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1136  Reddy : J ournal of AOAC I nternational Vol. 98, No. 4, 2015

( h ) Centrifuge tubes .—2, 15, and 50 mL. ( i ) Spatulas and scoops . ( j ) Centrifuge .—Thermo Fisher Scientific (http://www. thermofisher.com) Sorvall Legend XTR, or equivalent. ( k ) Glass centrifuge tubes with screw cap .—VWR (Cat. Nos. 99502-15 and 89001-048, respectively; https://www.vwr. com). ( l ) Water bath .—Thermo Fisher Scientific Precision model 2872, or equivalent. ( m ) Glass Pasteur pipets . ( n ) Vacuum manifold for SPE . ( o ) SPE cartridges .—Supelclean Envi-Chrom P, 500 mg, 6 mL (Cat. No. 57226; Sigma-Aldrich, https://www. sigmaaldrich.com). ( p ) SPE cartridge reservoirs .—25 mL (Supelco; Cat. No. 54258-U). ( q ) Positive displacement pipets .—Gilson (http://www. gilson.com) Microman (M); Model Nos. M10, M100, M250, and M1000. Part Nos. F148501, F148504, F148505, and F148506. ( r ) Positive displacement pipet tips .—Gilson Capillary Piston (CP); Reference Nos. CP10, CP25, CP100, CP250, and CP1000. Part Nos. F148412, F148414, F148014, and F148560. ( s ) Plastic syringes .—B&D 3 mL, or equivalent. ( t ) Syringe filters .—PTFE 0.2 µm, Acrodisc 13 mm, Part No. 28143-930, or equivalent. ( u ) Autosampler vials .—Glass, 2 mL, 12 × 32 mmwith screw neck (PTFE pre-split septa caps). Waters (Cat. No. 186000847C; http://www.waters.com), or equivalent. ( v ) Vial inserts .—300 µL (Waters; Cat. No. WAT094170). ( w ) Chromatography equipment and supplies.— ( 1 ) Mass spectrometer .—Waters Xevo TQ-S tandem quadrupole, or equivalent. ( 2 ) Liquid chromatograph .—Waters Acquity UPLC, or equivalent. ( 3 ) LC column .—Waters Acquity UPLC ® BEH C 18 , 1.8 µm, 2.1 × 100 mm (Part No. 186002352). C. Reagents ( a ) Sodium fluoroacetate 99.3% .—Fluka PESTANAL (Cat. No. 31220-100MG; Sigma-Aldrich). ( b )  13 C 2 , 2 H 2 -fluoroacetate .—Cambridge Isotope Laboratories (Cat. No. CDLM-7943-0; http://www.isotope. com). ( c ) Acetonitrile .—Fisher Scientific Optima LC/MS grade (Cat. No. L-1693). ( d ) Ethyl acetate .—Fluka LC/MS Chromasolv (Cat. No. 34972-R). ( e ) Ethanol .—ACS reagent grade (≥99.5%; Sigma-Aldrich, Cat. No. 459844). ( f ) Hydrochloric acid .—Trace metal grade (Fisher Scientific, Cat. No. A508-P500). ( g ) Pyridine .—Sigma-Aldrich (Cat. No. 270970). ( h ) Ammonium acetate.— Fluka (Cat. No. 73594). ( i ) 2 - NPH 97% .—Sigma-Aldrich (Cat. No. N21588). ( j ) EDC .—Sigma-Aldrich (Cat. No. 03449). ( k ) Laboratory water .—18 MΩ-cm. D. Solutions ( a ) Monofluoroacetate stock standard .—Approximately 1000 µg/mL in water.

( 1 ) Weigh 13.0 ± 1.0 mg sodium fluoroacetate, record weight ( m ) to the nearest 0.1 mg, and transfer to a 10 mL volumetric flask. ( 2 ) Dissolve in 4–5 mL laboratory water, dilute to volume with laboratory water, and mix thoroughly. Store at room temperature. Expiration 6 months. ( 3 ) Calculate exact concentration C (µg/mL) = m × 0.993 × 100 × 0.780 where m = amount weighed (mg), 0.993 = purity, and 0.78 = conversion factor from sodium salt to free acid. ( b ) Monofluoroacetate working standard .—8 µg/mL in acetonitrile–water (60 + 40, v/v). ( 1 ) Calculate volume of stock standard to be used V (µL) = 10 × 1000 × 8/ C . ( 2 ) Transfer V μL monofluoroacetate stock standard to a 10 mL volumetric flask. ( 3 ) Bring to volume with acetonitrile–water (60 + 40, v/v). Expiration 6 months. ( c ) Monofluoroacetate working standard ( 1 + 10) .—0.8 µg/ mL in acetonitrile–water (60 + 40, v/v). ( 1 ) Transfer 100 µL monofluoroacetate working standard, 8 µg/mL, to 2 mL autosampler vial. ( 2 ) Add 900 µL acetonitrile–water (60 + 40, v/v) and mix well. Expiration 6 months. ( d ) Internal standard stock solution .—Approximately 100 μg/mL in water. ( 1 ) Transfer the contents of the 13 C 2 , 2 H 2 -fluoroacetate ampoule (~10 mg) to a 100 mL volumetric flask. ( 2 ) Rinse the ampoule three times with laboratory water and transfer each rinse to the volumetric flask. ( 3 ) Bring to volume and mix well. Expiration 6 months. ( e ) Internal standard working solution.— Approximately 2.0 μg/mL in acetonitrile–water (60 + 40, v/v). ( 1 ) Transfer 20 μL internal standard stock solution to 2 mL autosampler vial. ( 2 ) Add 980 μL acetonitrile–water (60 + 40, v/v) and mix well. ( 3 ) Scale proportionally as needed for the worklist. Expiration 1 day. ( f ) QC1 overspike solution .—0.5 µg/mL monofluoroacetate in water. ( 1 ) Calculate volume of stock standard to be used V (µL) = 10 × 1000 × 0.5/ C . ( 2 ) Transfer V μL monofluoroacetate stock standard to a 10 mL volumetric flask. ( 3 ) Add water to the 10 mL mark and mix well. ( g ) QC2 overspike solution .—10 µg/mL monofluoroacetate in water. ( 1 ) Calculate volume of stock standard to be used V (µL) = 10 × 1000 × 10/ C . ( 2 ) Transfer V μL monofluoroacetate stock standard to a 10 mL volumetric flask. ( 3 ) Add water to the 10 mL mark and mix well. ( h ) Acetonitrile–water (60 + 40, v/v) . ( 1 ) Transfer 60 mL acetonitrile to 100 mL glass bottle. ( 2 ) Add 40 mL water and mix well. ( i ) Acetonitrile–water (25 + 75, v/v) . ( 1 ) Transfer 25 mL acetonitrile to 100 mL glass bottle. ( 2 ) Add 75 mL water and mix well. ( j ) 0.1 N HCl–ethanol (50 + 50, v/v). ( 1 ) Transfer 0.5 mL hydrochloric acid to 100 mL glass bottle. ( 2 ) Add 50 mL water.