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.

中文翻译：

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游离苯多羧酸 (BPCA) 的存在可能导致水样中溶解黑碳的高估

溶解黑碳（DBC）是有机材料热变（例如火）过程中产生的溶解有机物的浓缩芳香族部分。 DBC 浓度通常使用苯多羧酸 (BPCA) 方法测定，其中稠合芳香族结构被氧化成 BPCA 分子标记物以进行定量。然而，最近在受火灾影响的地表水中以及受热土壤和野火灰烬的渗滤液中发现了 BPCA 分子。如果它们在样品制备和分析程序中幸存下来，水中这些“游离”BPCA 的存在可能会导致水样中 DBC 浓度的高估。为了评估游离 BPCA 对 DBC 定量的潜在影响，我们在超纯水、盐水和有机物溶液中添加了 BPCA 标准品，并将它们作为环境样品进行 DBC 分析。每个 BPCA 标准品均以可检测的量回收，取代最多的 BPCA 的回收率低于取代较少的 BPCA。仅当使用的转换因子包括较少取代的 BPCA 时，加标有机物溶液的计算 DBC 浓度显着高于未修正的对应溶液。总体而言，我们的结果表明 DBC 定量可能会受到水样中游离 BPCA 的影响，但影响程度在很大程度上取决于单个 BPCA 分子标记的特性。