フローインジェクション分析法による水中の全シアン定量のための小型蒸留器を用いた蒸留前処理

摘要

Acid distillation is commonly carried out before the determination of total cyanide in aqueous samples to decompose metal-cyano complexes into HCN. We designed the miniature distillation apparatus, which consists of a 20 mL distillation tube, a 30 mL outer tube as a receiver, and an inner tube for air cooling. This apparatus (16 cm in width, 40 cm in height, and 27 cm in depth) was equivalent to about one-tenth of a standard distillation system in size. Sample and reagent solutions used were reduced to one-fiftieth of those used in the standard method. The proposed procedure is as follows: 5 mL of a sample, 0.2 mL of phosphoric acid (85 %), and 0.2 mL of EDTA (100 g L~(-1)) were added to the distillation tube. Then, 2 mL of NaOH (20 g L~(-1)) was added to the outer tube, in which the inner tube was covered. A maximum of 8 sets were heated by a dry block bath at 150 ℃ for 20 min. The CN~- in the distillate was determined by FIA. Under the distillation conditions, potassium hexacyanoferrate as well as KCN was converted into HCN, whereas thiocyanate was not. The CN~- was completely recovered from a KCN solution (0.05 mg L~(-1) as CN) in the presence of Fe(Ⅲ) (≦ 1000 mg L~(-1)), Mn(Ⅱ) ( ≦ 100 mg L~(-1)), and Zn(Ⅱ) (≦ 100 mg L~(-1)). Satisfactory recoveries of CN were found for a recovery test using the leaching solution from soils. The proposed distillation method is easier to operate, and reduces the distillation time, space, and consumption of chemicals and energy.%シアン化合物はその毒性の観点から，環境水，地下水，土壌で厳しい環境基準が定められており，全シアンとして検出されないこととなっている．測定は工場排水試験方法（JIS K 0102）の38で行うこととされ，38.1.2のpH2以下のリン酸酸性下の蒸留前処理で留出したシアン化水素をアルカリ溶液に捕集した後，捕集液中のシアン化物イオン（CN~-）を38.2のビリジンーピラゾロン吸光光度法あるいは38.3のもビリジンカルポン酸ーピラゾロン吸光光度法で定量する（以下，公定法と記す）．38.1.2でpH2以下で発生するシアン化水素を全シアンと定義しているため，試料の蒸留前処理は必須である．