Fig. shows calibration curves for LEA in plasma and neat solution without any correction, and Fig. after correction with PCIS. For comparison, a traditional peak area correction with spiked SIL-ISTD LEA-d4 was performed (Fig. ). The same was done for the other endocannabinoids and the resulting slope differences (% difference of the slope in plasma as compared to that in neat solution) are plotted in Fig. . This last figure reconfirms that the plasma matrix severely suppresses the signal of the endocannabinoids, as reflected by the slopes being 33% (PEA) up to 87% (SEA) lower in plasma as compared to neat solution. Quantifying these endocannabinoids without any correction based on the calibration curve in neat solution would result in a serious underestimation of the concentration.