Quechers

Acetone (Riedel-de Häen, purity 99.8%), acetonitrile (Sigma-Aldrich, purity > 99.9%), toluene (Merck), dichloromethane chromatography grade, and n-hexane (purity > 99.0%) were the solvents used. Agilent QuEChERs salts and buffers were prepackaged in anhydrous packages for EN 15662 containing 4 g magnesium sulfate (MgSO₄), 1 g sodium chloride (NaCl), 1 g sodium citrate, and 0.5 g disodium citrate sesquihydrate. Silica gel (60–120 mesh, Fluka) was activated at 150°C for 12 hours prior to use.
A 1000 μg/mL stock solution of 14 PAHs includes naphthalene, fluorene, fluoranthene, benz(a)anthracene, chrysene, pyrene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, acenaphthene, phenanthrene, anthracene, acenaphthylene, and pyrene-d₁₀ (surrogate standard) and reference standards obtained from Sigma-Aldrich with purity > 95% were prepared, while benzo(g,h,i)perylene and dibenz(a,h)anthracene were obtained as readymade of 100 μg/mL in methylene chloride and indeno[1,2,3-cd]pyrene 200 μg/mL in methanol. A 1 μg/mL working solution of all 16 PAHs was prepared in toluene. Calibration mixtures with concentration 2, 10, 50, 100, and 500 ng/mL were prepared from serial dilution of the working solution in toluene where pyrene-d₁₀ maintained at level 50 ng/mL in all calibration levels and all stored in refrigerator at 4°C.

The following materials were purchased from Sigma Aldrich (USA): acetonitrile, methanol, 1-butanol, LC-MS grade, ninhydrin reagent 2%, glacial acetic acid, and TLC plates (aluminum sheets). Formic acid (analytical grade) was obtained from Merck, USA. To detect pesticide residues in food, QuEChERS (a mixture containing magnesium sulfate, sodium acetate along with primary secondary amine, PSA, tubes) was purchased from Agilent (USA), as was the liquid chromatography (LC) column. Standards of pesticides, insecticides, and herbicides were purchased from Sigma Aldrich. All reagents and standards were prepared fresh in LC-MS grade water or solvent before use. The standards of organophosphate pesticide (OP) metabolites, diethyl dithiophosphate, diethyl thiophosphate, dimethyl thiophosphate, dimethyl dithiophosphate, dimethyl phosphate, and diethyl phosphate (DEP) were obtained from the National Centre for Environmental Health, CDC (Atlanta, USA).

An amount of 2 ± 0.1 g of each homogenized sample was suspended in 20 ml of water/acetonitrile (50:50, v/v), mixed with QuEChERS salts (4 g Na₂SO₄, 1 g NaCl, 1 g trisodium citrate dehydrate, and 0.5 g disodium hydrogen citrate sesquihydrate), vortexed for 1 min and centrifuged for 5 min at 3,900 × g. Afterwards, the extracts were cleaned up by dispersive solid phase extraction (dSPE). To this aim, 6 ml of extract was transferred into plastic tube containing 150 mg of primary and secondary amine exchange material (PSA), 150 mg of C18 powder, and 900 mg MgSO₄, vortexed and centrifuged for 5 min at 3,900 × g. Supernatant (1 ml) was again decanted and centrifuged, this time at 12,000 × g for 5 min. The final supernatant (hereafter called the sample extract) was analyzed by GC-MS, LC-MS (reference method analysis) and DART-HRMS. The QuEChERS and SPE kits were purchased from Agilent Technologies (Santa Clara, CA, United States).