A comparison between high-temperature catalytic oxidation and persulphate oxidation for the determination of total nitrogen in freshwater

摘要

Total nitrogen (TN) in freshwater samples (lakes, rivers, and atmospheric deposition) has been routinely analysed at the laboratory of the CNR Institute of Ecosystem Study in Italy by persulphate oxidation (PO) with UV determination of nitrate at 220 nm since the 1980s. In 2004, high-temperature catalytic oxidation (HTCO) with a chemiluminescence detector (CLD) began to be used for TN analysis. A mixed catalyst of cobalt-chromium and cerium oxide was selected, as this gave the best recoveries for ammonium and organic N. To assess the comparability of the new method with the reference one, almost 800 samples were analysed for TN using both methods. The average difference between paired data was low, as both absolute and relative values (0.06mgNL~(-1) and 3%, respectively, in the range of 0.1- 7.0mgNL~(-1) ). The results of our study confirmed HTCO as a reliable method for TN determination in freshwater samples. Compared with PO, HTCO proved to be faster and required less sample handling. From the point of view of linearity and repeatability, the HTCO results were comparable with those with PO UV 220. The LOD of HTCO calculated in this study was lower than that of PO UV 220 (0.04 with respect to 0.09 mg NL~(-1)).