Determination of sulphonamides in pork meat extracts by capillary zone electrophoresis

For sixteen sulphonamides the effective mobility was measured as a function of pH and from the effective mobilities determined in two different electrolyte systems the pK value and mobility at infinite dilution were calculated. A pH of 7.0 was found to be the optimum pH for the separation for both standard mixtures and mixtures of sulphonamides dissolved in pork meat extracts. For the determination of the sulphonamides in pork meat only a very simple pretreatment consisting of extraction with acetonitrile and centrifugation is suitable, as the matrix effects at pH 7.0 do not affect the separation. Calibration graphs for five sulphonamides were constructed, and regression coefficients of at least 0.999 were obtained. The limit of detection for the method varies from 2 to 9 ppm for a pressure injection time of 10 s (injection volume ca. 18 nl) using a Polymicro Technology capillary of length 116.45 cm, distance between injection and detection 109.75 cm and I.D. 50 microns.