Construction of Different Types of Ion-Selective Electrodes. Characteristic Performances and Validation for Direct Potentiometric Determination of Orphenadrine Citrate.

Three types of ion-selective electrodes (carbon paste, PVC membrane and screen printed electrodes) have been proposed for determining orphenadrine citrate (OphC) in pure solution and pharmaceutical preparation based on the ion-pair formation between OphC with sodium tetraphenylborate. The three types of electrodes were prepared using five types of plasticizers with each type of electrodes. The electrodes showed a linear response with a good Nernstian slope of 57.20 ± 0.70, 56.81 ± 1.6 and 57.09 ± 0.2 mV decade-1 over the concentration range 10-6 to 10-2 mol L-1 with CPE, PVC membrane and SPEs, respectively. The standard electrode potentials, E°, were determined at 10, 20, 30, 40 and 50 °C and used to calculate the isothermal coefficient (dE°/dT) of the electrodes. Temperatures higher than 60 °C affect the electrodes performance. The electrodes proved highly selective with selectivity coefficients ranging from 1.063-5.573, 1.323-6.798 and 1.073-6.504 for CPE, PVC membrane and SPE, respectively. The detection limits (signal/noise [S/N] = 3) were 1.016×10-6, 0.984×10-6 and 0.992×10-6 mol L-1 for CPE, PVC membrane and SPE, respectively. The practical applications of these electrodes were demonstrated by measuring the concentrations of OphC in pure solutions and pharmaceutical preparations with satisfactory results. The reliability and stability of the electrodes gave a good possibility for applying the technique to routine analysis.