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Selectivity enhancement for high-speed GC analysis of volatile organic compounds with portable instruments designed for vacuum-outlet and atmospheric-pressure inlet operation using air as the carrier gas.

Authors
Whiting-J; Sacks-R
Source
Anal Chem 2002 Jan; 74(1):246-252
NIOSHTIC No.
20029611
Abstract
A tandem ensemble of two 4.5-m-long x 0.25-mm-i.d. capillary columns with the first using a 0.50-microm film of nonpolar dimethyl polysiloxane and the second using a 0.25-microm film of polar trifluoropropylmethyl polysiloxane is operated with atmospheric pressure air as the carrier gas and an outlet pressure of 50.5 kPa established using a small vacuum pump. A thicker stationary-phase film is used in the first column to increase retention for very volatile compounds. This significantly increases the resolution of these compounds. The thicker film in the first (nonpolar) column decreases the polarity of the tandem column ensemble and, thus, changes its selectivity. A low-dead-volume valve, connected between the column junction point and a source of atmospheric pressure air, is used to obtain pulsed modulation of the carrier gas flow through the column ensemble. When the valve is open, the ensemble inlet pressure and the junction-point pressure are nearly the same, and carrier gas flow nearly stops in the first column, and flow in the second column increases. Enhanced resolution of a component pair that is separated by the first column but coelutes from the column ensemble can be obtained if the valve is opened for a few seconds after one of the components has crossed the junction and is in the second column, but the other component is still in the first column. A sequence of appropriately timed pulses is used to obtain enhanced resolution of several pairs of components that coelute from the column ensemble. These methods enabled the complete separation of an 18-component vapor mixture of common solvents in air in 3.5 min.
Keywords
Gas-chromatography; Vapors; Air-quality; Air-quality-monitoring; Air-quality-measurement; Gases; Analytical-instruments; Analytical-processes; Sampling-equipment; Sampling-methods
Contact
Department of Chemistry, University of Michigan, Ann Arbor 48109
CODEN
ANCHAM
Publication Date
20020101
Document Type
Journal Article
Funding Type
Grant
Fiscal Year
2002
NTIS Accession No.
NTIS Price
Identifying No.
Grant-Number-R01-OH-003692
Issue of Publication
1
ISSN
0003-2700
Source Name
Analytical Chemistry
State
MI
Performing Organization
University of Michigan, Ann Arbor
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