Applicable to products having boron oxide contents of more than 0.0006 % (m/m). With sufficiently sensitive apparatus, the lower limit of application may be extended to 0.00008 % (m/m). The test portion is dissolved in phosphoric acid. Separation of the boron by distillation as methyl borate. Formation of a red coloured complex between the boron and the curcumin reagent at pH 7. Spectrophotometric measurement of the complex at a wavelength of about 550 nm.