A Colorimetric Determination of Boron in Biological Materials

Abstract

To measure sodium mercaptoundecahydrododecaborate (I), Na₂B₁2H₁1SH, used for boron neutron-capture therapy, a colorimetric method with curcumine for determining boron in biological materials was developed. First, biological samples such as the tumor, surrounding tissues, and blood plasma were ashed gently using the radiofrequency combustion system with excited oxygen plasma. Urine samples were not ashed but usually required dilution with water. After oxidative degradation with potassium permanganate, boron in the degradation products was extracted with chloroform containing 2-ethyl-1, 3-hexanediol. Boron in the chloroform extract was converted into the boron-curcumine complex by adding an acetic acid solution of curcumine, followed by concentrated sulfuric acid. After dilution with 95% (v / v) ethanol, the absorbancy of the solution at 554 nm based on the complex was measured by spectrophotometry. The linear dynamic range for the assay was from 0.5 to 20 μg of boron per sample solution. Compared with the 1, 1'-dianthrimide method the present method is simple and safe, and is sensitive enough to be useful for the determination of boron in biological materials.