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

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  • Other considerations: Has the old column been in service for a long time and has it routinely been pushed to the edge of its max temp? Has the column been trimmed at either end a few times during its tenure? Did the earliest runs of this method on the old column match the RTs you are used to seeing, or are they closer to what you see with the replacement column?

     

    Some columns are WAY longer than they need to be to get a certain separation done because the method developer wanted to be able to use the same column for a while. This is often intended to include regular trimming of either or both ends whenever chromatography suffers because of one end of the column getting either fried or dirty over time. If you do this enough, you can experience significant changes in RTs while still meeting your SST requirements.

     

    In other words, establish whether you *really* have a problem, then if you do, try repeating the column manufacturer's QC test run on it, reinstalling it or whatever.  In general though, RTs will fall over time with any column and they do so to a larger extent with stationary phases that are thicker and more amenable to heat/oxygen/contamination damage.

  • The earliest runs of the old column match the RTs I am used to see, not the actual ones, so it is not a problem of being old or not...

    We have measured the old and the new column and practically they have the same length. 

     

    Thank you for answering!

     

    Emilian

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