Potentiometry:
A nitrate ion-selective electrode Orion 93-07 was used to check the analytical signal. The electrode potential was measured by an Orion pH/mVmeter 407 A to 1 mV. For calibration standard solutions of 10 -1 to 10-4M sodium nitrate were used. As a known addition reagent 10- 2 M sodium nitrate solution was used. For direct potentiometry a standard graph was used. The one-step known addition was performed .Six known addition (0.10, 0.15, 0.20, 0.25 and 0.30 ml of 10 .2 M sodium nitrate) were added to 10 ml of the sample and after each addition the electrode potential was checked and recorded. It is worth mentioning that the analysis was performed with constant stirring .
Determination of nitrate in waters, with sequential detection by potentiometric sensors, is done. The equipment used consisted of a potentiometer ( a potential measuring device), a reference electrode and an indicator electrode ( a nitrate ion selective electrode).The half cell potential of the reference electrode is a known constant and this electrode is completely insensitive to the composition of the solution under study. A series of standards
containing 10 – 100 micro grams per litre of nitrate are prepared.