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Re: EDTA chemistry
1. You can make FeEDTA by dissolving 75 grams of DIsodium EDTA into 3L of
distilled water. Once the EDTA is COMPLETELY dissolved, you can then add
54 g FeCl3.6H20. Once this is completely dissolved, you can then make
the solution up to 4 L. This will give you an FeEDTA stock solution of 50
mM. If you add this stock solution at 0.1 ml per liter you will end up
with 0.28 ppm Fe (5 uM). The stock solution should be stored in a dark
bottle preferably in the fridge (though this last is not absolutely
necessary). It is likely preferable to add the FeEDTA more than once per
week ... I add mine twice per week and Im sure some people add daily ...
the reason is that FeEDTA is not stable in light.
2. EDTA chelates all cations at a 1:1 ratio so that you need one molecule
of EDTA fro every atom of cation (regardless of charge). In my opinion,
however, a straight FeEDTA micronutrient is not the optimal solution. I
add the nutrients Cobalt, Copper, Zinc, Molybdenum, Manganese, and Boron
to my micronutrient stock solution. If you are concerned about
precipitating the cations you can add EDTA in excess of the iron
concentration (about 10% extra) and this will chelate the other cations
as well.
Dr. dave.