A Simple, Ecofriendly, and Fast Method for Nitrate Quantification in Bottled Water Using Visible Spectrophotometry

There are many works associating the presence of nitrate in water and the occurrence of cancer in humans. The most common method for quantifying nitrate in water is based on the use of toxic cadmium as a reductant. In this work, a new approach was developed for the quantification of nitrate in bottled water with indirect spectrophotometry using Zn⁰ as a reductant. Nitrate is reduced to nitrite using Zn⁰ in a buffered medium (acetate/acetic acid) and quantified with visible spectrophotometry using the Griess reaction between sulfanilamide and N-(1-naphthyl)-ethylenediamine. The influence of pH, buffer solution (constitution and concentration), Zn⁰ (mass and granulometry), and agitation time on the efficiency of nitrite generation was evaluated. The optimal conditions were an acetate-acetic acid buffer solution with a concentration and pH of 0.75 mol L^-1 and 6.00, respectively, and a Zn⁰ particle size of 20 MESH and Zn⁰ mass of 300 mg. The limits of detection and quantification (LoD and LoQ) were 0.024 and 0.08 mg L^-1, respectively. The method's accuracy and precision were evaluated using the analysis of commercial bottled water. In conclusion, the use of Zn⁰ instead of cadmium provided a green method with excellent LoD/LoQ. Further, the method proved to be simple and easy to apply during outdoor analysis.