From relative to absolute quantification. The value of metabolomics studies could be greatly enhanced if absolute concentrations would be reported. In the absence of an analytefree matrix, to quantify analytes that are also endogenous compounds, calibration curves can be made using the standard addition method (SAM), background subtraction, surrogate analyte or surrogate matrix approach . The SAM requires multiple analyses of the same sample spiked at different levels making it time-consuming and impractical. The background subtraction method uses a pooled sample to build the calibration curve, meaning that part of the samples will have a concentration below the lowest calibration point requiring extrapolation of the curve. The surrogate analyte approach needs a surrogate analyte per endogenous analyte (preferably a SIL analogue) to build the calibration curve in matrix, resulting in extreme costs when measuring many analytes. Finally, the surrogate matrix approach, using an alternative matrix (e.g. a neat solution) for the calibration curves, also needs an ISTD per analyte, unless there is (virtually) no matrix effect. If PCIS could correct for this matrix effect, it becomes possible to quantify endogenous analytes based on a calibration curve in neat solution instead of matrix.