That depends on several factors and particularly the sample matrix. When doing headspace SPME, the fiber does not touch the sample and you can then use the fiber for a very long time. We are presently running automated headspace SPME of relatively volatile hydrocarbons, and we have used the same fiber for several hundred injections. It is a good idea to include a reference sample for e.g. every 5 or 10 samples in order to assure that the fiber and the entire analytical system is stable, and possibly also for correcting for a drifting response.
As Philipp suggested the use of a reference sample every 5 or more sample is the most robust solution. For target analysis the best choise is to use stds compounds of interest, in case of profiling a convenient solution could be the inclusion of a quality control sample obtained mixing part of all your samples and use as reference every n samples. If you are dealing with matrix not stable in time or perishable and with and sample-set that requires days of weeks to be measured you can prepare the quality control sample at beginning of your experiment and store the reference at -80°C and use as above.
Hope may help
I agree with the other two specialists. Sometimes we met some problems with fiber duration but in limited cases in which we use very polar phases.
I agree with Philipp and Eugenio. Normally in the case of Head Space SPME, the fibre can be used many times. In the mode where the fibre dips into the sample, the reusability reduces, may be because of sample matrix, high boilers etc.
PDMS fibre is quite robust. Just periodically run recovery samples and use the fibre until it drops. Sometimes reconditioning helps (heat with carrier gas stream to a T higher than the one set at the GC injection port)
As mentioned by many before it mainly depends on:
- the sample (whether it is strongly matrix-loaden sample such as food or a simple matrix such as drinking water)
- the sampling technique (whether it is headspace, very gentle for the fiber, or immersion, depending on the matrix more stressing for the fiber
- other parameters such as desorption time and temperature have a lower impact
As a rule of thumb a fiber should last for around 100 extractions (if you do immersion in a challenging matrix it could be of course less), but I also know users that do up 3000 extraction with headspace and a simple matrix.
You should run control samples from time to time (every 10-20 injections) to test the fiber performance to be on the safe side.
the fiber does not touch the sample and you can then use the fiber for a very long time.
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