Determination of the rodenticides difenacoum and brodifacoum in finished baits by reversed-phase liquid chromatography

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Abstract
A specific method is described for the analysis of 0.005% difenacoum and brodifacoum baits with an error of less than 10%. The method involves maceration of 50 g of sample in methanol-formic acid (50 + 1) and clean-up by column chromatography on Florisil-silica gel. The dichloromethane-methanol solution of the residue, with 1,3,5-triphenylbenzene as internal standard, is injected into a liquid chromatograph, equipped with a 10-cm Partisil-5 ODS column and an ultraviolet detector set at 254 nm, methanol-water-glacial acetic acid (90 + 10 + 0.8) being used as the mobile phase at ambient temperature. The method is also applicable to technical difenacoum and brodifacoum, and to 0.1–10% liquid and powder concentrates, with simpler procedures for preparing the test solutions. A thin-layer chromatographic method, using silica gel GF254 and 1,4-dioxan-light petroleum (boiling range 80–100 °C)(3 + 7) as the developing solvent, was found to be adequate for establishing the relative purity of technical samples. Two major impurities were identified.

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