Sorry for the delay. Here is your chromatogram with and without the PFAS Delay Column.

Sometimes I hear this from customers: “I don’t need a delay column. I haven’t had any trouble without it so far.”

It might be true. You may not have any issues without the delay column, especially when your samples are, for example, highly PFAS contaminated soil samples because the interference is too small to affect your end result.

I’ll show you the difference between PFAS analysis with and without the delay column.

Don’t be surprised. The chromatogram on the left is a blank sample injection! As you can see, there are peaks at the retention times you would expect the compounds from your sample to come out. Imagine what can possibly happen if you don’t have the delay column and you inject your sample containing low levels of PFAS.

                    

The chromatogram on the right also shows a blank sample injection, but this time the PFAS delay column was installed. You can see that the sharp peaks disappeared, but where are those delayed ”peaks”?   The elevated signals coming AFTER the expected retention times of the compounds of interest are the system-related PFAS that were held up by the delay column.

Remember the PFAS delay column is installed BEFORE the injector in the LC-MS/MS workflow and system-related interference will enter the delay column in a continuum from the mobile phase bottle and make their way through the analytical column to the detector. Unlike the injections of your sample which focus analytes at the head of the analytical column before the gradient starts, the interferences are continuously fed and they will be retained as they go through the delay column, diluted as they go through the injector, then retained again on analytical column not necessarily being focused much at any stage; hence resulting in broad and elevated signals.

Yes, the delayed interferences are broad because they enter the system continuously, and the signal is only elevated instead of looking like a sharp peak because the interferences exist from the very beginning of your analytical workflow (mobile phase) and are never focused on the analytical column like your sample. The magnitude of the delayed signal elevation depends on how long you equilibrate your LC column (length of column equilibration is related to how much your LC-MS/MS system components leach out the interferences onto the delay column) and what LC-MS/MS system you use (different LC-MS/MS systems may have different levels of system-related interferences depending on the materials used in various component parts).

Another way of minimizing system-related interferences is to replace all plastic parts in the workflow which may have PFAS leachates with PFAS-free parts such as PEEK. Still, the possibility of having background interferences from the workflow is endless since different LC-MS/MS systems may need different parts to be replaced. This approach might be too time-consuming to be practical, and you can still struggle with finding unknown sources of the interferences.

Sometimes you may analyze PFAS samples with high concentration for remediation projects,  e.g. contaminated soil from military bases or fire department practice sites, and sometimes your samples can be drinking water samples, which usually require low level detection (parts per trillion or even below).

Regardless of the LC-MS/MS systems you use for PFAS analysis and the level of concentrations you work on, having the PFAS delay column installed in your workflow BEFORE the injector will make you headache-free in your method development, method validation, and your day-to-day PFAS analysis.

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2 Responses to “Sorry for the delay. Here is your chromatogram with and without the PFAS Delay Column.”

  1. Thomas Huff says:

    I would be far more convinced if the Y-axis scale was absolute and labeled in your example chromatograms. As it is, there is no way to know if the signal with the delay column is any different from the background without the delay column. There is not enough information here to determine whether this is a worthwhile investment in an expensive column. Perhaps you have a link to a rigorous peer-reviewed analysis you could provide.

  2. Mike Chang says:

    Hi Thomas. Sorry for the delayed reply to your comment. This is NOT due to the PFAS “delay” column, but because I’ve been away from the office and on the road. As I mentioned in the blog the level of the interference is very different from an instrument to another. Here is the list of the source for the contamination. Starting from your mobile phase (even just solvents may have some), the lining, pump seal, pump lining, degasser unit (very bad source for contamination), and more. Also the length of your run time, equilibration time in the method, gradient conditions, flow rate, etc. There are so many variables in the amount of interferences you can get and it’s not really meaningful to show the y-axis scale. I had the exact same question when we created some blank injection data, but as we change one variable same blank injection showed different magnitude of detection. For example, if you equilibrate your column 10 min vs. 40 min, you’ll see completely different level of interferences. Some folks use very old LC pump (more than 10 years old) coupled with brand new MS/MS unit and they don’t see much interference because much of the contamination source in the LC pump already leached out the interference in the past. I appreciate your comment and I’ll see what other way we can demonstrate the effect of the PFAS delay column, but it really depends on the conditions you run, which is the very reason for the PFAS delay column since it is a universal solution regardless of your instrument, run conditions, etc. Does it answer your question?

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