GO-META-TiO₂ composite monolithic columns for in-tube solid-phase microextraction of phosphopeptides

A novel composite monolithic column based on graphene oxide-trimethyl-2-methacroyloxyethylammonium chloride-titania (GO-META-TiO₂) was developed for the enrichment of phosphopeptides. META was proposed as a "bridge" to connect GO and TiO₂ species to prepare GO-META-TiO₂ composite. This high surface area composite (surface area = 196.93 m² g^-1) was fixed in the monolithic column via an in situ UV polymerization process. In-tube solid phase microextraction (IT-SPME) using this composite was coupled with matrix-assisted laser desorption ionization time-of-flight-mass spectrometry (MALDI-TOF-MS) for the enrichment and detection of phosphorylated peptides from a digestion mixture of α-casein, β-casein, and bovine serum albumin (BSA) in molar ratios of 1:1:1, 1:1:10, and 1:1:100. The key factors affecting the IT-SPME of the phosphopeptides, such as the elution solution concentrations, the extraction flow rate, and the elution flow rate were comprehensively investigated. For further demonstration, this method was employed for the enrichment and detection of phosphorylated peptides from digested chicken egg white. The obtained results indicated that the GO-META-TiO₂ composite monolithic column rapidly and efficiently captured the phosphopeptides present in these complex biological samples, even in the 10 fmol β-casein tryptic digest. We therefore propose that the reported GO-META-TiO₂ composite monolithic column possesses a suitable affinity for the selective extraction of phosphopeptides from biological samples. This method paves a way in extending the application of nanomaterials.