Question

If in a P&D experiment u have to determine by Atomic Absorption Spectroscopy whether two separate soil samples have the same amount of a certain compound. Well, I would like some help on how to start off the experiment, do u have to use an atomic absorption spectrometer to do the test? because i don't think solid samples can be tested in that spectrometer, unlike liquid samples or is there another way to do such a test? Plz help.

Answer 1

to use AAS your sample must be in the gas phase, so it doesn't matter if it's liquid or solid at first.

Answer 2

You're putting your sample in the machine ("oven" e.g. graphite furnace) heating it up to break up any matrices (if solid) to a couple of hundred of degrees then flash heating it to a couple of thousands of degrees to atomize everything in your sample.

Answer 3

is there any other way u could show the comparison without using Atomic Absorption Spectroscopy.

Answer 4

solid samples can easily be tested by atomic absorption spectroscopy but u have to dissolve the material in the HF acid and aquaregai and then dilute to the required ppm and find out by AAS using the standard known solution :) AAS can only give you the elemental analysis :) if u ned any assisatant let me know bcoz i have handled the AAS instrument :)

Answer 5

ok so, the compound I was speaking about is CaCO3. I think u'll have to liberate the Ca ions from the compound using some kind of acid. is this wat the HF acid and aquaregai are for? I know that the soil samples may have other compounds containing calcium other than CaCO3 (and the Ca will be liberated from them as well if u do it that way) but i guess that will be a limitation. and do u have to use other standard solutions with various concentrations of Ca ions in them, so as to compare their absorption with the absorption of the Ca ions in the soil.

Answer 6

ooh and by the way wat is the standard known solution u were speaking about?

Answer 7

HF acid and aquaregia (HNO3 and H2SO4) are acids to break up matrices.
introducing standards into different samples is a method called "standard addition" which can help you get an accurate value by plotting your absorbance values (on the y) versus concentration (on the x axis) and using linear regression (to the x axis).

To me it seems like you don't need to do AAS, you can do a titration instead, with something that binds calcium selectively strongly and is insoluble, like \(PO_4^{-3}\) and then weigh the precipitate. You do need to prepare your sample though.

You can always do the AAS if you want, but i don't think it's necessary.

Answer 8

Though it depends on what scale you need the detection in.

Answer 9

if you want picomolar, or lower, you need to use AAS.

Answer 10

@aaronq i think titration is more crude method then AAS :) the quantification by precipitating and titration is having more error :)

Answer 11

thanks both of u!!

Answer 12

titration is for sure a more crude method, but it depends on what kind of result they're looking for. If they just want an estimate, a titration is fine, if they're (for some reason) worried about very small amounts of calcium in water then AAS (though atomic emission spectroscopy (AES) is more accurate) is the way to go.