モリブドケイ酸の吸光度測定に基づく微量ケイ素のフローインジェクション分析法

ケイ酸(ケイ酸塩)の高感度定量法を目的としてFIA法を検討した.検出法として,モリブドケイ酸の350nmの吸光度測定法を採用した.試料溶液(モリブデン酸アンモニウムを含む希硫酸)の組成,反応コイル長,反応温度,測定波長,試料注入量,流速などの最適化により,高感度定量が可能になった.検量線はSi 10～1000ppbで良好な直線性を示した.検出限界(S/N=3)は2ppbであり相対標準偏差はSi 10ppb及び60ppbでそれぞれ4%及び0.5%であった.分析速度は毎時30サンプルであった.

Spectrophotometric determination of silicon based on the formation of molybdosilicic acid was examined by FIA. Two streams, a carrier and a reagent solution, were propelled at a flow rate of 0.7 ml min(-1) by a double-plunger micropump. Sample solution, 320 μl, was injected into the carrier (distilled water). The reagent solution comprised 0.006 M Mo(VI) and 0.075 M sulfuric acid. The reaction coil was 9 m long, and was heated in an air bath made of aluminium block and controlled at 100℃. Just behind the reaction coil, a cooling coil (0.5 mm i.d.×1 m), which was cooled in a water bath at 20°C, was incorporated. The molybdosilicic acid formed was detected at 350 nm by a UV-VIS detector. The calibration graph was linear over the range of silicon from 10 to 1000 ppb. The detection limit corresponding to a signal to noise ratio(S/N) of 3 was 2 ppb. The relative standard deviations for 6 determinations of 10 ppb and 60 ppb silicon were 4% and 0.5%, respectively. The sampling rate was 30 samples per hour.