This International Standard specifies a curcumin spectrophotometric method for the determination of the boron content of aluminium oxide primarily used for the production of aluminium. The method is applicable to boron contents, expressed as boron oxide (B2O3), greater than 0,000 6 % (i.e. 0,000 2 expressed as boron (B)). NOTE — The sensitivity of the method, as may be gathered from the calibration curve, is in fact higher. In the case of a very low blank reading, and with sufficiently sensitive apparatus, the lower limit of application of the method may be extended to 0,000 08 % of boron oxide (B2O3), corresponding to 0,000 025 % of boron (B).