Quantitative Fourier transform-infrared/attenuated total reflectance (FT-IR/ATR) analysis of trimethoprim and sulfamethoxazole in a pharmaceutical formulation using partial least squares.

An alternative procedure for the simultaneous determination of trimethoprim and sulfamethoxazole in an intravenous pharmaceutical formulation is presented. Infrared spectra of 14 calibration and 6 validation samples were collected using Fourier transform-infrared/attenuated total reflectance (FT-IR/ATR). Partial least-squares (PLS) analysis of the spectral data yielded an average relative error of prediction of 0.69% for trimethoprim and 0.38% for sulfamethoxazole. Analysis of a commercial formulation gave concentration values for sulfamethoxazole and trimethoprim in close agreement with those obtained by a modification of the high-performance liquid chromatography (HPLC) assay listed in the United States Pharmacopeia (USP).