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Charged Aerosol Detection

Migrated topic.
As I’ve mentioned elsewhere, I bought a Corona Veo RS, charged aerosol detector, to quantitate analytes which lack chromophores and ionizable side groups; nice addition to my mass spec and fluorescense detector (FLD-3400RS). It is an evaporative analytical method, along with evaporative light scattering detection (ELSD), CAD is relatively new, with the first patent filed in 2002, and the first commercial detector reaching the market in 2005. This particular detector is excellent for characterizing residues from solvents, and impurities in samples.

The detector is online. I was able to get compressed air to the nitrogen generator, and baseline the instrument, as well as run a few injections.

A detector like this is useful for screening samples which are UV-blind, and lack ionizable groups.. glycosides, carbohydrates, lipids, and surfactants, Nanoparticle conjugates, and counterions.
Another great use is full-spectrum purity determination. CAD is a mass-flow dependent method,
and the signal response is directly proportional to the amount of analyte present. So a more accurate purity assessment can be made from charged-aerosol detection, there is no ion suppression, and signal is independent of physicochemical/optical properties. For that reason, I may screen peoples' standards.
I ran an interesting experiment on DMT fumarate...
I injected a standard curve, prepared from serial dilutions, and detected using both CAD, and fluorescence.
DMT eluted at the expected RT, but a larger, earlier-eluting peak was prominent in the CAD scans, but absent from the fluorescence scans, indicating that it does not absorb UV @ 268 nm. The signal response did increase with increasing concentration, and was absent from the blank.

62.5 ng injection


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I got a couple new chromatograms. After reviewing the previous ones, and considering the relatively acidic gradient (using dilute formic acid), I realized at those elution times there may have been dmt formate, and dmt fumarate, the latter being a larger particle, and more polar, thus the earlier eluting peak.

I ran another experiment, diluting the DF in dilute ammonia, and injecting against DF in Milli-Q (LCMS-grade) water. These are the chromatograms.

Note: these chromatograms were performed in an isocratic, non-acidic mobile phase run, 60:40 acetonitrile:water, hence why the retention times don't match with the previous ones.


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