Simultaneous LC determination of trimethoprim and sulphamethoxazole in pharmaceutical formulations

In the present study, a simple, sensitive, precise and rapid reversed-phase high performance liquid chromatographic (HPLC) method with ultraviolet detection for the simultaneous analysis of trimethoprim (TMP) and sulphamethoxazole (SPM) is developed and applied to the determination in commercial pharmaceutical preparations. These compounds are well separated on a Bondapak C 18 reverse phase column using a mobile phase consisted of a mixture of methanol:water (60:40; v/v) adjusted to pH 3 with 10% orthophosphoric acid at a flow rate of 1.8 ml min −1. The proposed method was linear in the range 2.0–10.0 μg ml −1 for TMP and 10.0–50.0 μg ml −1 for SPM. The limit of detection were 0.45 and 1.21 μg ml −1 for TMP and SPM, respectively. The method which is rapid, simple and does not require any separation step, has been successfully applied to the assay of commercial tablet and oral suspension dosage forms containing TMP and SPM.