Resource Hub / ChromaBLOGraphy / SPME Arrow Sensitivity Speed

SPME Arrow Sensitivity = Speed

26 Oct 2017

We have demonstrated that the SPME Arrow is more durable and sensitive than a traditional SPME fiber. What more could you ask for? Well, truth be told that some analysts are content with the durability of their traditional SPME fibers. It is just like any other unhealthy relationship, where they have no clue how good things should be. I know, I digress… The other sensitivity component may not move the needle either, because clearly, they have the sensitivity they need with a traditional SPME fiber. So really a SPME Arrow does little to make their eyes stray from their beloved traditional SPME fiber (yes, relationship reference again). BUT… when you say speed, then everyone listens. Now all of a sudden, the 20- to 25-year-old relationship with SPME is met with the equivalent mid-life crisis solution of the shiny new sports car in the driveway. Enter the SPME Arrow speed!

On the heels of the sensitivity results we showed you last time, we thought that we could take advantage of the Arrow’s increased sensitivity and parlay that into speed. So, Colton and I took a 100 µm PDMS SPME Arrow and a 100 µm PDMS traditional SPME fiber. Again, we sampled headspace (HS) volatile organic compounds (VOCs) which had been spiked in drinking water at 2.5 ppb, as per method ISO 17943. Everything was equivalent (i.e., equilibration times, desorption temperatures, etc…), except for the fibers and the extraction times. We evaluated 15, 30, 60, 120, 240, 480, 960, and 1920 seconds of extraction time for each fiber (n=3 for each fiber and each extraction time). Here is what the results look like:

chart, scatter chart
HS extraction of ISO 17943 VOCs on 100 µm PDMS SPME Arrow and 100 µm PDMS traditional SPME fiber

Here are the following take-away messages we want you to have from the above graph:

  1. There should be no surprise in the increased response associated with the SPME Arrow, as we already demonstrated this last time.
  2. Both fibers equilibrated at ~120 seconds. This makes sense, because both fibers were 100 µm PDMS. Since the phase thickness is the same, equilibrium times are as well.
  3. Pay attention to the response of the SPME Arrow at 15 seconds vs the traditional SPME fiber at 120 seconds (see below).

chart, scatter chart
HS extraction of ISO 17943 VOCs on 100 µm PDMS SPME Arrow and 100 µm PDMS traditional SPME fiber

Right there lies your speed!!! You will notice the SPME Arrow produced 2x the response @ 15 seconds of extraction when compared to a traditional SPME fiber @ 120 seconds. That is twice the response in 1/8th the time. Admittedly, for the current example the rate limiting step would be a GC run time short enough to really capitalize on the 15 second extraction. Not exactly reasonable for the 90 some VOCs we looked at for ISO17943. However, if you were looking at less compounds and/or running a fast screening run, then you could really take advantage of this. It is also important to note that when using a CTC PAL, we were able to achieve ~5 RSDs on replicate runs using a 15 second extraction, which is about what the RSDs were for 120 seconds of extraction. It is important to note that if you are doing manual injections, a 1 second shift in extraction time could have a more significant impact on response with a target extraction time of 15 seconds compared to 120 seconds. So, you better keep a close eye on your watch!

Now picture this: you could potentially take your current 40-minute extraction time down to 5 minutes and walk away with two times the response. Time is money, so I know that I am now speaking in a language almost every analyst can understand.