Simultaneous Determination of Paracetamol and Codeine Phosphate in Combined Tablets by First-Order Derivative and Ratio Spectra First-Order Derivative UV Spectrophotometry

Two simple, accurate and reproducible UV spectrophotometric techniques have been developed for the simultaneous determination of paracetamol and codeine phosphate in combined tablets. The first one is based on the measurement of first-order derivative amplitudes at zero-crossing points, 263.5 nm and 218.4 nm for the assay of paracetamol (5.0 – 25.0 mgL^-1) and codeine phosphate (1.25 – 10.0 mgL^-1) respectively. The second one uses the amplitudes of ratio spectra first-order derivatives at 255.3 nm and 221.4 nm to quantify paracetamol (5.0 – 30.0 mgL^-1) and codeine phosphate (0.625 – 10.0 mgL^-1), respectively. Both techniques have been extensively validated and compared to an official HPLC method showing their applicability in the routine analysis.