DEVELOPMENT OF A RATIONAL OPTIMIZATION PROCEDURE FOR THE AUTOMATED SAMPLE CLEANUP WITH COLUMN SWITCHING IN PESTICIDE-RESIDUE ANALYSIS

Column-switching procedures usually involve at least one step gradient elution over the first column. In order to find optimal conditions for column switching in a rational way a computer program has been developed which calculates retention times and peak volumes for elution under step gradient conditions. Based on experimentally determined relations for retention versus mobile phase composition, the program calculates iteratively the displacement of analytes and sample interferences on the first column. Corrections for the distortion of solvent front and peak position of the solutes during step-gradient elution are included. The prediction of the peak volume is based on a diffusion model. The performance of the simulation procedure is evaluated with the application of a practical residue analytical method, the simultaneous determination of procymidone and iprodione in fennel. In this case, the program was shown to accurately predict retention times and peak volumes of a major fennel interference and the compounds of interest eluted under stepwise gradient conditions. Optimal conditions for reversed-phase liquid chromatography column switching are more rapidly found by the present procedure in comparison to trial and error optimisation.