安定同位体標識化合物を用いる固相抽出/親水性相互作用液体クロマトグラフィー/質量分析法による水試料中ジクワツトの定量

摘要

A target value for diquat residues in tap water is set at 5 μg/L in Japan. We succeeded in the quantitative analysis of diquat in water samples at 1/100 of the target value by hydrophilic interaction chromatography/electrospray ionization/mass spectrometry (HILIC/ESI/MS). For solid-phase extraction we used a new mixed-mode cartridge comprising a weak cation exchange and reversed-phase retention. A 50 mL of water sample spiked diquat-d_4 was passed through the cartridge. Diquat was eluted with 4 mL of acetnitorile and 2-propanol (60 : 40) containing 4% trifluoroacetic acid. The elute was evaporated to dryness at 40℃ under nitrogen gas. The test sample was dissolved in 100 μL of the mobile phase for analysis by HILIC/ESI/MS. The mobile phase consisted of acetonitrile and 10 mM ammonium formate (pH 3.7)= 50 : 50. In the ESI positive-ion mode, m/z 183, m/z 184, and m/z 157 were measured for diquat, and m/z 186 for diquat-d_4. The recovery rates at concentrations of 0.05, 0.5, and 5 μg/L in distilled water, tap water, and river water were 88 ～ 105%, and the CV values were 1.7 ～ 15%. The concentrations of diquat in water were determined using the proposed method. These were 12 tap water samples and 30 raw water samples (river, 14; lake, 5 ; shallow well, 9; deep well, 2) collected from Hyogo prefecture. As a result, diquat was detected in one raw water sample (shallow well, 2.8 μg/L).%水試料中ジクワットの親水性相互作用液体クロマトグラフィー/エレクトロスプレーイオン化/質量分析法（HILIC/ESI/MS）による定量法を検討し，水質管理目標設定項目（水道水）としての目標値5 μg/Lの1/100の濃度を定量可能とした．ジクワツト-d_4を添加した水試料を弱陽イオン交換と逆相分配の保持能を合わせ持つ固相に通し，4%トリフルオロ酢酸含有アセトニトリル·2-プロパノール（60:40）混液で溶出・乾固し，移動相溶媒で溶解，HILIC/ESI/MS分析に供した．移動相溶媒はアセトニトリル：10 mMギ酸アンモニウム（pH3.7）＝50∶50で，ESI正イオンモードで，m/z 183，m/z184，m/z157（ジクワツト），m/z 186（ジクワソト-d_4）で測定した．0.05，0.5，5 μg/Lを添加した純水，水道水及び河川水におけるジクワソトの回収率は88～105%であり，変動係数は1.7～15%であった．本法を用いて42試料を分析した結果，1試料（浅井戸原水）から2.8 μg/Lのジクワツトが検出された．