2. AOACRIChemContMethods-2018Awards

M astovska et al .: J ournal of AOAC I nternational V ol . 98, N o . 2, 2015  483

Table 2014.08B. ( continued )

No. of laboratories

No. of replicates

Mean concn, µg/kg

Mean recovery, % s r

PAH

, µg/kg s R

, µg/kg RSD r

, % RSD R

, % HorRat

9 8 9 8 8 9 9 9 9 8

18 16 18 16 16 18 18 18 18 16

18.4 27.7 84.1

92.1

1.1 2.8 5.6 9.7 0.5 1.5 8.6 0.9 1.6 2.9

1.9 2.8 8.8

5.7

10.5 10.3 10.5 21.6

0.36 0.37 0.45 1.02 0.26 0.24 0.47 0.29 0.32 0.25

Naph

110.7 105.1

10.3

6.7 6.1 3.3 3.1 5.1 6.1 3.8 2.5

158.7

99.2

34.2

Phe

15.1 49.7

100.5

1.2 3.0

7.8 6.0 9.9 8.8 8.2 5.4

99.4 96.0 98.5

168.0

16.6

Pyr

14.8 40.3

1.3 3.3 6.4

100.8

118.7

95.0

( d )  Dichloromethane.— ≥99.9%, for GC residue analysis. ( e )  Toluene.— ≥99.9%, for GC residue analysis. ( f )  Water.— Purified, free of interfering compounds. ( g )  Anhydrous sodium sulfate (Na 2 SO 4 ).— ≥99.0%, powder, heated at 600°C for 7 h and then stored in a desiccator before use (Na 2 SO 4 prepared and stored as indicated can be used for 1 month from preparation). ( h )  Silica gel SPE column.— Containing 1 g silica gel. Any commercially available silica gel SPE column can be used as long as it provides adequate fat cleanup and meets requirements for low background contamination specified in the laboratory qualification requirements: the concentrations of all analytes in the reagent blanks had to be below the concentrations in the lowest calibration level standard; for naphthalene, levels below the second lowest calibration standard (equivalent to 5 ng/g naphthalene in the sample) are still acceptable if the source of contamination could not be eliminated. Silica gel SPE columns can be prepared in-house using the following procedure: Activate the silica gel by heating at 180°C for 5 h, and then deactivate it by adding 5% deionized water, shaking for 3 h. Store in a desiccator for 16 h before use (silica gel prepared and stored as indicated can be used for 14 days). Place a piece of deactivated glass wool in a Pasteur pipet (5 mL), add 1 g activated silica gel (Silica gel 60, 0.063–0.2 mm, 70–230 mesh or equivalent) and top it with approximately 0.2 g muffled anhydrous Na 2 SO 4 . ( i )  Anhydrous magnesium sulfate (MgSO 4 ).— ≥99.0%, powder, heated (muffled) at 600°C for 7 h, and then store in a desiccator before use (MgSO 4 prepared and stored as indicated can be used for 1 month from preparation). Note : A preweighed (commercially available) mixture of 2 g sodium chloride and 4 g anhydrous magnesium sulfate (muffled) in pouches or tubes can be used. ( j )  Sodium chloride (NaCl).— ≥99.0%. ( k )  Helium 5.0 or better, nitrogen 4.0 or better. ( l )  Polypropylene centrifuge tubes.— 50 mL. ( m )  Glass Pasteur pipet.— 5 mL (for solvent transfers and/or in-house preparation of silica gel minicolumns). ( n )  Syringes/pipets.— Capable of accurate measurement and transfer of appropriate volumes for standard solution preparation and sample fortification (50–1000 μL). ( o )  Volumetric flasks.— 5–100 mL. ( p )  Glassware for evaporation steps . — Depending on the

and 4 mL hexane, followed by application of the 1 mL extract in hexane. The analytes are eluted with hexane–dichloromethane (3 + 1, v/v) using volume determined for the given silica gel SPE cartridges from the elution profiles of target analytes and fat, which are dependent on the silica deactivation. The clean extract is carefully evaporated, reconstituted in 0.5 mL isooctane, and analyzed by GC/MS. See Figure 2014.08A for the method flow chart. B. Apparatus ( a )  Homogenizer .—WARING blender Model 38BL40 (Conair Corp., Stamford, CT) or equivalent. ( b )  Solvent evaporator .—Any suitable solvent evaporator, such as a rotary vacuum evaporator, Kuderna-Danish evaporator, or a nitrogen blow-down system, may be used as long as it provides results meeting the laboratory qualification/ method set-up requirements (absolute analyte recoveries >70% in both evaporation steps). ( c )  Centrifuge .—Capable of centrifugation of 50 mL tubes at >1500 rcf for 10 min. ( d )  Furnace/oven .—Capable of 600°C operation . ( e )  Balance(s) .—Analytical, capable of accurately measuring weights from 1 mg to 10 g. ( f )  Gas chromatograph-mass spectrometer .—Any GC/MS instrument [single quadrupole, triple quadrupole, time-of-flight (TOF), or ion trap] with electron ionization (EI) may be used as long as it provides results meeting the laboratory qualification requirements (to provide reliable results for the calibration range specified in Table 2014.08A ). ( g )  GC column .—Capillary column BPX-50 (30 m, 0.25 mm id, 250 µm film thickness; Trajan Scientific, Austin, TX, USA) or equivalent (USP specification G3), such as Rxi-17Sil MS (Restek Corp., Bellefonte, PA, USA); DB-17MS, DB-17, or HP-50 (Agilent Technologies, Santa Clara, CA, USA); or any other column that enables adequate separation of PAHs as specified in the laboratory qualification requirements ( see G ). C. Reagents and Materials ( a )  Hexane.— >98.5%, mixture of isomers. ( b )  Isooctane.— ACS or better grade. ( c )  Ethyl acetate.— >99.5%, for GC residue analysis.