Gradient capillary electrochromatography of drug mixtures with UV and electrospray ionisation mass spectrometric detection

A simple method for forming reproducible mobile phase gradients with capillary electrochromatography (CEC) has been demonstrated. It allows short columns and low ionic strength buffers to be used and it lends itself to mass spectrometric detection. Mixtures of benzodiazepines, corticosteroids and thiazide diuretic drugs were separated using UV absorbance and electrospray ionisation mass spectrometric (ESI-MS) detection. Separations were performed on fused-silica capillary columns (33-50 cmX50-75 mu m I.D.) packed with CEC Hypersil ODS (3 mu m) and Apex ODS (3 mu m) particles. A stainless steel tee connector was used to interface the CEC column with samples and mobile phase delivered from a HPLC autosampler and pump. A voltage (30 kV) was applied to the tee connector causing electrokinetic transfer of samples and mobile phase into the CEC column. Pre-conditioning of the CEC column with mobile phase of low organic content allowed dilute samples to be stacked at the head of the column prior to elution.