Analysis acetic acid and formic acid GC-MS

Hi,

I am trying to create a GC-MS method for the headspace analysis of solid material. I will sample the headspace of this solid material with a SPME CAR/PDMS fiber. Some of the components in the headspace are acetic acid and formic acid, but I run into some problems while creating the method for this two components.  We only want to qualify the components, quantifying the components is not necessary. We are using a HP-5 column (30m) and we prefer to analyze using this column. Here are some details from the method I use:

Injection: splitless with SPME with a injection temperature of 220 C
Oven program: 30 C with a hold time of 2 minutes; then a ramp of 20 C/min to 220 C with a hold time of 10 minutes

Many thanks!

  • Thank you! I found this one earlier today, but this application note uses another column and I think that makes the difference between a good separation and a worse separation. If this is the only column which makes it possible to analyze these components I could discuss with the manager about buying this one, but rather not.

  • Hi Nipo,

    What kind of problems are you talking about? Bad resolution? Peak tailing?

    An HP-5 (being semi-standard non-polar) is not the best choice for polar compounds but we need to do with what we have (we do the same). As well, the liner needs to be deactivated (I suppose you have a liner for SPME, 0.75mm) and the column cannot have activated regions (it can happen over time with harsh samples). From the screenshot below (taken from our NIST database), you can see the retention indexes for those two compounds for different columns.

    If I were you, I would qualify the acids by their fragments ratio for example (still from screenshot):

    • for acetic acid: m/z 60 / m/z 43: 747/999 = 0.75/1,
    • for formic acid: m/z 46 / m/z 29: 609/999 = 0.61/1 (or less because AcOH also has a small fragment at m/z 29).

    If it is not enough, you might need to do a liquid extraction and a derivatization of the acids.

  • HP5 column is not correct choice of such analysis...

  • Hi, 

    Thank you for your response. The problem I am talking about is mostly a very bad and broad peak shape. 

    And thanks for your very good explanation. I know it will be better to change to another column, but we are not routine laboratory with many samples. I need to do 2 analyses every two weeks for 40 weeks. In the meantime other projects will be continue where I have to use the HP5 column. It will be very time consuming to change the columns every two weeks to do some analysis. That is the reason why I'd rather not replace the column.

    I am using a Agilent 5190-4048 liner and so far as I know it is a deactivated liner. But thanks for your help!

  • I know it will be better to change to another column, but we are not routine laboratory with many samples. I need to do 2 analyses every two weeks during 40 weeks. In the meantime other projects will be continue where I have to use the HP5 column. It will be very time consuming to change the columns every two weeks to do some analysis. That is the reason why I'd rather not replace the column. That's why I am looking for other options.

  • Then you to do method optimization as a try to get optimum result, like flow change, oven temp change, split ration change etc etc...

  • I'm still struggling as well with headspace SPME injection. I have a lot to learn and so little time...

    To understand even further, do you have an automatic injector? Do you sample automatically? I'm saying that because I use a PAL autosampler with a little oven for HS-SPME extraction and injection.

    So, from what I could understand, you might be overloading your column. Try to reduce the extraction time with the SPME and/or the extraction temperature. You can try to reduce the injection time as well (regenerate fiber after that). Reducing the ramp can help the separation of compounds. Eventually, because I have been told it can be done but I'm not convinced, you could use a split injection with a splitless liner (not the opposite) to reduce even further the amount of material injected.

    Finally, during data analysis, you can:

    • extract typical ions for formic and acetic acids from the chromatogram and visually assess if you have those compounds,
    • or try to use AMDIS (I have the feeling it can very useful but I lack time to understand it properly).

    Good luck

  • Excuse me for my late response. I took a few days off.

    Haha me too! I still have a lot to learn and too little budget and time to gain enough information....

    No, we don't have an automatic injector. We do our injections manually. Thanks for the tips! I didn't know AMDIS. I will use the tips in the method development. Good luck with your research and method development :) 

  • Hi I moved your question from the Gas Chromatography group to the GC/MS group for better visibility.  I see there was a lot of discussion here, were you able to come up with a solution to your problem?

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