The presence of free benzenepolycarboxylic acids (BPCAs) may result in the overestimation of dissolved black carbon in aqueous samples

Dissolved black carbon (DBC) is the condensed aromatic fraction of dissolved organic matter produced during the thermal alteration of organic material (e.g., fire). DBC concentrations are often determined using the benzenepolycarboxylic acid (BPCA) method where condensed aromatic structures are oxidized into BPCA molecular markers for quantification. However, BPCA molecules have been recently identified in fire-affected surface waters and leachates of heated soils and wildfire ash. If they survive the sample preparation and analytical procedures, the presence of these "free" BPCAs in water may result in an overestimation of DBC concentrations in aqueous samples. To assess the potential impact of free BPCAs on DBC quantification, we spiked ultrapure water, salt water, and organic matter solutions with BPCA standards and treated them as environmental samples being analyzed for DBC. Each BPCA standard was recovered in detectable amounts, with the most-substituted BPCAs having lower percent recoveries than less-substituted BPCAs. Spiked organic matter solutions had significantly higher calculated DBC concentrations than their unamended counterparts only when the conversion factor used included less substituted BPCAs. Overall, our results show that DBC quantification could be impacted by free BPCAs in aqueous samples, but the degree of impact is largely dependent upon the properties of the individual BPCA molecular marker.