3-Nitroso-4-hydroxy-5,6-benzocoumarin as a selective reagent for the spectrophotometric determination of ruthenium(III)

The pinkish-violet complex developed on interaction of ruthenium(III) with 3-nitroso-4-hydroxy-5,6-benzocoumarin (NHBC) in the pH range 5.5-8.0 can be extracted into n-butanol. The complex has an absorption maximum at 520 nm. Maximum colour development takes place after heating for 20 min on a steam-bath and the extracted complex is stable for at least 92 hr. Beer's law is followed up to 7.4 ppm of ruthenium. The molar absorptivity is 1.04 x 10(4) 1.mole(-1).cm(-1). The composition of the complex is 1 : 2 (ruthenium: NHBC). None of the other platinum metals was found to interfere in the determination of ruthenium, even though present in large excess.