Approaches for coupling solid-phase microextraction to nanospray

Biocompatible solid-phase microextraction (SPME) devices were prepared using two restricted access materials (RAM) as the SPME coating. The restricted access materials were immobilized on steel and platinum wires. The selective coating eliminated most of the matrix interference, which allowed the coupling to mass spectrometry without further purification. The SPME devices were interfaced to mass spectrometry by electronanospray. Several experimental set-ups are described and discussed herein. For the in situ extraction of peptides from the tryptic digests, trypsin was immobilized both on steel wires and on the inside wall of a vial. The devices were incubated together with the RAM-SPME devices and a protein (casein) solution. After the protein digestion, the resulting peptides were analyzed by SPME/nanospray. The vial approach provided the best results; up to eight peptides could be identified which corresponds to a sequence coverage of 58%. The limit of detection of SPME/nanospray for the extraction of peptides from an aqueous solution was about 50 fmol/mL. The results demonstrate that the direct coupling of SPME to nanospray can reduce analysis time and is an attractive alternative to conventional approaches like Zip-Tip purification.