Beta-agonists in animal feed. I: First intercomparison of methods of analysis for clenbuterol in animal feed materials.

The European Commission, Measurement and Testing Programme (BCR) has initiated a project to improve the methodology for analysis of beta-agonists in animal feeding stuffs. An intercomparison of methods for clenbuterol in animal feed is described. The study involved 13 European laboratories which analysed a blank feed and three feed samples with three different levels of clenbuterol contamination. The participants used a variety of extraction (organic or aqueous solvents), clean-up (liquid-liquid, silica and C-18 solid phase and immuno-affinity chromatography) and end-point detection (HPLC, GC-MS and TLC) steps. The purpose of this study was to identify and to quantify clenbuterol. The coefficient of variation from all the results for the low level (25 micrograms/kg) was 39%, for the intermediate level (100 micrograms/kg) 52% and for the high level (1000 micrograms/kg) 35%. The study showed that the initial extraction, the modular clean-up step and their compatibility to the HPLC and the GC-MS determination step were critical steps.