PREPARATION OF MILK SAMPLES FOR IMMUNOASSAY AND LIQUID-CHROMATOGRAPHIC SCREENING USING MATRIX SOLID-PHASE DISPERSION

The use of drugs to maintain the health and maximize the output of dai ry cattle has made the monitoring of milk for such agents essential. S creening tests based on immunological, microbial inhibition, and bacte rial receptor assays have been developed for the detection of violativ e levels of therapeutic substances. However, such assays are not infal lible, and false positive or negative results can occur when contamina nts bind receptors or compete for the binding of the target residues. Such effects may arise from dietary sources, diseases, or other variab les. Thus, a violation by such a test is not definitive until further confirmation is obtained. Our laboratory has developed extraction proc edures for several drugs used in dairy production. Our method uses mat rix solid-phase dispersion (MSPD) to isolate drugs away from contamina nts and to eliminate many possible interferences. MSPD can also be use d to enhance the specificity of such assays by fractionating various c lasses of drugs that may cross-react. Similarly, such methods may be u sed for liquid chromatographic screening and confirmation of a suspect sample.