Pesticide grade dichloromethane

¹³C-labeled surrogate standards for PCDD/Fs (EPA 1613-LCS) and PCBs (EPA 68A-LCS) and ¹³C-labeled injection standards for PCDD/Fs (EPA 1613-IS) and PCBs (EPA 68A-IS) were all purchased from Wellington Laboratories (Guelph, Canada). Pesticide-grade dichloromethane and n-hexane were purchased from J.T. Baker (Phillipsburg, USA); nonane was purchased from Sigma-Aldrich (St. Louis, USA). Silica gel (0.063–0.100 mm) was purchased from Merck (Darmstadt, Germany) and baked at 550°C for 12 h before use. Anhydrous sodium sulfate (baked at 660°C for 6 h), concentrated sulfuric acid and sodium hydroxide were of reagent grade (purity>99.8%) and were purchased from Beijing Chemistry Company (Beijing, China). Acid Silica gel was made by evenly mixing 70 g of activated Silica gel impregnated with 30 g of concentrated sulfuric acid, and basic Silica gel was made by mixing 100 g of activated Silica gel and 30 mL of sodium hydroxide solution (1 mol L^-1). Activated carbon was purchased from Supelco (Bellefonte, USA).
PUF disks (diameter: 14 cm; thickness: 1.35 cm) were pre-cleaned by accelerated solvent extraction (ASE350, Dionex, USA) using acetone and a mixture of dichloromethane:hexane (v/v, 1:1) in sequence. Then, they were wrapped with aluminum foil and preserved in sealed plastic bags until use. The other information of reagents and materials were provided in S1 File.

The commercial standards of the SCCPs (chlorine contents of 51.5%, 55.5%, and 63.0%, with the congener group patterns shown in Fig. 1) at concentrations of 100 ng/μL in cyclohexane and ε-hexachlorocyclohexane (ε-HCH, solution in cyclohexane, 10 ng/μL) were purchased from Ehrenstorfer GmbH (Augsburg, Germany). The ¹³C₁₀-trans-chlordane (100 ng/μL solution in n-nonane, purity 99%) was purchased from Cambridge Isotope Laboratories (Andover, USA). Pesticide-grade dichloromethane, n-hexane, acetone, cyclohexane, and toluene were purchased from JT Baker (Phillipsburg, NJ). Florisil (60–100 mesh) and silica gel (180–280 mesh) were purchased from Merck (Whitehouse Station, NJ). Anhydrous sodium sulfate was purchased from Sinopharm Chemical Reagent Beijing Co., Ltd.Fig. 1

Congener group pattern for commercial references of SCCPs (C_10-13, 51.5%, 55.5% and 63.0% chlorine content).

Fig. 1silica gel was activated at 550 °C for 12 h, Florisil was activated at 140 °C for 7 h, and Anhydrous sodium sulfate was activated at 660 °C for 6 h before use. A mixture of 30% (40%) acid silica gel was prepared by mixing 100 g of activated silica gel and 44 g (66 g) of concentrated sulfuric acid.