Validation of a spectrophotometric procedure for determining nitrate in water samples

Authors: ISEYEMI, O - Orise Fellow; Adviento-Borbe, Arlene; HAAS, L - Arkansas State University; FARRIS, J - Arkansas State University; Reba, Michele; Massey, Joseph

Submitted to: Journal of Environmental and Toxicological Studies
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2018
Publication Date: 6/13/2018
Citation: Iseyemi, O., Adviento-Borbe, A.A., Haas, L., Farris, J.L., Reba, M.L., Massey, J. 2018. Validation of a spectrophotometric procedure for determining nitrate in water samples. Journal of Environmental and Toxicological Studies. 2(1):1-6. http://dx.doi.org/10.16966/2576-6430.113.
DOI: https://doi.org/10.16966/2576-6430.113

Interpretive Summary: Nitrate is an essential nutrient for crop production, but poses serious threats to freshwater systems and human health. In order to assess nitrate in the environment, it is important to measure nitrate using accurate, robust, and reliable methods. One of the most popular and efficient methods used for measuring nitrate is the cadmium (Cd) reduction method. With this method nitrate reacts with cadmium and converts it to nitrite. When mixed with other chemicals, the solution turns increasingly pink with increasing concentrations of nitrite. One disadvantage in using this method is the high toxicity of Cd metal. This study described a colorimetric method that uses vanadium (VCl3) to reduce nitrate. Vanadium (III) is less toxic than Cd and has high reaction efficiency under acidic conditions. The aim of this research was to validate an optimized protocol using VCl3 for the measurement of nitrate in small volumes of water at low nitrate levels (10 mg nitrate per L). The VCl3 method was also compared with the Cd reduction method by analyzing in parallel samples from various agricultural environments. Greater than 97% recovery of nitrate was obtained when using the VCl3 method, and nitrate at low concentrations was more accurately measured with the VCl3 method than with the Cd reduction method. This research demonstrated that the VCl3 method is faster, easy to use, cost effective, less prone to interferences, requires less sample volume, is efficient at low nitrate concentrations, and is less toxic. Also, this new method may be applicable in other situations, such as testing nitrate and nitrite in medical, food, and research laboratories.

Technical Abstract: A single-reagent spectrophotometric procedure using vanadium (III) chloride (VCl3) was found to provide accurate and robust measurement of low levels of nitrate (lNO3-N) in agricultural runoff. Results of the VCl3 method produced data that correlated well (r=0.86; p<0.001) with NO3-N concentrations determined using the standard cadmium NO3 reduction method. For both natural waters and solutions prepared to mimic agricultural runoff, limits of detection and quantitation were 0.0 and 0.04 mg NO3-N L-1, respectively, while NO3 recoveries ranged from 97 to 100%. The VCl3 method was accurate at low nitrate concentrations (0.03 to 1.6 mg NO3-N L-1) and required 99% less sample than the standard cadmium method. These results indicate that the vanadium reduction method accurately quantify trace amounts of NO3-N in terrestrial water samples such as surface water and agricultural runoff.