Instrumentation and strategies for the analysis of light hydrocarbons using high-speed gas chromatography
Two inlets for high-speed GC have been developed for light hydrocarbon introduction. One is a low-friction gas-valve inlet which is designed for gaseous samples and is capable of producing initial bandwidths of a few milliseconds. The reproducibility of the inlet is better than 0.5% RSD for retention times and about 5% RSD for peak area. Little molecular weight discrimination was observed. Sampling characteristics and vacuum backflush operation are investigated. The other inlet is a cold trap which uses PoraPLOT Q and Al[sub 2]O[sub 3] porous-layer open tubular (PLOT) columns as the trap material. The greater retention of components on the PoraPLOT Q surface allows higher trap temperatures to be used but higher reinjection temperatures are needed. Initial bandwidths of 7 ms were measured for the Al[sub 2]O[sub 3] trap and 30 ms for the PoraPLOT Q trap. The sample capacities range between 0.5-2 nL which are about twenty times less than that of a bare metal trap. Short lengths of PLOT columns operated at carrier gas velocities of 150 cm/s are used to separate simple mixtures of light hydrocarbons in a few seconds. Porous polymer, Al[sub 2]O[sub 3], and carbon PLOT columns exhibit selectivity differences. The Al[sub 2]O[sub 3] column can show poor retention time stability due to irreversible adsorption of water and polar volatiles. The major sources of band broadening during the chromatographic separation on the PLOT columns are evaluated from experimentally obtained plots of plate height vs. average linear velocity. Resistance to heterogeneous mass transfer at the solid-gas interface is much larger for the PoraPLOT Q column than the Al[sub 2]O[sub 3] column. The use of a computer-controlled pressure regulator combined with a bare metal cold trap for inlet pressure programming with high-speed GC is described. Analysis times are reduced by half for a mixture containing C[sub 5]-C[sub 10] hydrocarbons.
- Research Organization:
- Michigan Univ., Ann Arbor, MI (United States)
- OSTI ID:
- 7267672
- Country of Publication:
- United States
- Language:
- English
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