アゾ化合物の接触酸化反応を利用する飲料水中の鉄のフローインジェクション分析

抄録

1-Amino-8-hydroxy-7-(o-hydroxy-p-methylphenylazo)-3,6-naphthalenedisulfonic acid (p-CH₃) reacts with KIO₄ in an acid solution to form a colorless azoxy compound. The reaction was enhanced with iron(III). Therefore, a flow-injection analysis (FIA) of iron was investigated by measuring the decrease in the absorbance of p-CH₃. The flow system used had three channels. Each carrier (distilled water), KIO₄ solution as a oxidizing agent and reagent(p-CH₃) solution was pumped at 1.0 cm³/min. A sample solution was injected manually into the carrier stream. Then, a p-CH₃ solution containing sample was mixed with a KIO₄ solution. Under the optimum conditions (temperature, 50°C; p-CH₃, 1.2×10⁻⁴ M; KIO₄, 1.0×10⁻⁵ M; HCl, 0.3 M; reaction coil length, 9 m, i.d. 1 mm; injection volume of sample, 1.0 cm³), Fe(III) could be determined in the concentration range of 1.4 to 16 ppb (ng cm⁻³) by monitoring at 556 nm. The detection limit of Fe(III) was 0.48 ppb (S/N=5). Also, 15 samples could be analyzed per hour. Mn(II), Cr(VI) and V(V) at more than 0.8-fold, 5-fold and 50-fold concentrations of Fe(III)(8 ppb) showed positive interferences, respectively. However, these metal ions did not interfere with the determination of iron in tap water. As a result, the proposed method was applied to the determination of iron in tap water without any masking agents. The results of a trace iron determination in tap water showed a good agreement with the values obtained by ICP-AES.