Chromatography Forum

hello everyone.
i have a question concerning the charged aereosol detector (corona) commercialized by ESA.
the vendor claims that the response is not influenced by gradient elution, and my (little, at the matter of fact) experience with the CAD supports this statement. however I fail to grasp the theoretical (and/or technological) motivations that let this happen. how is it possible that the ionization of the analytes is independent from the enviroment, i.e. the vaporized mobile phase?
besides , if gradient is really not an issue, why Goreki et al. (ANal.Chem. 78, 2006, 3186-3192) developed an empirical method to compensate the effect of the gradient with the very same detector?

thanks in advance

I think that regular ELSD is not very sensitive to mobile phase composition while CAD can be very sensitive to it.

Poke around inthe literature a little more, paying strict attention to the variety of detector used...

With the "evaporative" detectors, what you are measuring is the dust particles left behind after the volatile solvent is removed from the droplets. That's why the chemistry of the analyte has little effect (dust is dust!). On the other hand, I would expect anything that affects the size or number of droplets formed in the nebulizer (e.g., the viscosity or surface tension of the liquid) *will* have an effect on the response. I'm willing to be proved wrong, but I really don't see any fundamental difference between the CAD and ELSD in that respect.

Actually, the higher the organic content the higher the response
(it has something to do with the viscosity of the mobile phase..).
Only if you have a very shallow gradient probably you will not notice
a variation in response between early and late eluters. The paper,
and the method, you are referring to is also present as application note
below:
http://www.esainc.com/docs/spool/70-791 ... adient.pdf