Optional determination techniques in Atomic Absorption Spectroscopy

Question

I have tried to find information about this case but I couldn't find anything specific.

The key point of instrumental methods of analysis, is for the student to be able to know which one of the possible methods to use for a specific determination. As for me, that is not an easy thing to do because every method has its pros and cons. For the moment I am analysing AAS (Atomic Absorption Spectroscopy), and I simply cannot tell:

What's the reason that $\ce{As}$, $\ce{Te}$, $\ce{Se}$, $\ce{Ge}$, $\ce{Sn}$, $\ce{Pb}$ is preferred to be determined only by the hydrid method? $\ce{Pb}$ for example can be determined also with the other methods in AAS

Does anyone have any tip, how to choose between methods if it's required for any element?

I replied with a similar question earlier about the mercury determination.

Answer 1

Remember this is "atomic" spectroscopy so it is expected that the "sample" is being totally ripped apart. So one "best technique" per element.

$\ce{As}$, $\ce{Te}$, $\ce{Se}$, $\ce{Ge}$, $\ce{Sn}$, $\ce{Pb}$ are analyzed by the graphite tube technique rather than in a flame because the technique provides more sensitivity.

$\ce{Hg}$ is an odd one since you use a cold vapor technique.

Of course depending on the particular sample matrix what you might need to change.

Answer 2

Inductively coupled plasma Optical emission spectroscopy (ICP-OES) is best know technique for the determination of different elemental concentration in a sample even at ppb level simultaneously. you don't need to change the lamp every time and don't need to bother for calibration before running the actual sample.

But when it's come to these elements ( As, Te, Se, Ge, Sn, Pb) the best result you can only obtained by ASS using hydride generation in a graphite furnace. Using hydride generation technique the measurement can be done at ppb level in a dilute sample. This technique is used to provide higher sensitivity compared to other techniques.

Answer 3

You are right, every method has its pros and cons and if you were to choose one, the choice depends on what are you trying to analyse. The important things to keep in mind are:

• With AAS you will rarely be looking for every single element in the sample, but only the ones you expect to find or the ones you're specifically searching for

For example, you have an organic product and during its synthesis you used the metal catalyst (Pt is a common one). You want to make sure the catalyst is not present in your product. You will then want to search only for that particular metal. Based on what your analyte is, you choose on a method.

• The other important thing to consider is how sensitive your technique needs to be. You don't need ultra high sensitivity in all analyses and this will depend on your research (again, what are you trying to find with your measurement)

For example, if some product that's sent to you for analysis (e.g toys, pharmaceuticals) is regulated to have <5 ppb lead concentration, it is enough to use a technique which has sensitivity on ppb level. The sample may still contain traces of lead on ppt level and there are techniques which are that sensitive, but they are in this case unnecessary

I hope this answer is satisfactory to you because I don't believe any analyst can give you a singular answer. You may use different kinds of techniques for the same type of analyte.