Hydrophobic Treatment Enabling Analysis of Wettable Surfaces Using a Liquid Microjunction Surface Sampling Probe/Electrospray Ionization-Mass Spectrometry System

An aerosol application procedure involving one or more commercially available silicone-based products was developed to create hydrophobic surfaces that enable analysis of otherwise wettable, absorbent surfaces using a liquid microjunction surface sampling probe/electrospray ionization mass spectrometry system. The treatment process resulted in a hydrophobic surface that enabled formation of the requisite probe-to-surface liquid microjunction for sampling and allowed efficient extraction of the analytes from the surface, but did not contribute significant chemical background in the mass spectra. The utility of this treatment process was demonstrated with the treatment of wettable high-performance thin layer chromatography plates, post-plate development, and their subsequent analysis with the sampling probe. The surface treatment process for different surface types was described and explained and the effectiveness of the treatment and subsequent analysis was illustrated using alkaloids from goldenseal (Hydrastis canadensis) root separated on a normal phase silica gel 60 F-254S plate and peptides from protein tryptic digests separated on a ProteoChrom HPTLC Silica gel 60 F254S plate and a ProteoChrom HPTLC Cellulose sheet. This simple surface treatment process significantly expands the analytical surfaces that can be analyzed with the liquid microjunction surface sampling probe, and therefore, also expands the analytical utility of this liquid extraction based surface sampling approach.