摘要：Combined method of the extraction of borate with 2-ethyl-1, 3-hexanediol (EHD)/CHCl3 solution, and the color development by use of protonated curcumin was successfuly applied to the determination of borate in food. Conditions obtain low blank value, reliability and reproducibility were examined, and the following procedure was established. Solid sample was pretreated with dryashing method. The sample solution was acidified and extracted with 10% EHD solution. In the case of aqueous sample, the sample was acidified and extracted with the EHD solution dircetly. To an 1 ml aliquot of the EHD extract, 1 ml of 0.1% curcumin/acetic acid solution and 0.5 ml of concentrated sulfuric acid were added. The reaction mixture was allowed to stand for 30 min at room temperature. The curcumin was protonated and allowed to react with boric acid in this period. Then, ethanol (25ml) was added to the reaction mixture to decompose the excess protonated curcumin, and the absorbance of resulting solution was measured at 550 nm. Common ions other than fluoride ion did not interfere. The interference from fluoride ion up to 100μg/ml was negligible in this extraction. When the presence of large amounts of fluoride ion, the addition of lanthanum ion was more effective than that of zirconium ion for the masking of fluoride ion.
