The long term stability of a commercial polyamine coated capillary (eCAP) is described. The capillary, which can be used in the CZE and MEKC mode, is based on coating with a polyamine after conditioning with 1 M NaOH and regeneration of this coating after each run. The stability was tested over 6 months on the drug trimethoprim and the R.S.D. values for migration time and peak area were 2.86 and 3.62% respectively (n = 8, each time of determination) (> 600 sample injections over the period). This stability was utilised in the validated method developed for trimethoprim and four of its related impurities. The repeatability of peak area for trimethoprim (without normalisation or external standard) was, within-day R.S.D. = 1.02% (n = 8) and between-days R.S.D. = 2.02% (n = 8 each day). Linearity was good (for 50 micrograms ml-1 target) (y = 249.6x + 17.3 (r = 0.992, n = 6). These results for trimethoprim and for other drug mixtures were comparison with conventional capillaries and the advantage of reducing the polyamine treated eCAP capillary to a minimum length is described, to achieve rapid assay of the 5 component timethoprim mixture in < 2 min.
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