It could be expected that analytes with similar ionization efficiencies can be corrected with a single PCIS. This is exemplified with the method for endocannabinoids, for which the result of the matrix effect exploration is visualized in Figure . Notably, using stable isotope labeled standards for this exploration is beneficial as it avoids endogenous analyte peaks in the matrix effect profiles. Fig. shows that the PCI profiles are all relatively stable between 1 and 10 min. However, as more clearly visible in Fig. , the signals drop frequently during the last 4 min, and this high-suppression zone coincides with the elution region of our analytes. The variability in the matrix effect over the last minutes of the run shows that quantification would be compromised if only one or two ISTDs would be spiked to a sample to correct the whole set of analytes for matrix effect and that this method could benefit from PCIS correction. Selection of a PCIS candidate. To successfully correct for matrix effects in LC-MS/MS analysis and to be applied in routine analysis, a PCIS candidate should possess certain characteristics. A high-potential PCIS candidate: