Extractive spectrophotometric method for boron in steel samples without regulated organic solvents

The Methylene Blue extractive spectrophotometric method is a simple analytical method for boron and has been adopted as a JIS method for the determination of boron in steel samples. However, 1,2-dichloroethane, which is used in the method as an extraction solvent, is now one of the items of Environmental Quality Standards for water pollutants in Japan, and its use is severely restricted. Thus, we developed a Rhodamine 6G extractive spectrophotometric method of boron in steel to replace the Methylene Blue method. We use Rhodamine 6G as an extractive reagent and 4-methyl-2-pentanone as an extraction solvent. This method is based on an ion pair extraction process, i.e., BF4- and 10 μM Rhodamine 6G form an ion-pair in the water phase and the ion-pair is extracted into 4-methyl-2-pentanone. The absorbance of the organic phase was measured with a spectrophotometer at 530 nm. The calibration curve was linear up to 7 μM of boron. The method could be applied to the determination of boron in the steel standard sample (JSS-174-7).