RI Baseline Periodic Drift Down and Shoots back up

[clasperj]

Dear all,

I am wondering if anyone has a similar problem with their RI detectors occasionally. This problem happened to me on a Shimadzu and Waters RI detector. I am grateful if anyone can give me some pointers. Thanks!

Problem:
The baseline drift down slowly and steadily, and then suddenly rise back to the starting level.


URL: https://ibb.co/Zz29NBB


URL: https://ibb.co/0tb89J0

Condition: HPX-87H column, 60oC, 0.5mM H2SO4 0.6mL/min, Waters RI detector.
The mobile phase is properly degassed (sonicator + vacuum for about 1 hr)

[Gerhard Kratz]

Anyhow, that looks like gas bubbles in the reference cell. Connect a 30cm small ID capillary ´to the outlet of your RI detector. That will help.

[clasperj]

Hi Gerhard,

Thanks for the tip. As a RI detector novice, I worry this could put backpressure to the flow cell and break it.
Can you explain a bit more why this backpressure can be helpful? If I get asked by my technical officer, at least I want to be able to explain it. Thanks!

[uzman]

It prevents out-gassing and bubble formation in the flow cell.

Yes , the outlet tubing for RI detector must be carefully chosen , to prevent much backpressure , 1 meter of 0.5mm ID tubing recommended.