Journal of Chromatography A, 855 (1999) 215–226 www.elsevier.com / locate / chroma Comparison of capillary electrochromatography with high- performance liquid chromatography for the analysis of pirimicarb and related compounds * F. Moffatt , P.A. Cooper, K.M. Jessop Zeneca Agrochemicals, Jealotts Hill Research Station, Bracknell, Berkshire RG42 6ET, UK Received 10 March 1999; received in revised form 4 May 1999; accepted 25 May 1999 Abstract 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 k9 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.  1999 Elsevier Science B.V. All rights reserved. Keywords: Electrochromatography; Selectivity; Retention factors; Pirimcarb; Pyrimidines 1. Introduction ing [13–15], the possibility of using sub-micron particles in beds of lengths that would create too Capillary electrochromatography (CEC) is a well high back pressures in HPLC, and the unique reviewed technique both from a practical perspective selectivity brought about by the superimposition of [1–5] and from theoretical or physical chemical chromatographic and electrophoretic effects. perspectives [6–12]. The advantages that CEC offers The differences between CEC and HPLC with over HPLC that have been cited include superior regards to the parameters that control resolution is efficiency as a consequence of lower band broaden- therefore of crucial importance in understanding the relative merits of the two techniques. Resolution ( R ), between two peaks, is related to retention, s separation and number of plates as follows: *Corresponding author. Tel.: 144-1344-414-689; fax: 144-1344- 413-677. 1/2 E-mail address: Frank.Moffatt@aguk.zeneca.com (F. Moffatt) R 5 (1/4)( a 2 1)( N ) ( k9 /1 1 k9 ) (1) s 0021-9673 / 99 / $ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S0021-9673(99)00690-1