Abstract:

Perfluorinated/polyfluoroalkyl compounds (PFASs) are a group of synthetic chemicals. Since the 1940s, PFASs have been widely used in industrial and daily consumer fields. PFASs can enter the human body through various pathways, such as drinking water, food, and air. Toxicological studies have shown that PFASs feature developmental and reproductive toxicity. Thus, the accurate assessment of PFAS exposure levels plays an important role in determining the health risks of these compounds. Biological monitoring is considered the most ideal means of monitoring and evaluating PFAS levels in the human body. The concentration of PFASs in serum can directly reflect their level of absorption in the human body after exposure; therefore, serum is widely used as a biological matrix for evaluating PFASs.

In this study, a high-throughput solid-phase extraction (SPE)-ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was developed for the determination of 17 PFASs in serum. A laboratory-made straight-through SPE column was used to purify serum samples. The SPE column used a new inorganic material with a low perfluorinated compound background. Unlike traditional SPE columns, the extraction column does not require activation before use, and the sample can be directly loaded into it for purification. The straight-through SPE column adopts a stepped design, which does not require a large sample volume and is suitable for the pretreatment of precious biological samples such as serum. The serum sample size adopted in this study was only 50 μL, which is much lower than that required by other extraction methods. The straight-through SPE column can be used in conjunction with a 96-well plate, and the purification treatment of 96 serum samples can be completed within 30 min with high efficiency.

The mass spectrometry parameters were optimized, and the results indicated that the electrospray ionization source temperature had a significant impact on the PFASs with later elution peaks. The effects of ion-source temperatures of 400 and 500 ℃ on the peak shapes and response values of the target compounds were compared, and 400 ℃ was selected. The sample pretreatment and ultra-high performance liquid chromatographic conditions were optimized. Briefly, 50 μL of the sample was loaded into the SPE column and extracted twice using 200 μL of acetonitrile each time. The purified solution was collected, blown with nitrogen at 40 ℃ to near dryness, dissolved in a 50% methanol aqueous solution, and then separated on a Poroshell 120 EC-C18 chromatographic column (100 mm×3 mm, 2.7 μm) with 5 mmol/L ammonium acetate aqueous solution and methanol as mobile phases. Detection was conducted in multiple-reaction monitoring mode, and quantification was performed using an isotope internal standard method. The 17 detected PFASs had good linear relationships within the corresponding mass concentration ranges (r²>0.995), with limits of detection ranging from 3.6 ng/L to 14 ng/L and limits of quantification ranging from 11 ng/L to 42 ng/L. The recoveries in spiked serum samples were 89.3%-110.2%, the intra-day RSDs were 2.5%-9.8%, and the inter-day RSDs were 3.6%-10.2%. The method was applied to the detection of 20 human serum samples, and all 17 compounds were successfully detected. The proposed method is easy to operate, highly sensitive, has a small sample size and high detection efficiency, and is suitable for the large-scale monitoring and exposure assessment of PFASs in human serum samples.

Key words: solid-phase extraction (SPE), ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), perfluorinated/polyfluoroalkyl compounds (PFASs), serum