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- Posts: 8
- Joined: Tue Jul 11, 2017 9:37 am
We just installed yesterday a new column HPX_87H (amminex Bio-rad) and precolumn 125019. In case it matters, we also had yesterday some service in the equipment to change some parts that had been running too long: plunger seal, low pressure valve and lamp of the PDA detector.
We have been running for years with this column and precolumn setting with the following conditions:
Flow: 0.6mL/min, temp: 63C, injection volume 40uL, eluent: H2SO4 12mM.
Our analysis runs for 43 min, and we always observed a small negative peak at around 20 min (RI detector). This was generally not an issue, but with the new column this peak has become bigger, so it covers the peak corresponding to one of our analytes.
link to the image:https://ibb.co/zJyXFKY
In the picture attached you will see a chromatogram of the same sample runned last week (black- with the previous column) and today (blue- with the new column). The peaks are: lactic acid, glycerol, acetic acid, propionic acid and butyric acid. As you can see, we do not see anymore the peak of butyric acid because it is covered by the negative peak.
For further information, I have to say that this big negative peak has always appeared as well in blank samples (eluent h2SO4 12mM), but it was generally much smaller…
The sample that you see in the chromatogram is the compounds I mentioned at 0.05 g/L prepared in 12mM H2SO4. And to make it clear, it is exactly the same sample (two aliquots of the same sample saved in the freezer).
Do you have any explanation?
Might it be that the column is not properly installed?
Do you know what is this peak? Is it unretained stuff from the injection?
Any help would be very very much appreciated.
Thanks in advance,
Anna