INDIRECT DETERMINATION OF BILIRUBIN BY LINEAR SWEEP POLAROGRAPHY

A polarographic method for the determination of bilirubin is described : In hydroquinone-sodium phosphate buffer (pH 11.2) medium, bilirubin can be rapidly oxidized to a green product, which causes a sensitive p olarographic wave at -0.83 V (vs. SCE); the peak current of the wave i s linear with the bilirubin concentration over a range of 3 x 10(-7) t o 5 x 10(-6) mol/l. It has also been found to be more stable than that produced by bilirubin; in general, it can remain unchanged for about 1 h at room temperature and exposure to air. This overcomes the instab ility of bilirubin for its direct assay to a certain extent. If a smal l amount of EDTA is added to the solution, the stability of the wave c an be further improved. In addition, the characteristics of the wave h ave been investigated and it has been confirmed to be an adsorptive ca talytic wave. The chemical reaction mechanism is discussed and the gre en product is confirmed to be biliverdin.