Graduate Thesis Or Dissertation
 

Mass-flow control system utilizing flow-feedback for gas chromatography

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/m039k7529

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  • A unique mass-flow control system for the carrier gas in gas chromatography is described and evaluated. Carrier gas flow is controlled by a flow sensor, feedback electronics, a flow-control valve and a microcomputer. The flow-rate is monitored by a mass-flow meter by this system and the flow is adjusted in response to computer instructions. The flow control system was adapted to a new separations method in gas chromatography; optimized flow programming with temperature programming. According to empirically derived flow optima vs. temperature relations, the microcomputer adjusts the carrier flow-rate according to a measured-temperature vs. flow-rate format. Improvements in theoretical plate heights are obtained with this system and results are compared to those achieved via conventional temperature programming. In another application, a similar system was used to maintain constant mass-flow within 3% (RSD), even during temperature programming. Thus accurate measurements are feasible with detectors which require constant flow throughout their measurement interval, despite temperature changes. Use of the constant-flow system was demonstrated via measurements made by response factor calibration using a Hall Electrolytic Conductivity Detector. Quantitative measurements of impurities in solutions of dieldrin, heptachlor and 1,2,4-trichlorobenzene were achieved without analyte identifications. Similarly, toxaphene was measured without reference compounds identical to each toxaphene eluate.
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