# Fe Test Kit & Dtpa/Eddha



## rjordan393 (Nov 23, 2012)

Hello,
Does anyone know of an iron test kit that will test for Fe DTPA/EDDHA? A fellow aquarist from Germany has posed this question on "Tom Barr's Report".


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## Zapins (Jul 28, 2004)

In my opinion iron tests don't work well at all. 

From JeffyFunk's water testing results (using a proper machine) we figured out that only EDTA and DTPA chelated iron show up in water samples. Gluconate and citrate chelated iron does not show up at all in his tests. I suspect the same is true for the titration kits you can buy.


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## rjordan393 (Nov 23, 2012)

Thanks,
I'll pass it on.


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## JeffyFunk (Apr 6, 2006)

That's not quite how I interpreted the results... My interpretation of the results was that Fe(EDTA) was able to accumulate in the water column while Fe(glucconate) was not. It's really difficult to say what the cause of that difference is from. I can think of a couple of scenarios: (1) Fe(EDTA), being a Fe(III) species, is more difficult for the plants to assimilate than Fe(glucconate), which is a Fe(II) species. Similarly, the plants could just prefer the higher energy Fe(II) species over the oxidized (and lower chemical energy) Fe(III) species. (2) Fe(glucconate) is less stable than Fe(EDTA) so the Fe(glucconate) precipitates out of the water column faster. Maybe it reacts with phosphates faster? Without doing, say, isotopic labeling studies, it's not clear what mechanism is going on. (In that experiment, u would label the Fe species being dosed, then check the plants for signs that they took up the labelled Fe species. If the plants were not taking up the Isotopically labelled Fe, it would remain in the water column or precipitate out.)

My take home message would be that Fe analysis in the water column is complicated and u have to be knowledgeable of how it's chelated, what ur water chemistry is like, etc. Most importantly, u have to watch ur plants to c if they r showing signs of Fe deficiency - that's ur best indicator.


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## Mac120 (Sep 21, 2012)

hi,
I am Peter and the one from Barreport.
And I would like to thank you very much Robert for asking here.
(english is not my native language, so it is sometimes a little bit difficult for me to adress the questions right)

About me: I am a plant lover from Germany.
(what plants I keep in my tanks is listed here: http://www.nanoplants.de/plants/ )
During the first years I was using Toms Estimate Index method for fertilzing.
Doing so works fine, but I also noticed that not all Rotalas will get vivid colours if you just "estimate nutritions". So, the idea was born to mix my own fertilizers. Some APC Treads from Zapin like this were also very helpfull for me: http://www.aquaticplantcentral.com/...-toxicity-deficiency-literature-research.html

The fertilizer itself contains B, Mg, Mo, Zn (EDTA/citric), Cu (EDTA/Citric) and EDTA-Mn ( I tried Cu/Zn/Mn unchelated first, because I know Seachem Trace didn´t use trace chelators, but doing so hasn´t worked out that good on my own mixture.)
Iron sources: Ferrous Gluconate, FE-EDTA, FE-HEDDTA, Fe-DTPA, FE-EDDHA
(The idea behind this is that the iron will be availible for the plants @different time steps/stages)
Certainly I now want to know if my own fertilizer is well balanced or if there would be any hidden Iron build up. (Fe-EDDHA is very stable stuff)

Unfortunatly, my titration iron test kit is still able to meassure Fe-EDTA, Fe-Gluconate, Fe-Citrate and some parts Fe-HEDDTA - but, it failures on Fe-DTPA, Fe-EDDHA.:-?
So, I am searching for a better test kit.


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## JeffyFunk (Apr 6, 2006)

Mac120 said:


> Unfortunately, my titration iron test kit is still able to measure Fe-EDTA, Fe-Gluconate, Fe-Citrate and some parts Fe-HEDDTA - but, it failures on Fe-DTPA, Fe-EDDHA.:-?
> So, I am searching for a better test kit.


lol - and this is your problem. A hobby grade test kit is going to rely on the formation of a chelated compound to form an Fe-chelated compound that absorbs in the UV-Vis spectrum. The presence of stronger, multi-dentate ligands like DPTA or EDDHA means that it is thermodynamically and/or kinetically unlikely (i can't remember which) for those ligands to dissociate in order to form a compound with the test reagent chelate like you want.

I checked the Hach Water Analysis handbook for Fe analysis methods and there are two methods that are not inhibited by chelaters: The FerroVer Method (using 1,10-phenanthroline (which is a bidentate ligand, i think)) or the TPTZ Method (i have no idea what TPTZ stands for...). In either case, both methods clearly that that you need to digest your samples first in order to destroy the chelaters.

The standard methods handbook states the following for Fe Analysis (SM 3500-Fe B):



> If noticeable amounts of color or organic matter are present (Read - chelators), it may be necessary to evaporate the sample, gently ash the residue, and redissolve in acid.... The presence of excessive amounts of organic matter may necessitate digestion before use of the extraction procedure.


Here's my take on this: The UV-Vis based test kits you have are fine. The problem is that you need to digest the samples prior to analysis. (And for the record, i would not recommend digesting samples in your house without VERY good ventilation - nothing like concentrated acid vapors to do wonders to your stainless steel appliances...) Otherwise, i would suggest sending your samples to a certified laboratory where they will digest the samples and analyze them by ICP-OES.


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## Mac120 (Sep 21, 2012)

> first in order to destroy the chelaters.


Bottle 1 uses sodium hydroxide & acetic acid (to destroy the chelators, so that the iron gets unbound & detectable), bottle 2 Phenantrolin and so Ferrous gluconate can be measured. (so this means it is wrong too say, this can´t be measured if many 5$ hobby test kits can do this) By adding bottle 3 (Ascorbin acid), some chelated iron like EDTA can be measured, too. Well, since EDDHA is pretty stable on a very wide PH range, it just seems not too work with those ingredients to destroy such "harder" chelators.

On the other side, 
Fertilisers like the Elos series contain lots of very stable chelated Iron and it is hard to believe that there should be no iron test availible for such folks.

Certainly, sending samples to a certified laboratory would do the job, but for doing this you need to have and find any affordable laboratory. And even if you would find one, it will not help much if want to track the iron uptake daily.


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## JeffyFunk (Apr 6, 2006)

Mac120 said:


> Bottle 1 uses sodium hydroxide & acetic acid (to destroy the chelators, so that the iron gets unbound & detectable), bottle 2 Phenantrolin and so Ferrous gluconate can be measured. By adding bottle 3 (Ascorbin acid) = some chelated iron like EDTA can be measured.
> Since EDDHA is pretty stable on a very wide PH range, it just seems not too work with those ingredients to destroy such chelators.
> 
> So the Billion $$$ questions is:
> Is there any hobby grade test kit out there which can handle such chelated stuff?


lol - i stand by my references. There is no way that NaOH and acetic acid (which should neutralize each other, btw) can compare to the oxidizing ability of concentrated, boiling acids in the digestion procedures (as the test methods require). Yes, lewis bases like OH- are better at cleaning organic substances but without using a very concentrated solution, they are just not the same as a digestion.

Furthermore, a digestion is going to chemically oxidize or destroy the chelates. The addition of a strong base like NaOH is probably not destroying the chelators but rather attempting to out compete the chelater for binding sites via a change in equilibrium or something like that. In other words, there's no comparison between the addition of NaOH and an acid digestion in terms of how they liberate the Fe from the chelater.


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## Iggy8194 (Jan 7, 2014)

If digestion I.e. oxidation is the issue why not use nitric acid, although do so with caution. An excellent oxidizer, it should annihilate any chelators present. As JeffyFunk stated use ventilation or go outside.

- Iggy


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## Mac120 (Sep 21, 2012)

> lol - i stand by my references.


Well LOL, ok - lots off theoretical stuff  - but at last all this didn´t adress the simple question what aquatic test can NOW measure ALL iron in our aquatic tanks. 
And I am little bit surprised that noone here can name any good iron test kit by (brand name).

So, I now contacted some companies and figured out that many kits just seem to be trash.
But I had some luck and found a good iron test kits: http://www.wasserpantscher.at/produ...tiv---der-wohl-empfindlichste-eisentest-.html
They claim it measures all iron sources and this seem to be true.
Results are attached, i tested different chelates with the iron test kit and the kit was able to measure each off it:


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## rjordan393 (Nov 23, 2012)

Will this kit be sold on the American market and how much does it cost and how many tests can it do?


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## Zapins (Jul 28, 2004)

Mac120 those are nice looking results, but what about a sample with 0 iron in it so we can see the difference between 0 and 0.1 ppm?


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## Mac120 (Sep 21, 2012)

Zapins, 0 ppm iron will certainly result in no discoloration (/water will stay clear)
The test kit will measure iron levels from 0,008 ppm to 0,8ppm
Attached is the colour chart:



The colour chart itself is (like you see) tiny and a little bit poor, but we need to consider that this company has also a primary focus on saling their photometers  for aquatic tanks. 
So if you want to use the iron kit without photometer, it would be a good idea to make first some reference iron solutions and to print after doing so yours own colour chart ( for easier & better ppm reading )

@rjordan393
The kit costs 17Euro and you can use it for 40 tests.
It is not that cheap test kit, but I think the price is fairly ok if it can measure all chelated iron. 
(iron II and III)


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## Zapins (Jul 28, 2004)

Hmm interesting. Yes the color chart helps a lot.

How much is their photometer?

I found a couple of digital photometer tests that were pretty nicely priced a while ago. I wonder how they stack up vs. the test you have? I'm not sure we can get that iron test kit you have in America.

Digital test kits:
http://www.aquaticplantcentral.com/...eficiency-literature-research.html#post664222


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## Mac120 (Sep 21, 2012)

The Hama photometers are nice, but are still single and not multi photometers - so you need to buy one for iron, one for nitrate and so on. At last you will end up expensive.

The Wasserpantscher photometer ($140-170) is a multi photometer and as far I know they have test kits for it: Mg, nitrate, potassium, chloride,phosphate, co2, ph, nitrite, kh, ammoniak, silikate, O2 (and certainly iron).
From Söll there is also a Multiphotometer availible: http://www.aqua-check.de/en/
I personaly never buyed those photometers, so I cant say anything about it.
I still know most ppl.in Germany buy photometers to check their potassium levels in planted tanks, because there are no potassium test kits around from JBL, Sera, Tetra or so.
I personally use a DIY Kalignost test for testing potassium levels and doing so works pretty fine without photometer.

Since I am mixing my own fertilizer, I am certainly somehow interested to test uptake rates from stuff like zn, cu, boron - unfortunatly there are no affordable photometers around which can measure each stuff. 



> I'm not sure we can get that iron test kit you have in America.


I am not sure, I think you need to ask them - perhaps they will ship the iron test kit abroads?


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