I'm ok with the theory behind AAS and how the machine works, but I'm really struggling with answering questions relating to AAS - the ones where you are required to work out the concentrations of samples and graph calibration curves etc. I really can't get my head around the process. Plz help!
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Aas (1 Viewer)
- Thread starter nesstar
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You should get a set of values of AAS readings for known ppm concentrations, plot them on a graph accurately. You should then be given a AAS value for your sample, find that value on the graph and you can see the ppm of it aswell
oh yea, talk abt aas... cm_tutor: learning the molecular orbital theory, i am starting to think that aas can be applied to any ions, not only cations... because doubtlessly, there will be a energy gap regardless if tis cation or anion... but then i was readin my chem notes from hsc, i wrote down (as instructed) that it only works for cations???
can you plz verify this for me???
thx in adv =)
can you plz verify this for me???
thx in adv =)
AAS will only work on species that can be present in a flame as isolated (unbonded) atoms or ions - hence the name of Atomic Absorption Spectroscopy. This restricts it practically to most metal cations, as there aren't many other species that survive the conditions.
For example, if you want to measure Ca<sup>2+</sup>, then you can't get a decent reading in the presence of phosphate, colloidal aggregates form that don't readily come apart to release the metal cation, even in a flame. You can reduce this problem by forming a complex - the EDTA<sup>4-</sup> complex with calcium is good, [CaEDTA]<sup>2-</sup>, as the ligand combusts in the flame, releasing the calcium cations.
Remember that we are talking about a high temperature flame, so we are talking about an environment with a lot of unusual, and highly reactive species. For example, the C<sub>2</sub> radical is common in a flame, but you won't encounter it in many other places.
For example, if you want to measure Ca<sup>2+</sup>, then you can't get a decent reading in the presence of phosphate, colloidal aggregates form that don't readily come apart to release the metal cation, even in a flame. You can reduce this problem by forming a complex - the EDTA<sup>4-</sup> complex with calcium is good, [CaEDTA]<sup>2-</sup>, as the ligand combusts in the flame, releasing the calcium cations.
Remember that we are talking about a high temperature flame, so we are talking about an environment with a lot of unusual, and highly reactive species. For example, the C<sub>2</sub> radical is common in a flame, but you won't encounter it in many other places.
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uhm, ok... aas is alot mroe complicated than i thought...
so aas only works by exciting electrons around an ATOM rather than any complex/ions???
i thought it work similar as IR spectroscopy, where if the frequency is right, the molecule absorbs that wavelength of light hence a dark band in the spectrum @@
so aas only works by exciting electrons around an ATOM rather than any complex/ions???
i thought it work similar as IR spectroscopy, where if the frequency is right, the molecule absorbs that wavelength of light hence a dark band in the spectrum @@
ohhh... no... not at all... chem is one of the most interestin subjects you will do in uni =D (aprt from maths that is)...
and the fact that something is more complicated than you thought should be another reason for you do the course ~~~ so that you can endavour on the great journey in finding out the truth ~~~ =D simply fascinating...
Since a complex will have 'molecular' orbitals that are different from the atomic orbitals of the cation, it is not surprising that the exitation wavelength would have changed, even if you assume that the orbital into which the electron would have been promoted remains vacant.
Remember with IR that the frequencies change with the environment. This is fine if you are going to scan the spectrum (as in IR), but is a problem if you are using monochromatic light, as in AAS
Nesstar, I agree with xiao that Chem can be (and frequently is) interesting. Remember that xiao is a Uni student, and so has much more background theory than you do - For an HSC student, none of the complications that can interfere with AAS are an issue. Also, AAS is really not that complicated a technique. It works on monatomic cations in a flame, and anything that stops a cation being monatomic will interfere. Xiao's question begins to address the interference issue, which is why I brought it up
yea... thanks for the explanation cm_tutor =)
i asked those questions because this question was asked by an other bos'er previously, during the period when you were away... i wrongly stated that aas would work on all species, nto just the cations... so i wish to get this clarified... =D
i asked those questions because this question was asked by an other bos'er previously, during the period when you were away... i wrongly stated that aas would work on all species, nto just the cations... so i wish to get this clarified... =D
