Measuring PO4: Hanna ULR versus Triton ICP

[Randy Holmes-Farley]

There is also some leeway in the amount of reagent you can spill and get the same results. @Rick Mathew talked with Hanna technical support about the variable amount of reagent in each packet and found out that there is excess reagent.

I have run the PO4 test with 5 mL of sample, split the powder and obtained the same results without being very exact about splitting the powder (5-10 % high or low).

When the amount of reagent deviates substantially, say on the high side, the zero point might be effected. Zero PO4 gives a reading more than zero. Going the other, shorting the reagent substantially might start to effect the color intensity because of the incomplete conversion of PO4 to the colored adduct. But, we are talking about major goofs, the kind of goof that you can’t miss.

Thanks, Dan.

 

[ScottB]

Sorry. I've been slacking off.

Just pulled a couple samples. One is resting in a clean, plastic pee cup now. Will test that Jan 4th. My son will run the current sample this afternoon. Thanks for the reminder. Happy New Year.

@chimbo84

So I did the little test: testing a fresh sample gave me a reading of .07
Letting a sample drawn at the same time rest for 5 days in a pee cup then testing came back at .037

Fun stuff!

Thanks all for your brilliant input to this discussion.

 

[Rick Mathew]

I'm sure it is beyond most folks interest level, but here's a similar (not identical) assay for phosphate, where the author tested the sensitivity of the assay for various aspects of the test. note that in Figure 2 on page 8, for example, if you have enough molybdate to react with the phosphate, more does not lead to more absorbance:

https://inis.iaea.org/collection/NCLCollectionStore/_Public/04/042/4042323.pdf

Thanks for the link...The curve is pretty much what the tech from Hanna described...They put enough in the packet to insure that you have the minimum amount to carry out the reaction even if you leave some behind

rick

 

[Randy Holmes-Farley]

Thanks for the link...The curve is pretty much what the tech from Hanna described...They put enough in the packet to insure that you have the minimum amount to carry out the reaction even if you leave some behind

rick

Thanks, Rick.