Confirmation and 3D profiling of anabolic steroid esters in injection sites using imaging desorption electrospray ionisation (DESI) mass spectrometry

In this study, desorption electrospray ionisation (DESI) linear ion trap tandem mass spectrometry (MSn) was applied for the confirmation and three-dimensional profiling of anabolic steroid esters in an injection site of bovine muscle. The spatial resolution of the DESI-MSn was demonstrated by scanning hormone esters and marker ink lines drawn at various distances on a microscopic slide at set distances, using an x-scanner with manual y and z adjustment. Tissue slices of bovine muscle injected with a hormone cocktail were analysed. All anabolic steroid esters could be directly detected in the sample and confirmed on the basis of identification points awarded for selected MS/MS transitions according to the performance criteria given in Commission Decision 2002/657/EC. Moreover, the injection site could be mapped by two-dimensional and three-dimensional imaging MS, showing a horizontal and vertical distribution through the muscle tissue. This DESI approach offers potential for analysis of injection sites of steroid esters from illegally treated animals; moreover, direct analysis by ambient imaging DESI-MS still allows conventional extraction and analysis of the whole tissue for further confirmatory or contra-analysis afterwards.