After collecting and analyzing a sample, what needs to be done before the fiber can be used again?
Usually once the desorption happened in the GC liner the fiber should be ready for a new analysis. Anyway, you can check re-inject the fiber and check that it gives back no signal. Sometimes it could happen that the fiber undergoes to contamination. In this case check the technical datasheet of the fiber for extraordinary cleaning instruction. It is also a good practice to leave the fiber in the injector at least 10 min in the morning when you start your analysis routine.
Everyday, I put the fiber into heated inlet (250ºC) during 5-10 minutes to clean it up. During thermal desorption, the fiber is cleaned. You can perform headspace analysis with other samples, without repeating the procedure since thermal desorption promotes the fiber cleanliness.
The conditions under which you want to bake out your fiber depends on your fiber type. 250C is a typical approach and usually eliminates the contaminants. However, there are fibers (e.g., 7um PDMS) that can handle temperatures up to 340C, and depending on your application and matrix (e.g., direct emersion vs. head space), you might have to increase your temperature or exposure time to clean up your fiber sufficiently. However, you also want to keep in mind the max temp for your GC column (if doing GC over LC analyses).
Hope that helps, good luck!
We have set method where in we expose fibre at 250C for 10 min. We usually put 3-4 cycles of such conditioning method to clean fibre after every sample run. Kindly run blank run to ensure everything is eluted out because if matrix is strong in aroma it take more number of cycles to clean fibre.
You can purchase specific bake out stations for CTC type autosamplers, that are beneficial if you are running lots of samples. I must admit from experience with SPME its a much more reproducible technique if its automated. The correct vials and use of merlin microseals will also extend fiber life considerably.
Hi Malini - do not forget to condition SPME fibers before first use according to manufacturers directions (time and temperature). After that, those shorter desorptions in GC injector before each use should do the job. Contaminants in lab air and/or storage can also be extracted by SPME fibers even if they are not in use.
Jacek
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