Silica microparticles as guiding substrates for the fabrication of polyamide-coated stainless-steel sheets by dip-coating technique: Application to the determination of opioids in saliva samples by direct infusion mass spectrometry.

Background: Dip-coating is a simple and cost-effective technique for synthesizing thin film sorptive phases in microextraction. The success of the coating (amount and homogeneity) relies dramatically on the wettability of the substrate, thus making the covering of smooth-surface substrates challenging. In these cases, prior to the slurry (particles and binder) deposition, the smooth-surface substrate typically requires an aggressive etching step (e.