MULTIVARIATE EVALUATION OF THE SEPARATION PERFORMANCE IN MICELLAR ELECTROKINETIC CAPILLARY CHROMATOGRAPHY OF PEPTIDES - OPTIMIZATION

A simultaneous optimization of resolution, efficiency and migration ti mes of enkephalin-related peptides in micellar electrokinetic capillar y chromatography (MEKC) was performed. Six experimental variables; the surfactant concentration, the percentage of organic modifier, the ion ic strength of the buffer, the injected plug length, the applied tempe rature and the sample solution composition were studied via central co mposite design (CCD). Large differences in separation performance were observed at a commonly used level of organic modifier in the backgrou nd electrolyte. Partial least squares regression of the responses reve aled that the experimental domain was too large and complicated to be explained by the model. A new CCD model was obtained with improved pre diction ability at narrower ranges of the experimental factors, especi ally of the organic modifier. A conflict between maximum resolution an d efficiency within the shortest analysis time was observed. Therefore , constraints were set on maximal resolution and analysis time, while solving for maximum efficiency. Optimal operating conditions were foun d at 35 mM sodium dodecyl sulfate (SDS), 5 % v/v of acetonitrile, 1.9 mm injected plug length, 35 degrees C and sample solution with no adde d micelles, giving high efficiency and resolution at short analysis ti me. The value predicted by the model was found to agree very well to t he observed values, at the optimal experimental conditions, even on a new capillary.