Polyester-coated stainless-steel sheets using silica gel microparticles as surface pre-modifiers: a novel approach to determine selective serotonin reuptake inhibitors in saliva samples by direct infusion tandem mass spectrometry.

Stainless-steel substrates have grown in importance in the development of planar sorptive phases. However, the reduced wettability of polished sheets makes difficult their functionalization. This limitation can be solved by using amorphous silica gel microparticles as superficial guides. These particles increase both the wettability and the surface area of the final sorptive phases, which has a key influence on the extraction kinetics. In this article, double-sided thermal-resistant adhesive tape was used as the binder to pre-immobilize the silica particles over the stainless-steel surface, thus avoiding aggressive etching procedures. A linear polyester (synthesized by conventional free melt polycondensation from 1,4-butanediol and phenylsuccinic acid) was deposited onto the particulate area by the drop-casting technique. The resulting polyester-silica gel sheets (PSG-sheets) have been evaluated for the extraction of four selective serotonin reuptake inhibitors (SSRI) (fluoxetine, paroxetine, sertraline, and venlafaxine) in saliva samples, followed by direct infusion mass spectrometry analysis. The method allows the determination of the target compounds at the low µg·L(-1) range, and it was successfully applied to analyze a saliva sample from a patient under paroxetine treatment. The method also fulfills the typical validation criteria in terms of precision (intrer-day precision better than 16.5% at the limit of quantification) and accuracy (relative recoveries in the interval 87-123% at the limit of quantification), both parameters having been evaluated at four concentration levels.