Development of membrane electrodes for selective determination of some antiepileptic drugs in pharmaceuticals, plasma and urine.

Newly developed, simple, low-cost and sensitive ion-selective electrodes have been proposed for determination of some antiepileptic drugs such as lamotrigine, felbamate, and primidone in their pharmaceutical preparations as well as in biological fluids. The electrodes are based on poly(vinyl chloride) membranes doped with drug-tetraphenyl borate (TPB) or drug-phosphotungstic acid (PT) ion-pair complexes as molecular recognition materials. The novel electrodes displayed rapid Nernstian responses with detection limits of approximately 10(-7) M. Calibration graphs were linear over the ranges 5.2 x 10(-7)-1.0 x 10(-3), 1.5 x 10(-6)-1.0 x 10(-3), and 2.6 x 10(-7)-1.0 x 10(-3 )M for drug-TPB and 5.8 x 10(-7)-1.0 x 10(-3), 1.8 x 10(-7)-1.0 x 10(-3), and 6.6 x 10(-7)-1.0 x 10(-3) M for drug-PT electrodes, respectively, with slopes ranging from 52.3 to 62.3 mV/decade. The membranes developed have potential stability for up to 1 month and proved to be highly selective for the drugs investigated over other ions and excipients. The results show that the selectivity of the ion-selective electrodes is influenced significantly by the plasticizer. The proposed electrodes were successfully applied in the determination of these drugs in pharmaceutical preparations in four batches of different expiry dates. Statistical Student's t test and F test showed insignificant systematic error between the ion-selective electrode methods developed and a standard method. Comparison of the results obtained using the proposed electrodes with those found using a reference method showed that the ion-selective electrode technique is sensitive, reliable, and can be used with very good accuracy and high percentage recovery without pretreatment procedures of the samples to minimize interfering matrix effects.