Chicken egg white coated paper, a sustainable mixed-mode cationic exchange biocomposite to extract antidepressants from saliva samples prior to their determination by direct infusion mass spectrometry

Proteinaceous materials are useful precursors for preparing sustainable and cost-effective sorptive phases. Among them, chicken egg white is an excellent alternative, serving as a source of ovalbumin that can be used as a biosorbent. In this article, the combination of egg white with cellulose paper is evaluated to synthesize a planar protein-based sorptive phase with high porosity and surface area. For this purpose, the paper was dip-coated in egg-white, followed by thermal curing that induced protein denaturation and self-crosslinking. The preparation was quite simple and affordable, since it did not require subsequent functionalization procedures, allowing the preparation of 25 sorptive phases with only 1 mL of pasteurized egg white. The resulting egg-white paper (EW-paper) enabled the isolation of the analytes through a mixed-mode interaction mechanism, comprising both hydrophobic and cation-exchange interactions. This potential was corroborated by evaluating the extraction capacity of the EW-paper towards some selective serotonin reuptake inhibitors (SSRI) (fluoxetine, paroxetine, sertraline, and venlafaxine) from saliva samples. The analytes were finally determined by direct infusion mass spectrometry analysis. Once optimized, the method allows the determination of the target compounds in the low µgL-1 range, also fulfilling the validation criteria in terms of precision (better than 9.1 % and 11.8 % in intra- and inter-day precision, respectively) and accuracy (in the range 84 -118 %). Finally, the applicability of the method was demonstrated by analyzing real saliva samples from a patient under paroxetine treatment.