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Re: Diethylene triamine pentaacetic acid
On Sun, 7 Apr 1996 19:35:28 -0500
Paul Krombholtz wrote....
> Subject: Re: EDTA photodegredation
>
> When I was growing aquatic plants in algae-free culture back around
> 1966-68, I noticed that I had a precipitate in flasks of nutrient solution
> plus iron EDTA that had been exposed to light, but no precipitate in
> identical flasks kept in the dark. However, enough iron stayed in solution
> to grow the plants satisfactorily.
>
> Currently, I am using iron DPTA, (diethylenetriaminepentaacetic acid),
> which appears to stay in solution a lot longer. CIBA-Geigy, agricultural
> chemicals division, makes it, but it is hard to find in your average
> garden store.
>
Yes. There are three chelates commonly used to sequester trace metals.These
are: EDTA ethyline diaminetetra acetic acid
DTPA diethylene triamine pentaacetic acid
EDDHA ethilene-diamine dihydroxyphenyl acetic acid
EDDHA and DTPA chelate iron only. EDTA associates with copper, zinc,
manganese, bivalent iron(Fe++), and trivalent iron(Fe+++). All three chelates
are less stable at higher pH than lower pH. The stabilities of all three are
also adversly affected by light.
FeEDDHA is by far the most stable at higher alkalinities and it is the
preferred form where there is a high concentration of calcium bicarbonate.
FeEDDHA is expensive and often difficult to obtain. It is very efficient and
only a fraction is needed to do the job as compared with FeEDTA. The company
that sells it is CIBA-GEIGY Corp, Box 11422, Greensboro, NC 27409. But they
won't sell you just a spoonful. :-).
FeEDTA is at least stable. At pH above 7.0 80% will decompose after two weeks.
It is used commonly because it is cheap and because it is a good product to
chelate all four trace metals.
To maintain greater iron solubility FeDTPA is often added to FeEDTA. The former
is slightly more stable than the latter. When added together a boosting effect
occurs and the mixture is as stable as FeDTPA alone.
By the way Paul where did you get it ??
Further reading... P. Fisher Stability of various forms of chelated iron in
nutrient solutions of different pH values, ISOSC Proceedings 6th International
Congress on Soilless Culture 1984, pp. 225-233
Franc Gorenc franc at golden_net
Kitchener, Ontario http://www.golden.net/~franc
Canada