Determination of pethidine hydrochloride using potentiometric coated graphite and carbon paste electrodes

A new approach for lowering the detection limit of a pethidine ion‐selective electrode is presented. A coated graphite (CGE) and carbon paste (CPE) electrodes for pethidine ions based on pethidine‐phosphotungstate (PD‐PT) as ion‐pair complex are described. The sensors exhibit a Nernstian slope of 58.1 and 54.2 mVdecade^?1 for pethidine ion over a wide concentration range from 2.6 × 10^?7 to 1.0 × 10^?2 M and 2.1 × 10^?6 to 1.0 × 10^?2 M with a detection limit of 1.8 × 10^?7 M and 7.3 × 10^?7 M for pethidine coated graphite (PD‐CGE) and pethidine carbon paste electrode (PD‐CPE), respectively. These sensors exhibited a fast response time (about 5–8 s) and good stability. The standard electrode potentials, E^o, were determined at different temperatures and used to calculate the isothermal temperature coefficient (dE^o/dT) of the PD‐CGE and PD‐CPE, which was 0.0062 and 0.0071 V/ °C, respectively. Selectivity coefficients, determined by matched potential method (MPM) and separate solution method (SSM), showed high selectivity for pethidine hydrochloride (PDCl) over a large number of inorganic cations, organic cations, sugars, urine components, and some common drug excipients. The sensors were applied for determination of PDCl in ampoule and in spiked urine samples using potentiometric determination, standard addition and the calibration curve methods. The results obtained were satisfactory with excellent percentage recovery comparable and sometimes better than those obtained by other routine methods for the assay. Copyright © 2011 John Wiley & Sons, Ltd.