Development of an azo functionalized oligomeric chitosan sensor for rapid visual, spectrophotometric and spectrofluorometric detection of KMnO4 up to micromolar concentrations

Abstract

A water-soluble azo functionalized oligomeric chitosan reagent (β-NAC) has been developed for the visual detection and quantification of KMnO₄ at micromolar concentrations. The β-NAC sensor was also explored as a detection probe for the spectrophotometric and spectrofluorometric detection of several metal ions and anions. The synthesized reagent was characterized by TGA-DTA-DTG analysis, DLS studies, BET analysis, and spectral analysis. The β-NAC reagent produces conspicuous colours with different concentrations and different pH values of KMnO₄ solution. This provides evidence for high selectivity in the visual detection of KMnO₄ up to the micromolar level because of its interactions in the case of KMnO₄ only. The colour of the β-NAC reagent after interacting with KMnO₄ (10⁻³ M) changes from brown to blood red. Furthermore, the β-NAC sensor was employed for the spectrophotometric detection of KMnO₄. The absorption spectrum of β-NAC shows a peak at 327 nm and on interacting with KMnO₄, it shows a bathochromic shift to 331 nm. The intensity of the peak at 331 nm increases as the concentration of KMnO₄ was increased from 1 μM to 0.01 M. The detection and quantification limits in the spectrophotometric detection of KMnO₄ were found to be 4.55 μM and 15.17 μM, respectively. The results of pH studies show that there is a pH effect of the KMnO₄ solution on KMnO₄ detection. The stability of the complex was determined by investigating the effect of time on the absorption intensity. In the spectrofluorometric detection, the fluorescence intensity of β-NAC at the 427 nm emission maxima was decreased on adding KMnO₄ solution. The fluorescence quenching increased on increasing the KMnO₄ concentration from 1 μM to 0.008 M. The optimum pH for fluorescence quenching was found to be 8. The detection and quantification limits in the spectrofluorometric detection of KMnO₄ were found to be 0.967 μM and 3.223 μM, respectively. The Stern–Volmer constant value was found to be 41 366.2 L mol⁻¹, confirming the significant complexation between KMnO₄ and the β-NAC reagent. Interference studies were conducted to analyse the effect of various metal ions and anions on KMnO₄ detection. Electrochemical studies were also performed to analyse the mechanism of complex formation.