Headspace Sampling and Gas Chromatography of Plants: a Successful Combination to Study the Composition of a Plant Volatile Fraction

Abstract

This chapter is a critical overview on headspace ( HS ) and gas chromatography ( GC ) and gas chromatography combined with mass spectrometry (GC‐MS) in the analysis of the plant volatile fraction. The volatile fraction of a matrix of vegetable origin can in general be defined as a mixture of volatiles that can be sampled because of their ability to vaporize spontaneously or under suitable conditions, or else, by adopting appropriate techniques. The above‐mentioned techniques can successfully be combined online thanks to their high compatibility. The first part includes the description of headspace techniques in sampling the plant volatile fraction, in particular, basic concepts, advantages, and limits of static and dynamic headspace (S‐HS and D‐HS), and of high concentration capacity headspace techniques (HCC‐HS) are discussed. The second part concerns fundamentals of GC and its evolution mainly in view of analyzing the plant volatile fraction. In particular, conventional and fast GC as such or coupled to mass spectrometry (GC–MS), enantioselective GC with cyclodextrins derivatives as chiral selectors, and multidimensional GC are described. Moreover, new stationary phases for GC, derivatization reactions in GC, qualitative analysis (identification), and analyte quantitative determination in plant matrices are also discussed.

Analytical strategies for in-vivo evaluation of plant volatile emissions - A review

“…Of the possible approaches for the in vivo collection of volatiles, the most common is headspace (HS) sampling, i.e. the analysis of the gaseous/vapour phase in equilibrium with the plant [1,13,14]. The HS technique can be either in dynamic (D-HS) or static (S-HS) modes, depending on the instrumentation and procedures employed.…”

“…The use of D-HS for plant volatile analysis dates back to the 1960s, when it was introduced by Wahlroos [16], and immediately applied by Herout to the sampling of flower volatiles [17]. D-HS is nowadays one of the most heavily explored approaches in this research area [1,14]. As shown in Figure 1A, its success is largely due to its versatility related to the possibility to choose different trapping system and materials that enables to recover the target analytes also in function of their chemical characteristics.…”

“…The desorption of the trapped volatiles is crucial and requires intense treatments, such as solvents or heat desorption, to ensure full compound release [18]. A proper D-HS set-up requires a relatively complex equipment and the standardisation of several parameters if a reliable in-vivo sampling is to be obtained [14]. In general, the whole plant or the living part(s)…”

“…The trapping mechanism depends on the nature of the material that conditions its specific interactions with the analytes. PDMS and other inert and thermally stable sorbent polymers [18,20,33,38,51], have recently been introduced in alternative to the widely used adsorption carbon-based (Carbotrap, Carbograph) and polymeric (Tenax, Porapak) materials [22, 30-32, 34-36, 39, 40, 42-44, 46, 47, 50, 52, 53], limiting the presence of artefacts in the final profile [14]. The trapping step is often avoided when D-HS is coupled with a PTR-ToF MS detector,…”

“…In S-HS, a liquid or solid sample reaches the equilibrium with its vapour phase and the target analytes are transferred to the headspace, according to their partition coefficients [14]. In the original method, the gaseous phase was manually transferred to the GC using a gas-tight syringe but, over the years, different automatic systems have been developed to improve its reliability.…”