1. Department of Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5C9 Canada, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5B4 Canada, and Canadian Food Inspection Agency, Centre for Veterinary Drug Residues, Saskatoon Laboratory, 116 Veterinary Road, Saskatoon, Saskatchewan, S7N 2R3 Canada