Retention time problem

Good morning,

we have a GC-MS with a DB-HeavyWax Column. Yesterday we changed the column for a new one (the same). The retention times of our samples shifted 8-11 min. Now, the peaks appear 8-11 min later. We are using a flow of 1.8 mL/min, if we try to do a retention lock, the pressure would be so high. The new column is the same model as the old one. We don't understand why we have this change in the RT's. Column : 123-7132.

 

Thank you!

 

Emilian

Parents
  • Hi,

     

    As I already mentioned before, I'm not a wiz at GC. I just try to read a lot.

     

    I do have retention times shift during my injections but this is due to a slow degradation of the column because of the type of compounds injected. When I change column, the retention times are completely off.

    It is not worrying because the relative retention times remain unaltered. Check those for both columns.

    Maybe you (we) should stop worrying about retention times and consider, instead, relative retention times or, even better, Kovats retention index.

     

    After installing the column according to the 'Column Installation Guide' that came with it, check the 'Column Performance Summary', provided as well, and compare it with the one of the older column. If differences exist in rt for the same compounds (assuming GC conditions are the same), columns are not the same to begin with.

    Try to reproduce the injections of the standards, used in the summary, at the same chromatographic conditions of course. If you have big differences, maybe you should talk with the column manufacturer.

     

    Finally, in GC, I believe we should be talking about average carrier gas linear velocity instead of flow. Did you see if the velocity of the carrier gas was the same for both columns?

Reply
  • Hi,

     

    As I already mentioned before, I'm not a wiz at GC. I just try to read a lot.

     

    I do have retention times shift during my injections but this is due to a slow degradation of the column because of the type of compounds injected. When I change column, the retention times are completely off.

    It is not worrying because the relative retention times remain unaltered. Check those for both columns.

    Maybe you (we) should stop worrying about retention times and consider, instead, relative retention times or, even better, Kovats retention index.

     

    After installing the column according to the 'Column Installation Guide' that came with it, check the 'Column Performance Summary', provided as well, and compare it with the one of the older column. If differences exist in rt for the same compounds (assuming GC conditions are the same), columns are not the same to begin with.

    Try to reproduce the injections of the standards, used in the summary, at the same chromatographic conditions of course. If you have big differences, maybe you should talk with the column manufacturer.

     

    Finally, in GC, I believe we should be talking about average carrier gas linear velocity instead of flow. Did you see if the velocity of the carrier gas was the same for both columns?

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