A simple and rapid spectrophotomitric method has been developed to determine orphenadrine citrate and paracetamol in tablet formulations. The first step was based on the reaction of orphenadrine citrate with 1-amino naphthalene and sodium nitrite with heating for 6 min at 50 ºC to give an orange colour having a maximum absorbance at 462 nm. The optimization of the reaction conditions is investigated. In the second step, paracetamol was analyzed after solving it in distilled water by taking the first order derivative spectroscopy and that to eliminate spectral interference with orphenadrine citrate. Beers law is obeyed in the concentration ranges 4.61-80.76 µg/mL and 0.75-30 µg/mL for orphenadrine citrate and paracetamol, respectively. The molar absorptivity, limit of detection, limit of quantification, Sandell sensitivity and linearity are also calculated. The average per cent recovery was found to be 99.90 ± 0.14 % for paracetamol and 99.80 ± 0.05 % for orphenadrine citrate.

Two UV-visible methods are described, method A to determine paracetamol and caffeine in tablet formulations by spectroscopic derivative. Paracetamol was determined after solving it in sodium hydroxide by taking the first order derivative spectroscopy at 314 nm and caffeine was determined after solving it in bidistilled water by taking the second order derivative spectroscopy at 280 nm. Beers law is obeyed in the concentration ranges 0.78-31.07 µg/mL and 1.51-30.23 µg/mL for caffeine and paracetamol, respectively. Method B to determine paracetamol in tablet and oral formulations. This method is based on the reduction of Fe 3+ to Fe 2+ by paracetamol, the resulting Fe 2+ reacts with 1,10-phenanthroline to give a soluble orange-red complex in acetic acid medium. The maximal absorption is at the wavelength 510 nm. The complete reaction was achieved during heating time 25 min at 45 °C. Beers law is obeyed in the concentration range 1.21-7.56 µg/mL. The limit of detection, limit of quantification and linearity are calculated for both methods.

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