The standard curve with HRP-anti-SAM 4 in direct competitive ELISA using 4-parameter logistic non-linear regression model. The 0.25 µg/ml of SAM coating standard (Cat # ACT00201) was coated on micro-titer wells. Serial dilution of SAM standard (Cat # AST00201) was added along with 1 :8000 diluted HRP-anti-SAM 4 and was incubated for about 60 minutes. The substrates were then added and OD450 was measured.