Direct ELlSAs for Sulfathiazole in Milk and Honey with Special Emphasis on Enzyme Conjugate Preparation

Direct competitive enzyme‐linked immunosorbent assays (ELISAs) were developed for sulfathiazole (ST) analysis. Polyclonal antibody rabbit serum adsorption to polystyrene microtiter plates was enhanced using a 1 μg/mL Protein A precoating solution. Detection limits (20% reduction in maximum enzyme signal) for ST in milk and honey were 12.0 and 34.7 ppb (ng/L), respectively. ST‐horseradish peroxidase (HRP) conjugates prepared by linking the N 4 ‐amino group of ST to periodate‐treated HRP were more efficient than those prepared using a more conventional two‐step glutaraldehyde method. This represents a new method of preparing sulfonamide conjugates for use in ELlSAs.