Publication Date:
2012-06-14
Description:
Research on dissolved organic nitrogen (DON) in aquatic systems with high dissolved inorganic nitrogen (DIN, the sum of NO3−, NO2− and NH4+) concentrations is often hampered by high uncertainties of the determined DON concentration. The reason is that DON is determined indirectly as the difference between total dissolved nitrogen (TDN) and DIN. In this standard approach to determine DON concentrations, even small relative measurement errors of the DIN and TDN concentrations propagate into high absolute errors of DON concentrations at high DIN:TDN ratios. To improve the DON measurement accuracy at high DIN:TDN ratios, we investigated the DON measurement accuracy of this standard approach in dependence of DIN:TDN ratio and compared it to the direct measurement of DON by size-exclusion chromatography (SEC). For this, we used standard compounds and natural samples with and without DIN enrichment. We show that for the standard approach, large errors of the determined DON concentrations at DIN:TDN ratios 〉0.6 occur for both standard compounds and natural samples. In contrast, measurements of DON by SEC always resulted in low errors at high DIN:TDN ratios due to the successful separation of DON from DIN. For SEC, DON recovery rates were 90.7–107.9% for five pure standard compounds and 89–103% for two standard compounds, enriched with DIN. Moreover, SEC resulted in 93–101% recovery rates for DON concentrations of natural samples at a DIN:TDN ratio of 0.8. With 2.5 h of measurement time per sample, SEC is a moderately fast and accurate alternative to the standard approach for the determination of DON concentrations in freshwaters with DIN:TDN ratios 〉0.6. The direct DON measurement by SEC will enable the scientific community to gather accurate information on DON concentrations, especially in anthropogenically disturbed systems with high DIN concentrations.
Print ISSN:
1810-6277
Electronic ISSN:
1810-6285
Topics:
Biology
,
Geosciences
Permalink