Determination of chlorophacinone in formulations by reversed-phase ion-pair chromatography

Abstract

The retention behaviour of chlorophacinone [2-( p-chlorphenyl)phenylacetyl-1,3-indandione] has been studied using an octadecylsilica column and different eluents, e.g., methanol-water, methanol-aqueous phosphoric acid, methanol-aqueous McIlvaine buffer-tetramethylammonium bromide and tetrahydrofuranaqueous McIlvaine buffer-tetrabutylammonium bromide. The dependence of log k′ on the organic modifier content and the apparent pH of the eluents was determined. The retention behaviour could be interpreted by assuming that chlorophacinone existed mostly as a weakly acidic enol that could dissociate depending on the pH of the eluent. Chlorophacinone could be separated and determined quantitatively in 0.25–25% (w/w) oily formulations and in 10–100 ppm crushed grain bait using diphacinone [2-(diphenylacetyl)-1,3-indandione] as an internal standard.