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While documenting myself on the detectors used in HPLC, I came across one that I did not know: ELSD.

I understood that the sample with the mobile phase was nebulized at the column outlet but I do not understand what is measured next.

Could you clarify this for me?

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ELSD is an acronym for Evaporative Light Scattering Detector. It is used as a quasi-universal detector for HPLC.

The first step is the nebulization of the column effluents with a dry gas as you have mentioned. If the column effluents contain any non-volatile analyte, then those will form minute particles. The mintue particles become suspended in the gas stream and form an aerosol. The gas stream is made to pass through a focused light beam (usually a diode laser) which is perpendicular to the flow direction.

If aersol is present, the light will be scattered, and can be detected/analysed by a detector photodiode which is placed perpendicular to both the light beam and flow direction.

There is a nice picture that I got from this site:

ELSD detector internal workings


Reference- Analytical Chemistry, G. D. Christian, P. K. Dasgupta, K. A. Schug, 7th ed., Wiley, 2013

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    $\begingroup$ Nice explanation, the key point is that the analyte has to relatively non-volatile with respect to the mobile phase. $\endgroup$ – M. Farooq Feb 13 at 17:27

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