Abstract
In relation to the preliminary separation of boron to be determined with a curcumin-oxalic acid reagent, the volatilization loss of boron from a borate solution by evaporation and fuming with sulfuric acid, and that from a methanolic solution by evaporation have been studied in detail. It has been found that the evaporation loss is prevented completely by the addition of orthophosphoric acid to an acid solution of borate, and that the presence of water more than 43% is required to prevent the volatilization loss when a methanolic solution is evaporated in the presence of calcium hydroxide.
Comparison of boron recoveries between several methods of distillation as methyl borate whereby hydrochloric, sufuric, phosphoric and picric acids have been used shows that double distillation with 15ml portions of methanol is required for the complete recovery except in the case of phosphoric acid wherein triple distillation is required. A distilling apparatus provided with an inlet for carrier gas has been designed for its convenient use.
The author recommends the following procedure to separate whole of 0.052.50μg. of boron associated with large amounts of sulfuric, hydrochloric and nitric acids: to an appropriate amounts of a sample solution placed in a transparent quartz ware, 0.5ml of concentrated phosphoric acid and, if necessary, 12ml of concentrated sulfuric acid are added. The solution is evaporated to about 2ml or fumed with sulfuric acid. It is transfered in a distilling apparatus and the boron is distilled into 50ml of water containing 1m. eq. of calcium hydroxide by triple distillation with 15ml portions of methanol. The distillate is evaporated to dryness on a water bath and the boron is determined as described in the preceding report {M. Miyamoto, this Journal, 11, 635, 115 (1962)}.
Methods of preparation also have been studied to obtain boron-free inorganic acids, calcium oxide and alcohols.
