Potentiometric determination of diazepam, bromazepam and clonazepam using solid contact ion-selective electrodes

Newly developed solid contact ion-selective electrodes (SC-ISE) have been proposed for determining diazepam, bromazepam and clonazepam 1, 4-benzodiazepines in pure forms and in pharmaceutical preparations. The electrodes are based on polyvinylchloride (PVC) membranes doped with drug-tetraphenyl borate (TPB) or drug-phosphotungestic acid (PTA) ion pair complexes as electroactive materials. The new electrodes proved highly selective with selectivity coefficients ranging from 10^-4 to 10 ^-6 and detection limits ranging from 0.1 to 0.63μg/ml. Successful application of developed electrodes for drugs determinations in pharmaceutical preparations was obtained. Calibration graphs were linear over the ranges of 0.29-71.20, 0.79-31.62 and 0.32-31.57μg/ml for diazepam, bromazepam and clonazepam, respectively with slopes of 50-65mV per decade in the optimum pH range of 4-7. Relative average errors ≤1.72% and relative standard deviations ≤1.13% were obtained. Statistical student's t-test and F-test showed insignificant systematic error between measured and real values and also between developed ion-selective electrodes methods and a standard HPLC method.