SIMULTANEOUS DETERMINATION OF PARACETAMOL AND CODEINE BY FIRST-ORDER DERIVATIVE SPECTROPHOTOMETRY

A simple first derivative spectrophotometric method has been developed for the simultaneous determination of paracetamol and codeine in phar maceutical formulations. Dimethylformamide was used as solvent for ext racting the drugs from the formulations and subsequently the samples w ere evaluated directly by first order derivative spectrophotometry. Si multaneous determination of the both drugs can be carried out using th e graphical and zero-crossing methods for paracetamol and codeine, res pectively. The method does not require simultaneous equations to be so lved as it is commonly necessary in zero-order spectrophotometry. The calibration graphs were linear between the ranges 4.3 . 10(-5) M to 1. 0 . 10(-3) M for codeine and 6.1 . 10(-5) M to 1.6 . 10(-3) M for para cetamol. The simultaneous determination is reliable only when the mola r ratio of paracetamol to codeine is lower than 4/1. Commonly the phar maceutical formulations contain both drugs in a mass ratio between 5/1 to 33/1, therefore a previous enrichment of the samples were carried out with pure codeine in order to reach the above mentioned ratio. The ingredients commonly found in commercial pharmaceutical formulations do not interfere, hence the proposed method can be applied to the dete rmination of these drugs in tablets.