In-line coupling of low-pressure short capillary electrochromatography columns to electrospray ionisation mass spectrometry

A new in-house designed and constructed injection valve for capillary elect rochromatography (CEC) based on a rotating injection part with compartments for the eluent as well as for the sample has been coupled to a mass spectr ometer via a sheath flow electrospray ionisation (ESI) interface, using sho rt capillary columns of 15 cm length. The CEC columns were packed with 3 mu m Cls bonded silica particles, and a mixture of peptides was analysed using an ammonium acetate/acetonitrile eluent. A significant increase in the sig nal-to-noise ratio was obtained when the peptides were dissolved in water w ith the same content of organic modifier as in the eluent with an addition of 0.5% (v/v) acetic acid. When the CEC analysis was performed without any additional pressure, the separation current sometimes dropped tremendously due to bubble formation, caused by different permeability in the frits and packed part of the column causing an extremely low electroosmotic flow. The separation current was restored to its original value by applying only 7 b ar at the inlet of the CEC column, and the separation performance for the t est peptides was recovered. A comparison of the CEC performance of: peptide s in pure CEC mode and in low-pressure CEC mode is reported. Copyright (C) 2001 John Wiley & Sons, Ltd.