Determination of piroxicam in pharmaceutical formulations and urine samples using europium-sensitized luminescence

A simple, selective and sensitive luminescence method for the assay of piroxicam (PX) in aqueous solution is developed. The method is based on the luminescence sensitization of europium (Eu³⁺) by formation of ternary complex with PX in the presence of TOPO and Tween-80 as surfactant. The signal for Eu-PX-TOPO is monitored at λ_ex=359 nm and λ_em=615 nm. Optimum conditions for the formation of the complex in sequential injection analysis (SIA) were 0.01 M Tris buffer, pH 7.5, TOPO 5.0×10^-5 M, Tween-80 0.15% and 1.5 mM of Eu³⁺, which allows the determination of 100-1000 ppb of PX with limit of detection (LOD) of 29 ppb. The relative standard deviations of the method range between 0.5% and 3.9% indicating excellent reproducibility of the method. The proposed method was successfully applied for the assay of PX in pharmaceutical formulations and in urine samples. Average recoveries of 100.8±1.7% was obtained in tablet, whereas a recovery of 97.5±2.0% was obtained for the total PX (PX+hydoxy-PX) in urine sample.