In-line desalting of proteins from buffer and synthetic urine solution prior to ESI-MS analysis via a capillary-channeled polymer fiber microcolumn.

Presented here is a novel in-line solid phase extraction (SPE) method utilizing a capillary-channeled polymer (C-CP) fiber microcolumn prior to introduction to an electrospray ionization (ESI) source. The high permeability of the microcolumn allows for operation under syringe pump or HPLC driven flow, ultimately providing greater mass spectral clarity and accurate molecular weight determinations for different protein/buffer combinations. Studies presented here focus on the desalting of several target proteins from a standard phosphate buffered saline (PBS) matrix and a synthetic urine solution prior to ESI-MS determinations. In every case, responses for μM-level proteins in PBS improve from the situation of not permitting molecular weight determinations to values that are precise to better than ±10 Da, without internal standards, with relative improvements in the signal-to-background ratios (S/B) on the order of 3,000×. De-salting of a myoglobin-spiked (12 μM) synthetic urine results in equally-improved spectral quality.