Quantification of some nonsteroidal anti-inflammatory drugs as reducing agents of Cu(ii)/4,4′-dicarboxy-2,2′-biquinoline complexes in cationic micellar medium

A simple method was developed for spectrophotometric determination of some nonsteroidal anti-inflammatory drugs (meloxicam, piroxicam and tenoxicam) based on the reduction of copper(II) in buffered solution (pH 7.0) and micellar medium containing 4,4′-dicarboxy-2,2′-biquinoline acid. The absorbance values at 558 nm, characteristic of the formed Cu(I)/4,4′-dicarboxy-2,2′-biquinoline complexes, are linear with the concentrations (5.7–40 μmol L−1, n = 5) of these oxicams (meloxicam r = 0.998; piroxicam and tenoxicam r = 0.999). The limit of detection values, in μmol L−1, calculated for meloxicam (2.7), piroxicam (1.2) and tenoxicam (1.3) was obtained with 99% confidence level and the relative standard deviations for meloxicam (3.1%), piroxicam (5.1%) and tenoxicam (1.2%) were calculated using a 25 μmol L−1 solution (n = 7). Mean recovery values for meloxicam, piroxicam and tenoxicam forms were 100 ± 6.9, 98.6 ± 3.6 and 99.4 ± 2.5%, respectively. The conditional potential of Cu(II)/Cu(I) in complex medium of 7.5 mmol L−1 BCA was determined to be 629 ± 11 mV vs. NHE.