Re: Iron test - how it works ?

[Luca Specchio <lucspec at tin_it>]

Hi List!,

 >From: dc <dennis_chua at excite_com>
>Need some help from the chemical savvy...
>When we use any aquatic Fe test kit and got a reading, say, 0.1ppm Fe.
>What does it really measured ?

We generally measure the ionic forms of Fe. That's to say Fe2+ AND Fe3+.

>(1) Does it breakdown all the available Fe chemical bound (include all
>available FeEDTA from the trace mix dosage.) and indicate the total Fe++
>available ?

Absolutely not. The most of iron test kit cannot break down the bonds of 
FeEDTA... so you don't have any reading about the total chelated iron which 
is present into the iron.

>(2) Or it just measured the existing free Fe++ in the water ? while the
>FeEDTA are very much untouched ?

No, the all free Fe2+ plus the free Fe3+. Some of the test kit are able to 
differentiate the readings. So you will have e separate reading for the 
ionic free Fe2+ and the total ionic form of Fe2+ plus Fe3+. The difference 
will be the free Fe3+.

Any how some of the test kit can read the total iron (chelated + ionic) 
after a process of digestion that breaks the bonds with chelating agents. 
Hach, La Motte,and Merck works this way. Some other I have the possibility 
of reading chelated iron directly, I guess Hagen i.e. can do that. Maybe 
also Seachem can after a period of waiting.

I work mainly with La Motte and Merck, if you need more info, ask me 
freely. For example look here:
http://www.merck.de/english/services/labor/l_uba/applic/Metaledta.html

Hope this helps!

Ciao,
Luca

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