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NIRE Annual Report
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 1999

Improvement of the Sensitivity of Quartz Crystal Microbalance Coated with Lipid Film for Continuous Monitoring of Volatile Chloroorganic Compounds

Water Analysis Division
Hydrospheric Environmental Protection Department
Objectives
A large amount of chloroorganic compound, such as trichloroethylene (TCE) and tetrachloroethylene (PCE) have been used. These compounds have caused severe contamination in groundwater. In addition, the contamination of surface water in wide area and air pollution becomes serious problems. To prevent such pollution rapid and on-site monitoring method for these compounds is strongly needed. We have investigated a continuous monitoring method using a quartz crystal microbalance (QCM) sensor. In the present study, specific adsorption of volatile chloroorganic compounds on a synthetic lipid film was detected by observing frequency changes of a lipid coated QCM.
Results
The responses of three different kinds of lipid coated QCM to several kinds of organic gases was shown in Fig. 1. From this Figure, not only the chloroorganic compound but also other organic compounds, such as alcohol and hydrocarbon, gave rise to frequency changes. This is probably caused because the lipid film works as hydrophobic layer and it dissolves many kinds of organic compounds. However, this does not mean that the lipid coated QCMs have no selectivity to gases. The difference of the selectivity pattern appears to be based on the molecular interaction between the volatile chloroorganic compound and the lipid. The lipid, having different functional groups, modified the surface of the QCM, and it would form the layer with a high affinity for chloroorganic compound.
Fig.1. Response patterns to several kinds of organic compounds obtained with three different lipids coated QCMs.
Fig.1. Response patterns to several kinds of organic compounds obtained with three different lipids coated QCMs.
Effects of the temperature on the sensitivities of three QCMs coated with three different kinds of lipids are shown in Fig. 2. These QCMs gave the highest sensitivities at the lowest temperature examined.
Fig.2. Effects of the temperature on the sensitivity of the three QCMs coated with differen kinds of lipids.
Fig.2. Effects of the temperature on the sensitivity of the three QCMs coated with differen kinds of lipids.
The Sensitivity of the lipid coated QCM was improved by running it at 5°C. Further improvements were conducted by using a 12 MHz-QCM and by increasing the application amounts of the lipid up to 15 mg. The detection limit for trichloroethylene (TCE) was 870 ppb/Hz. Contrary to the detector tube method, the QCM sensor enable the continuous monitoring of volatile chloroorganic compounds, and therefore, it would be applied to the continuous monitoring of these compounds in the factory.
Selected Publications
1) Detection of Chloroorganics by Lipid Coated Quartz Crystal Microbalance Sensor, Trans. IEE of Japan, 590, 118-E, 12, 1998.
2) The Seventh Japanese-German Workshop on Waste Water and Sludge Treatment, 91, 1998.
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