Paracetamol estimation: a new approach to reducing salicylate interference.

It is now well established that although acetylsalicylate does not interfere with the commonly used nitration method for measuring paracetamol, salicylate does interfere. Several methods have been used to remove this interference, by solvent extraction, or to make allowance for the interference, for example, by arithmetical correction. We describe a new approach to the problem by modifying the reaction conditions in an attempt to find the optimum conditions for the nitration of paracetamol while at the same time minimising salicylate interference. A method is proposed in which the concentration of nitrite is reduced and a time delay is introduced after the addition of sulphamic acid. This method is shown to be accurate, precise, and linear and exhibits minimal interference from salicylate.