1432 Pang et al.: J ournal of AOAC I nternational V ol. 98, N o. 5, 2015

(f)  Centrifuge tube .—80 mL. (g)  Millipore filter membrane (nylon) .—13 mm × 0.2 μm. D. Preparation of Standard Solutions (a)  Prep aration of stock solutions.— Accurately weigh 5–10 mg individual pesticide and chemical pollutant standards (accurate to 0.1 mg) into a 10 mL volumetric flask. Dissolve and dilute to volume with methanol, toluene, acetone, acetonitrile, isooctane, etc., depending on each individual compound’s solubility. All standard stock solutions are stored in the dark at 0–4°C and can be used for 1 year. (b)  Preparation of mixed standard solution.— Depending on properties and retention times of compounds, all compounds are divided into a series of groups. The concentration of each compound is determined by its sensitivity on the instrument for analysis. Mixed standard solutions are stored in the dark below 4°C. (c)  Working standard mixed solution in matrix.— Prepare working standard mixture solution in matrix of pesticide and chemical pollutants by diluting an appropriate amount of mixed standard solution with blank extract, which has been taken through the method with the rest of the samples. Mix thoroughly. Used for plotting the standard curve. Working standard mixture solution in matrix must be freshly prepared. E. Apparatus and Conditions (a) GC/MS analysis.— ( 1 )  System .—Model 7890A gas chromatograph connected to a Model 5975C mass selective detector with electron ionization (EI) source and equipped with a Model 7683 autosampler and Chemstation data processing software system (Agilent Technologies), or equivalent. ( 2 )  Column .—DB-1701 capillary column (30 m × 0.25 mm × 0.25 μm; J&W Scientific, Folsom, CA), or equivalent. ( 3 )  Column temperature .—40°C hold 1 min, 30°C/min to 130°C, 5°C/min to 250°C, 10°C/min to 300°C, hold 5 min. ( 4 )  Carrier gas .—Helium, purity ≥99.999%, flow rate 1.2 mL/min. ( 5 )  Injection port temperature .—290°C.

A. Principle Test samples are extracted with acetonitrile using a homogenizer, and the extracts are cleaned up with Cleanert TPT (Agela Technologies, Tianjin, China), EnviCarb/PSA or ECPSACB506 (UCT, Bristol, PA), BE Carbon 500 g/PSA (Agilent Technologies, Santa Clara, CA), or InerSep GC/PSA (GL Sciences, Tokyo, Japan), or equivalent cartridges. The pesticides are eluted with acetonitrile–toluene (3 + 1, v/v), concentrated, dried, dissolved in the recommended solution, and analyzed by GC/MS, GC/MS/MS, or LC/MS/MS. Quantifications is with a matrix-matched standard calibration curve. B. Reagents (a) Solvents .—Acetonitrile, toluene, and n -hexane (HPLC grade). (b)  Acetonitrile–toluene.— 3 + 1 (v/v). (c)  Ultrapure water .—Obtained from a Milli-RO plus system together with a Milli-Q system (EMD Millipore Corp., Billerica, MA). (d)  Anhydrous sodium sulfate .—Analytically pure. Baked at 650°C for 4 h and stored in a desiccator. C. Materials (a)  SPE cartridges .—Cleanert TPT (2000 mg, 12 mL; Agela Technologies), or EnviCarb/PSA (500 mg/500 mg, 6 mL; Supelco, Bellefonte, PA), or equivalent. (b)  SPE tube adapter .—For 12 mL SPE tubes (57267), for 6 mL SPE tubes (57020-U; Sigma-Aldrich Shanghai Trading Co., Ltd, Shanghai, China), or equivalent. (c)  Disposable flow control valve liners .—For Visiprep TM-DL (57059; Sigma-Aldrich Shanghai Trading Co., Ltd). (d)  Pear-shaped flask .—80 mL (Z680346-1EA; Sigma- Aldrich Shanghai Trading Co., Ltd), or equivalent. See Figure  2014.09A . (e)  Reservoir .—30 mL (A82030; Agela), or equivalent. See Figure 2014.09A .

Figure 2014.09A. SPE equipment.

Made with FlippingBook flipbook maker