- Jan 23, 2005
Yeah, but this is exactly the problem. They are standard methods, they don't consider special scenarios such as the presence of strong Fe complexes. Those are usually dealt with during the "sample preparation" phase, but not in our case.
I will try to test it in the lab when I have some free time.
They list interferences(special scenarios) with the method in the Standard methods protocol.
If you use a triazine color reagent, then 10% EDTA can impact the results.
High pH etc. But they generally use a reducing agent as part of the protocol.
They want all the Fe converted to the free Fe2+ form. Most every method does this, but the reducing agents can vary.
Since you suggest that your revised method is true/better/superior/more true, why not do this for all test regarding Fe? Should that not be listed in the protocols for the methods?
Why is that not suggested?
Is a standard reference solution of FE being made also? I see a lot of test and talk, but little on the methods.
No mention of a standard reference being used in testing.
If someone brings it up after the question is posed.......it does not instill much confidence.
Still, as long as it is done.......and included, that does not matter.
Make a standard solution of the Fe. Then you can compare your method with that of the sample and change from the method/s.
Many hobbyists noted that the Fe test kits changed color and became more intense over long time frames. But it goes back to the method.
None of them made a standard reference solution to compare that I recall. Getting them to use a standard reference for NO3 and PO4 test was bad enough.
This way you get around the method time issue and make sure your method is correct(and you can set a new time reaction to correlate with your own data).
Say your data suggest a rx time of 4.25 hours to match your known reference sample using X method.
Note, you can add tank water to make known references and use distilled/RO water etc(say for each type of chelator of interest).
I would do both.
You may also freeze tank water samples and then measure all at once later on. Better than testing several times a week etc.