Comparison of capillary electrochromatography with high-performance liquid chromatography for the analysis of...

The applicability of capillary electrochromatography (CEC) to the analysis of pirimicarb and structurally related pyrimidines has been investigated. Methods were developed to improve the separation of closely related compounds. Resolution was achieved both by the use of running buffers containing a mixture of two organic modifiers to increase selectivity and reduce retention times. Solvent composition step gradients were used to separate compounds of widely differing retention factors. A comparison has been made between HPLC and CEC using identical separation parameters and the same stationary phase, from which two important conclusions are drawn. First, it has been shown that values of k' for the compounds analyzed were the same in both techniques. Secondly, although it is evident that CEC produces higher efficiencies than HPLC when running buffers with high organic solvent content are used, as the aqueous content of the running buffer is increased the efficiencies achieved in CEC and HPLC converge until they become equivalent. This is contrary to the theoretical model which predicts efficiencies are inherently higher using electrically rather than pressure driven flow. Disadvantages of the limited control of flow-rate in CEC in comparison with HPLC, are shown.