In absence of various sources of matrix and SIL standards, PCIS performance can be assessed by its ability to improve the linearity and the precision of the endogenous analytes across a dilution series (Method 3 of Scheme 1). In this case, plasma was spiked with the compounds-of-interest, but interestingly, if the sensitivity to the endogenous analyte concentration allows, this is even possible without standards. When plotting the non-corrected peak area of LEA against the plasma CF, (left in the Method 3 pane) it gives a flattening curve with a coefficient of determination (r2) of only 0.86. The matrix effect causing this was effectively corrected using 2F-AEA as PCIS, as demonstrated by the increased r2 to 0.99. In the absence of matrix effect, dividing the peak area by the CF would give the same value across all CFs. This ratio is plotted for LEA, and it can again be observed that the matrix effect has effectively been corrected with 2F-AEA. The CV of these values indicates the precision of the dilution series and these, as well as the r2 values are plotted for each endocannabinoid at the right Method 3 pane. Excluding d8-NADA, which was not well corrected by the PCIS used, the range of r2 values improved from 0.10 -0.97 to 0.9-0.99 and the precision from 54% -110% to 5% -27%.