Simultaneous determination of tenoxicam and 2-aminopyridine using derivative spectrophotometry and high-performance liquid chromatography

Derivative spectrophotometry and high-performance liquid chromatography (HPLC) were used to determine tenoxicam and one of its decomposition products (2-aminopyridine) simultaneously and in the presence of each other. The derivative procedure was based on the linear relationship between the tenoxicam concentration and the second derivative amplitudes al 390-348 nm (peak-to-trough) measurement. The 2-aminopyridine was determined through measuring the second derivative amplitude at 241 nm (zero-crossing for tenoxicam). For the HPLC procedure. a reversed-phase Cs column with a mobile phase composed of 0.02 M sodium acetate-methanol-acetonitrile (11:8:1) with 0.005 M heptane sulfonic acid sodium salt, as an ion pair, was used to separate both compounds with 2,4-dinitrochlorobenzene, as an internal standard, in reasonable time. The flow rate was 1.5 ml min(-1) with a programmable ultraviolet (UV) detection at 300 and 375 nm. Both UV derivative spectrophotometric and HPLC approaches were followed for confirming the purity of tenoxicam in bulk and tablets dosage form. (C) 1997 Elsevier Science B.V.