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 at 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 C8 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.