Comparison between liquid chromatography and supercritical fluid chromatography coupled to mass spectrometry for beta-agonists screening in feeding stuff.

β-agonistic drugs have been forbidden as growth promoters in rearing animals in Europe since the late 1980s (Dir 96/22/EC). Specific and sensitive analytical methods based on UHPLC-MS/MS allow to monitor a large set of these substances. However, optimal performances are not observed for all the target analytes, especially for those exhibiting the highest polarities. We developed an SFC-MS/MS approach to cover the huge elution window of β-agonists, from the most polar which are usually eluted in the void volume when using reversed phase chromatography in conventional HPLC to the most apolar ones. The objective was to reach performances in accordance with the European Union recommended level in feeding stuff, i.e. 50 μg kg. LC/MS and SFC/MS performances were thoroughly compared in terms of analytical validation data (linearity, selectivity, recovery rates, reproducibility, compounds identification, trueness, decision limit (CCα) and detection capability (CCβ)) for 6 β-agonistic drugs, namely bromobuterol, clenbuterol, isoxsuprine, ractopamine, salbutamol and zilpaterol. As a result, the SFC approach appeared complementary to the LC one because the elution order of compounds was totally different from the one obtained with a classical C18 stationary phase. Moreover, the UPLC-MS/MS approach gave a better response linearity and more accurate values, whereas SFC-MS/MS provided greater data for identification purposes, reproducibility and sensitivity. Both analytical approaches enabled the detection of targeted β-agonists at a lower concentration than the recommended one (50 μg kg).