Rapid and selective quantitative colourimetric analysis of nitrite in water using a S-Nitrosothiol based method

Abstract

This study introduces a novel S-nitrosothiol based method for the rapid and highly selective detection of nitrite in complex water matrices. Sodium 3-mercapto-1-propanesulfonate forms a distinctive pink S-nitrosothiol compound upon interaction with nitrite in acidic media, allowing both visual and quantitative detection. Various factors affecting the absorbance of the final product were investigated, including pH, reaction time, acid type, and sodium 3-mercapto-1-propanesulfonate concentration. UV-Vis spectrophotometric analysis demonstrated an excellent linear correlation (R² = 0.99) across a broad detection range (0.05 to 80 mmol l^-1), while showing no interference from common ions such as nitrate or dissolved organic matter, a limitation frequently observed in conventional UV-based nitrite detection methods. The assay was further adapted into a pellet form to simplify field use, operating effectively at room temperature with a low detection limit (1.4 ppm). The S-nitrosothiol based method represents a safer and more environmentally friendly option for nitrite detection and shows a promising potential as a valuable addition to both field and laboratory water testing kits for nitrite analysis.

Keywords: Colourimetric detection; Nitrite; Wastewater; Water analysis.

Graphical abstract

Fig. 1

(a) Visible spectra of the 3-MPSNa nitrite colourimetric detection assay compared to various combinations of reagents. Inset shows a digital image of the corresponding solutions. (b) Effect of the pH on the visible spectrum for the assay. (c) Proposed assay reaction mechanism.

Fig. 2

(a) Effect of acid type on visible spectrum for nitrite assay. Parameters for all experiments in (a-c) were T = 20 °C, [NO₂^-] = 20 mmol l^-1, [3-MPSNa] = 20 mmol l^-1, [acid] = 1 mol l^-1. (b) Effect of the time on the absorbance at 547 nm in presence of [3-MPSNa] = 50 mmol l^-1, [CH₃COOH] = 1 mol l^-1 and [NO_2.] = 1, 5, 10, 20, 50 mmol l^-1, T = 20 °C.

Fig. 3

(a) Effect of 3-MPSNa concentration on UV–Vis absorption spectrum recorded in [NO₂^-] = 100 mmol l^-1, [CH₃COOH] = 1 mol l^-1, [3-MPSNa] = 1, 5, 10, 20, 50, 100 mmol l^-1, T = 20 °C. Inset shows a digital image of the assays. (b) Plot of peak absorbance values against 3-MPSNa, showing a linear relationship.

Fig. 4

(a) Effect of nitrite concentration on UV–Vis absorption spectrum recorded in [3-MPSNa] = 100 mmol l^-1, [CH₃COOH] = 1 mol l^-1 and [NO₂^-] = 0, 0.05, 0.1, 1, 2, 5, 10, 15, 20, 30, 40, 50, 60, 80 mmol l^-1. T = 20 °C. (b) Plot of peak absorbance values against NO₂^- concentrations.

Fig. 5

(a) Selectivity of the 3-MPSNa assay in presence of DOM and various commonly found ions. (b) The difference in absorbance of the assay with an addition of 50 mmol l^-1 NO₂^- and 50 mmol l^-1 of common ions. n = 3.