Gum guaiac is a tree resin and crude source of 2,5-di-(4-hydroxy-3-methoxyphenyl)-3,4-dimethylfuran (α-guaiaconic acid).The phenolic α-guaiaconic acid acts as a colorimetric peroxidase substrate.When reacted with an organic or inorganic oxidizing agent, the α-guaiaconic acid is oxidized to a blue-colored quinone. The guaiac reaction has been used to detect trace amounts of heme from hemoglobin in the presence of peroxide.
