Anion-selective light-addressable potentiometric sensors (LAPS) for the determination of nitrate and sulphate ions

The technology of fabrication of anion-selective light-addressable potentiometric sensors (LAPS) by using a solid-state microelectronic device integrated with an ion-recognition membrane has been elaborated. The nitrate sensor with ion-exchange membrane exhibits a linear response interval of 3×10−5 to 1×10−1 mol/l NO3− with an ionic sensitivity of 58±2 mV/pNO3. The detection limit was found to be 1×10−5 mol/l of nitrate ions and the working pH interval of the sensor is 2.0–11 for 10−2 mol/l NO3−. The sensor has a high selectivity for nitrate over chloride, sulphate, hydrogen phosphate and acetate ions with selectivity coefficients, KNO3/X, of 7×10−3, 1×10−3, 2×10−4 and 5×10−3, respectively, and a response time of about 1 min. The SO4-LAPS with polymeric membrane containing neutral sulphate ionophore demonstrates a sensitivity of 26±1 mV/pSO4 in a concentration range of 3×10−6 to 1×10−2 mol/l with a reasonable selectivity over chloride, hydrogen carbonate and hydrogen phosphate ions. Selectivity coefficients, KSO4/X, were found to be 0.6, 0.15 and 0.03, respectively.