Anhydrous mg sulfate

Milk samples were thoroughly mixed, followed by transferring 5 mL of homogenate in 50 mL PFTE tube containing a mixture of 10 mL deionized water and 10 mL acidified acetonitrile with acetic acid (Scharlau, Barcelona, Spain). The mixture was shaken manually, then added 4.0 g of anhydrous Mg sulfate, 1.0 g of Na Cl, 1 g of Na citrate, and 0.5 g Na hydrogen citrate sesquihydrate (Merck, Darmstadt, Germany). Finally, the content was mixed by shaking for 1 min, followed by centrifugation at 1792 × g for 3 min. Subsequently, 1 mL of the supernatant clear solution was transferred into 15 mL of polyethylene tube containing 25 mg amine sorbent (Supelco, Bellefonte, USA) and 150 mg anhydrous Mg sulfate (Merck). Then the tube was shaken vigorously manually for 1 min then centrifuged (Sigma, Darmstadt, Germany) for 1 min. at 2800 ×g. Finally, 0.5 mL of supernatant was taken into a glass vial, evaporated to dryness, and re-dissolved in 0.5 mL n-hexane for gas chromatograph-microelectron capture detector (GC-μECD) analysis (Agilent Technologies, Santa Clara, CA, USA).