Tunnel Frit: A Nonmetallic In-Capillary Frit for Nanoflow Ultra High-Performance Liquid Chromatography-Mass Spectrometry Applications

In this study, an easy method to fabricate a durable in-capillary fit was developed for use in nanoflow liquid chromatography (nanoLC). A small orifice was tunneled into the sol-gel fit during the polymerization process resulting in the simple fabrication of a tunnel fit. A short packing tunnel fit column (2 cm, C-18 particles) was able to sustain over 10 000 psi continuous liquid flow for 10 days without observation of particle loss, and back pressure variation was less than 5%. The tunnel fit was successfully applied to the fabrication of nanoflow ultra high-performance liquid chromatography (nano-UHPLC) trap and analytical columns. In the analysis of tryptic peptides, the tunnel fit trap and analytical columns were demonstrated to have high separation efficiency and sensitivity. In analysis of phosphopeptides, the use of the nonmetallic tunnel frit column showed better sensitivity than the metallic frit column. This design can facilitate the preparation of nano-HPLC and nano-UHPLC columns and the packing material can easily be refilled when the column is severely contaminated or clogged.