these criteria are met, the tested matrix can be used for assays. The utility of the two criteria has been illustrated with case studies.
Keywords: LC-MS; background subtraction method; biomarker; endogenous level criterion; parallelism; pharmacokinetic assay; relative matrix effect; slope acceptance criterion; surrogate matrix.