ABSTRACTDirect 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 N4‐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
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