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.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.
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.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.
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.first in order to destroy the chelaters.
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.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?
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.lol - i stand by my references.
I am not sure, I think you need to ask them - perhaps they will ship the iron test kit abroads?I'm not sure we can get that iron test kit you have in America.