Spectrophotometric method for the simultaneous determination of piroxicam and 2-aminopyridine

A rapid and simple spectrophotometric method is proposed for the simultaneous determination of piroxicam (Pi) and 2-aminopyridine (2-Ap). Piroxicam is stable under basic hydrolysis, but yields 2-Ap as one of the degradation products under acid hydrolysis. The method is based on the measurement of absorbances of 2-Ap and Pi at 300 and 360 nm, respectively, and the calculations are based on the binary method. The absorbances of both compounds obey Beer-Lambert's law over the concentration range of 5-25 μg L^-1 with good linearity (r²>0.99). The recoveries are within 100.8-106.4% for Pi and are within 96.4-98.9% for 2-Ap. Precision is good with acceptable limits of detection (LOD) and quantitation (LOQ) for both compounds. The method has been applied for the determination of Pi and 2-Ap in piroxicam capsules. The average content of two different brands of piroxicam is 97.4 and 98.5% (n = 3), which complies with the USP 26 (92.5-107.5%). Under the stress condition (refluxing with 0.1 N HCl), the percentages of piroxicam decrease from 100% (0 h) to 18.9% (21 h) and 2-Ap increase from 0% (0 h) to 63.6% (21 h).