Optimization of solid phase microextraction ‐ capillary zone electrophoresis ‐ mass spectrometry for high sensitivity protein identification

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Abstract
We have previously described the use of a solid phase extraction (SPE) ‐ capillary zone electrophoresis (CZE) ‐ tandem mass spectrometry (MS/MS) system for protein analysis at the low femtomole to subfemtomole level. Here we describe the systematic optimization of a number of parameters which facilitate the use of the SPE‐CZE‐MS/MS system and further enhance its performance. Specifically, we describe a robust SPE cartridge design which can be assembled without the use of glue, the evaluation of procedures to chemically modify the inner wall of the fused‐silica capillaries used in the system to improve separation and reproducibility, and the comparison of different reverse‐phase (RP) resins used for the SPE cartridge. We also explored the effects of transient isotachophoresis with respect to system performance and compatibility with different fused‐silica surface coatings, the RP resins used, and MS/MS. The enhanced performance of the optimized system is demonstrated by the analysis of calibrated tryptic digests of bovine serum albumin (BSA).