New plastic membrane ion‐selective electrode for determination of trimethoprim

Trimethoprimium‐phosphomolybdata, (TM) 3 PM, 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.