Spectrometric determination of trimethoprim and sulfamethoxazole in tablets by automated sequential injection technique

Abstract

An automated sequential injection analysis with spectrometric detection for the determination of trimethoprim and sulfamethoxazole in tablets is proposed. The concentration of sulfamethoxazole is determined by monitoring the absorbance at 540 nm due to the intensively colored complex formed by derivatization reaction of sulfamethoxazole with nitrite and N-(1-naphthyl)ethylenediamine in acidic media. With knowledge of the sulfamethoxazole concentration, the trimethoprim concentration can be calculated from the absorption of the sample solution at 264 nm, where both analytes absorb, and the additivity of individual absorbances according to Beer-Lambert law can be used. The developed method has a linear dynamic range of 0.03–5.0 mg dm⁻³ and a detection limit of 0.03 mg dm⁻³ for trimethoprim and a linear dynamic range of 0.1–10.0 mg dm⁻³ and a detection limit of 0.01 mg dm⁻³ for sulfamethoxazole. The sampling frequency of the method is 24 h⁻¹. The method was successfully applied on pharmaceutical dosage form of tablets, as the results of the determination are in a good agreement with the official pharmacopoeial method (HPLC). The developed sequential injection analysis is simpler, cheaper, and faster than already published methods and pharmacopoeial assay. So it appears to be suitable for quality control in the pharmaceutical industry.

Graphic abstract