Simultaneous Determination of PMS, PDS, and H2O2 Concentrations with Multi-Step Iodometry

Peroxodisulfate (PDS), peroxymonosulfate (PMS), and hydrogen peroxide (H2O2) might coexist in a persulfate system. It leads to the mutual interference in concentration determination due to their similar structures. Simultaneous detection of the three peroxides involves limited reporting. Herein, a multi-step iodometry was established to simultaneously determine the concentrations of PDS, PMS, and H2O2 coexisting in a solution. Firstly, molybdate–NaHCO3-buffered iodometry was proposed to uplift the overall detection of peroxides since the recovery rate of H2O2 was unexpectedly lower in the peroxide mixture than in the single H2O2 solution with reported NaHCO3-buffered iodometry. Then, multi-step iodometry was proposed based on the established molybdate–NaHCO3-buffered iodometry using the combination with catalase and revised acetate-buffered iodometry (pH 3). The multi-step iodometry determined the coexisting PMS, PDS, and H2O2 with the recovery rate of 95–105% and a standard deviation of ≤7% of two replicates at the individual centration of 13–500 μmol∙L−1. The recovery rates of peroxides were within 95–105% at pH 3–11 and within 90–110% in the presence of Cl− (0–150 mg∙L−1), F− (0–1.5 mg∙L−1), SO42− (0–150 mg∙L−1), or NO3− (0–20 mg∙L−1). The recovery rate of H2O2 was lowered down to 91% or 87% in the sample containing 100 mg/L Ca2+ or Mg2+, respectively, but was lifted up to 100% or 93% once pretreated by adding 0.11–1.06 g∙L−1 Na2CO3. In the background of tap water, surface water, and ground water, peroxides were all detected in 90–110%, which indicates the applicability of multi-step iodometry in real waters.