If diverse matrices and stable isotope labeled standards are available, then the PCIS performance can be tested by calculating the matrix effect and precision across matrices, both with and without correction by the PCIS. The Method 1 pane in Scheme 1 shows the results of such an analysis for the endocannabinoids. Here, 9 diverse plasma samples and the lab plasma pool were spiked (after sample preparation) with a "LOW" (50%), "MID" (100%) or "HIGH" (200%) concentration of deuterated endocannabinoids. The left plot of the pane shows that without correction, d4-LEA suffers from relative matrix effect (d4-LEA is more suppressed in plasma 3 and the plasma pool than in other samples) and non-linearity (the relative peak area increase between the levels is not constant). Both issues are solved by PCIS correction as all corrected peak areas fall within the 20% region of the nominal value. The plot on the right gives the mean matrix effect and coefficient of variation (CV, also referred to as precision and visualized by the error bars) for each labeled endocannabinoid across all samples and levels. While this plot clearly shows that 2F-AEA is an unsuitable PCIS for d8-NADA, it also shows that for the other analytes, the matrix effect was improved from 30% -121% to 85% -123%, and the precision from 21% -90% to 5% -20%.