Trimethoprimium‐phosphomolybdata, (TM)3PM, was used as an ion‐exchanger in the construction of a TM‐responsive plastic membrane electrode. The calibration graph slope of the electrode is 56·5 mV per TM concentration decade when preconditioned by soaking in water, over a concentration range of 2·3 × 10−6–10−2 M with instantaneous response. The electrode has a life span of 24 h when soaked in 10−3 M TM solution and 5 days when soaked in distilled water. The working pH and temperature ranges of the electrode are 1·6–6·2 and 30–65·C, respectively. The isothermal coefficient of the electrode is 0·00091 V·C−1. The electrode is highly selective for TM towards inorganic cations, sugars and amino acids. It can be employed as a potentiometric sensor for determination of TM in pure solution and in tables.
A new coated-wire electrode based on PVC membrane plasticized with dioctyl phthalate (DOP) and containing the diltiazem-tetraiodido bismuthate (III) ion association coated on a silver wire was constructed and used for potentiometric determination of diltiazem hydrochloride. The electrode performance was characterized and optimized according to the following experimental criteria: membrane composition, soaking time, working pH range, and response time. The interference caused by different species was investigated as well. The best membrane composition was found to be 49.75% of PVC and DOP, 0.5% ion pair. This sensor showed a linear response with a good Nernstian slope of 57.60±1.38 mV/decade over the concentration range5.0×10-5 – 2.50×10-2 M, the detection limit was 2.88×10-5 M, and it was usable within a wide pH range of 2.5–8.0. The electrode showed a fast response time (18 sec), with a relative long lifetime (2.4 months, 2 h a day). The isothermal coefficient (dE°/dT) of the electrode was calculated and found to be 5.36×10-4 V/℃ within 20 – 80℃, which exhibits a good thermal stability. The coted-wire electrode was successfully applied for the potentiometric determination of diltiazem hydrochloride both in pure form and pharmaceutical preparations. The dissolution test of the drug was carried out as well.
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