Comparison of conventional water testing methods with ion-selective electrodes technique for NO3-, Cl-, Ca2+, K+, and Na+

The development of strategies to improve the efficiency of nutrient uptake by crops and to minimise leaching to surface and drainage water needs to be considered at various scales: catchment, field, soil and crop type. Theref ore, methodological approaches for routine sample preparation and analysis are crucial to agricultural and environmental policies aimed at reducing nu trient losses. While the official way of analysing water is time consuming and requires a laboratory with standard equipment, the ion-selective electr odes (ISE) technique presents a method with the advantages of precision, sp eed and portability. Analysis of water by ISE has become an accepted practi ce for the detection of certain elements and this technique could replace s tandard testing currently being used. Accuracy and reproducibility of NO3-, Cl-, Ca+2, K+ and Na+ ion-selective electrodes were achieved by comparison with standard methods. The apparatus used consists of a sensor unit, which contains multielement ISE's, and a measurement unit for operational and da ta storage functions. Samples of water, obtained from runoff and drainage o f agricultural catchments, ground water, were selected from different locat ions to represent a wide range of ion concentrations. Using the ISE measure ments values varied from 0.42 to 83.5 (mg L-1) for NO3-, 3.89 to 241 for Cl -, 1.3 to 76.4 for Ca2+, 0.12 to 131 for K+ and 0.63 to 59 for Na+. The inv estigation confirms the good correlation between standard and ISE methods f or almost all ions with correlation coefficients of 0.97 for NO3-, 0.99 for Cl-, 0.96 for Ca2+, 0.98 for K+. Only Na+ coefficient is below 0.9. Variat ions in the slope and intercept of the regression equations were slight or small for NO3- and Ca2+, and larger for Cl-, K+ and Na+.