Identification of incurred sulfonamide residues in eggs: methods for confirmation by liquid chromatography-tandem...

Two complementary methods for identifying and measuring sulfonamide residues in eggs were developed for use in surveying eggs for potential drug residues. The first method uses liquid chromatography-tandem mass spectrometry (LC-MS-MS) to confirm the presence of sulfonamide residues in eggs. During its validation the limit of confirmation was estimated to be 5-10 ng/g (ppb) depending on the drug. Also, a method for measuring residue level by liquid chromatography with ultraviolet detection (LC-UV) was validated using the same extraction procedure as the confirmatory method. The determinative method was validated over the 50-200 ppb range. Samples were prepared by homogenizing whole egg, extracting with acetonitrile, and cleaning up with a C(18) solid-phase extraction cartridge. For confirmation, analytes were separated by gradient LC on a C(18) column, ionized by electrospray ionization (ESI), and detected by MS-MS with an ion trap mass spectrometer. For determination, analytes were separated by a different gradient LC procedure and detected by UV at 287 nm. Fifteen drugs were dosed individually in laying hens, and residues of parent drug and/or metabolites were found in eggs for all the drugs. Validation was based on repetitive analyses of control samples, control samples fortified at 100 ppb sulfonamides, and samples of blended incurred eggs.