Surrogate matrix and surrogate analyte approaches for definitive quantitation of endogenous biomolecules

Background: Quantitation of biomarkers by LC–MS/MS is complicated by the presence of endogenous analytes. This challenge is most commonly overcome by calibration using an authentic standard spiked into a surrogate matrix devoid of the target analyte. A second approach involves use of a stable-isotope-labeled standard as a surrogate analyte to allow calibration in the actual biological matrix. For both methods, parallelism between calibration standards and the target analyte in biological matrix must be demonstrated in order to ensure accurate quantitation. Results: In this communication, the surrogate matrix and surrogate analyte approaches are compared for the analysis of five amino acids...