アセチルアセトンをデマスキング剤とする水中フッ素の直接定量  [in Japanese] Direct determination of fluoride in water by use of acetylacetone as a demasking agent.  [in Japanese]

アセチルアセトンがアルミニウムと無色の安定なキレートを生成することに着目し,これをデマスキング剤として水中フッ素の直接定量を試みた.アセチルアセトンは,アルミニウムと錯陰イオンを形成しているフッ素のデマスキングのみならず,ランタン-アリザリンコンブレクソン(以下ALCと略記)光度法でALCキレート生成のため見掛け上の負誤差を与えるアルミニウムや正誤差を与える鉄の影響の抑制にも有効であった.又,フッ素イオン電極を用いる電位差法にも有用であった.試料を採取時にpH12とし,数時間後に上澄液につき定量を行えば,一般的な水については分離を行うことなく直接適用することができる.

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 eflicient 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), 5.0ml of 5.0% lanthanum-ALC (Dotite Alfusone) and 10ml 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 8 μg 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.