Can PLOT columns, specificaly those with the particle traps, be trimmed?

I am seeing a drop in Area Counts across Standards, even with fresh, new stock. I am trying to identify any other possibility besides having contaminated the column as it was just installed 4-5 months ago, but haven't had much luck. In my other lab, we had different columns and trimming was a way of life there. However, I remember reading somewhere that it was not advisable to trim these types of columns. Is this correct? I haven't trimmed this particular column yet but was beginning to think about it, and thought I should "ask the experts."

Parents
  • I should clarify that this is attached to an auto-sampling headspace analyzer. Removal of septa, liner (and thereby gold seal) is usually only done during the yearly PM in order to minimize variations. Also, the column had not been removed or re-inserted when the loss occurred, so I don't see the inlet depth being the issue. Since the samples presented are almost entirely gaseous (headspace) I am not too sure even how necessary a trim would be. I am just trying to eliminate any other possibilities other than column degradation. This column is only a few months old at the onset of area loss, and I don't want to have to replace the column that often.

  • Hi Jason,

     

    then your inlet should be ok. Let's talk column and components then:

    • What column do you use?
    • What components are analyzed?
    • Are all components effected by the area loss?
    • What is your detector?
    • Where there changes in the matrix, incubation time or temperature?
  • All Q-polymers are made by radical polymerization and the process leaves free electrons (radicals) in the polymer. EO and PO are prone to radical polymerization and can react with the polymer's surface very slowly. This reaction changes the column's selectivity irreversibly. The longer a Q-column stays at high temperatures, the more migration of the free electrons take place and therefore reaction with reactive monomers like EO and PO increase.

     

    You could use an apolar liquid phase (100% dimethylpolysiloxane) with a very thick film (5 or 8 µm) for the separation. EO has a retention index of ca. 420 and PO of ca. 450, so they can easily be separated without any polymerization reactions.

  • Column: HP-PLOT/Q+PT 30M +5M Duraguard (2.5M on either end) 0.530 mm megabore, 40Micro film

    Primary components residual EO and PO in various acceptor chemistries. Separate STDs for each, both are showing area decline, on FID, recently switched out flame tip due to blockage/non-ignition. Area counts were already down before blockage of flame tip, and did not return after replacement.

    No changes to matrix or method/procedure. I had seen this issue before and finally determined that it was due to column contamination. Replaced the column in November of last year and area counts were good for 2.5-3 months. Initially thought the recent loss was due to STD age, and replaced both STD cyliders. Area counts remained low.

    I have put a filter on our Hydrogen, carrier line, from our benchtop hydrogen generator but that may have been closing the barn door after the horses have escaped. Otherwise, I'm not sure what could be getting into the column at this point.

  • If EO and PO react with the phase baking out is not helping as it is a chemical reaction. Check your baseline before and after bake-out, if it is comparable no bake-out is needed. In fact a bake-out would bring more free electrons to the surface of the phase making it more reactive for the polymerization. At least don't do bake-outs longer than necessary.

  • So, in addition to this, would you suggest fewer bake outs? We have been baking out frequently due to carry-over between samples, and negative effects on the baseline between runs. The method itself is isothermal at only 140c. The bake out takes the oven to 250c and holds until baseline stabilizes, but frequently people have been leaving it on the bake between runs. We may need to re-train on some best practices.

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  • So, in addition to this, would you suggest fewer bake outs? We have been baking out frequently due to carry-over between samples, and negative effects on the baseline between runs. The method itself is isothermal at only 140c. The bake out takes the oven to 250c and holds until baseline stabilizes, but frequently people have been leaving it on the bake between runs. We may need to re-train on some best practices.

Children
  • If EO and PO react with the phase baking out is not helping as it is a chemical reaction. Check your baseline before and after bake-out, if it is comparable no bake-out is needed. In fact a bake-out would bring more free electrons to the surface of the phase making it more reactive for the polymerization. At least don't do bake-outs longer than necessary.

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