Fabrication of portable colorimetric sensor based on basic fuchsin for selective sensing of nitrite ions

An economically feasible, readily accessible colorimetric probe based on basic fuchsin (BF) was developed to detect NO2- in water and wastewater systems. The study is divided into two phases; liquid phase and solid phase (colorimetric strip). Initially, the parameter optimization was carried out in the liquid phase, followed by sensing via colorimetric strips. Naked eye-colorimetric detection of NO2- in liquid phase was in the range of 0.92-9.2 mg L-1 whereas for strips detection range was observed as 0.005-9.2 mg L-1. Proper diffusion of BF on the Whatmann filter paper (W) enhanced the sensitivity of colorimetric strip. The investigation also showed high selectivity towards NO2- in the presence of several anions and cations. The colorimetric strips prior to and after interaction with NO2- were characterized using FT-IR, Raman, UV-DRS, and XRD. Results confirmed that diazotization reaction between secondary amine portion of the BF and NO2- was responsible for the specific color change (pink to colorless). The leaching test reported no leachable fraction from the coating, and this was accompanied by the use of Tween-80 as a surface coating agent. The solid colorimetric probe was showed potential selectivity towards NO2- over several interfering ions. Furthermore, the applicability of the prepared strip for detecting NO2- in real water samples indicated satisfactory performance. Cost analysis confirmed that the synthesized BF@W strip is a low-cost (0.01$/strip) and a portable colorimetric sensor for the detection of aqueous NO2-.