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- Posts: 7
- Joined: Fri Jan 06, 2012 8:40 pm
I am having an issue with the appearance of a negative peak after injection on my Agilent 1260 LC II system. The system is currently configured with a Phenomenex GuardColumn, 250mm x 4mm RP-C8 column and RID detector. Mobile phase is 100% Water, flow rate is 0.9ml/min, Column temp is 50C (both left and right) and Detector temp is 35C.
When I first got the LC I did not have this issue. My main analyte was Ethyl Alcohol. I ran Alcohol analysis for a month without issue. At some point, I had a need to analyze for Vanillin, so the 250x4mm column was swapped for a 125mmx4mm RP-C18 column and the mobile phase was changed from 100% Water to a changing gradient ratio of Acetonitrile and Acidified Water with Phosphoric Acid, pH <2.8 analyzed via DAD detector.
Between all of this switching the system was flushed with IPA and Water.
The need to analyze Alcohol arose again, so the original configuration was returned. This is when the negative peak problem arose. Longer story shortened a little, after multiple visits by the Agilent Tech, a swap of the degasser, replacement of the Needle, Needle Seat and Coil, multiple system flushes with the Agilent HPLC Flush solution, the problem still exists.
Strangely enough, when the system is in idle just running Mobile phase or when a no-injection blank is run the peak does not show up. The peak only shows after an injection. It even appears when injecting a vial with the mobile phase (100% Water).
I am at a loss. I can always explain further in more detail but I wanted to lay the ground work. I have attached a few screen shots of the Peak. Some screen shots show the negative peak while a column is installed, others show the negative peak with the column removed and a union installed connecting the column inlet capillary and outlet capillary together. Why this is even worse is that the negative peak elutes at the same place as my Alcohol peak.
https://drive.google.com/open?id=183AAbrKiNGJUsNIZcn2rjAcT_Bjb67jp
https://drive.google.com/open?id=1LCwDqIVLZa39Frary1xq2nJenadGXvRD
https://drive.google.com/open?id=1gD_IlAfNwTAGFhjcjn42MJkC1C75owyn