Multi-wavelength spectrophotometric measurement of persulfates using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as indicator

A spectrophotometric method using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as the indicator was proposed for measuring persulfates, i.e., peroxymonosulfate (PMS) and peroxydisulfate (PDS). This method was based on the direct oxidation of the colorless ABTS by PMS/PDS to generate the green-colored ABTS + at neutral pH and room temperature . The generated ABTS + had four different characteristic absorption peaks at 820 nm, 732 nm, 650 nm and 415 nm. The absorption values at these wavelengths increased with the increase of PMS/PDS concentration, and there were well linear relationships (R 2  > 0.998) between the corresponding absorption values and the concentrations of PMS/PDS in the range of 3–500 μM. Monitoring the change of PMS/PDS concentration by the proposed ABTS method was in good agreement with that monitored by the common spectrophotometric method using potassium iodide as the indicator. The green-colored waste solutions produced after PMS/PDS analysis with the ABTS method showed no bactericidal effect towards Escherichia coli . The proposed multi-wavelength spectrophotometric method using ABTS as the indicator could be employed as a candidate method for the accurate and convenient measurement of PMS/PDS in water.