Colorimetric determination of boron in nitrate solutions

A method has been developed for the determination of microgram amounts of boron in nitrate solutions. Nitrate is destroyed with formic acid and sulphuric acid under reflux conditions. As much as 3 millimoles of nitrate are reduced completely by refluxing 1 ml of the nitrate solution with 1 ml of 88% formic acid for 15 minutes. Boron is determined by the carminic acid method after forming the colored complex in situ. This method has been applied to the determination of boron in uranyl nitrate solutions after extraction of uranium with tri-n-octylphosphine oxide dissolved in cyclohexane.