Surface-crosslinked poly(3-mercaptopropyl)methylsiloxane-coatings on silica as new platform for low-bleed mass spectrometry-compatible functionalized stationary phases synthesized via thiol-ene click reaction

• Poly(3-mercaptopropyl) methylsiloxane coated onto vinyl silica.
• (Chiral) ligand immobilization and surface crosslinking by thiol-ene click reaction.
• Bonding characterized by 29Si cross-polarization/magic angle spinning NMR spectra.
• Enantioselectivities comparable to brush-type chiral stationary phase (CSP).
• Reduced background signal of polysiloxane-bonded CSP in LC-MS.

A thin functional film of poly(3-mercaptopropyl)methylsiloxane was coated onto vinyl-modified silica particles (5 μm, 100 Å pore size) and chemically crosslinked to the surface. Excess of thiol functionalities allow bonding of alkene containing ligands by thiol-ene click reaction in a second step (QN-VII). Besides that a single step surface modification procedure was established in which alkene functional ligands were directly added to the polysiloxane coating solution and thus, after evaporation of the solvent, crosslinking to the vinylized surface and bonding of chromatographic ligand to the thiolated polysiloxane film occur simultaneously in one step (QN-VI). Successful bonding of the polysiloxane film was confirmed for both approaches by 29Si cross-polarization/magic angle spinning NMR spectra. The new surface functionalization concept can be utilized as a new platform for the preparation of various low-bleed, mass spectrometry-compatible stationary phases with a variety of functional ligands. The concept was demonstrated by thiol-ene click reaction with quinine carbamate and its subsequent use for enantiomer separation by HPLC-UV and HPLC-ESI-QTOF-MS of acidic chiral analytes. Chromatographic enantioselectivities were similar to a comparable brush-type CSP (QN-V0). The greatly reduced background signal in LC-MS, however, comes at expense of somewhat lower chromatographic efficiencies (C-term by factor of 2 larger compared to brush-type CSP). For quantitative analysis in single reaction monitoring (MRMHR) in high sensitivity mode, limit of detection and limit of quantification results are comparable for both surface-polymer modified CSPs, with only slightly higher values for the conventional brush-type CSP (QN-V0).