The calibration concentrations ranged up to 172.1 mg Na2S2O8 L1.
Note that volume changes in the calibration solutions were taken
into account for calculating the calibration concentrations. All sample
solution analysis was conducted in accordance with the calibration
preparation procedure with exception that we propose a
volume of 100 lL of liquid to be withdrawn from the sample solution
and added into an EPA glass vial. For example, when 100 lL of
10 mM (2380 mg L1) Na2S2O8 solution (i.e., sample solution) is
withdrawn and added into a prepared 40 mL water/KI/NaHCO3
solution, the solution (i.e., measurement solution) would contain
5.94 mg Na2S2O8 L1 for spectrophotometric measurement. Therefore,
sodium persulfate concentration in a sample solution can be
calculated as follows: