Taylor Iron Test Accuracy

[pinguy]

How prone is the Taylor Iron test to false negatives?

I've tested water that I am 200% sure has large amounts of iron and the test shows absolutely nothing.

Is there any accurate way to test for metals without using a lab?

 

[JoyfulNoise]

Which iron test is it?

Both sequestrants and precipitated iron (iron oxide and iron hydroxide) can interfere with getting accurate results.

 

[pinguy]

It's the K-1716

I'm testing the fill water as well, which wouldn't be sequestered or precipated.

I know there's iron because

A) Staining
B) The water turned green, I brought it up to SLAM level, and it turned coffee brown.

Not my pool BTW.

 

[JoyfulNoise]

Staining and coloration indicate that the iron is the 3+ oxidation state (ferrous iron). TPTZ (tripyridyl-s-triazine, the indicator in that test) is only sensitive to soluble iron which the ferric form or Fe2+ oxidation state. Copper causes a positive interference (more color so a false high value) while sodium causes a mild negative interference (interferes with color formation and so gives a false low value). Treated water from a water softener or a salt water pool might have too much sodium in it.

The R-0851 reagent #1 is essentially 8% HCl with a reducing agent (hydroxylamine) which is supposed to digest any sequestrant and cause iron 3+ compounds to become iron 2+ BUT there has to be iron particles in the water to do that. If the water sample is clear, then there might not be enough iron (3+) in the sample to be measurable.