An efficient slurry packing procedure for the preparation of columns applicable in capillary electrochromatography and capillary electrochromatography‐electrospray‐mass spectrometry

A procedure is described for the slurry packing of 50‐μm ID fused silica capillaries with 3‐μm octadecyl silica (ODS) particles for capillary electrochromatography (CEC) and its hyphenation with electrospray ionisation mass spectrometry (ESI/MS). A homogeneous packed bed is obtained by using a slow packing process in an upward direction with a balanced density slurry solvent and MeOH as packing solvent. Special attention was paid to the in‐ and outlet frit preparation in order to avoid gas bubble formation which renders CEC‐ESI/MS problematic. Frits were made out of the packed bed itself, sintered in water, by using a perforated heating ribbon; they were not longer than 1 mm. In CEC‐UV, column efficiencies up to 300,000 plates per meter were obtained. Absence of gas bubbles was ascertained by the straightforward coupling to ESI/MS. A make‐up flow of 3 μL/min H2O/MeOH containing 0.1% HCOOH was used in the sheath flow interface. Steroids and carbamates were analysed with a 0.1% triethylamine‐acetic acid buffer (pH 8.9) containing varying amounts of acetonitrile. In CE‐ESI/MS, efficiencies dropped by ca. 20% but spectral data were excellent.