Evaluating the ability of PCIS to correct for differences in matrix effect. With the PCIS concentration optimized, the next step is to test its ability to correct. The best way for this is to induce a matrix effect by varying the matrix or its concentration and assess the ability of the PCIS to correct for this. Various methods exist to do this, and we will here present three alternatives using the endocannabinoid analysis as an example. The method of choice for future method development with PCIS will depend on the availability of stable isotope labeled standards and diverse sources of matrix, as illustrated in the flowchart of Scheme 1.