Determination of gamithromycin residues in eggs, milk and edible tissue of food-producing animals by solid phase extraction combined with ultrahigh-performance liquid chromatography-tandem mass spectrometry.

A high throughput method was developed and validated for the quantitation of gamithromycin residues in eggs, milk and animal tissues (leg muscle, kidney, liver and fat) of different species and genera. This was undertaken using ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The samples were extracted with acetonitrile and purified using an Oasis MCX solid phase extraction cartridge. Subsequently, a C18 column was used for chromatographic separation using acetonitrile and 0.1% formic acid as the mobile phase. LC-MS/MS in positive ESI and multiple reaction monitoring mode with gamithromycin-D4 as the internal standard was used for detection and quantification of gamithromycin. The method was successfully calibrated in the range of 1.0-200 µg/kg. The limit of detection (LOD) and limit of quantification (LOQ) for gamithromycin was 0.30-0.40 µg/kg and 0.80 - 1.0 µg/kg, respectively. The average recoveries of the analyte fortified at three levels ranged from 84.2% to 115.9%, with a relative standard deviation <10%. The proposed method has been successfully used to monitor real samples, and shown to be sensitive, rapid, and convenient. Hence, this method could be used for regulatory purposes to screen for the presence of gamithromycin residues in eggs, milk and target tissues.