To protect public health, analyzing drinking water for contaminants such as inorganic anions, cations, heavy metals, organic pollutants, and nutrients is an essential requirement. Within the range of contaminants, measuring nitrate levels — specifically — is important because, after ingestion, nitrate is reduced to nitrite, which disrupts the blood’s ability to carry oxygen, resulting in methemoglobinemia. Methemoglobinemia is especially serious for infants under the age of six months.1
The U.S. Environmental Protection Agency (EPA) sets the maximum contaminant level (MCL) for nitrate at 10 mg/L. Accurate determination of nitrate concentrations in drinking water requires measurement of the sum of nitrate + nitrite, referred to as total oxidized nitrogen (TON).
Traditional methods based on cadmium reduction columns reduce nitrate to nitrite, followed by quantitation of nitrite via the Griess reaction. However, these methods have several limitations:
- Frequent column replacement – Cadmium is a carcinogenic heavy metal, and the column used in these methods must be replaced every few measurements to reduce the risk of harmful exposure.
- Exposure to hazardous chemicals, plus high cost of disposal – Column regeneration requires handling additional hazardous chemicals and produces waste that must be carefully disposed of at a significant cost.
Time-consuming manual steps – These processes, as well as downstream analyses using flow injection or colorimetric analyzers, involve time-consuming manual steps that are potential sources of measurement inaccuracies.
These challenges have triggered the need to develop a different way of doing the analysis.
A step forward: an alternative to the nontoxic enzymatic method
In 2016, the EPA approved the alternative nontoxic enzymatic nitrate + nitrite in drinking water method, developed by NECI and published in the U.S. Code of Federal Regulations. Not only is the method less hazardous compared to many other nitrate methods, but it can also be performed using Thermo Scientific™ discrete analyzer technology. The enzymatic method uses nitrate reductase to catalyze the reduction of nitrate to nitrite via NADH (reduced nicotinamide dinucleotide) to drive conversion. The resulting nitrite then reacts with the Griess reagents, producing an intensely colored compound that can be quantified using a photometer at wavelength 540 nm ±20 nm.
The Thermo Scientific Gallery™ and Gallery™ Plus Aqua Master discrete analyzers support the National Environmental Laboratories Accreditation Conference (NELAC) and EPA-approved enzymatic reduction methods for safer TON measurements.
Even better: Further advancements bring more environmental friendliness
The Thermo Scientific Drinking Water Method: Drinking Water Total Oxidized Nitrogen for Thermo Scientific Gallery Discrete Analyzer details an equivalent method for testing drinking water for nitrate + nitrite in a nonhazardous and environmentally friendly way. The method is applicable to the Thermo Scientific Gallery or Gallery Plus Aqua Master discrete analyzer in combination with ready-to-go test procedures and the required enzyme kit (Part# 984187 TON (enz)).
The 40 CFR Part 141 compliant method makes it possible to monitor hazardous nitrate levels in compliance with the Safe Drinking Water Act (SDWA) regulations while accessing the benefits of discrete analyzer technology. In addition to providing a greener and safer approach to TON measurement, the method is easily automated and allows simultaneous analysis of multiple parameters from the same sample aliquot, automatic spiking procedures, flexible test and QC parameter configuration, and flexible result reporting with versatile features for configuring report templates.
Read more about the method and recent study results in this application note.
What resources are available to help me learn more?
To learn more about the Gallery Aqua Master for wet chemical analysis, check out these online resources:
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- Ward, M.H., et al. Drinking Water Nitrate and Human Health: An Updated Review. Int J Environ Res Public Health. 2018 Jul 23;15(7):1557. DOI: 10.3390/ijerph15071557. PMID: 30041450; PMCID: PMC6068531.