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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, Eo, were determined at different temperatures and used to calculate the isothermal temperature coefficient (dEo/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. [ABSTRACT FROM AUTHOR]

The detection limit of tramadol hydrochloride was effectively improved by proper selection of a plasticizer and ion exchanger. Two plastic membrane electrodes for the determination of tramadol hydrochloride (TDCl) were fabricated and fully characterized in terms of composition, life span, usable pH range and working concentration range. The membranes of these electrodes consist of an ion-exchanger such as tramadolium-silicotungstate (TD-ST), silicomolybdate (TD-SM), dispersed in PVC matrix with different plasticizers, namely 2-nitrophenyl octyl ether (2-NPOE), dioctyl phthalate (DOP), dibutyl phthalate (DBP), tris(2-ethylhexyl) phosphate (TEPh), dioctyl sebacate (DOS), tributyl phosphate (TBPh) and dibutyl butyl phosphonate (DBBPh). Experiments showed that DBP was the best plasticizer and TD-PT The best ion pair for their combination produced the lowest detection limit. The present electrodes show clear discrimination of tramadol hydrochloride from several inorganic, organic ions, sugars and some common drug excipients. The sensors were applied for determination of tramadol hydrochloride in urine, milk and pharmaceutical preparations 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. [ABSTRACT FROM AUTHOR]