インクジェットを用いる迅速平衡ヘッドスペース法の開発と水中揮発性有機化合物分析への適用

摘要

Head space (HS) extraction is known as a sample-preparation method of gas chromatography (GC) for volatile organic compounds (VOCs). It is classified into a static HS method and dynamic HS method, such as the purge-and-trap method. Though the purge-and-trap method accelerates sample evaporation, it has drawbacks, such as a poor reproducibility and a need for large equipment. The static HS method is based on the vapor-liquid equilibrium. Though the static HS method is very easy to perform, it takes a long time to attain an equilibrium state. In this work, a compact and rapid vapor-liquid equilibrium system was developed. To attain the acceleration of vapor-liquid equilibrium, an ink-jet was used to generate ultra-small sample liquid droplets. The ink-jet is a well-known technology for printers. It can eject many small liquid droplets in a short time with good reproducibility, and it is expected to increase the area of the vapor-liquid interface of unit volume of the liquid. An inkjet microchip was fitted on the cap of an extraction vial with epoxy glue. The proposed system with the inkjet was compared with the conventional static HS method by applying it to the extraction of VOCs in water. The vapor-liquid equilibrium for both methods was evaluated by ECD-GC with the peak area. The results showed that the proposed method accelerated the vapor-liquid equilibrium. The length of the vial was effective in reproducibility. When the length was changed from 80 mm to 98 mm, RSDs were improved from 3.2 ~ 22% to 3.0 ~ 14%. Considering the flight time of the droplet from ejection to touchdown to the bottom of vial, and the diffusion time of the target ingredients, the vaporizing efficiency would be thought to depend on the droplet flight time. The proposed system showed good linearity for 0.01 — 1 ppm VOCs in a short equilibrium time. The regression coefficients for an extraction time of 0 min were 0.992 — 0.999. It was applied to tap water and wastewater, then demonstrated to be useful for the detection of VOCs.%ヘッドスペース（HS）法は，揮発性有機化合物（VOCs）のガスクロマトグラフィー（GC）分析の前処理rnとして知られている．静的HS法は簡便な装置で実現可能であるが，平衡到達までに長時間を要する．そこrnで静的HS法において，気液平衡を迅速に達成するため，インクジェットによる迅速平衡HS法を考案し，そrnの特性について検討した．すなわちインクジェットを利用して，試料溶液を微細液満として密閉容器内に吐rn出することで気液界面の面積を大幅に拡大した．これにより迅速な気液平衡達成が期待される．本法を水中rnのVOCsモデル試料の測定に適用し，従来の静的HS法と比較したところ，平衡到達時間を半分に短縮できrnることを確認した．RSDsは3.0~14％,0.01~1ppmのVOCsの相関係数は0.992~0.999が得られ，再現rn性及び直線性ともに良好であった．更に本法を水道水と排水中のVOCsの測定に適用し，VOCsを検出できrnることを確認した．