Methyl nitrate as a byproduct in advanced water treatment systems: Liquid chromatographic determination method and cause of formation

• Published in: Chemosphere (Oxford) 2023-12, Vol.344, p.140308-140308, Article 140308
• Main Authors: Kodamatani, Hitoshi, Sugihara, Kenta, Mezyk, Stephen P., Ishida, Kenneth P., Roback, Shannon L., Plumlee, Megan H.
• Format: Article
• Language: English
• Subjects: Advanced oxidation process; Chemiluminescence; Determination method; Liquid chromatography; Methyl nitrate; Photochemical reaction; Treatment byproduct
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2023.140308

Neutral low-molecular-weight organics such as methyl nitrate that can readily pass through reverse osmosis (RO) membranes employed in potable water reuse facilities attract interest owing to public health considerations. In this study, a novel determination method based on high-performance liquid chromatography, online photochemical conversion to peroxynitrite, and luminol chemiluminescence detection was developed for methyl nitrate measurement in treated water. The maximum photochemical conversion efficiency of methyl nitrate to peroxynitrite was found to be 6.5% using a 222-nm excimer lamp. The calibration curve for the developed method was linear between 1.0 × 10−9 and 1.0 × 10−7 M, and the limit of detection was 0.3 nM (0.03 μg/L) given an injection volume of 200 μL. The methyl nitrate concentrations in RO permeate from reclaimed wastewater and product water after subsequent treatment by a UV/H2O2 advanced oxidation process (AOP) were 2.2 and 22.5 nM (0.17 and 1.7 μg/L), respectively. UV irradiation of RO permeate in the laboratory using a low-pressure Hg lamp confirmed the formation of methyl nitrate in the permeate in the absence of H2O2 and residual chloramines. This chemiluminescent detection method for methyl nitrate will promote a greater understanding of the origin and formation of this treatment byproduct in reclaimed wastewater. [Display omitted] •A sensitive HPLC system was developed for the analysis of methyl nitrate.•Methylnitrate was converted to peroxynitrite through online 222-nm UV irradiation.•The method detection limit for methyl nitrate by the proposed system was 0.3 nM.•Methyl nitrate was detected in treated waters at nanomolar concentrations.•Methyl nitrate is generated through UV-based advanced oxidation process.