18.104.22.168. Solvent desorption of volatiles
The most common method for dynamic headspace collection is to use adsorbent materials that require a solvent wash to remove trapped volatiles (Heath and Manukian, 1994; D’Alessandro and Turlings, 2006; Tholl et al., 2006; Carroll and Duehl, 2012). In general, adsorbent techniques that employ solvent extraction are best adapted for large scale sampling over longer periods of time. Solvent-based adsorbent techniques can also be used to quantify volatiles in closed airspace systems or when the relative capture rate can be calculated.
headspace air is actively pulled through an adsorbent filter trap where the
volatiles adhere onto the adsorbent matrix. Commonly used adsorbent materials
include Super Q, Haysep Q, Porapak Q, Tenax TA, and speciality adsorbents that
target specific chemical groups (Núñez et
al., 1984; D’Alessandro and Turlings, 2006). Most of these adsorbents trap
large quantities of volatiles without much bias toward specific chemical
classes. The captured volatiles are desorbed off the matrix by a solvent
(chosen on the basis of the polarity of the target compounds i.e. polar solvent
for polar volatiles, non-polar solvents for non-polar volatile) rinse. An
active vacuum source is required to draw the sample air through the
tightly-packed adsorbent material. Refer
to paragraphs 22.214.171.124. and 126.96.36.199. for application examples
Pros: A distinct feature of solvent desorption is that only a small fraction of the sample solution is normally used during analysis. Thus, a single volatile sample can be analysed separately by different instruments and also tested for bioactivity.
Cons: On the negative side, analysing just a small fraction of the sample also decreases sample sensitivity. Another disadvantage of solvent desorption is that highly volatile compounds may co-elute with the solvent peak during separation (Núñez et al., 1984).