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
  • Just to be careful, count the number of loops on the old one and the new one.

    Also read in the manual how to calibrate the column length.

     

    and 1.8 ml/min is high flow into an Agilent GCMS ion source. It will work in the orthogonal (SS,Inert,Extractor,CI) source but not be optimum.  The axial HES source does not like that high flow at all. 

     

    If you think you need that high a flow to get your peaks out in a timely manner, either your column is too long or your oven ramp is not not aggressive enough early enough, or both.   

Reply
  • Just to be careful, count the number of loops on the old one and the new one.

    Also read in the manual how to calibrate the column length.

     

    and 1.8 ml/min is high flow into an Agilent GCMS ion source. It will work in the orthogonal (SS,Inert,Extractor,CI) source but not be optimum.  The axial HES source does not like that high flow at all. 

     

    If you think you need that high a flow to get your peaks out in a timely manner, either your column is too long or your oven ramp is not not aggressive enough early enough, or both.   

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