I have another question regarding SPME analysis. We are interested in how some of our products interact with flavor components. Right now I am working with spearmint oil and cinnamaldehyde.

My basic method is that I introduce a small quantity of cinnamaldehyde, 10uls into an empty vial, sample and record peak area. Next, I add the same volume to 0.5g of sample, the samples being various mineral products. I then sample and note the reduction in peak area, in this way we can rank one product relative to the other in terms of compatibility with different components. I am using a 65umDVB/PDMS SPME fiber and 60m Stabilwax column, sampling at 22-23C for 5minutes.

What has happened recently is that I notice a large increase, almost double, in cinnamaldehyde peak area for the mineral sample relative to 10uls neat in vial. The mineral is fairly dense, 0.5g does not change the volume of the headspace by more than 10%, if that. So I don't think it is a change in volume. And this phenomenon is repeatable. I've pretty ruled out temp and other outside considerations.

I think, and I'm guessing, that the increase in peak area is related to surface area and or surface tension. Either, being dispersed on the mineral, the cinnamaldehyde has more surface area exposed to the headspace, and this results in increased concentration. Or, the mineral somehow changes the surfae tension of the liquid and makes it volatilize more readily.

But, I am guessing. Any thoughts?

Thanks,

Mike

Headspace SPME involves three steps, each has it's own thermodynamics and kinetics

Sample--Headspace--Fiber

Each transition from one phase to another depends on many variable such as temperature, pressure, chemical composition or surface.
Comparison of various spiked solid matrices can be a challenge. I would not assume this procedure a reproducible approach. (Though I might be proven otherwise)
Can you use static headspace sampling instead? It would reduce the parameters that you have to take into account.
(The SPME Book from that Canadian researcher with the Russian name that I can't recall right now is really expensive but very good)

The book is: Solid Phase Microextraction Theory and Practice by Dr. Janusz Pawliszyn. It is published by Wiley. His web page is: http://www.science.uwaterloo.ca/chemistry/pawliszyn/

Good Luck.

Chris

What is the mineral and physical form?

Regards,

Ralph

It is an amorphous precipitated silica.

I think you are right about the surface tension being disrupted by the mineral. Are you using a stir bar? Is your vial deactivated?

I am interested about chemical thermodynamics of cinnamaldehyde hydrogenation reaction.
Thank you!
Best regards,
Nadia