By Anonymous on Tuesday, February 22, 2000 - 08:19 am:
I wonder if anyone has an idea how to perform absolute quantification by SPMEing the headspace of a sample.
By Anonymous on Tuesday, February 22, 2000 - 10:04 am:
You prepare standards in the same matrix and sample their headspace under exactly the same conditions as your sample.
By Anonymous on Friday, February 25, 2000 - 03:09 am:
I need to quantify volatiles from a solid matrix (plant material)so I can not simply add standards to the sample, because it is impossible to achieve identical conditions. ANother point is that when adding standards to my sample the concentrations of the other analytes in the headspace is quenched due to
P =p1*x1+p2*x2...pn*xn. Any further ideas ?
By Ron S. on Friday, February 25, 2000 - 06:26 am:
One of the classical methods for determining the concentration using headspace sampling is to perform successive injections of aliquots of the headspace from the same vial, then plot the response versus extraction number. By extrapolation of the results, the initial concentration in the sample can be determined. You should be able to find a detailed writeup on this procedure in many of the standard analytical reference books. I am not aware of anyone doing this procedure for headspace SPME, but the basic principles should be the same.
By Dave Gratson on Friday, February 25, 2000 - 01:33 pm:
You might sift through this list of references.
http://cbmfw5.cm.utexas.edu/groups/brodbelt/spme_refs.html
Its long but the best I've seen on the web. You can always search for the page using edit;find in frame option.
Cheers
Dave Gratson
http://www.suite101.com/welcome.cfm/analytical_chemistry
By Anonymous on Monday, February 28, 2000 - 07:46 am:
As mentioned above I have plant material as a matrix. There are about 200 compounds that are of interest for example for variety idetification. So far I have performed relative quantification with a Headspace autosampler - which works really fine. Multiple Headspace Extraction was no problem then of course. But when applying SPME at room temperature it takes you a large number of extractions to observe a decrease. If this is caused by the SPME device or by the septa which have been pierced several times is another question.
My impression is that SPME seems to offer a lot of new possibilities on first sight but that established strategies for headspace analysis do not help yielding the advantages.
pizzamonster@gmx.de
By Anonymous on Monday, February 28, 2000 - 09:48 am:
Contact Bob Shirey through Supelco Technical Service: 800-359-3041. He is the SPME guru.
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