- Development of clenbuterol reference materials: lyophilized bovine eye samples free of clenbuterol (CRM 673) and containing clenbuterol (CRM 674). Part 2: certification. Pfaffl, M.W., van Ginkel, L.A., McEvoy, J.D., Maghuin-Rogister, G., Meyer, H.H. Fresenius' journal of analytical chemistry. (2001)