Rapid determination of persulphate in aqueous solutions by visible spectrophotometry

Peroxynitrite-advanced oxidation technology generates strong oxidising and reactive radicals and is considered one of the most effective and attractive methods for degrading toxic organic pollutants, but studies have found that peroxynitrite utilisation during wastewater treatment is low, so it is essential to choose a simple and fast method for measuring the persulphate concentration during and after degradation of organic pollutants in a treatment system to improve their utilisation. This study investigated the spectrophotometric quantification of persulphate (S2O82-) based on the classical iodometric titration method. Instead of a back-titration step, the absorbance of yellow iodide colour was measured at 400 nm (A(400)) in the presence of a bicarbonate buffer. The resulting A(400) calibration graph was linear in the S2O82- concentration range of 0.0-0.1 mM. With dilution, the method could be used for all concentrations typical of field applications. It has been shown that there was no significant error in the measurement results when the solution was close to neutral pH. Measurement of A(400) effectively avoided the influence of other interfering ions, such as Cu2+, SO42-, Cl- and CO32-. In addition, the method exhibited little dependence on other matrix components and A(400) stable (<2% change) for more than one week. Overall, this method was fast and simple and offered a new option for measuring persulphate during the treatment of organic pollutants.