September 2, 2014

Publication of a method for analysis of volatile compounds present in the plant material

Laurie Caron - Summary of articles

During my graduate studies in natural products chemistry at the University of Quebec at Chicoutimi (UQAC), I had the opportunity to publish a few articles related to the topic of my research. Today, I present the first of them deals with a new method for analysis of volatile compounds from plant material:

"Volatile compounds in the foliage of balsam fir Analyzed by static headspace gas chromatography (HS-GC): An example of the spruce budworm defoliation effect in the boreal forest of Quebec, Canada" published in the journal Michrochemical in 2013.

Using the traditional method of analysis by GC-MS analysis of volatile compounds during my study would have been a tedious process of manipulation in the laboratory. This method requires a first step of extracting the compounds of interest and then in the following analysis. Having so many samples to analyze for my research (about 200 for this component) the development of this method by HS-GC (Static Headspace Gas Chromatography) was more useful. My mastery is already divided into three separate components analysis and just by itself, it could have been the sole object of my memory.

The HS-GC method differs from that normally used (by GC-MS) by eliminating the step of extracting the volatile compounds and the addition of a step of preheating the sample. This preheating allows volatile compounds to break free of the initial matrix and concentrate in the headspace of the bottle containing the sample. Then the principle of analysis of the compounds are the same as gas chromatography, principle explained in a post previously done by my colleague: Analyses by GC - Part I. Principles of separation.

The HS-GC method has saved me a lot of time and get ultimately a reliable analysis. For my study, the interest compounds were monoterpenes and sesquiterpenes compounds ending up in major part in essential oils and known to be composed of plant defenses. These are already well known and goods listed in the literature and several databases, it was possible for me to easily move the qualitative identification of each compound present in my samples by their retention index.

The difficulty in applying the method lay in finding first the right amount of sample for inclusion in the analysis and secondly the proper warm-up time so that they bottle the GC column is not saturated by volatiles. Once these are found, it was necessary to make sure that the method can provide an alternative to more quickly qualify a plant sample volatile compounds, but also be able to quantify these compounds.
 
Figure 1: Samples of balsam fir needles was analyzed by HS-GC

For quantification of specific molecules such as β-phellandrene (monoterpene), an internal standard (geraniol) and a commercial standard (for the preparation of a calibration curve) were used. Furthermore, to ensure the stability of the method, each sample was prepared and analyzed in triplicate, for the injection of a single sample several times could be due to the preheating step of the sample. Similar results have been obtained to suggest that the method seemed to be as reliable as those traditionally used.

In addition, some preliminary results of my research on the influence of spruce budworm (SBW) (Choristoneura fumiferana Clemens) on the chemical composition of balsam fir have also been included in this article. These data demonstrated that among other defoliation this conifer needles in the wild brought an impact on the production of these defensive compounds (monoterpenes, sesquiterpenes, etc). In connection with these results, the hypothesis that increased production of β-phellandrene (monoterpene) by fir needles during severe defoliation period in June was also raised.

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