Abstract. Sensitive and fast-responding potentiometric sensors are described for the determination of warfarin and ibuprofen. They consist of PVC matrix membranes containing the drug-ferroin ion-association complexes as electroactive materials and dioctylphthalate as a solvent mediator. Linear dynamic response range between 1 x 10 -2 and 2 x 10-SM with Nernstian slopes of 59-60mV/decade concentration and a detection limit of 0.8-1.3 gg/ml are obtained. A wide range of organic anions and drug excipients do not interfere. Titration of the drugs with a standard ferroin solution using either a drug-ferroin or ferroin-TPB PVC sensor in conjunction with an Ag-AgC1 reference electrode displays S-shaped titration curves with sharp potential breaks at stoichiometric 1:2 (ferroin:drug) reaction. Differential titration curves with well-defined peaks at the equivalence points are obtained using drug-ferroirdferroin-TPB PVC membrane sensors. Direct potentiometry and potentiotitrimetry of warfarin and ibuprofen in various pharmaceutical preparations are presented and compared. Several advantages over the pharmacopoeial methods and other techniques in current use are offered by the proposed technique. [21]. Many of these methods, however, involve several manipulation, extraction and derivatization steps [6,[18][19][20][21], suffer from lack of sensitivity [3,4,20], and require sophisticated instrumentation [5][6][7][11][12][13][14][15][16]. The advantages offered by capillary electrophoresis and HPLC techniques are the detection of enantiomers and metabolites of the drugs. The recent amendment of U. S. P described an HPLC method for the assay of warfarin and ibuprofen [22].Although potentiometric sensors have found many applications in pharmaceutical analysis [23][24][25], no such sensors are available for quantification of warfarin and ibuprofen in drug formulations. The only biosensor available for determining warfarin was based on immobilization of a thick suspension of Nocardia corallina as a biocatalyst on a treated vitreous carbon rod and the corresponding alcohol
A novel plastic membrane ion-selective electrode for determining the diclofenac anion is described. The sensing membrane of the electrode consists of diclofenac-nickel(rr) bathophenanthroline as an ion-exchanger site in a poly(viny1 chloride) matrix plasticized with o-nitrophenyl phenyl ether. In borate buffer solutions of pH 8-12, the electrode exhibits a fast, stable and linear response for 1 X 10-t5 X 10-5 mol dm-3 diclofenac with an anionic slope of 55.1 k 0.2 mV decade-' at 25 OC. Potentiometric selectivity measurements revealed negligible interferences from 14 different anions including aromatic and aliphatic carboxylic acid salts. The electrode displays useful analytical characteristics for the direct determination of diclofenac in various pharmaceutical preparations. Results with an average recovery of 98 +, 0.6% of the nominal value were obtained.
Novel miniaturized carboxylated poly(vinyl chloride) and poly¯uoro sulfonate (Na®on) matrix membrane sensors in an all-solid state graphite support were developed, electrochemically evaluated and used for the assay of verapamil drug. These sensors incorporate the native polymers without plasticizer and/or drug-ion pair complex. Upon soaking these sensors in verapamil test solution, electroactive self regenerated membranes are formed and a near-Nernstian potentiometric response is induced for verapamil over the concentration range 1Â10 À2 ±1Â10 À5 M with a cationic slope of 56±57 mV decade À1 of concentration. Inherent advantages of these sensors include fast response (< 10 s), long life time (> 6 months), good thermal stability (up to 60 C), high sensitivity (down to 1 mg ml À1 ), extended working pH range (2±8) and reasonable selectivity. Verapamil could be determined in various dosage forms with an average recovery of 98.8% (st.dev. 0.8%) of the nominal concentration without any signi®cant interferences from various excipients and diluents commonly used in drug formulations.
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