| مستخلص: |
In this study, a thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) method following sorbent tube sampling was developed for the determination of monoterpenoids (MTs), sesquiterpenoids (SQTs) and diterpenoids (DTs) in gas-phase samples. The analytical method performance was tested by conducting experiments related to, for example, sampling recovery, storage stability, ozone reactivity and general method validation. The limit-of-quantification values were 13-518 pg (0.5-9.3 pptv), intermediate precision was in the range of 3-10 % and the expanded measurement uncertainty was in the range of 17-40 % for terpenoids. The sampling recoveries of terpenoids were approximately within 100±20 % with different inlet lines (15 m long Teflon and 1 m long heated stainless-steel) and branch enclosure cuvette (6 L Teflon bag) tested. The ozone reaction rate coefficient (kO3) of ent-kaurene was experimentally estimated to be 2 orders of magnitude greater than the respective literature kO3 value, demonstrating the potential underestimation of DTs contribution to atmospheric reactivity. The preliminary comparison between offline and online mode TD-GC-MS sampling and analysis revealed that diterpenes and oxygenated sesquiterpenes are lost in excessive amounts in online mode sampling, hindering the online mode applicability for the quantitative analysis of these compounds. A few applications to real samples were tested to identify DTs potentially emitted by boreal forest tree species. In dynamic headspace samples of pine needles and spruce twigs heated to 60 °C, five and 13 DTs could be detected in emissions, respectively. The semi-quantitatively estimated emission rates of DTs were roughly 1 to 3 orders of magnitude lower than those of MTs and SQTs. Similarly, in spruce branch enclosure emissions from a living tree, seven DTs were detected once the enclosure was heated to ca. 60 °C. In summary, the developed analytical method was demonstrated to be applicable for the analysis of MTs, SQTs and DTs. In addition, DTs could be detected in needles, twigs and branch enclosure emissions, however, high temperatures were required to promote the emissions and for obtaining detectable concentrations. [ABSTRACT FROM AUTHOR] |
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