Determination of ractopamine in animal hair: Application to residue depletion in sheep and residue monitoring

• A method for determination of ractopamine (RAC) in hair containing RAC was established and validated by incurred hair.
• Depletion of RAC in hair was studied in healthy sheep.
• The method was successfully applied to residue monitoring in RAC.

An ultra-performance liquid chromatography tandem mass spectrometry method to determine ractopamine (RAC) in hair samples from swine, sheep, and cattle was developed. The procedure to extract from incurred hair was optimized. The samples were extracted with 0.1 mol/L HCl solution. The mixture was heated to 60 °C in water bath for 4 h. The extracts were purified by solid-phase extraction, dried under a stream of nitrogen, and then reconstituted in mobile phase for analysis, which was performed with a Waters BEH-C18 column. The limit of detection was 0.3 ng/g, the limit of quantification was 1 ng/g, the recoveries were between 87% and 105%, and the coefficient of variation was less than 15%. The depletion of RAC in hair was studied in healthy sheep after administration of RAC at 1000 ng/g body weight for five consecutive days. The RAC residues were still detected with 82.5 ± 7.2 ng/g hair 27 days after drug administration. Five samples tested positive, in which the amount of RAC detected was 13–253 ng/g from 569 hair samples collected from farms and slaughterhouses. These results show that animal hair is a suitable medium to monitor the illegal use of RAC in livestock production.