Reproducibility problem

Hello

I apologize, I have looked all over for something already in this forum but have not come across it yet.

I am running Ethanol on a Agilent 7890B with an internal standard of Acetonitrile.  We run 6 consecutive injections to show that the machine is stable. I normally have no problems, however, I have a problem today that the ratio of ethanol to acetonitrile is constantly increasing with consecutive runs. I had this problem before and just running it until it stabilized worked, but I was wondering if you all have an idea of what could be causing this. 2 days ago we replaced the needle, but the same day we were able to run with no problem, if this is helpful knowledge. Aside from that nothing else has been done to the machine since.

I appreciate any advice/insights

Thank you

KH

Parents
  • Hello

    Sorry for taking so long to respond, I did not realize that I had replies. To fix it, I had to change the injection size to a lower amount (2 uL to .2 uL). The liner was being overwhelmed. I went to Vapor Volume Calculator and it showed that I was using the liner at over 300% capacity. Changing the injction size and getting a new needle has helped significantly.  Thank you everyone for your answers.

Reply
  • Hello

    Sorry for taking so long to respond, I did not realize that I had replies. To fix it, I had to change the injection size to a lower amount (2 uL to .2 uL). The liner was being overwhelmed. I went to Vapor Volume Calculator and it showed that I was using the liner at over 300% capacity. Changing the injction size and getting a new needle has helped significantly.  Thank you everyone for your answers.

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