Extraction-spectrophotometric determination of boron with 2,6-dihydroxybenzoic acid and 4-(4-diethylaminophenylazo)-N-methylpyridinium iodide, with application to steels

The sensitive and selective method reported is based on the reaction of boric acid with 2,6-dihydroxybenzoic acid in acidic aqueous solution to form a 1:2 complex anion which can be extracted into chloroform as an ion-pair with 4-(4-diethylaminophenylazo)-N-methylpyridinium ion. The ion-pair formed by the excess of reagents and co-extracted into chloroform, is removed by washing the organic phase with phosphate buffer solution (pH 7.0) and 0.025 M sulfuric acid solution. The absorbance of azo dye in chloroform is measured at 570 nm. Calibration graphs are linear in the range 0-1.5 x 10-5 M of boron. The molar absorptivity is 6.6 x 104 l mol-1 cm-1 and the absorbance of the reagent blank is 0.030. The method was applied to the determination of boron at the 0.001% level in steels. (Auth.)