Ehsan,

first you need an absolute quantification of your components in terms of peak area / amount of component (preferrably in mass units).

Then relate this absolute amount (µg) to your your original "tree sample" given in themass unit kg (this gives you directly ppb as results), or sample volume (then you have µg/m³).

Regards

Stefan

Dear Ehsan,

at first you have to substract background of your chromatogram, and after you should check all the peaks and their mass-spectra to exclude possible contaminants such as phthalates and related compounds. The next step is integration of chromatogram. The result of it step is the composition of analysed mixture given in mas.-%. If you need to obtain absolute content of each of component in your samples, so you will have to use internal standards techniques.

Than you for the answers Stefan and Roman,

Dear Stefan, As I am new to Chromatography methods, I do not know what is the unit of peak area or hight to calculate the absolute values. I attached the results of one analysis. I will be very thankful if you just calculate one of the substances, specially Isoprene.

Dear Roman, the sample has many compounds and if I use just one standard of one compound I think it wouldn't work.

To quantify VOCs sampled with SPME fibers, you'll need an appropriate calibration curve related to your samples. The establishment of such curve is not always easy because of the properties of the fibers and their limitations but the journal of chemical ecology once released a short guideline that you may find useful (see also the references therein).

Dear Ivan, I took samples in a way that said in your upload article. I want to use the formula mentioned in this article for my calculations, But I don't know how can I calculate the mass of adsorbed analyte (n) by SPME using GC/MS outputs.

For SPME quantitation can be problematic and you can run into issues with precission (even with an ITSD), linearity of calibration, and matrix affects since everything affects binding to the fiber and binding capacity is often a limiting factor.

The best is to keep everything constant, use a blank matrix of something as close as possible to spike your reference standards to for the calibration and pick a good ITSD>

Ehsan,

SPME can be seen as a solvent less, smart and automated alternative to conventional sampling and extraction methods. This often leads to challenges related to callibration and potential matrix effects. Some of these issues and the steps dealing with them were already discussed here. Another appraoch is to allign the working principle and the measurement endpoint to the given research question or context. Since the 1990s, SPME has for instance provided completely new possibilities for measuring freely dissolved rather than total analyte concentrations in aqueous solutions and suspensions. These new approaches take advantage of the fact that it (generally) is the freely dissolved concentration rather than the total concentration that controls the uptake into the SPME fiber coating. The articles below might give some inspiration on additional ways to apply SPME to (semi)volatile organic analytes from trees.

Sheehan E, Limmer MA, Mayer P, Karlson UG and JG Burken. 2012. Time weighted average SPME analysis for in planta determination of cVOCs. Environmental Science and Technology 46: 3319−3325.

Legind CN, Karlson U, Burken JG, Reichenberg F and P Mayer. 2007. Determining chemical activity of (semi)volatile compounds by headspace solid phase microextraction. Analytical Chemistry 79: 2869-2876.

Limmer, M. A.; Balouet, J.-C.; Karg, F.; Vroblesky, D. A.; Burken, J. G. Phytoscreening for Chlorinated Solvents Using Rapid in Vitro SPME Sampling: Application to Urban Plume in Verl, Germany. Environ. Sci. Technol. 2011, 45 (19), 8276−8282, DOI: 10.1021/ es201704v.

Hello Ehsan,

as an alternative you can decide to determine the absolute amounts of analytes extracted by your coating, calibrating the analysis by the injection of liquid standards.

In this case, for both liquid injection and SPME fibre injection, usually more than 95% of the sample is supposed to be transferred into the capillary column by splitless GC injection. It is critical to perform liquid and SPME injections in splittless mode since the transfer efficiencies need to be as close as possible in order to successfully apply this calibration strategy.

You can easily built a calibration curve using liquid standards: the plot will consider amount injected in ng or pg ( you can calculate taking in consideration the concentrations of your solutions and the volume injected) versus peak area of your analytes. In this way you can convert the peak areas obtained by SPME extraction in absolute amount extracted.

In order to minimize the differences in transfer of the analytes into the GC column it is suggested the use of a PTV injector.

For any other information about calibration methods for SPME, please refer to "Handbook of Solid Phase Microextraction" Pawliszyn, J., Ed.; Elsevier.; 2012.

Dear Emanuela, thank you for your concise answer. I've read about response factor in Wikipedia. Is response factor of two martial constant for all GCs which use same detector, nut with different temperature program?

For instance, someone obtained the response factor of Alpha-pinene and camphene with same temperature program (it must be the same to calculate RF). If I use another program, can I use that RF?

Hello Ehsan,

the detector response especially for GC/MS can vary more than for other detectors, such as FID, consequently also the response function may be affected.

Also, using the same instrument you can have different responses in the time based on your detector performances.

For the calibrations of your SPME injections I would suggest to select your compounds of interest and create a mix solution in solvent, thus using this mix for obtaining your response function. In this way you can obtain your calibrations curves for all your compounds minimizing the number of runs needed. I also recommend to perform the liquid injections runs using the same GC conditions you use for SPME injections ( GC temperature program, carrier gas flow rate etc....).

In order to monitor your detector response you can run periodically QC injections. Also, in order to have reliable data, it is extremely important to perform again the calibration each time maintenance of the system and/or tuning the MS are performed.

I hope this information can be useful for you and good luck with your research.

Hello Ehsan,

Try read and apply the method in the attchment.

Thank you very much Najat

You are well come hope it helps.