Chromatography Forum

Hi,

I have several questions pertaining to a CAD that is producing strange results.. please let me know if anyone can help with CAD questions.

please let me know what kid of issues you have, we are constantly using Corona CAD (older versions), personally I think it is easy to work with ELSD...by far. Less issues, although sensitivity and linearity are worse for ELSD

please let me know what kid of issues you have, we are constantly using Corona CAD (older versions), personally I think it is easy to work with ELSD...by far. Less issues, although sensitivity and linearity are worse for ELSD

Hi Vlad, using a ELSD is not an option as we only have a CAD in our space. To explain the issue: we just had a PM performed on the CAD, all dirty parts/filters were cleaned or replaced. The engineer did not see anything wrong. he tested by flowing 100% IPA through the detector until he saw the current drop and stabilize. The issue is when we mix two solutions- for instance water in line A and IPA in line B, the current jumps super high to 200-400pA and then drops again when switching to one solvent. We have ruled out this being a LC issue as we have connected 3 different LC systems to the CAD. We have also tried different lots of IPA and switched out the water/ bottles we used. We have also tried different columns, although we are noticing this trend even with a union on. We did even mix two solvents in one single bottle on one single line and the current remains high. It seems to be one two solutions (such as org and aqueous) are mixed the CAD does not function properly? Do you have any ideas? I am completely out of options.

I have no experience with the CAD, but have you tried any other organic solvents? To me, this sounds like your mobile phase is "degassing" on the unit and you may see air-bubbles generate which could be picked up by your CAD? Do you guys degas your mobile phase/have a degassing unit?

Take this with a grain of salt as I have not used this detector, but this may be the cause of your issue

I have no experience with the CAD, but have you tried any other organic solvents? To me, this sounds like your mobile phase is "degassing" on the unit and you may see air-bubbles generate which could be picked up by your CAD? Do you guys degas your mobile phase/have a degassing unit?

Take this with a grain of salt as I have not used this detector, but this may be the cause of your issue

Yes, I have tried MeOH and the current looked ok. I did degas the IPA and it did not help the issue. Very strange that it is only occurring with IPA.

Hi, Chromacolor,

What is your Evaporation Temperature in the CAD?

Robert

Hi, Chromacolor,

What is your Evaporation Temperature in the CAD?

Robert

Hi robert,

I have tried a 25C and 35C for the evap temps

Keep evaporate temp at 35c. All cad solvents must be LCms grade. A perfect UV baseline with lc grade ipa will look terrible on the cad