Disturbing peak H-Class

Hi all,
I have a prblem with our H-Class. For qualification purpose, I inject a caffeine solution. The eluent is MeOH/water 20/80, isocratic. My caffeine peak elutes at approx. 1 min. Unfortunately there is a huge solvent/system "peak" which elutes from approx. 0.6 min to 1.2 min.
We changed all reagents (several times) already and tried different grades of them. Additionally we filtered the eluent. But the "peak" is still there. Please see the attached file.

Has anybody an idea what we could do to eliminate the "peak"?

Thanks in advance!


  • Hi Juwe,

    I'm sorry that it has taken so long to get a response but it looks suspiciously like a difference between the Mobile Phase and the sample diluent.  Is there any chance that the Caffeine is prepared in something other than MeOH and Water?  Also, how large is the injection volume (this effect becomes even worse at high injection volumes).

    You can also do a search on the Waters Knowledge Base if you have other questions.  Support.waters.com.


  • MJS
    If you are using the Waters test kit, you should be following the Waters protocol (included with the SQT projects disc) for your system.  Those protocols outline the mobile phase, column, system prep, etc.  The H-class SQT tests do utilize ACN and water vs the Alliance's Methanol and Water as MarcNoble alluded to.