# Making Own Trace Liquid (Dtpa Or Edpa?)



## andeekaii (19 Jul 2011)

_Before I go into it, please note that I do not want to buy a premade trace mix. I want to make my own._

I am making my own fertiliser and I'm looking at whether to use EDPA or DTPA chelator? I've sourced EDPA but cannot find DTPA. Any suggestions?

Also could someone explain to me exactly how it works, and which micro nutrients actually need to be chelated?
Do you have to mix the iron and chelator together before mixing with the other micros? Or do you put all the micros together and then the chelator?

I am planning on using these chemicals for the trace mix. Is there a potential problem with any of these?
Ferrous Sulphate FeSO4 (For Fe)
Manganese Sulphate MnS04 (For Mn)
Zinc Chloride ZnCl2 (For Zn)
Copper Carbonate CuCO3 (For Cu)
Cobalt Sulphate CoSO4 (For Co)
Boracic Acid H3BO3 (For B)
EDTA Ethylenediaminetetraacetic acid Chelator // DTPA Diethylenetriaminepentaacetic acid Chelator

Cheers, Andy


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## dw1305 (19 Jul 2011)

Hi all,
You can't chelate any other cations with iron (Fe) as FeEDTA has the highest stability as a complex, and as long as Fe3+ ions are available they will bind 1:1 with EDTA4- ions. If other cations are already bound, the ligand will be broken, and they will be "bumped off" and replaced by the Fe ions. There are advantages to the other chelating agents in terms of their pH range and stability, but they are pretty minor differences and EDTA is absolutely fine to use. You only need to chelate the iron as most of its compounds are insoluble, and will precipitate out of solution as iron phosphate complexes etc.

You can chelate any metal ion with EDTA, but there isn't much point for most of them, and you won't be able to mix them for storage. <http://scifun.chem.wisc.edu/chemweek/chelates/chelates.html>

You would be best starting with disodium EDTA, because Na is the least tightly bound ion to EDTA.
Details here: <http://www.sigmaaldrich.com/life-sc...-culture-protocols/iron-chelate-solution.html>

It should probably be cobalt chloride hexahydrate (CoCl2.6H2O) and copper sulphate pentahydrate (CuSO4.5H2O) in your mix, and you need to take the water of crystallization (.nH2O) into account when you make the solutions up.  

Details are here <http://www.sigmaaldrich.com/life-sc...ue-culture-protocols/classic-plant-media.html>

Even if you have access to lab. glassware, pipettes and balances you will want to make the solutions more concentrated than you need, and then use serial dilution to get the ppm you want in your stock solution. It is much easier to work in grams rather than 0.1 or 0.001g (or 0.1 cm3). The other advantage to weaker solutions is that you can regard them all as H2O in terms of density, so at room temperature 1cm3 = 1g. 

Also you need to get your dilutions right, so remember that mg/l is the same as ppm. I usually write them all as powers of 10 10(-3) etc, as that gives you a quick check (1 mg/l is 10(6) dilution). 

1000 mg in a gram (10(3)), 1000g in a litre (10(3)) - 1 mg/l is 1 followed by 6 zeros is 1ppm (1,000,000 10(3+3 = 6)).

cheers Darrel


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## andeekaii (20 Jul 2011)

Darrel,

Thank you very much for the excellent reply. I have spent the whole day trying to digest the information, and now I have a few questions.

Are you saying I should make an FeEDTA liquid mix up first, and then add the rest of the micro nutrients to the solution?
Do I need to mix any of them with EDTA or can they just be added to the solution?

Can this solution then be mixed with a macro solution to make an all-in-one solution?

Also, why do you say it should be CoCl2.6H20 and CuSO4.5H20 rather than the non H2O equivalents?

Thanks again, Andy


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## dw1305 (20 Jul 2011)

Hi all,


> Are you saying I should make an FeEDTA liquid mix up first, and then add the rest of the micro nutrients to the solution? Do I need to mix any of them with EDTA or can they just be added to the solution?


You can keep the FeEDTA and micro-element solutions separate, but it doesn't matter if you add them together, FeEDTA is the most stable chelate. If you chelated any of the other trace elements (MnEDTA for example) and then add FeEDTA it will remove the Mn and replace it with a Fe.



> Do I need to mix any of them with EDTA or can they just be added to the solution?


All the other traces should go into solution, the boric acid keeps the pH down and stops the other elements from precipitating out of solution.



> Can this solution then be mixed with a macro solution to make an all-in-one solution?


Could possibly, but almost certainly insoluble phosphorus compounds will be formed, so I'd keep it as 3 separate solutions - macro, micro & FeEDTA.



> Also, why do you say it should be CoCl2.6H20 and CuSO4.5H20 rather than the non H2O equivalents?


Because these are the stable forms of the compounds, and as soon as the anhydrous forms are exposed to the air they will pick up atmospheric moisture and become the hydrated forms. You can only keep most anhydrous compounds water free by heating them, to drive off the water, and then placing them straight into a desiccator.

cheers Darrel


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