β‐Agonists in animal feed I: First intercomparison of methods of analysis for clenbuterol in animal feed materials

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Abstract
The European Commission, Measurement and Testing Programme (BCR) has initiated a project to improve the methodology for analysis β‐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 μg/kg) was 39%, for the intermediate level (100 μg/kg) 52% and for the high level (1000 μg/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.