Thin Layer Chromatographic Method for Rapid Quantification and Identification of Trimethoprim and Sulfamethoxazole in Pharmaceutical Dosage Forms

Abstract

A densitometric and a spectrophotometric method for rapid but accurate determination of sulfamethoxazole (SMA) and trimethoprim (TMP) present in combined dosage forms were described. SMA and TMP were extracted with 90% acqueous methanol and the interfering and related contaminants were removed by thin layer chromatography (TLC) or high performance TLC (HPTLC) on silicagel plates using chloroform : isopropanol : diethylamine :: 10 : 6 : 1 (v/v) as mobile phase. Assay was done at the respective absorption maxima of the drugs by in situ densitometry and by spectroscopy after extracting the drugs from TLC plates with 90% acqueous ethanol. Results obtained by both the methods agreed well with those obtained by the method prescribed by the United States Pharmacopoeia XXI edition. Total time required for HPTLC and densitometric assay of 32 samples using 4 standards was 30 min. Probable source of errors in densitometric studies and their rectification was discussed.