Determination of clotrimazole in mice plasma by capillary electrophoresis

In addition to its antifungal activity, clotrimazole attracts interest as an anti-inflammatory drug. In order to correlate this effect with plasma concentrations in mice, a capillary electrophoretic method was developed. Sample preparation was carried out by protein precipitation using methanol. Quantification of clotrimazole was achieved by means of capillary electrophoresis using ketoconazole as an internal standard (IS). The background electrolyte (BGE) composed of a Tris buffer solution (100 mM, pH 3.0, adjusted with acetic acid) and methanol (8:2, v/v). Injection was carried out electrokinetically with 10 kV over a time period of 20 s. A special rinsing procedure utilizing a sequence of a SDS/methanol solution, a sodium hydroxide solution, water and BGE, was applied to enhance the reproducibility. With this procedure, an intermediate precision (day-to-day precision) of the area ratios of clotrimazole and IS of 5.0% for 0.5 μg ml⁻¹ and 2.6% for 10 μg ml⁻¹ was obtained. In summary, with the described capillary zone electrophoresis (CZE) method it is possible to handle small sample volumes of 60 μl, to detect clotrimazole concentrations of 0.3 μg ml⁻¹ (limit of detection), and to quantify clotrimazole down to concentrations of 0.5 μg ml⁻¹ (limit of quantification).