Abstract
The formation of boric acid ester with curcumin is usually performed in highly acidic solution in the absence of water. Small water contents are permissible, but the efficiency is lowered. The water content of a sample can be eliminated by a reaction with propionic anhydride catalyzed by oxalyl chloride, thus avoiding methyl borate distillation or evaporation processes. An advantage is that the reaction between boron and curcumin takes place in a completely homogeneous liquid medium. The excess of protonated curcumin is best destroyed with an ammonium acetate buffer. For trace amounts of boron, extraction of the coloured complex with a mixture of methyl isobutyl ketone, chloroform and phenol is recommended. Standard procedures for aqueous solutions with boron contents between 0.0033–40.0 μg B/l are described.
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