Stain and Color Interference Correction in Nitrite Sensing for Enhanced Continuous Water Quality Monitoring

Nitrite is a widespread pollutant in water sources that poses severe threats to human health and the environment. Most of the existing techniques for measuring nitrite levels in water are often costly, laboratory intensive, and less suitable for continuous and long-term measurement. They require trained operators and complex instruments and involve multiple steps that can affect the sample integrity and accuracy of the analysis. Some alternative methods based on image processing or colorimetric sensors have been proposed, but they have low sensitivity, and high interference, and most of those are not automated. Therefore, there is a clear need for development of an automated system and a technique capable of providing precise and continuous detection of nitrite in water, overcoming the challenges posed by staining of the detection chamber and variations in the sample color. The sensing technique presented in this paper is based on a simple colorimetric method. The proposed system utilizes a commercially available test kit, API Nitrite Kit, for nitrite detection, uses a modified detection chamber, and improves the detection range from 5 mg/L (found in the existing systems) to 10 mg/L of nitrite concentration. The test results showed that the final output from the prototype, using the proposed estimation method, had negligible sensitivity to the stain in the detection chamber wall and color of the sample due to inert colored compounds. The prototype sensor achieved a LoD of 0.04 mg/L for nitrite below 2 mg/L range and 0.66 mg/L in the 2 to 10 mg/L range. A sensitivity of 8.92 (mg/L)<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> was obtained for nitrite concentration in the range below 2 mg/L and 2.58 (mg/L)<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> in the range of 2 to 10 mg/L. The entire detection procedure is automated, and the validity of the detection is confirmed under the influence of staining of the cuvette and external colored compounds in the water.The system thus developed is a stain and color-independent model template for aqueous nitrite detection with an improved detection range.