Final answer:
Tartrate is added to azobilirubin in the Jendrassik-Grof method for bilirubin to stabilize the reaction, enhance color development, and increase the sensitivity of the test.
Step-by-step explanation:
In the Jendrassik-Grof method for bilirubin, tartrate is added to azobilirubin to stabilize the reaction and enhance color development. Tartrate helps to prevent interference from substances like hemolysis, which could affect the accuracy of the measurement. By stabilizing the reaction and enhancing color development, tartrate increases the sensitivity of the Jendrassik-Grof method for bilirubin.