RESUMO
A water-soluble azo functionalized oligomeric chitosan reagent (ß-NAC) has been developed for the visual detection and quantification of KMnO4 at micromolar concentrations. The ß-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 ß-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 ß-NAC reagent after interacting with KMnO4 (10-3 M) changes from brown to blood red. Furthermore, the ß-NAC sensor was employed for the spectrophotometric detection of KMnO4. The absorption spectrum of ß-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 ß-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 ß-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.