SPME disadvantages!!!

[xeim]

Hello,

I'm describing the methods are applicable for beer aroma extraction and analysis. Could you tell me please what sort of methods do you know and where can I find the reliable literature sources for SPME technique disadvantages discription. From my own experience I found SPME is low in reproducibility, not precise enough for quantification measurement and fibers itselves are fragile and easy to break. However I can't find any proof of that in literature. Could you tell me please where I can find it?
Best regards,
Ksenia

[Peter Apps]

I think that you might find a problem with publication bias. To get into a journal a method has to work properly, so if someone tried to develop a SPME method and failed, it will never appear in the literature. Your best hope is to look for reviews of sample preparation techniques.

I would also note that there are very few techniques that are intrinsically poor - and there is overwhelming evidence that SPME can form the basis of sound sample prep techniques, so you might need to look elsewhere for the cause of your particular problems.

Peter

[rb6banjo]

I use SPME for quantitative analysis daily. The matrices that I encounter are varied and they include beer volatiles. Sometimes I use an internal standard, sometimes I don't. Even when I don't, I get repeatable results. My fibers last for hundreds of injections.

In my opinion, there are relatively few disadvantages compared to the large number of advantages that the technique offers. As I see it, the main disadvantage is that none of the sorbents I've tried are particularly good at trapping very light materials (acetaldehyde, dms, etc.). Certainly, you can't get methane and ethane is only barely retained on a carboxen/pdms (black) fiber. Another disadvantage is that heavier materials can be preferentially adsorbed to the fibers (phenomenon called displacement). You can control this by controlling the sampling time.

I'm a huge proponent of SPME. As we say in the US, "it's better than sliced bread". I can sample things/places that I could never stuff into a standard purge-and-trap apparatus.

[MSCHemist]

I've used SPME for complex matrices there are some disadvantages I've found.

Everything effects the results. It is often necessary to use a blank matrix for calibration rather than simple water. I tried adding a few ul of a standard mix in acetone rather than water and the signal of many early volatiles dropped 30%.

Some compounds have very good repeatable results such as pyrazines. Some samples had very high %RSD even with int standards or poor linearity (Hexanal).

[rb6banjo]

Agreed. I generally calibrate in whatever matrix I'm studying at the time. I tried external-standard calibration a few times but the results I obtained didn't match up with what I obtained by standard addition. I would highly recommend calibration in your matrix when using SPME for analysis of complex samples.