Nitrate-selective electrodes containing an amino acid betaine as sensor

A novel type of nitrate-selective electrode is reported in which the sensor is glycine betaine hydrochloride. A membrane, hot-pressed from a mixture of glycine betaine hydrochloride (sensor 5% mim), dicumyl peroxide (initiator, 7.5% mim), 2-nitrophenyloctyl ether (mediator, 41.5% m/m) and the acrylonitrile polymer Krynac (50.75) (46% m/m), gave a Nernstian response to nitrate from 0.1 to 1 x 10-(5) mol dm(-3) with a selectivity coefficient, k(NO3-)(pot),(Cl-), of 9 x 10(-4) for 0.1 mol dm(-3) chloride, The figures of merit and the limit of detection, 1 x 10(-5) mol dm(-3), were comparable to those for an established commercial electrode, Glycine betaine also functioned well as the sensor, provided that the membrane was treated with 5 mol dm(-3) hydrochloric acid for 24 h, Possible correlations between nitrate selectivity and the role of betaines in marine plants are suggested.