[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Iron: a factoid and two questions

Dan Drake asked...

>One common chelating agent is EDTA 
>(That's _Mister_ EthyleneDiamineTetraacetic Acid to you, buddy). Ferric
>sodium EDTA is easily available, if anyone is crazy enough to want to
>make up a trace element solution from scratch.  However, a technician at
>Hach tells me that no ordinary test kit can hope to measure it; you need
>something like an acid digestion, heating the sample with successive
>additions of nitric and hydrochloric acids.  Not the routine aquarium
>sampling technique you want to use.

One wishes to measure only the iron available to the plants. An acid
digestion might catch iron which is normally not available. Several
people have claimed that the test they use requires an extended wait
to obtain results with EDTA. Check the Archives. Personally I think
that the Emperor has no clothes, but then I'm not a fashion expert.
Craig Bingham suggested using one of the Hach kits with a potassium
persulfate digestion to oxidize the chelating agent. It would be best
to read his post on this. I'd love to test for iron, but like you, I
am unsure of what each is measuring.
>BTW I have experimented with this.  The LaMotte kit won't detect iron in
>a sample of FeNaEDTA at 1:10,000, which is about 10 ppm iron, or 100
>times what you want in the tank.

Someone has mentioned this in a previous post.

>Question 1:
>EDTA, however, is not what the commercial chelated trace mixes seem to
>use.  Does anyone know for sure what they do use?  (And, if it's a
>4-letter abbreviation, what the _name_ is?)  (And how does the strength
>of the complex compare with EDTA?)

The following are found in various micronutrient mixes.

EDTA(ethylene-diamine tetra acetic acid)
DTPA(diethylene triamine pentaacetic acid)
EDDHA(ethylene-diamine dihydroxyphenyl acetic acid)
Iron gluconate
Iron sulfate
lignosulfonic chelants of iron

Dave Whittaker
Gloucester, Ontario
ac554 at FreeNet_Carleton.ca