Abstract
Introduction: The main objective is to develop a new analytical method for selective and rapid quantification of individual monoterpene isomers. This is especially relevant for atmospheric chemistry because different isomers exhibit highly variable reactivity with the OH. radical [1] and their role in formation of pollutants may be different for individual isomers.
Thus, the precise measurements of their fluxes and concentrations will refine input data for numerical models. Methods: Soft chemical ionization technique of SIFT-MS [2] and its drift tube variant [3] have been used for absolute quantification of monoterpene isomers.
Because SIFT-MS can quantify only the total concentration of monoterpene isomers, we employed more traditional separation method of fast gas chromatography, GC, [4] and thermal desorption, TD, and coupled them with Profile 3 instrument. Results: Separation by the fast GC was carried out on an electrically heated 5 m long non-polar MXT capillary column.
Elution times of the isomeric compounds through short, rapidly heated column were characterised and optimised. Using the fast GC coupled to a Profile 3 SIFT-MS instrument we successfully separated eight of the most abundant plant monoterpene isomers (α-pinene, β-pinene, Camphene, Myrcene, 3-carene, R-limonene, α-terpinene and γterpinene).
A combination of TD with SIFT-MS showed the ability for partial separation of isomers achieved by a slow temperature desorption profiles in contrast to the common approach of rapid desorption from TD tubes. The characterization of several sorbents was experimentally researched and tested.
The optimal conditions for the TD approach such as the amount of sorbent, sampling flow rate, or sampling volume were defined. Conclusions The combination of fast GC or TD with SIFT-MS represents a promising and robust analytical method for selective and rapid quantification of monoterpene isomers.
The advantage of fast GC is better separation in time of a minute, can be used in-situ, but does not allow the use of eddy covariance method. TD based method is very useful for long term monitoring of atmosphere and sample storage on TD tubes.
Novel Aspect: Separation by TD profiles of the isomeric compounds trapped on sorbent was researched. Separation by fast GC using short capillary column was characterised and optimised.
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