Sample extraction, filtration and concentration

Weigh 2.5 or 5 g of crop matrix into a blending vessel. Fortify samples at this point with the appropriate analytical standards. Allow the solvent to evaporate. Add 100 mL of acetone-water (4 1, v/v) and blend the mixture using an Omni mixer equipped with a macro generator for 5 min at 6000-7000 rpm. Filter the sample through a Whatman 934 AFI glass-fiber filter paper on a Buchner funnel/vacuum flask setup. Rinse the blending cup and filter cake with 100 mL of acetone. Transfer the filtrate into a 200-mL TurboVap vessel. 

Concentrate the sample (remove acetone) under nitrogen to ca 20-25 mL using a TurboVap (water-bath at 50 °C). Transfer the sample into a 50-mL polypropylene centrifuge tube. Rinse the TurboVap vessel with 5 or lOmL of pFI 6 buffer solution. The amount of pH 6 buffer required depends on the matrix being analyzed and should be determined as needed. All matrices need 5 mL of the buffer solution to adjust the sample to pH 6, except for sweet corn (ears, forage, and stover), which requires 10 mL. Add the rinse buffer to the sample. Rinse the TurboVap vessel with 10 mL of hexane and add the hexane to the sample. 

Vigorously mix the aqueous and hexane fraction to partition carfentrazone-ethyl into the hexane fraction. Centrifugation may be necessary to break any emulsion that occurs. Remove and collect the hexane fraction for analysis of carfentrazone-ethyl. Partition the aqueous fraction with an additional 10 mL of hexane and add the hexane to the hexane from the first partition step. The aqueous fraction will be used for the analysis of the acid metabolites (see below). 

Concentrate the hexane fraction (20 mL) from the previous hexane-aqueous partition to 3 mL in a TurboVap at ca 50 °C. 

For fodder, hay or straw matrices, in order to exclude an interference which only occurs in the dry matrices, a slightly less polar elution solvent (7.5% vs 10% ethyl acetate in hexane) and a larger volume (18 mL) are used. 

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