The Atrazine Tube Kit uses polyclonal antibodies that bind both atrazine and an atrazine-enzyme conjugate. Any atrazine present in the sample competes with an atrazine-enzyme conjugate for a limited number of antibody binding sites. Antibodies, which bind atrazine, are immobilized to the inside of the test tubes. In the assay procedure you will:

•   Add samples or calibrators containing known amounts of atrazine and an atrazine enzyme conjugate to test tubes coated with anti-atrazine antibodies.
•   Wash away any unbound molecules, after you incubate this mixture for 20 minutes.
•   Add clear substrate solution to each tube. In the presence of bound atrazine-enzyme conjugate, the substrate is converted to a blue compound. One enzyme molecule can convert many substrate molecules.

Since the same number of antibody binding sites are available in every tube, and each tube receives the same number of atrazine-enzyme conjugate molecules, a sample containing a low concentration of atrazine allows the antibody to bind many atrazine-enzyme conjugate molecules. The result is a dark blue solution.

Conversely, a high concentration of atrazine allows fewer atrazine-enzyme conjugate molecules to be bound by the antibodies, resulting in a lighter blue solution.