Any suggestions please

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edm01
edm01
in Instrumentation and Mass Spectrometry
My instrument is passing all the diagnostic tests, leak, back pressure, desgasser,etc; however, there are no peaks in our samples, and they look like blanks. I cleaned with magic mix, prime seals, A/B, and changed columns, but still there are not good results. The only thing that I can think of is that the pressure now is around 4000 when it used to be around 5000 (after changing the column), but before that the pressure was normal but still no peaks. Any suggestions will help

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  • MarcNoble
    MarcNoble
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    What instrument and detector are you working on?  Can you share a chromatogram?
  • edm01
    edm01
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    It is a UPLC Acquity and SCIEX6500+. Now our results are not giving peaks for other analytes just for Riboflavin and Biotin

  • lizh
    lizh
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    A change in column pressure does suggests a leak, or the RT window is now wrong. But, could be a number of things, this is difficult to say it's this w/o a chromatogram and ideally a pressure trace, before and after. You do need to go back to basics. Can you select a known good column and method - a standard that you know works, from another system and replicate? Or you can take your method and check on another system. But if this is a well known method I recommend running fixed loop injections, to eliminate the effect of needlewash and then troubleshoot to see if this is a leak? You will need to check each piece of tubing. It's better to start with the one closest to MS. Have you also consulted Sciex as could be a source leak too, or similar leak or sensitivity issue.
  • edm01
    edm01
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    I ran diagnostics tests, but they all look good. I tried the same sample with another instrument (that is not passing the dynamic leak test) and the problem is the same. We changed the column and cleaned everything with magic mix, but it still has the same problem. Before starting to have problem, we ran another analyte that was fat, and after that, we started to have problems with our results. 
  • edm01
    edm01
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    Is there a possibility that it could be fixed by tuning/calibrating the instrument? It is weird for me that two analytes look good, but the others do not give any peaks and look like blanks

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