Gas chromatography may be used to qualitatively detect the presence of compounds in a liquid sample and, within limited ranges, to measure or estimate concentrations present. The principles of acoustical gas detection instrumentation were investigated and an acoustical detector was constructed and added to a GOW-MAC 150 gas chromatograph. This detector was tested and compared to the thermal conductivity detector already in the chromatograph. Additional electronics were designed and added to interface the outputs of both detectors to a Universal Lab Interface (Vernier Software, Portland, Oregon) for more convenient data collection and analysis.
The two detectors (thermal and sonar) were found to have comparable response times and sensitivities. The sonar detector was found to be more sensitive for detection of compounds such as cyclohexane, acetone and acrylonitrile. It was less sensitive to temperature variations, but more sensitive to ambient air circulation and pressure changes.
Students at Green Lake High School used the Universal Lab Interface to collect data from a GOW-MAC 150 gas chromatograph. These experiences provide an opportunity to introduce many topics, such as instrumentation, circuit design, signal conditioning, and use of the computer interface to acquire data. The computerized data collection system freed the students to think more about the principles of the experiment and analysis of the data. A series of experiments are included which may be incorporated into a gas chromatography unit.