A new derivatization procedure for the determination of cephalexin with 1,2-naphthoquinone 4-sulphonate in pharmaceutical and urine samples using solid-phase extraction cartridges and UV–visible detection

The present report shows how to derivatize cephalexin with 1,2-naphthoquinone-4-sulphonate (NQS) into solid-phase extraction cartridges (C₁₈) using UV–visible detection. Optimum conditions for this new procedure are: hydrogen carbonate/carbonate buffer pH=10.5, 5 min reaction time at 25°C and NQS concentration of 7.1×10⁻³ mol l⁻¹. The accuracy and the precision of the method were tested. The procedure was used to measure cephalexin in pharmaceutical and urine samples. The results obtained were contrasted with those reported by UV-spectrophotometric and HPLC methods for pharmaceutical samples and with HPLC method for urine samples. The H-point standard additions method was used to measure cephalexin in pharmaceutical samples, and the generalized H-point standard additions method was used to measure cephalexin in urine samples.