Optimization of conditions for the determination of boron by a ruthenium(II) complex having diol moiety: A mechanistic study

Two ruthenium(II) complexes, [Ru(bpy)₂(dhbpy-H_-1)]⁺ and [Ru(bpy)₂(dhphen)]²⁺ (bpy = 2,2′-bipyridine, dhbpy = 3,3′-dihydroxy-2,2′-bipyridine, dhphen = 5,6-dihydroxy-1,10-phenanthroline) were examined for use as a colorimetric reagent for the determination of boron. The reactions of boric acid with these two complexes were thermodynamically and kinetically studied in detail in order to specify the reactive species and to set up optimum condition for the determination of boron. The detailed analysis of the kinetic data for the reaction of the latter water-soluble complex showed that both boric acid and borate ion were reactive in an alkaline solution. The thermodynamically and kinetically optimum pH for the determination of boron was ca. 9 at 25 °C. A spectrofluorimetric determination of boron with the latter complex was attempted at 600 nm with excitation at 360 nm, and at pH 8.9 using CHES (N-cyclohexyl-2-aminoethanesulfonic acid) buffer. It was found that a trace amount of boron as low as ca. 2 × 10^-5 M (∼1 ppm) could be detectable.