| Abstract: | Groundwater samples collected at sites where in situ chemical oxidation (ISCO) has been deployed may contain binary mixtures of groundwater contaminants and permanganate (MnO4–), an oxidant injected into the subsurface to destroy the contaminant. Commingling of the oxidant and contaminant in aqueous samples may negatively impact the quality of the sample as well as the analytical instruments used to quantify contaminant concentrations. In this study, binary mixtures comprised of (1) a multicomponent standard with permanganate and (2) groundwater samples collected at two ISCO field sites were preserved with ascorbic acid. Ascorbic acid reacts rapidly with the MnO4– and limits the reaction between MnO4– and the organic compounds in the mixture. Consequently, most of the compounds in the multicomponent standard were within the control limit for quality assurance. However, despite timely efforts to preserve the samples, the rapid reaction between permanganate and contaminant caused the concentration of several sensitive compounds to fall significantly below the lower control limit. Concentrations of volatile organic compounds in the field‐preserved binary mixture groundwater samples were greater than in samples refrigerated in the field and preserved upon arrival at the laboratory, indicating the time‐dependency and benefit of field preservation. The molar ratio of ascorbic acid required to neutralize KMnO4 was 1.64 (mol ascorbic acid/mol KMnO4); this provided a baseline to estimate the volume of ascorbic acid stock solution and/or the weight of crystalline ascorbic acid required to neutralize MnO4–. Excess ascorbic acid did not negatively impact the quality of the aqueous samples, or analytical instruments, used in the analyses. |
