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Excellent SPME question Hailey!!!

26 May 2017

Last time, I told you I hunt for organic compounds with SPME Arrows, as opposed to the traditional SPME fibers, because I greatly appreciate the mechanical robustness and increased phase volumes afforded by the SPME Arrow. That blog has since received the following excellent comment/question from Hailey: The “sheath” part of the Arrow looks to be much thicker than the traditional setup; is septum coring an issue when injecting manually into a GC?

I thought this warranted the current blog. So first off, let me start by saying Hailey is spot on with her observation of the increased sheath. I plan to talk more about dimensions in a future blog, but for now you should know that everything but the hub (i.e., the screw end) on a SPME Arrow is bigger than a traditional SPME fiber. As my one colleague would say, the SPME Arrow is “heavy duty!” But if we take a look at the following picture, you will notice the SPME Arrow (left side) has an arrow-like tip, from which it garners its name.

This arrow tip accomplishes the following 2 things:

  1. Facilitates the smooth (i.e., core-free) penetration of vial and gc septa.
  2. Acts as a cap when the Arrow is retracted, thereby protecting the phase from any contamination.

You will also notice from the above picture that the traditional SPME fiber (right side) has an open-ended syringe-like tip, which is just begging to grab a hold of some septum and do some coring. So, truth is Hailey, we have more coring issues with traditional SPME fibers than the SPME Arrow.

BUT… like my father always said: a picture is worth a thousand words. So, let us take a look at the following septum, which has received over 150 injections from a SPME Arrow.

Here is the top side:

Here is the bottom side:

Do you see any coring? I do not! But let us take a closer look. The following picture is the same septum, but with me applying pressure:

When I apply pressure to the septum what you see is what I describe as a slit. The SPME Arrow’s tip appears to cut (not core) the septum and make its own “duckbill-like” lips, something you might be familiar with on a Merlin Microseal.

So Hailey… I greatly appreciate your question, as you touched on an excellent topic that I am sure other potential end users will be asking as well. Oh… the short answer to your question is “NO.” And yes, my fiancée says I tend to get a little long-winded.