Patent 2019-756

Method for determining the presence and concentration of persulphate (s) in water, in particular in groundwater, in which at least one other oxidising agent is additionally present

A method of determining the presence and concentration of persulfate(s) in water, in particular groundwater, in which at least one other oxidising agent is additionally present, whereby mixing a sample of the water of interest and an indicator dye acid blue 40 or acid blue 25 prepares a solution for determining the presence and concentration of persulfate(s) in the water of interest with an indicator dye concentration of 30 to 70 mg/l. This solution is then heated to a temperature of 90 to 110 °C, at which temperature it remains for 15 to 50 minutes, activating the persulphate(s) contained therein, which oxidises the indicator dye to form an intermediate containing anthraquinone as a chromophore. After this time, the absorbance of this solution is measured for light of wavelengths 450 to 500 nm, and the corresponding calibration curve is fitted with a linear regression function to give a relationship for calculating the concentration of persulphate/persulphate in the water of interest in the form x = (y/A - B) * d, where x represents the concentration of persulfate in the water of interest in µM, y represents the measured absorbance of the solution in absorbance units AU, d is the dilution factor, A is the linear coefficient of the regression function overlaid on the calibration curve and B is the coefficient representing the absolute term of the regression function overlaid on the calibration curve divided by its linear coefficient A, from which the concentration of persulfate/persulfate in the water of interest is calculated.