二流路系を用いた洗剤の溶媒抽出/フローインジェクション分析

洗剤(陰イオン界面活性剤)の抽出/FIAについて,実用分析の観点から,装置面と試薬面について再検討した.プランジャー型ポンプを用い,従来の三流路系を二流路系とし,試薬溶液流れに試料を注入した.ポンプについて検討したところ,ダブルプランジャー型ポンプ1台で間に合い,三流路法と比較しても,感度的にはほぼ同程度であることが分かった.内径0.5mm,長さ1m以上のポリテトラフルオロエチレン製チューブを抽出コイルとして用いたとき,長さ25mmと約2mmのセグメントにおいてピーク高さはほとんど同じであった.陰イオン界面活性剤の対イオンとなる染料陽イオンについては,メチレンブルー(MB)(抽出溶媒:ο-ジクロロベンゼン)と1-メチル-4-(4-ジエチルアミノフェニルアゾ)ピリジニウムイオン(MEP)(抽出溶媒:クロロホルム)を比較した.二つの染料陽イオンを比較すると,MB法のほうが感度は高いが,試薬から試験液のピークが負ピークとなり,又ピークのテイリングが大きいため,分析所要時間が若干長い.1×10(-6)Mラウリル硫酸ナトリウムを10回注入したときのピーク高さ,標準偏差及び相対標準偏差はMB法でそれぞれ,200.6mm,0.8mm及び0.4%,MEP法でそれぞれ,121.1mm,0.3mm及び0.3%であった.S/N=3に相当する検出限界は両法において約1×10(-8)Mであるが,実際の定量下限は3×10(-8)M程度となる.分析所要時間は,1サンプル当たりMEP法で2分,MB法で3分(流量0.6ml min(-1)の場合)及びメチレンブルー法で2分(流量0.8ml min(-1)の場合)となる.

FIA of anionic surfactants was examined by using a double-line system in respect to practical application. A reagent solution and an extraction solvent were propelled by a double-plunger pump. Sample solutions were injected into a reagent solution stream, which was marged in a extraction solvent stream. An improved segmentor with an outlet of 0.25-mm bore and 13-μl space made smaller segments (averaged length, 2 mm), which enabled to have higher peaks. The efficiency of the smaller segments on the peak height was higher when the extraction tubing was shorter than 1 m. Three kinds of reagent solutions were examined ; one comprised 1-methyl-4-(4-diethylaminophenylazo) pyridinium (MEP) chloride (extraction solvent, chloroform ; MEP · Cl method), another an iodide of MEP (extraction solvent, chloroform ; MEP· I method) and the other methylene blue (extraction solvent, ο-dichlorobenzene ; MB method). By the MEP· I method, negative peaks were obtained in the range below 10(-6) M of anionic surfactants. The highest peaks were obtained by the MB method. The peak height, the standard deviation and the relative standard deviation obtained by 10 times injection of 10(-6) M laurylsulfate (LS(-)) were 200.6 mm, 0.8 mm and 0.4%, respectively, by the MB method ; 121.1 mm, 0.3 mm and 0.3%, respectively, by the MEP·Cl method. The detection limit corresponding to a signal to noise ratio (S/N) of 3 was about 1 × 10(-8) M of LS- by the MB and MEP·Cl methods. This method was capable of analyzing 2030 samples per hour.