Modified Gran’s Plot Method for Calibrationless Potentiometric Nitrate Determination

This article demonstrates a new approach of multiple additions direct potentiometric determination of nitrate ion in natural and potable freshwater. The main feature of this approach is no need to pre-calibrate the electrode and to use the slope in the calculations. The experimental procedure is very similar to one of classic potentiometric titration. To test and illustrate the approach, ion-selective electrodes with tridodecylmethylammonium nitrate as ion-exchanger in plasticized membrane were produced. The application of the proposed mathematical algorithm for processing of data obtained by the method of multiple standard additions simplifies and speeds up the analysis by reducing the number of required manipulations, while maintaining high accuracy of analysis. The work of the method and calculation algorithm were tested on real samples of natural river water taken from the rivers Saone and Rhone (Lyon, France); possibility of nitrate determination in low mineralized natural waters at the level of 10 mg L-1 corresponding to 1/5 of maximum allowable concentration was shown.