Flow injection spectrophotometric determination of tenoxicam Original Research Article

A new spectrophotometric flow injection method has been established for the determination of tenoxicam [4-hydroxy-2,methyl-N-2-pyridyl-2H-thieno(2,3-e)-1,2-thiazine-3-carboxamide-1,1-dioxide]. The method is based on the reaction of tenoxicam with iron(III) nitrate. The produced iron(II) reacts with potassium hexacyanoferrate(III) forming Prussian blue measurable at 724 nm. Maximum colour formation was obtained through heating. The blue complex that gradually adhered to the flow lines and the flow cell walls was removed by employing an alkaline oxalate solution. Linearity was in the range 0.5–100 μg ml−1 tenoxicam with a limit of detection (signal:noise=3) of 0.4 μg ml−1. The method was successfully applied to the determination of tenoxicam in pharmaceutical preparations. The correlation coefficient was 0.99943 (n=8) with a relative standard deviation of 1.04%, for five determinations of 5 μg ml−1 drug.