A comparison of the properties of contactless conductivity and diode-array photometric detectors in analyses of low-molecular, biologically active substances by capillary electrophoresis in acetic acid solutions

The performance of the contactless conductivity (CD) and diode array photometric (DAD) detectors has been compared for CE separations of creatinine, arginine and 3-methylhistidine in acetic acid background electrolytes. The contactless conductivity detector response has also been modeled. It has been found that the two detectors provide similar responses and can readily be used for dual CE detection. Changes in the acetic acid concentration affect the (CD)-D-4 noise less than the DAD noise, but their effect on the (CD)-D-4 response to the analytes is greater than with DAD. In general, (CD)-D-4 provides better detection results at higher acetic acid concentrations, while DAD is more sensitive and reliable at very low ones. Capillaries with greater internal diameters are preferable for both detectors, provided that the separation efficiency is not adversely affected. Acetic acid is a suitable background electrolyte for CE separations of small, basic organic molecules.