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My teacher said that AAS doesn't work for non-metals - only works for cations. I asked why and he said that was how things go. Now, perhaps someone could give a more fulfilling explanation? Is that really the case? https://boredofstudies.org/threads/aas-for-non-metals.34815/ There are users from 2004 here saying that it works.

What???

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  • $\begingroup$ Certainly ThermoFisher (thermofisher.com/us/en/home/industrial/…), a supplier of such instruments, makes no such claim. $\endgroup$
    – Jon Custer
    Apr 21 at 16:12
  • $\begingroup$ Percival, Please ignore the 2004 discussion thread. It is complete non-sense. $\endgroup$
    – AChem
    Apr 21 at 19:54

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Your teacher is partially correct. Flame AAS is more feasible for metals, almost all of them. Mention to your teacher that flame AAS does not know whether you are introducing anions or cations in the flame. As the name indicates, we deal with neutral atoms in atomic absorption spectrophotometry. For example, if we introduce chromate, which is an anion, it works fine. When it comes to a majority non-metals the key problem is the location of absorption wavelengths. These wavelengths are located in the vacuum UV. Second issue that air-acetylene is a "cold" flame by atomic standards. One would need much higher temperatures to excite non-metals. This also means you cannot carry out the experiment in air because air will absorb all the vacuum UV light from the source.

For example, if we consult Perkin-Elmer's Analytical Methods for Atomic Absorption Spectroscopy or informally "Cookbook" as it is called. The entry for chlorine says:

Atomic absorption has not been reported for chlorine. Chlorine wavelengths at which atomic absorption might occur are below the lower wavelength limits of conventional atomic absorption.

Iodine has absorbing lines, but they are located in the vacuum UV region of the spectrum. As a result, iodine cannot be determined by normal atomic absorption techniques.

Sulfur has absorbing lines, but they are located in the vacuum UV region of the spectrum.

As a result, sulfur cannot be determined by normal atomic absorption techniques but phosphorus is fine with a special nitrous-oxide flame. It is a high temperature flame and glows orange-red with acetylene. Watch here:

https://www.youtube.com/watch?v=kvj7gH-wfUs&ab_channel=PGInstruments

The camera did not do justice here. Recall racing cars but the analytical sensitivity is very poor for P, which means Flame-AAS is essentially useless for non-metals.

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