Capillary electrochromatography (CEC) in columns with different inner diameters

Summary Capillaries with different inner diameters (50–250 μm) were packed with the same stationary phase and their electrochromatographic performance was studied. 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 numbers was observed for a capillary with an I.D. of 180 μm and the corresponding 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 diameters. No mass overloading could be observed if sample concentrations up to 5000 ppm were injected. On the other hand, when the injected sample volume exceeds 1% of the packed bed volume a decrease of the separation efficiency occurred. When the capillary I.D. was changed from 50 μm to 180 μm, peak heights and peak areas increased 5 to 6-fold. As a consequence the detection limits of the 180 μm I.D. capillary were 5.6–7.5 times lower than those obtained in a 50 μm I.D. capillary. Dedicated to Professor Dr. Heinz Engelhardt on the occasion of his 65^th birthday.