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A novel duloxetine ion-selective poly(vinyl chloride) membrane electrode based on the ion-pair complex of duloxetine with phosphomolybdic acid was prepared with diocyl phthalate as a plasticizer. The electrode exhibits a linear response with a slope of 56.9 mV decade :1 of duloxetine concentration at 25 AE 0.1 C for the optimum electrode prepared with a membrane consisting of 10.0% ion pairs. The electrode response was not sensitive to pH changes from 4.30-8.35 and was not affected by possible interfering species such as common inorganic cations, sugars and amino acids. It has a relatively fast response time less than (15 s) and the lifetime was about 2 months during which it could be used without any measurable divergence. The electrode was successfully used for the potentiometric determination of duloxetine hydrochloride both in pure solutions and in pharmaceutical preparations.

Aim: To study complex formation equilibria between [Pd(V)(H2O)2]2+ and sulphur containing amino acids (L). The concentration distribution relations of the various complex species will be evaluated. Materials and Methods: [Pd(FLX)Cl2] was prepared by heating PdCl2 (0.89 g, 5 mmole) in 100 mL water and KCl (0.75 g, 10 mmole) to 100.0°C for 30.0 min. After the precipitate was filtered off, it was washed sequentially with water, ethanol and diethyl ether. [Pd(V)Cl2] was converted into the diaqua form treating with two equivalents of AgNO3 overnight, and removing the AgCl precipitate by filtration through a 0.1 µm pore membrane filter. Results and Discussion: The acid-based equilibria of [Pd(V)(H2O)2]2+ have been characterized by fitting their potentiometric titration data to various acid-base models. The pKa1 and pK a2 values for [Pd(V) (H2O)2]2+are 4.01 and 8.15, respectively, methionine was found to form a less stable complex than S-methyl cysteine, plausibly due to the fact that the six-membered chelate ring in the former complex is energetically less favoured than the five membered ring in the latter complex. Penicillamine has three binding sites, carboxylic, amino and sulfhydryl groups. It forms the complexes 110 and 111. Conclusion: Study indicates that sulphur containing amino acids easily react with Pd(II) because of the great tendency of sulphur (a soft Lewis base) to form bonds with these metals (soft Lewis acids).

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