dc.description.abstract | Oxygenated volatile organic compounds ( OVOCs ) are originated from biogenic and anthropogenic sources, as well as from photochemical reactions of volatile organic compounds (VOCs). The high reactivity and lability of OVOCs makes preparation of diluted mixture and storage in high-pressure cylinders unstable. Thus, it is preferred using the dynamic dilution method to the static dilution method and cylinder storage. As the result, this study presents the dynamic dilution method of preparation of OVOC standards to produce gas mixture standards with any chosen composition and at any desired concentration level.
In this study, self-made permeation tubes, including alcohols, ethers, aldehydes, ketones, esters, were selected as our OVOCs sources. To verify the applicability of permeation tubes, a self-made preconcentration system and GC/FID were used as the assessment tool throughout the study. Thirteen OVOCs, i.e., isopropanol, n-butanol, propylene glycol mono-methyl ether, formaldehyde, acetaldehyde, propanal, acrolein, acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate and propylene glycol mono-methyl ether acetate were prepared as permeation tubes to generate continuous flow of gas mixture at ppbv level. Repeated analyses by GC/FID showed RSD less than 2% and R2 better than 0.99, verifying the stable output of the method. A few non-oxygenated VOCs such as benzene, toluene, ethylbenzene and o-xylene were also included in the mixture to serve as surrogates for estimating dilution factors based on flame ionization detection (FID).
As the number of added compounds increased in the mixture, single column GC became difficult to meet our demands for complete separation. As a result, the two-dimensional technique was adopted for greater separation efficiency. The use of the comprehensive GCxGC technique was able to successfully separate the mixture. Ultimately, this technique of OVOC permeation method will be applied to field measurements for on-site automated calibration and quality-control of ambient OVOC monitoring.
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