MULTI-RESIDUE ANALYSIS FOR BETA-AGONISTS IN URINE AND LIVER SAMPLES USING MIXED-PHASE COLUMNS WITH DETERMINATION BY RADIOIMMUNOASSAY

A method is described for the extraction of four beta-agonists, clenbu terol, salbutamol, mabuterol and terbutaline from bovine urine and liv er samples using radioimmunoassay (RIA) as the method of determination . Following enzymic digestion of the liver samples using protease enzy me, the digest is centrifuged and the harvested supernatant is saturat ed with sodium chloride and adjusted to pH 11.0. An ethyl acetate-prop an-2-ol mixture is used to extract the beta-agonists from the liver di gest. The samples of urine and liver extracts ace adjusted to pH 6.0 a nd applied to mixed phase (XtrackT) columns. The column is washed with water and methanol and the beta-agonists are eluted with methanol con taining 2% ammonia. After evaporation of the eluting solvent and recon stitution in ethanol the beta-agonist residues are determined by RIA, with standard graphs prepared in residue-free sample extract. The proc edure has been validated for clenbuterol, salbutamol, mabuterol and te rbutaline. The mean recovery of the beta-agonists from urine and liver is > 75% and > 85%, respectively. The detection limit is 0.13 ng ml(- 1) and 0.46 ng g(-1) of clenbuterol in urine and liver, respectively. The high recoveries attained for both types of beta-agonists are a res ult of an efficient liquid-liquid extraction step coupled with a selec tive mixed solid-phase extraction procedure.