A high-throughput and cost-effective microplate reader method for measuring persulfates (peroxydisulfate and peroxymonosulfate)

Frequent use of persulfates as oxidants, for in situ chemical oxidation and advanced oxidation processes, warrants the need for developing a fast and efficient method for measuring persulfate concentrations in aqueous samples in the lab and on site. Here, we propose a modified method, based on Liang et al.'s (2008) spectrophotometric method, for measuring both peroxydisulfate (PDS) and peroxymonosulfate (PMS) in the aqueous samples. Our method involves a deep 96-well plate, multi-channel pipettes, a small orbital shaker, and a microplate reader; allowing the preparation and analysis of up to 96 samples in one run. Our proposed method shortens the time by 10 folds, consumes only ∼2% of the original reagents, and generates only ∼2% of the liquid waste compared to the Liang et al.'s method, thus, making our method high-throughput, time-efficient, and cost-effective with reduced environmental impact. The presented microplate reader method is validated in terms of linearity, LOD, LOQ, accuracy, precision, robustness, and selectivity. All the parameters satisfied the acceptance criteria, according to ICH guidelines. The linearity of calibration curves was evaluated by performing the F-test. In general, our method has linear ranges from 20 to 42,000 and 5 to 40,960 μM for PDS and PMS, respectively. Accuracy (% recovery) results suggested that the LOD and LOQ based on the standard deviation of y-intercepts of the regression lines were the most reliable. The LOD/LOQ values for PDS and PMS were 14.7/44.1 and 4.6/14.4 μM, respectively. The proposed method was also modified to work with a standard cuvette spectrophotometer and was validated. A comparison with the UHPLC analysis of PDS showed that our microplate reader method performed equivalently or even outperformed the UHPLC method, in the presence of common groundwater constituents and organic contaminants.