Simultaneous determination of dissolved organic nitrogen, nitrite, nitrate and ammonia using size exclusion chromatography coupled with nitrogen detector

• Published in: Journal of environmental sciences (China) Vol. 125; pp. 309 - 318
• Main Authors: Ji, Wen-Xiang, Tian, Ye-Chao, Cai, Min-Hui, Jiang, Bi-Cun, Cheng, Shi, Li, Yan, Zhou, Qing, Li, Bo-Qiang, Chen, Bai-Yang, Zheng, Xing, Li, Wen-Tao, Li, Ai-Min
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2023
• Subjects: Ammonia; China; dissolved inorganic nitrogen; Dissolved organic nitrogen; gel chromatography; groundwater; lakes; landfill leachates; Nitrate; nitrates; Nitrite; nitrites; Nitrogen detector; oxidation; river water; Size exclusion chromatography; wastewater; China; Size exclusion chromatography; Ammonia; Nitrate; Nitrite; Nitrogen detector; Dissolved organic nitrogen
• ISSN: 1001-0742; 1878-7320
• DOI: 10.1016/j.jes.2021.11.026

•An independent VUV oxidation device was developed to set up the SEC-OND system.•The dissolved O2 in mobile phase limited the capacity of VUV oxidation device.•SEC-OND can accurately quantify DON in water sample with DIN/TDN ratio up to 0.98.•SEC-OND can determine TDN, DON, NH+ 4-N, NO- 2-N, and NO- 3-N with one injection. Accurate quantification of dissolved organic nitrogen (DON) has been a challenge due to the cumulative analytical errors in the conventional method via subtracting dissolved inorganic nitrogen species (DIN) from total dissolved nitrogen (TDN). Size exclusion chromatography coupled with an organic nitrogen detector (SEC-OND) has been developed as a direct method for quantification and characterization of DON. However, the applications of SEC-OND method still subject to poor separations between DON and DIN species and unsatisfied N recoveries of macromolecules. In this study, we packed a series of SEC columns with different lengths and resin materials for separation of different N species and designed an independent vacuum ultraviolet (VUV) oxidation device for complete oxidation converting N species to nitrate. To guarantee sufficient N recoveries, the operation conditions were optimized as oxidation time ≥ 30 min, injection mass (sample concentration × injection volume) < 1000 µL × mg-N/L for macromolecular proteins, and neutral pH mobile eluent. The dissolved O2 concentration in SEC mobile phase determined the upper limit of VUV oxidation at a specific oxidation time. Compared to conventional HW50S column (20 × 250 mm), HW40S column (20 × 350 mm) with mobile phase comprising of 1.5 g/L Na2HPO4·2H2O + 2.5 g/L KH2PO4 (pH = 6.85) could achieve a better separation of DON, nitrite, nitrate, and ammonia. When applied to river water, lake water, wastewater effluent, groundwater, and landfill leachate, the SEC-OND method could quantify DON as well as DIN species accurately and conveniently even the DIN/TDN ratio reached 0.98. [Display omitted] .