AnsweredAssumed Answered

late eluting peak area fluctuation

Question asked by wmbigham on Dec 5, 2019
Latest reply on Apr 20, 2020 by james_jenkins

I'm running a 7890/5975 for 625/8270 analysis and have been getting poor reproducibility in the late eluting peak areas.  The early peaks are very stable.  I have 6 internal standards where the first 4 are stable and the last two are not.  The compounds that use these internals fluctuate at approximately the same rate.  I use a S/SL inlet and have tried in splitless and pulsed splitless modes with the same results.  I am using a 5 uL syringe with a 0.2 uL injection.  I've tried upping the volume with same results but was overloading the column with higher injection volumes (shark fin peaks).  It is about a 20 minute run on a HP5MS column (30mX250umX0.25um).  I just installed a new column but the same was happening prior to the change.  I installed a new syringe with no affect.  Any thoughts?  Thanks,