The Calbiotech Cotinine kit is a solid phase competitive ELISA. The samples and Cotinine enzyme conjugate are added to the wells coated with anti-Cotinine antibody. Cotinine in the samples competes with a Cotinine enzyme (HRP) conjugate for binding sites. Unbound Cotinine and Cotinine enzyme conjugate is washed off by washing step. Upon the addition of the substrate, the intensity of color is inversely proportional to the concentration of Cotinine in the samples. A standard curve is prepared relating color intensity to the concentration of the Cotinine.