6. AOACSPIFANMethods-2018Awards

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Table 2015.02E. Performance values of analytes a

Between-day CV (WLR)

U (for 95% CI)

Recovery, % (SD)

Compound

LOD, µg/kg LOQ, µg/kg LOR, µg/kg Within-day CV

1.0 b

97 c (8.8)

Fluoroacetic acid

0.028

0.085

8.8 NA

9.1 NA

18

13 C 2 70 d (12) a LOD = Limit of detection; LOQ = limit of quantification; CV = coefficient of variation; WLR = within-laboratory reproducibility; U = uncertainty of measurement with a 95% confidence interval; SD = standard deviation. b  Limit of reporting (LOR) set according to New Zealand maximum permitted residue limits. See reference 1. D 2 Fluoroacetic acid NA NA NA NA

c  Relative recovery. d  Absolute recovery.

hydrochloric acid at about 30 drops/min. Remove residual hydrochloric acid solution into the collecting tubes under vacuum. ( 9 ) To the matrix standard tube only, add 125 µL WS2 and 40 µL ISWS, cap, and vortex mix. ( 10 ) To all tubes add 1.25 mL of 20 mg/mL 3-nitroaniline and 0.25 mL of 100 mg/mL EDAC solution followed by 0.5 mL of 2 M potassium hydroxide and 1 mL of 0.05 M potassium dihydrogen phosphate buffer. Cap and mix. ( 11 ) Place tubes in a 40 ± 2°C water bath for 20 min. ( 12 ) Remove tubes and cool to room temperature. ( 13 ) Set up a vacuum manifold with Oasis HLB, 60 mg, 3 mL cartridges. ( 14 ) Condition the cartridge with 1 mL methanol. Close the stopcock when the methanol reaches the top frit. ( 15 ) Load a portion of the derivatized extract onto the conditioned SPE cartridge. ( 16 ) Place an adapter and 10 mL reservoir on top of the cartridge. ( 17 ) Transfer the remaining derivatized extract into the reservoir and open the stopcock. Allow to drip slowly to waste at about 30–40 drops/min. ( 18 ) When the extract has passed through the cartridge, remove the adapter and reservoir. ( 19 ) Wash the cartridge with 2 mL 25% (v/v) sulfuric acid, 1 mL deionized water, 1 mL 0.1 M sodium hydrogen carbonate, and a further 2 mL deionized water to waste. ( 20 ) Dry cartridge by applying full vacuum for 5 min. ( 21 ) Place 15 mL polypropylene tubes beneath each SPE. Elute the derivatized extract with 2 × 2.5 mL TBME– n -hexane (70 + 30, v/v) into the tubes. ( 22 ) Dry the cartridge by briefly applying a full vacuum. ( 23 ) Check tubes for remaining water. There should be minimal water present. Presence of more than about 50 µL water would indicate inadequate vacuum. ( 24 ) Add approximately 200 mg sodium sulfate, anhydrous, to each tube and vortex mix. ( 25 ) Centrifuge at 2400 × g RCF for 1 min.

E. Sampling and Sample Preparation Preparation of test portion .—Accurately weigh 2.5 ± 0.03 g of room temperature sample into a labeled 50 mL polypropylene tube. In addition to the analytical samples, there are four recovery samples per batch, a reagent blank, and an extra blank for the matrix standard. F. Procedure ( a ) Fortification .—( 1 )  Analyte .—Fortify the recoveries as shown in Table 2015.02A using the working solutions prepared in D ( d ). Note : Do not add any WS to the matrix blank to be used for the matrix standard. ( 2 ) Internal standard .—Add 40 µL ISWS to all unknown and recovery samples. Note : Do not add any ISWS to the matrix blank to be used for the matrix standard. ( 3 ) Allow test portions to equilibrate for 10 min at room temperature. ( b ) Extraction .—( 1 ) Place the resin chromatography columns onto a vacuum manifold and fill with 1.4 (±0.2) mL resin. Add 2.5 mL deionized water above the resin bed and close stopcock. Fit suitable reservoirs above the columns. ( 2 ) To each test portion add 5 mL water and briefly shake vigorously by hand, cap, and then shake tubes at medium speed on a reciprocating shaker for 5 min to dissolve. Variation to this procedure may be required for atypical matrixes. ( 3 ) Add 10 mL acetone to each tube and briefly shake vigorously by hand followed by 2 min on a reciprocating shaker at medium speed. ( 4 ) Centrifuge at 4200 × g RCF for 10 min. ( 5 ) Carefully pour the top solvent layer into the reservoirs above the resin, taking care not to transfer any precipitate. ( 6 ) Allow samples to pass through the resin columns under gravity or gentle vacuum, if required. ( 7 ) After samples have passed through the resin columns, remove the reservoirs and wash the resin columns with 1 mL of 0.2 M hydrochloric acid. Close stopcock. Do not allow the resin to dry. ( 8 ) Place 15 mL polypropylene tubes beneath each resin column. Elute samples with one 5 mL volume of 0.2 M

Table 2015.02F. Relative retention time (RRT) and limits of acceptance Compound (3-nitroaniline derivative of analyte) Monitored compounds

Acceptance limit a

RRT

1.004 b

2-Fluoro-3 ʹ -nitroacetanilide

Analyte/internal standard

RRT ± 2.5%

a See reference 2. b  Representative relative retention time. These values are indicative and should be measured for each individual batch.