Injection and/or detection problem????

I am having a problem with injection and/or detection, I guess.....When I inject the same solution with a known concentration 6 times in a row (after a solvent), the first one does not show any peak signal and, while the other 5 have reproductable signals. After this batch I inject another solvent and I have the same signal as the previous 5 injections of the known standard, as you can see in the table below. Considering this behaviour, I think it is some kind of delay in injection or detection?? Can you help to understand which can be the problem??? Does anyone already had the same problem?? Thank you



  • First thing to check is whether your peak is really eluting at ~2min.
    Set your run time to about 6 min and confirm this. If my suspicion is correct, your real RT is between 4 and 5 min.
  • Hi soraiasa,

    Did you perform the test that Dan noted above?  It does appear that you may be seeing some "late eluting" peaks.  If so, could you share the result?

    There may also be some additional help in the Waters Knowledge Base.  Try this link.

  • Thank you Marc. We already knew for sure the peak retention time, but I thank you both for trying to help.