Correlation of ELISA and LC–MS/MS methods in determination of urinary ractopamine residual concentrations in treated pigs

Abstract

Ractopamine is a phenethanolamine β-adrenergic agonist that promotes muscle growth in swine. It appears to reduce fat deposition through a direct action on adipose tissue, thus increasing the rate of lipolysis and decreasing lipid synthesis. As the use of β-agonists, including ractopamine in farm animals for meat production is banned in EU, and in order to monitor for their illegal use, sensitive analytical methods able to detect low concentrations in appropriate matrices should be employed. The aim of the study was to correlate residual ractopamine concentrations in urine of pigs during fattening, using previously validated enzyme-linked immunosorbent assay (ELISA) as a screening method and liquid chromatography tandem mass spectrometry (LC-MS/MS) as a confirmation method. On days during the 28-day treatment and 24 hours of withdrawal of ractopamine administration in anabolic dose, ractopamine residual concentrations were determined in urine of 9 treated and 3 control pigs, with and without sample enzyme hydrolysis with β-glucuronidase. The level of ractopamine and its conjugates in pig urine processed with enzyme hydrolysis for both analytical methods was 2-fold to 10-fold that of urine samples analyzed without enzyme hydrolysis, with maximal mean value of 768.6±202.7 ng/mL on day 24 of treatment. The correlation coefficient for ELISA and LC-MS/MS methods was 0.991 with hydrolysis and 0.958 without hydrolysis, yielding a high correlation between the analytical methods in determination of ractopamine residues in urine as a matrix for monitoring its abuse.