johnboy
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measuring concentrations of iron and manganese without spec.
I don't have a spectrophotometer. Is there another method of measuring concentrations of iron and/or manganese? I'm sampling some pretty toxic
streams from coal mining days and know that streams nearby had problems with these two guys, and the concentrations are probably way higher than the
ranges found in test strips.
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JohnWW
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If you have the same colorimetric analytical reagents that are used for the analysis of Fe and Mn on a spectrophotometer, you may be able to analyze
for them in aqueous solution, with less accuracy, using a visual colorimeter. O-phenanthroline is the most common colorimetric reagent for Fe,
inducing an intense red color, which can be measured spectrophotometrically and colorimetrically. Mn in aqueous solution is usually analyzed for by
oxidation to permanganate(VII) with sodium plumbate(IV) or bismuthate(V), and using its intense purple color to analyze for it spectrophotometrically
or colorimetrically; but this cannot be done in the presence of Fe, because any Fe present is oxidized to purple/magenta-colored ferrate(VI), the
visible absorption bands of which fairly closely overlap with those of permanganate(VII).
However, by far the best method, more suitable for analyzing large numbers of samples, but more expen$ive, would be by use of an atomic absorption
spectrometer.
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unionised
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If you know the iron concentration and it's not too big compared to the manganese then you can still measure the Mn- using Bi(V) you just need a
different set of calibration curves for each Fe concentration. It's possible, but it's a PITA.
Your best bet is to separate the two metals. I think the easy way is to add nitic acid to oxidise Fe to Fe+++. Add excess HCl to convert it to
[FeCl4]- and extract that into ether. That should leave the Mn behind and you can measure that by conversion to MnO4-
Anyone got any other ideas?
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IPN
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In the lack of instruments for spectrometric determinations there are always the titrimetric (complexometric, oxidation-reduction) and gravimetric
methods available.
They do require a bit more in terms of reagents and glassware but those can be had relatively cheaply.
Downside of the gravimetric methods is of course the need for an analytical balance.
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johnboy
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method
Is the there a titrimetric procedure that is available online?
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IPN
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Complexometric Titrations by Schwarzenbach and Flaschka gives several references to the determination of Fe-Mn mixtures.
One procedure titrates the Fe first at pH 2-3 with sulphosalicylic acid indicator using EDTA and then adds tartrate and hydroxylamine, buffers pH to
10 and titrates manganese with Erio SE indicator (acid chrome blue).
Second example uses DCTA (diaminocyclohexanetetra-acetic acid) instead of EDTA, this has the advantage of a simpler procedure:
Fe is titrated at pH 2-3 with salicylic acid indicator and after that pH is buffered to 10 and Mn is titrated with Erio T indicator (much more common
than Erio SE).
References:
Radko, V.A., and Yakimets, E.M., Trilonometric determination of Mn in the systems Mn-Fe and Mn-Al.
Trudy Uralsk Politekh. Inst., 166 (1960).
Pribil, R., Komplexometrische Titrationen (Chelatometrie). XI. 1,2-Diaminocyclohexan-N,N,N',N'-tetraessigsäure als Massreagens. Stufenweise
Bestimmung von Fe und Mn (Mg, Ca); Bestimmung von Cu neben Fe, Ni, Co und Mn.
Collection of Czechoslovak Chemical Communications., 20, 162 (1955)
Chemicke Listy, 49, 179 (1955)
I can try to find the second reference from the uni library next week..
You can search for some modern references through google scholar for example.
Hope this helps.
[Edited on 8.3.2010 by IPN]
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