Sounds like you might already have this information, but just in case you haven't seen it, here is some info on Care and Use of your column from the Knowledge Base .
Anybody have link or information for H-Class spare parts (HCLASS with column manager CM-A and PDA)
ie standard capillary tubing for inlet /outlet from to column ?
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.