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ND

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"gather, process and present information to interpret secondary data from AAS measurements and evaluate the effectiveness of this in pollution control"

I've looked in CC, pathways, surfing and the CSU site; this is not addressed in any of these (well CSU has some stuff, but it doesn't evaluate the effectiveness of AAS in pollution control), can anyone tell me where they got their info for this from?
 

Frigid

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straight from my notes...

3.2.2 Describe the use of atomic absorption spectroscopy (AAS) in detecting concentrations of metal ions in solutions and assess its impact on scientific understanding of the effects of trace elements.

Atomic absorption spectroscopy (AAS) is an important technique in measuring the concentrations of metal ions in very minute quantities. In atomic spectroscopy a liquid sample containing the metal ion to be tested is aspirated through a plastic tube into a flame hot enough to vaporise the molecules into atoms. A cathode lamp of the specific metal passes through the vaporised sample. A detector measures the amount passing through the flame and gives out the absorbance (amount absorbed) reading.

The basis of AAS is the result of the electron structure of the atom. Under quantum theory, electrons move to higher or lower energy levels by absorbing or releasing electromagnetic radiation of a particular frequency. Since each element has a different set of electron energy levels, each has its own set of absorption lines. The greater the concentration of the metal ion, the more radiation is absorbed and the less reaches the detector. According to the Beer-Lambert Law, the amount of light absorbed is proportional to the amount of a substance present. A calibration graph using solutions of known concentrations allows the concentration of the unknown to be determined.

The development of the AAS has allowed chemists to measure accurately and rapidly concentrations of metal ions in water systems and in animals and plants. Such has lead to our understanding of trace elements, those elements which are required by living things in very minute quantities. Prior to this understanding, there were instances where animals had health problems in seemingly good pastureland due to deficiencies in cobalt and human illnesses, due to lack of trace elements in their diet, could not be diagnosed. Now, with atomic absorption spectroscopy, these problems are easily and effectively rectified.

In the University of Sydneys High School Chemistry Workshop, an AAS machine was demonstrated to us and used to test the concentration of Fe2+ ions in various samples of water. The results were as follows:

SOURCE OF WATER, ABSORBANCE, READING CONCENTRATION (PPM)
Tap, 0.003, 0.0
Creek, 0.0012, 0.2
A rusted rainwater tank, 0.252, 4.0

As can be seen, the ability of the AAS technique to measure in parts per million (ppm) allows chemists to measure metal ions of a very low concentration. However, the AAS must be daily calibrated with the ion to be measured for the machine to measure accurately. By monitoring the ions that are known pollutants, atomic absorption spectroscopy is a very effective and inexpensive method to control pollution.


i think some of the info was off Chemistry Contexts, and others were from the sheet given on the day at USYD... but yeah, if you're smart you will reuse the Beer-Lambert law as the chemical principle used for testing water quality at SydneyWater with AAS machines (Monitoring dp 1.2.1).
 
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ND

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Originally posted by Frigid
As can be seen, the ability of the AAS technique to measure in parts per million (ppm) allows chemists to measure metal ions of a very low concentration. However, the AAS must be daily calibrated with the ion to be measured for the machine to measure accurately. By monitoring the ions that are known pollutants, atomic absorption spectroscopy is a very effective and inexpensive method to control pollution.

Do you think that's enough to evaluate its effectiveness as polution control? I guess it'll have to be if there are no other resources anywhere. Thanks.
 

Frigid

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yes, because the definiton of evaluate is "make a judgement based on criteria; determine the value of". i have given the value of its effectiveness (the ability to measure in parts per million), a pro (can measure low concentration) and a con (needs calibration) and a judgement (yeap, very effective).

i think it should be right. :)
 

mon_mon

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Cheers, that works out well. At least i hope it will. though id prefer not to have to talk about it in the exam. sounds like a bastard of a point.
 

Constip8edSkunk

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just add to to that,

criteria: for high effectiveness, readings must be taken regularly, must be accessible and accurate

pros:
-AAS allows high selectivity, due 2 specific hollow cathode lamps, enabling specific metal concentrations to be targetted
-it is accurate, able to give values to 0.01 ppm (this is especially applicable to monitoring trace element)
-procedure is easy and quick, as sample is simply aspirated into the atomiser and analysed according 2 standards

cons:
-Only able to measure metals, ie unable to measure PO4, SO4 and the likes
-expensive to purchase, (but relatively cheap to maintain [confirm please?])
-requires to be operatinf for a period of time to give accurate results(Syd Uni said 1hr)

Judgment, the advantage far outweigh the disadvantages, a much simpler and more accurate methos than alternative methods using gravimetric analysis, volumetric analysis and colorimetry... the main draw back is that it can only test metals, so it is best used in tandem with other monitoring procedures for non metals.
 
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ND

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Originally posted by Frigid
yes, because the definiton of evaluate is "make a judgement based on criteria; determine the value of". i have given the value of its effectiveness (the ability to measure in parts per million), a pro (can measure low concentration) and a con (needs calibration) and a judgement (yeap, very effective).

i think it should be right. :)
Yeh i guess you're right.

Cheers, that works out well. At least i hope it will. though id prefer not to have to talk about it in the exam. sounds like a bastard of a point.
In the exam i don't think you'd have to recount all those values, it's be more like them giving you a table of values and asking you to do stuff with it.

Btw, what shape is a calibration curve? (i haven't seen one and i'm too lazy to plot)
 
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Originally posted by Constip8edSkunk

-it is accurate, able to give values to 0.01 ppm (this is especially applicable to monitoring trace element)
Actually i think it's accurate to 1ppb, when you use some other flame or something (don't remember, gotta revise).
 

Frigid

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Originally posted by ND
Btw, what shape is a calibration curve? (i haven't seen one and i'm too lazy to plot)
bcoz it is proportional, it is a linear relationship... you graph absorbance on the y-axis, concentration on the x-axis. the result should be a straight line with a positive gradient. when you chuck in an unknown concentration, after you calibrated the AAS, it will work it out for you (nice-nice)...

but one of these babies cost like $100K (the value of 200 data-logger sets), so yeah, not exactly affordable for any public school just to demonstrate one point of the syllabus... :(

edit: btw, mathematically, a straight line is a curve. not that my maths is that flash but anyway.
 

Constip8edSkunk

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is that using the argon plasma furnace? hmmm got look over that again as well... meh only did it only 2 days ago... cramming isnt working :\
 

Frigid

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Originally posted by Constip8edSkunk
is that using the argon plasma furnace? hmmm got look over that again as well... meh only did it only 2 days ago... cramming isnt working :\
let us try not to grow too big for our shoes... if it's out of syllabus, let's not cram it...
 

Constip8edSkunk

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no standards of the sample to be tested, say by 2ppm additions each standard, plot a graph, test sample then link absorbance w/ concentration on the graph

Originally posted by Frigid

let us try not to grow too big for our shoes... if it's out of syllabus, let's not cram it...
hehehehe agreed :D
 

Frigid

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Originally posted by mon_mon
so is a really simple basic substance used for the calibration ?
oopsie, forget to tell you how it works. okay, to calibrate it, say for Fe2+, we first prepare very accurate aqueous solutions of 0.5ppm, 1ppm, 1.5ppm, 2ppm say... and then we put it into the AAS for it to suck up and vaporise. in this case, we have a Fe2+ lamp, which will emit a wavelength of particular frequency, and the amount of Fe2+ in our solution will be detected (i forget what the prism at the end of the machine is called...?). then the computer will graph and set the calibrated values.

now then we chuck in our unknown and do let the machine do the rest...
 
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toknblackguy

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wow frigid
yuo're gonna get 100 for this and all your other subjects easy?
btw..what school?
i forgot where i posted..
 

Frigid

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nah, if you're talking about chem knowledge, spice girl and phenol definitely know more than me... it's just that i made my own notes so a lot of this is in my memory already... hopefully i'm looking at a 94+ in chemistry, coz i need it to offset a bad maths rank :)

oh, and i go/went to sydney boys' high.
 

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