A simple, specific, and rapid 1H nuclear magnetic resonance spectroscopic method for the assay of phenylbutazone and oxyphenbutazone is described. Spectra are recorded in CDCI3 containing 1,3-dichloro-5-nitrobenzene as an internal standard. The aromatic proton resonances for the standard, at delta 7.7 and 8.2, are well separated from those of phenylbutazone and oxyphenbutazone, which are in the region of delta 6.5-7.3 ppm. Average percent recoveries of phenylbutazone and oxyphenbutazone were 98.9 and 98.6 with standard deviations of 0.6 and 0.7, respectively. Commercial formulations were analyzed and the results obtained by the proposed method closely agreed with those found by the British Pharmacopoeia method.
