Analysis of aged sulfadiazine residues in soils using microwave extraction and liquid chromatography tandem mass spectrometry.

An efficient extraction of sulfadiazine residues from soils is difficult, as sulfadiazine is known to form quickly sequestering residues. The objective of this study was to optimize an exhaustive extraction for aged residues of sulfadiazine and its two major metabolites, N-acetylsulfadiazine and 4-hydroxysulfadiazine, from soil. For this purpose two representative used agricultural soils (Luvisol, Cambisol) were blended with manure derived from [(14)C]sulfadiazine-treated pigs and incubated at 10 degrees C in the laboratory. After different extraction tests with various solvent mixtures (two- to four-component mixtures with water, methanol, acetonitrile, acetone, and/or ethyl acetate), different pH values (pH 4 and 9), and extraction temperatures (up to 200 degrees C), soil extracts were measured by liquid scintillation counting and liquid chromatography coupled to tandem mass spectrometry. With respect to sulfadiazine yields, stability of soil extracts, and the amount of coextracted matrix, a microwave extraction of soil (15 min, 150 degrees C) using acetonitrile/water 1:4 (v/v) is the method of choice for the exhaustive extraction of aged sulfadiazine residues from soils.