Cerium (IV) has a catalytic effect on the very slow redox reaction between
gallocyanine and bromate in acidic media. The reaction was monitored
spectrophotometrically at 525 nm by a fixed time method of 4.0 rnin from initiation
of the reaction. The decrease in absorbance at 525 nm is proportional to the Ce (IV)
concentration in the range of 0.005-1.000 and 1.00-10.00 pg. ml-l. The limit of
detection is 2.0 ng.ml-'. The relative standard deviation for ten replicate analyses of
0.100 pg.ml-' is 1.5%. The method is used for the determination of cerium in synthetic and in real samples, with good accuracy. The effect of interfering cations and anions was also studied.