March 28, 2024, 04:02:41 PM
Forum Rules: Read This Before Posting


Topic: components separation by means of Py-GC-MS and preparative GPC  (Read 12941 times)

0 Members and 1 Guest are viewing this topic.

Offline bjorndaryl89

  • New Member
  • **
  • Posts: 6
  • Mole Snacks: +1/-0
Hi guys,

I'm working on a study about the identification of components in hot-melt adhesives (HMAs).

They consist out of three main components: polymer, tackifier and wax/oil.

It is possible to separate these components by means of Py-GC-MS, but there is an issue with this method. The polyethylene wax/oil will not completely go out of the GC-system, which results in carry-over.

Now my solution was to preparative separate, by means of GPC, the components by dissolving the HMAs in dichloromethane. Only problem is the polyethylene wax/oil (and a part of the polymer) are high in molecular weight and will not dissolve properly.

I'm at a dead end with this problem, maybe one of you as any suggestions or solutions.

Much appreciated ;)
« Last Edit: March 26, 2015, 06:23:36 AM by bjorndaryl89 »

Offline Arkcon

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7367
  • Mole Snacks: +533/-147
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #1 on: March 26, 2015, 07:28:59 AM »
I don't have a quick answer to your problem, but I am intrigued.  Tell us more about your GPC method, what conditions are you using, and tell us as much as you can about the polyethylene wax.  If you can completely separate out this troublesome component, then maybe you can analyze it separately under different conditions.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline bjorndaryl89

  • New Member
  • **
  • Posts: 6
  • Mole Snacks: +1/-0
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #2 on: March 26, 2015, 08:35:21 AM »
Not at liberty to give any info about the GPC method.

There is not much to say about the polyethylene wax other than it is the Sasol Wax H1 (Fisher-Tropsch) by Sasol Wax GmbH in Germany.

I've read some information about using xylene as a solvent to dissolve the wax in and I'm looking into that now, but for now no real results.

Offline Furanone

  • Chemist
  • Full Member
  • *
  • Posts: 211
  • Mole Snacks: +34/-2
  • Gender: Male
  • Actually more a Food Chemist
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #3 on: March 26, 2015, 10:56:22 AM »
Can I ask what type of Pyrolyzer you use? Is it platinum filament (ie Pyroprobe), Curie-point induction, or the constant temperature furnace? I am assuming it is fixed (stationary) to GC inlet, or is it removable? What pyrolysis temperature are you using? I have a few ideas but need a bit more information. You may be able to do it without any GPC whatsoever.
"The true worth of an experimenter consists in pursuing not only what he seeks in his experiment, but also what he did not seek."

--Sir William Bragg (1862 - 1942)

Offline marquis

  • Full Member
  • ****
  • Posts: 389
  • Mole Snacks: +35/-3
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #4 on: March 26, 2015, 12:18:15 PM »
Most of the GPC work we did was based on THF.  It dissolved most waxes
pretty well.  Will it work on your wax?

The THF dissolved some polymers as well.  These  were mostly vinyl based.
Will THF work on your polymers?

Always had some carryover with Pyrolysis GC.  Can you burn out the
pyrolyzer and heat the column high enough to clean it out?

Good luck.

Offline bjorndaryl89

  • New Member
  • **
  • Posts: 6
  • Mole Snacks: +1/-0
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #5 on: March 27, 2015, 04:31:41 AM »
Can I ask what type of Pyrolyzer you use? Is it platinum filament (ie Pyroprobe), Curie-point induction, or the constant temperature furnace? I am assuming it is fixed (stationary) to GC inlet, or is it removable? What pyrolysis temperature are you using? I have a few ideas but need a bit more information. You may be able to do it without any GPC whatsoever.

I use a vertical pyrolyser unit with a sample cup oven. It is removable of the GC inlet. Pyrolysis temp. is 600 degrees Celsius.

Offline bjorndaryl89

  • New Member
  • **
  • Posts: 6
  • Mole Snacks: +1/-0
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #6 on: March 27, 2015, 05:33:33 AM »
Most of the GPC work we did was based on THF.  It dissolved most waxes
pretty well.  Will it work on your wax?

The THF dissolved some polymers as well.  These  were mostly vinyl based.
Will THF work on your polymers?

Always had some carryover with Pyrolysis GC.  Can you burn out the
pyrolyzer and heat the column high enough to clean it out?

Good luck.

I used THF as a solvent, but the wax and polymers do not dissolve. The tackifier does.
I also used xylene as a solvent. The wax did not dissolve, but the polymer and tackifier seemed to dissolve (which is a good thing, because if I can dissolve two of the three components I can put the polymer and tackifier on the Py-GC-MS and have no carry over of the wax).

Pyrolyser is on 600 degrees Celsius, which is already pretty high. Column is a polar one and can't take too high of a temperature though.

Offline Furanone

  • Chemist
  • Full Member
  • *
  • Posts: 211
  • Mole Snacks: +34/-2
  • Gender: Male
  • Actually more a Food Chemist
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #7 on: March 27, 2015, 05:34:08 AM »
Can I ask what type of Pyrolyzer you use? Is it platinum filament (ie Pyroprobe), Curie-point induction, or the constant temperature furnace? I am assuming it is fixed (stationary) to GC inlet, or is it removable? What pyrolysis temperature are you using? I have a few ideas but need a bit more information. You may be able to do it without any GPC whatsoever.

I use a vertical pyrolyser unit with a sample cup oven. It is removable of the GC inlet. Pyrolysis temp. is 600 degrees Celsius.

The setup I use that is quite nice is where I no longer have the pyrolysis unit attached (stationary) to the GC inlet and instead it is now offline, where I cut a 20-30 cm length of a separate GC column and have that at the outlet of now stand-alone pyrolyzer to act as the chemical trap. Then, I use methanol in a syringe to wash the pyrolysis products out of cut column length into a GC vial and can now load in GC autosampler.

The benefits of this are you can run nitrogen (cheap) through pyrolyzer while you can use hydrogen as carrier gas (hydrogen & pyrolysis don't mix!  ;) ). Also, sample throughput is higher since all sample prep is performed at one time and vials with collected pyrolysates are loaded in autosampler with it running non-stop as opposed to having to pyrolyze a new sample every 30 minutes for only 8 hours in the day. Not to mention, the GC-MS is no longer designated to only pyrolysis but can be used for any other preparations.

You may have to play around with your setup to get it right (It took me a while to get it working right but was worth it). There may be some losses of the early eluters (low boiling point compounds eg. acetaldehyde), but for me these are lower information value. I suppose a cold trap could be set up on the cut length of GC column to possibly help in collecting these low boiling point compounds, if they are necessary.

Anyway, my thought was you may be able to control the pyrolysis products you get by the amount of methanol you rinse cut length of column with, so that only the compounds of interest (GC injectable) and not the crud that is causing carry-over are extracted into GC vial. You can then either dispose of that cut length again or further rinse with methanol and use again (you can test to see that only methanol is coming out -- and this will tell you if all compounds were extracted for first methanol rinse). I have only used methanol as solvent, since this is the known solvent for cleaning GC columns. If you need a stronger solvent, check with the column manufacturer to make sure you won't destroy the cut column length, but you could also do some experiments with solvents since it is only 20 cm of column you may be destroying).

So, if this works then perhaps you won't have to run the prep GPC prior to Py-GC since carry-over products (not fully fragmented  polyethylene wax/oil) will not get injected into GC since not extracted by methanol.

As Marquis said above, another option then (if above idea is too much set-up/experimenting with conditions) is depending on the column max temperature, set GC program to a higher inlet temp (pulsed split if possible) and end GC oven temp and let hold for longer to ensure all carry over products are 'burned' out of column before next run, and run a blank run in between to ensure it is in fact blank.
"The true worth of an experimenter consists in pursuing not only what he seeks in his experiment, but also what he did not seek."

--Sir William Bragg (1862 - 1942)

Offline Furanone

  • Chemist
  • Full Member
  • *
  • Posts: 211
  • Mole Snacks: +34/-2
  • Gender: Male
  • Actually more a Food Chemist
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #8 on: March 27, 2015, 05:36:51 AM »
Most of the GPC work we did was based on THF.  It dissolved most waxes
pretty well.  Will it work on your wax?

The THF dissolved some polymers as well.  These  were mostly vinyl based.
Will THF work on your polymers?

Always had some carryover with Pyrolysis GC.  Can you burn out the
pyrolyzer and heat the column high enough to clean it out?

Good luck.

I used THF as a solvent, but the wax and polymers do not dissolve. The tackifier does.
I also used xylene as a solvent. The wax did not dissolve, but the polymer and tackifier seemed to dissolve (which is a good thing, because if I can dissolve two of the three components I can put the polymer and tackifier on the Py-GC-MS and have no carry over of the wax).

Pyrolyser is on 600 degrees Celsius, which is already pretty high. Column is a polar one and can't take too high of a temperature though.

OK I see you use a polar column with low max temperature. That would present a problem. Can you switch to a mid-polarity DB-5MS with much higher max temp? Can I ask the reasons you are using the polar column?
"The true worth of an experimenter consists in pursuing not only what he seeks in his experiment, but also what he did not seek."

--Sir William Bragg (1862 - 1942)

Offline bjorndaryl89

  • New Member
  • **
  • Posts: 6
  • Mole Snacks: +1/-0
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #9 on: March 27, 2015, 05:48:01 AM »
Most of the GPC work we did was based on THF.  It dissolved most waxes
pretty well.  Will it work on your wax?

The THF dissolved some polymers as well.  These  were mostly vinyl based.
Will THF work on your polymers?

Always had some carryover with Pyrolysis GC.  Can you burn out the
pyrolyzer and heat the column high enough to clean it out?

Good luck.

I used THF as a solvent, but the wax and polymers do not dissolve. The tackifier does.
I also used xylene as a solvent. The wax did not dissolve, but the polymer and tackifier seemed to dissolve (which is a good thing, because if I can dissolve two of the three components I can put the polymer and tackifier on the Py-GC-MS and have no carry over of the wax).

Pyrolyser is on 600 degrees Celsius, which is already pretty high. Column is a polar one and can't take too high of a temperature though.

OK I see you use a polar column with low max temperature. That would present a problem. Can you switch to a mid-polarity DB-5MS with much higher max temp? Can I ask the reasons you are using the polar column?

Not allowed to switch to a more apolar column, because of other projects and analyses being run on the GC-system.

Offline Furanone

  • Chemist
  • Full Member
  • *
  • Posts: 211
  • Mole Snacks: +34/-2
  • Gender: Male
  • Actually more a Food Chemist
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #10 on: March 27, 2015, 05:52:34 AM »
That is really too bad, since I think this would be the easiest option and would most probably solve your problem of carry over. Maybe with the polar column, you could keep max temperatures within its range but just have longer in between 'blank' runs to ensure all carry-over products are eluted, but now you sacrifice sample throughput.
"The true worth of an experimenter consists in pursuing not only what he seeks in his experiment, but also what he did not seek."

--Sir William Bragg (1862 - 1942)

Offline bjorndaryl89

  • New Member
  • **
  • Posts: 6
  • Mole Snacks: +1/-0
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #11 on: March 27, 2015, 07:42:31 AM »
That is really too bad, since I think this would be the easiest option and would most probably solve your problem of carry over. Maybe with the polar column, you could keep max temperatures within its range but just have longer in between 'blank' runs to ensure all carry-over products are eluted, but now you sacrifice sample throughput.

Yeah. Thats why I was focusing on the preparative separation part. Thanks for the information and effort to help me
Much appreciated

Offline Furanone

  • Chemist
  • Full Member
  • *
  • Posts: 211
  • Mole Snacks: +34/-2
  • Gender: Male
  • Actually more a Food Chemist
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #12 on: March 27, 2015, 07:50:21 AM »
That is really too bad, since I think this would be the easiest option and would most probably solve your problem of carry over. Maybe with the polar column, you could keep max temperatures within its range but just have longer in between 'blank' runs to ensure all carry-over products are eluted, but now you sacrifice sample throughput.

Yeah. Thats why I was focusing on the preparative separation part. Thanks for the information and effort to *delete me*
Much appreciated

*Delete me*? In what context do you mean this? I have seen it posted before, but was never 100% sure why people post this, since in the future people who may have the same problem search the internet for this exact topic and find this old thread and reading it solves their problem.

Anyway, I digress  :)  Do you think the offline pyrolysis, I mention above, might be a viable option to try? You mentioned your vertical pyrolyser is removable from GC.
"The true worth of an experimenter consists in pursuing not only what he seeks in his experiment, but also what he did not seek."

--Sir William Bragg (1862 - 1942)

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27633
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #13 on: March 27, 2015, 07:53:07 AM »
*Delete me*?

That's an automatic joke hard coded into the forum ;)
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline Furanone

  • Chemist
  • Full Member
  • *
  • Posts: 211
  • Mole Snacks: +34/-2
  • Gender: Male
  • Actually more a Food Chemist
Re: components separation by means of Py-GC-MS and preparative GPC
« Reply #14 on: March 27, 2015, 08:41:03 AM »
That would be nice if you solve your problem and share the solution with us. That's what makes these forums very useful.

If you had a different type of pyrolyzer specifically the platinum filament type (Pyroprobe), you would have other options to try, since with this type you can control rate of heating and length of time for total pyrolysis, so a slower rate and longer pyrolysis time might help more completely pyrolyze the material that is causing you GC carry over. I also found that a very even spreading of sample on the filament ensured a more reproducible chromatogram and less carry over. So I would place a few mg of sample on filament then use 50 ul of isopropanol to spread it followed by a drying step turning filament to 80 C for 5 sec and this would make a nice thin layer on filament and a great pyrolysis. Maybe you can try using smaller amount of sample if sensitivity is not an issue, and you may get more complete pyrolysis. Anyway, best of luck. I have enjoyed chatting with you about this.

"The true worth of an experimenter consists in pursuing not only what he seeks in his experiment, but also what he did not seek."

--Sir William Bragg (1862 - 1942)

Sponsored Links