[Spectrophotometric determination of boric acid by the curcumin method].
We have contrived an improved curcumin method for a spectrophotometric determination of the boric acid content, suitable for use on biologic materials to determine cases of poisoning. The use of this method enables detection of boric acid from a level of 10 micrograms/ml up to 5 mg/ml. The steps of this measurement method follow. Initially, boric acid was extracted by using a modification of Agazzi's method, i.e., to 1 ml of the sample solution, 0.2 ml of a 50% solution of sulfuric acid is added, along with 4 ml of 10 v/v% 2-ethyl-1,3-hexanediol/chloroform (an EHD solution). This mixture was then shaken for 5 min and then centrifuged for 10 min at 3,000 rpm. The extract of this chloroform phase was dehydrated with anhydrous sodium sulfate and used for the coloring reaction sample. The colorimetry procedure for determining the boric acid content follows. Fifty microliters of the extract solution was placed into a dry tube, to which 0.5 ml of a 0.3% curcumin/acetic acid solution and 50 microliters concentrated sulfuric acid were added, and the contents mixed thoroughly. The reaction mixture was then allowed to stand for 30 min at room temperature. (Rosocyanin is formed by the reaction of boric acid and protonated curcumin). Next, ethanol (3-138 ml) was added to the reaction mixture to decompose the excess protonated curcumin. Then, the absorbancy of the resulting solution was measured at 550 nm against a blank test solution. Ethanol was added to enable the measurement of the absorbancy (ethanol amounts tested were 3, 6, 12, 24, and 138 ml).(ABSTRACT TRUNCATED AT 250 WORDS)