1979 Volume 28 Issue 11 Pages 680-685
Acetylacetone is proposed to use as a demasking agent for determination of fluoride most of which forms anionic complex with aluminum in environmental water samples. Acetylacetone forms a stable and colorless chelate with aluminum. It is also efficient to prevent the formation of aluminum alizarin complexone (ALC) chelate which gives apparent negative error in lanthanum-ALC photometry. By use of acetylacetone, aluminum ten times as much as fluoride does not interfere in the photometry, and 1 mg of aluminum is permissible in the potentiometry using fluoride-selective electrode. Other interferring metals (Co, Cu, Ni, Zr) are removed by taking the supernatant of the sample which has been made alkaline (pH 12). Lanthanum-ALC photometry.-Dissolve 2 ml of acetylacetone in 25 ml of sample containing 3 to 50 μg of fluoride, with stirring. Add 2 ml of sodium acetate-acetic acid buffer (pH 5.0), 5.0 ml of 5.0 % lanthanum-ALC (Dotite Alfusone) and 10 ml of acetone, and dilute to mark with water in 50 ml flask.Measure the absorbance at 620 nm against blank. Potentiometry.-Dissolve 1 ml of acetylacetone in 40 ml of sample containing more than 8μg of fluoride, with stirring. Add 2 ml of 1 M sodium citrate, adjust the pH to 7.0 to 7.5 with 2 M sodium hydroxide or 2 M hydrochloric acid and dilute to 50 ml with water.Immerse electrodes in the solution and observe the meter reading while mixing.
