Phosphate vs. Phosphorus

[Scubajoe1]

So regarding the hanna checkers for these two species"¦.are they both reading the same thing or does the phosphate checker read PO4 only (phosphate bound to 4 oxygen atoms) and does the phosphorus checker read all species including organic and inorganic.

I have both kits and measured my phosphate twice and got 0.03 ppm or 30 ppb both times.

I then used the phosphorus kit and got 13 ppb and 15 ppb so pretty reproducible.

If the phosphorus kit measures both organic and inorganic species then shouldn't this be higher?

I suppose the error on the phosphate kit it greater so it the phosphorus kit the one I should be going by if I am at these low levels?

Thanks

Joe

 

[Scubajoe1]

So I see to convert to phosphate I should use this equation.

Example:
Phosphorus reading x 3.066 / 1000 = ppm PO4

So if this is the case then they are pretty close to each other.

Does anyone know why the 3.066 multiplication factor? Curious minds want to know.

Thanks

Joe

 

[bertoni]

The atomic weight of phosphate is about 31. Oxygen is about 16. Phosphate contains four oxygen atoms, so its molecular weight is about 31 + 4 * 16, or 95. 95 / 31 is about 3. To get more digits, you'd need to look up more digits on the atomic weights.

The Phosphorus ULR is more useful at the low end, but both kits measure only orthophosphate, despite the names.

 

[Scubajoe1]

Things that make you go hmmmm. Ph.D. chemist here and get your math but not sure how the molecular weights come into play. I guess the kit is assuming that all P that is being measured is in the form oh Phosphate then or that is a close assumption. Does it measure organic phosphorus as well and does the phosphate kit measure the same things? Do you know if the chemistry is the same for the phosphate and phosphorus kit? Looks like they both use the ascorbic acid reagent. Why do they even bother with a phosphorus kit? Just have it multiply but 3.066 in the algorithm and spit out PPB phosphate no and call that the Ultra low phosphate kit.

 

[ClownMan727]

Wow, why don't you call the people at Hannah and ask them? Share your findings here please.

 

[Scubajoe1]

That's on my agenda actually unless someone can answer……I just got the phosphorus kit today. Just seems like it has a more sensitive detector and the reagent is probably less concentrated.

 

[bertoni]

Neither kit measures organic phosphorus. They measure only orthophosphate, PO₄. Hach makes a total phosphorus kit, but it's not easy to use, and requires handling some toxic chemicals.

The measurements are given in ppm or ppb, which are weight-based ratios, hence the atomic weights.