The effect of hematocrit on solid-phase microextraction.

Solid-phase microextraction (SPME) is an approach to sample preparation that has demonstrated its appropriateness for isolating/enriching analytes present in complex biofluids with minimum sample pre-treatment. Several prior in vitro and in vivo studies have used SPME to monitor the concentrations of various drugs and metabolites in blood samples. In this work, we present the results of an investigation into how various levels of hematocrit (Hct) affect SPME recoveries. The matrices for this study consisted of whole blood samples that had been adjusted at three different Hct levels (20%, 45%, and 70%), and the selected model compounds were drugs with different physicochemical characteristics (log P range from 0.33 to 6.36). In addition, two experimental setups were employed to conduct the extractions: hydrophilic lipophilic balanced (HLB) coated SPME devices (HLB-D) at 1500 rpm (vortex agitation), and mixed mode SPME fibres (MM-F) at 400 rpm (orbital shaking agitation). Our results demonstrated that the Hct effect in SPME is dependent on the analytes of interest, and that different outcomes can be attained by altering experimental conditions, such as coating type, convection, and extraction time. Interestingly, a target compound's relative affinity for the matrix components and for the coating material proved to be one of the main factors that determine the final effect that different erythrocyte levels have on SPME recoveries. Finally, although the Hct content affects each analyte differently and the final Hct effect depends on the experimental parameters, matrix variability can be corrected by using appropriate internal standards, thereby resulting in correct quantification.