Diode array spectroscopy in pharmaceutical analysis: determination of acetaminophen/codeine phosphate tablets

The use of diode array spectrophotometry for the analysis of tablets containing acetaminophen and codeine has been investigated. The technique was found to be applicable to the analysis of tablets which nominally contain 300 mg acetaminophen and 15, 30 or 60 mg codeine phosphate (Tylenol Nos 2-4, respectively). The concentration of codeine in extracts of Tylenol No. 1, which contains 7.5 mg codeine phosphate, was found to be too low for precise determination. First-derivative spectroscopy is required for the analysis of Tylenol Nos 2 and 3. Tylenol No. 4 can be determined using either the zero or the first-derivative spectra; however, the former was found to give consistently lower values for each component. The influence of derivative order and analytical wavelength range on the precision was investigated. The accuracy of the procedure was assessed by comparing the results from spectroscopy with those from liquid chromatography. Finally, some general conclusions on the applicability of diode array spectroscopy for the multicomponent analysis of pharmaceuticals are presented.