Diatomaceous earth columns used with reversed and normal solid phase extraction (SPE) cartridges were evaluated for the quantitative determination of a number of organophosphorus (OP) and organochlorine (OC) pesticide residues in edible vegetable oils and butterfat. An oil or fat sample (about 2 g) in hexane was passed through a diatomaceous earth (Extrelut QE) column and a Cis bonded silica (ODS) SPE cartridge, resulting in the separation of the pesticides from about 98% of the lipids. The eluate was split in half, with the first portion concentrated into acetone for the determination of OP pesticides by gas chromatography with flame photometric detection (GC–FPD). The other half was passed through an Alumina-N SPE cartridge for additional cleanup of lipid matrix to determine OC pesticides by GC with electron-capture detection (GC–ECD). Average recoveries from fortified samples were greater than 89% for the pesticides studied.
Separation of trace levels of toxic pesticides and other chemical contaminants (e.g., PCB) from edible fats and oils in preparation for quantitation by gas chromatography (i.e., GC-EC, GC-MS, etc.) continues to be an important analytical concern. Commercial HPLC silica columns were evaluated for practical application to the fractionation of selected compounds of different polarity from butterfat. Samples were injected in hexane solution and fractionated usinq isocratic hexanemethylene chloride mobile phases. Fat was readily purged from the columns with methylene chloride. A 254-nm UV detector was used to monitor elution patterns of concentrated standard solutions and of lipid material. Analyte fractions subsequently collected from samples fortified at sub-ppm levels were analyzed by GC-EC after concentration into hexane. A semipreparative HPLC silica column (25 cm x 9 . 4 mm i.d., 6 um spheres) provided complete separation of organochlorine compounds and partial separation of organonhosDhorous pesticides tested from at least 5 0 0 mg of fat. This column was shown to be superior to the "official" (AOAC) Florisil column with regard to resolution, speed of elution, solvent volume required, and loading capacity. The column, which operated at mod-2111
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