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