Chromatography Forum

I would like to pose a question to folks out there that have a lot of experience with ELSD or CAD detectors.

My question is: Are there any analytes that one cannot quantitate with these detectors. In other words, is it possible that a molecule - such as a polymer - could be too big; such that after the desolvation step, very heavy particles are formed which crash out on the wall instead of traveling through the drift tube and being detected.

I have only limited experience with ELSD and would appreciate any suggestions regarding what types of analytes may be problematic by this method of detection.

Much Thanks

What you're actually measuring with an ELSD is an aerosol. My guess is that the molecule would have to be colloidal in size to start causing that kind of problem (but it's only a guess!)

we analyzed polymers with molecular weight 200,000 and never had problems. You can probably play with ELSD set up to avoid problems lie you describe.

Hi Vlad

So can you offer any specific recommendations on how would you set the parameters.

I imagine the drift tube temperature could be set towards the high end. But what else would you suggest.

Thanks very much.

playing with flow rate/pressure of nitrogen/air. Playing with temperature and flow rate. Usually you operate at very low concentration of analyte and if you consider amount you are injecting I would not expect a problem.

Vlad

I would like to ask a few more questions, since you seem to have experience in this area.

- What is the level of sensitivity you get with ELSD. It may vary, but generally, what is your LOD.

- Are you doing these runs with Size Exclusion or some other technique.

- Have you evaluated Reversed Phase and HILIC for fairly polar polymers; and if so which do you find is better.

Much Thanks For Your Help