Flunixin is approved for use in veterinary medicine as a nonsteroidal anti-inflammatory agent. There is a need for the control of residues and development of methods to monitor its compliance with legislation. However, few methods have been reported for the analysis of flunixin in the animal liver, kidney, and fat. Therefore, the aim of this work was to develop a relatively rapid sample preparation and sensitive using liquid chromatography–tandem mass (LC-MS/MS) confirmatory method to detect flunixin residues in the liver, kidney, muscle, and fat of swine and chicken. After acid hydrolys...