DETERMINATION OF SULFAMETHAZINE RESIDUES IN MILK BY A SURFACE-PLASMONRESONANCE-BASED BIOSENSOR ASSAY

The use of antibiotics and chemotherapeutics in animal husbandry has l ed to the occurrence of veterinary drug residues in all types of food of animal origin. Due to the specification of toxicologically based ma ximum residue levels for a large number of substances, existing contro l strategies need even faster acid more sensitive methods to meet new and more rigorous regulations. The applicability of an immunosensor de vice for biospecific interaction analysis was investigated and the dev elopment of an assay for analysis of sulfamethazine (SMZ) in milk is d escribed. SMZ was covalently immobilized to a carboxymethyldextran-mod ified gold film. Spiked samples with known concentrations of SMZ were prepared in HBS buffer and skim and raw milk for construction of stand ard curves. Polyclonal antibodies against SMZ were added to the sample and the immobilized surface was used to determine the amount of free antibodies by surface plasmon resonance detection. After each measurem ent the surface was regenerated by NaOH and HCl. In milk, the mean rel ative standard deviation of the assay was approximately 2% and the lim it of detection less than 1 ppb. By introduction of a secondary sheep anti-rabbit antibody, the use of specific antibody could be reduced. M ilk samples from the individual cow, herd, and tanker levels were anal yzed and the relative standard deviations within each sample category were 4.4, 2.4, and 2.2%, respectively. The effect of some potential in terferences, e.g., high somatic cells, bacterial contamination, and pr eservatives, was investigated. The results were not influenced in such a way that the risk for so-called false-positive findings was obvious . (C) 1995 Academic Press, Inc.