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A new procedure is described for the determination of polybrominated biphenyls (PBBs) in dry animal feeds and developmental results are discussed. Finely ground feed is packed into a chromatographic column containing Celite and then eluted with methylene chloride. The concentrated extract is cleaned up by elution with petroleum ether through Florisil before gas-liquid chromatographic quantitation. Chromatograms thus obtained were essentially free of the interfering peaks encountered when using AOAC methods for pesticide residues in dry products. Results of feed analyses by the proposed procedure averaged 30% higher than those obtained by AOAC procedures. Recoveries of PBBs from samples fortified at levels of 0.04 to 0.4 ppm ranged from 90 to 104%, with an average of 98%.

Many residue laboratories use the retention ratio data compiled by the Food and Drug Administration in its Pesticide Analytical Manual (PAM) for the tentative identification of pesticide and industrial chemical residues detected in food samples. These data were compiled using packed gas chromatographic columns. A study was undertaken to determine if these retention ratios could be used when applying capillary gas chromatography to residue analysis. Retention ratios of a selected group of 108 of the materials listed in the PAM tables were determined isothermally with split injection on 4 WCOT capillary columns obtained from 3 commercial suppliers and coated with 4 different methyl silicone coatings. Of the tested reference materials, 90 displayed retention ratios that matched the PAM values on all columns, 10 differed on at least one of the 4 columns, and only omethoate and monocrotophos gave retention ratios differing on all 4 columns.

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