Capillary electrochromatography (CEC) in columns with different inner diameters

Capillaries with different inner diameters (50-250 mum) were packed with th e same stationary phase and their electrochromatographic performance was st udied. Special focus was put on the currents measured in these capillaries and the necessity of controlling temperature, especially in capillaries of larger inner diameter. With a commercial instrument no loss in plate number s was observed for a capillary with an I.D. of 180 mum and the correspondin g Ohm plot was linear. A test mixture consisting of polar (weakly basic and acidic) and non-polar compounds was separated on packed capillaries with a range of inner diamete rs. No mass overloading could be observed if sample concentrations up to 50 00 ppm were injected. On the other hand, when the injected sample volume ex ceeds 1% of the packed bed volume a decrease of the separation efficiency o ccurred. When the capillary I.D. was changed from 50 pm to 180 mum, peak heights and peak areas increased 5 to 6-fold. As a consequence the detection limits of the 180 pm I.D. capillary were 5.6-7.5 times lower than those obtained in a 50 pm I.D. capillary.