Automated capillary electrochromatography tandem mass spectrometry using mixed mode reversed-phase ion-exchange chromatography columns

An automated injection system for capillary electrochromatography (CEC), combined with a short­in-house designed and constructed micro-electrospray CEC mass spectrometry interface, for automated CEC/MS(/MS), electro-osmotic flow (EOF) infusion and flow-injection analysis, is coupled to an electrospray mass spectrometer. The system is used with C18, C6 strong cation exchange (SCX) and SCX columns, resulting in good reproducibility, sensitivity, selectivity and high efficiencies for small cationic compounds, even with the use of the SCX columns. Linear calibration lines with good correlation for these basic compounds were constructed from high picomolar to low micromolar range on the C6/SCX and from low nanomolar to low micromolar on the SCX column. Efficiencies up to 360 000 and 400 000 plates/m are reproducibly obtained for the same charged compounds on the C6/SCX and SCX column, respectively, and detection limits in the high picomolar range on the C6/SCX and in the low nanomolar range on the SCX column are achieved. Application to the separation of 14 tags (used in code reading in combinatorial chemistry) on a SCX column is demonstrated.