Per- and polyfluoroalkyl substances (PFAS) are a class of chemicals including over 4700 substances. As a limited number of PFAS is routinely analyzed in human serum, complementary analytical methods are required to characterize the overlooked fraction. A promising tool is the total oxidizable precursors (TOP) assay to look for precursors by oxidation to perfluoroalkyl acids (PFAA). The TOP assay was originally developed for large volumes of water and had to be adapted for 250 μL of human serum. Optimization of the method was performed on serum samples spiked with model precursors. Oxidative conditions similar to previous TOP assay methods were not sufficient for complete oxidation of model precursors. Prolonged heating time (24 h) and higher oxidant amount (95 mg of Na₂S₂O₈ per 225 μL of serum) were needed for complete conversion of the model precursors and accomplishing PFAA yields of 35–100 %. As some precursors are not fully converted to PFAA, the TOP assay can only provide semi-quantitative estimates of oxidizable precursors in human serum. However, the TOP assay can be used to give indications about the identity of unknown precursors by evaluating the oxidation products, including perfluoroalkyl sulfonic acids (PFSA) and perfluoroalkyl ether carboxylic acids (PFECA). The optimized TOP assay for human serum opens the possibility for high-throughput screening of human serum for undetected PFAA precursors.

全氟和多氟烷基物质 (PFAS) 是一类化学品，包括 4700 多种物质。由于在人血清中常规分析的 PFAS 数量有限，因此需要补充分析方法来表征被忽视的部分。一种有前途的工具是总可氧化前体 (TOP) 测定法，用于通过氧化为全氟烷基酸 (PFAA) 寻找前体。TOP 检测最初是为大量水而开发的，必须适应 250 μL 人血清。对掺有模型前体的血清样品进行了该方法的优化。类似于以前的 TOP 测定方法的氧化条件不足以完全氧化模型前体。延长的加热时间（24 小时）和更高的氧化剂量（95 毫克的 Na ₂ S ₂ O_{每 225 μL 血清需要8}个）才能完全转化模型前体并实现 35-100% 的 PFAA 产率。由于一些前体没有完全转化为 PFAA，TOP 测定只能提供人血清中可氧化前体的半定量估计。但是，TOP 测定可用于通过评估氧化产物（包括全氟烷基磺酸 (PFSA) 和全氟烷基醚羧酸 (PFECA)）来指示未知前体的身份。优化的人血清 TOP 检测开启了对人血清进行高通量筛选以寻找未检测到的 PFAA 前体的可能性。