Department of Mechanical and Industrial Engineering, University of Toronto, 5 King's College Park, Toronto, ON M5S 3G8, Canada.
Department of Mechanical Engineering, McGill University, 817 Sherbrooke Street West, Montreal QC H3A 0C3, Canada.
Water Res. 2021 Sep 1;202:117410. doi: 10.1016/j.watres.2021.117410. Epub 2021 Jul 5.
Excessive total nitrogen (TN) in the aqueous environment causes a notable negative impact on agriculture, human health, and the economy on a global scale. Conventional analytical techniques for determining TN in water usually involve long and tedious procedures with extensive sample preparation for digestion and titration. In recent years, lab-on-a-chip platforms have enabled in-situ measurements of water pollutants such as nitrate, nitrite, and ammonium. However, the digestion of organic nitrogen compounds in aqueous solutions still remains to be a challenge for portable analytical systems. In this paper, a portable TN analytical system is developed for on-site measurement of TN in a short assay time. It contains a TN reaction chamber for nitrogen digestion and reduction, and an optical measurement chamber for colorimetric determination of total nitrite. The ultraviolet-C (UVC)-thermal digestion method and the United States Environmental Protection Agency (EPA)-standard nitrate-nitrite determination method are implemented on the TN analytical system. Thorough investigations are performed to explore the optimum reaction conditions and reagent volumes in the process of TN oxidation, nitrate reduction, and nitrite detection, including oxidation time, temperature and substrate, oxidizer concentrations, nitrate reduction time, nitrite colorimetric reaction time, and reagents stability over time. Our system can complete fast oxidation and colorimetric determination of TN within 36 min, with a measurement range of 1 μg/L to 10 g/L and a limit of detection of 1.2 mg/L (lower than the World Health Organization standard of 10 mg/L). This portable TN analytical system enables the digestion and measurement of TN in a quick, portable, and low-cost manner.
水环境中过量的总氮（TN）对农业、人类健康和全球经济造成显著负面影响。传统的水中 TN 测定分析技术通常需要经过冗长繁琐的程序，需要对样品进行大量的消解和滴定前处理。近年来，微流控芯片平台已经实现了对水中硝酸盐、亚硝酸盐和氨等污染物的原位测量。然而，对水溶液中有机氮化合物的消解仍然是便携式分析系统面临的挑战。本文开发了一种便携式 TN 分析系统，用于在短时间内现场测量 TN。它包含一个 TN 反应室，用于氮的消解和还原，以及一个光学测量室，用于比色法测定总亚硝酸盐。该 TN 分析系统采用了紫外线-C（UVC）-热消解法和美国环保署（EPA）标准的硝酸盐-亚硝酸盐测定方法。本文对 TN 氧化、硝酸盐还原和亚硝酸盐检测过程中的最佳反应条件和试剂体积进行了深入研究，包括氧化时间、温度和底物、氧化剂浓度、硝酸盐还原时间、亚硝酸盐比色反应时间以及试剂随时间的稳定性。我们的系统可以在 36 分钟内完成 TN 的快速氧化和比色测定，测量范围为 1μg/L 至 10g/L，检测限为 1.2mg/L（低于世界卫生组织规定的 10mg/L）。该便携式 TN 分析系统能够快速、便携、低成本地实现 TN 的消解和测量。
