Nitrate/Nitrite determination in water and soil samples accompanied by in situ azo dye formation and its removal by superabsorbent cellulose hydrogel

Abstract

In the present work, an efficient method is developed for the spectrophotometric determination of nitrite and nitrate ions in water and soil samples by in situ formation of azo dye (Griess reagent) which showed λmax at 385 nm. The reaction condition and the concentration of reagents used are optimized. The molar absorptivity, Sandell’s sensitivity, detection limit and quantification limit of the method are found to be 3.22 × 104 L mol−1 cm−1, 1.98 × 10−6 µg cm−2, 0.0030 µg mL−1 and 0.0092 µg mL−1 respectively with the linearity range up to 2.6 µg mL−1. The formation of azo dye is confirmed by 1H and 13C Nuclear Magnetic Spectroscopy. The azo dye formed during the determination is effectively removed using custom made ecofriendly cellulose modified hydrogel in order to reduce organic load in the test samples. The structure, morphology and the thermal properties of hydrogel are determined by Fourier-transform infrared spectroscopy, scanning electron microscopy and thermogravimetric analysis respectively. The dye removal mechanism involves pseudo second order kinetics, adsorption is found to be spontaneous based on the thermodynamic parameters and it is befitting to Freundlich isotherm model.