Chemical Forums
Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: awais on May 18, 2007, 08:03:30 AM
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How I can detect the presence of iron in solution. The solution is methanol and water and contains a compound having ferrous/ferric. Any test, simple one , a quick one,,,
thanks
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- What concentration are you talking about?
- Does the test have to discern between ferrous and ferric?
- What other possible contaminant metals are in solution, or is it just iron for sure? (Need to figure out what other metals could give a false positive).
The question is essentially unanswerable until we have more information.
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Thanks for answer,
I would explain the situation shortly. I have some organic compounds, mainly sulfides and mercaptans containing 3 to 4 sulfur atoms in a chain, e.g. Diallyl trisulfide. I want to check whether they bind metals or not. I have to check with Fe3+, Fe2+, Cu+, Cu2+ and Zn. Normally I take equimolar solutions of organic compounds (in MeOH) with metal solutions (in H2O) and stirr them for an hour. After that I checked via HPLC if there is any change in spectrum or formation of new peak but i could not get any result.
If you can suggest me some other way to solve this problem except titration.
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If you have access to a Magnetic Susceptibility balance, it should be fairly easy; as the ferric and ferrous might have a different number of unpaired electrons, so the reading should be quite distinct. No guarantee, depending on the binding and what little info you provided, but still worth a try.
You would have to create some standards, but that should not be to hard.
While they are not cheap enough for anybody to buy, as far as good chemistry equipment goes, the magnetic susceptibility balance is relatively cheap; and always under used in my experience. You should ask around your chemistry department, someone might have one, even the organic chemist and some inorganic chemist should have one!
The bonus is it takes very little of the sample, and you do not alter the sample in anyway and as a result you can reuse it for whatever else you are doing. It is also incredibly quick.
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You may also be able to get away with a cheap UV spectrometer for the iron and copper since they are colored in solution. Find the absorbance, and then run a few standards. The bound copper and iron shouldn't give the same peaks as the free material, so you should be able to determine concentration of material in solution. The zinc I'd titrate.
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A very sensitive chemical means of detecting iron (not distinguishing between +2 and +3 oxidation state ratios) is first oxidizing all of it to the +3 oxidation state (e.g. by adding acidified aqueous hydrogen peroxide) and then adding either a large excess of a solution of a thiocyanate (gives a very intensely colored red complex), or adding some excess potassium hexacyanoferrate(II). The latter gives an intensely colored blue complex.
Absorption measurements and comparison with reference solutions can give you an idea of the concentration.
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I think simple mercaptans and organic sulfides and polysulfides such as you have been trying are unlikely to form complexes except with the most thiophilic cations such as Hg2+ and Pb2+; Zn may possibly bind but it and its complexes are colourless, as indeed are many of Hg and Pb - and where these are coloured this is due to charge-transfer bands rather than unpaired electrons. Try chelating compounds such as ethanedithiol HSCH2CH2SH