Codeine, which is generally used as phosphate form in pharmaceutical preparations, is often administrated orally with aspirin or paracetamol as an effective analgesic agent or with cough syrups as an antitussive agent in pharmaceutical preparations [1]. The molecular structure of codeine phosphate with general formula of C18H24NO7P was given by Gulland et al. [2]. It is a derivative of morphine and belongs to the poppy alkaloid group of opiates which can produce euphoria. Codeine is qualified as a drug abuse, while is used as a local anesthetic in many pharmaceutical preparations [3]. In the present research, a novel codeine selective PVC membrane electrode based on ion pair is developed for determination of codeine in pharmaceuticals. The effect of the ISE membrane composition on the characteristics of the codeine electrode has been investigated. The plasticizers used were 2-nitrophenyl octyl ether (2-NPOE), dioctyl phtalate (DOP) and dibutyl phtalate (DBP) and the ion pair complex was codeiniumtetraphenylborate (TPB-CO). Constructed electrode at the optimized composition showed a near Nernstian slope of characteristic (54.8 mV decade-1) in the measurement range (10-5 - 10-2 mol L-1) and a limit of detection of 5.0 Ï 10-6 mol L-1. The electrodes were fully characterized in terms of composition, response time, usable pH range and working concentration range. The electrodes were applied for the determination of codeine in tablets by the standard addition method. The results obtained were satisfactory with excellent percentage recovery.

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