Measuring PO4 (phosphate) in RO/DI water?

[einsteins]

I have basically rebuilt my whole water system (thanks to the great help from Jim at the Filter Guys) and I used my Hanna Low Range PO4 meter to measure the PO4 in the water coming out of my dual DI. The water measured out at .02 on the Hannah Meter.

Does anyone know if measurements using a Hanna meter would be accurate on RO/DI water as there are no Ions in the water?

I was told that test kits have problems accurately measuring PO4 in RO/DI water, just wondered if this might be true for the Hannah meter.

Thanks
einsteins

[Billybeau1]

I'm not sure I believe that.

My ro/di is perfectly clear when testing PO4. As it should be. :)

Unless, you ro/di unit is not funtioning properly. :)

[einsteins]

Do you test with a Hanna?


thanks
eins

[Billybeau1]

Salifert, Api and Elos :) All the same.

[sjfishguy]

I was gonna say the same thing, if your TDS is 0, your phosphate should be 0 as well. PO4 is an ion and should show up as tds (or at least the way I understand the chemisty).

[TheFishGuy,LLC]

Quit contaminating your sample.

[bertoni]

I would try testing the RO/DI water with another kit and see what that shows. Also, a TDS meter might be useful.

[einsteins]

I have a TDS meter that registers 0 TDS after the Dual DI. Water entering the Dual DI has a TDS of 3 to 6 TDS.
my tap water measures 1.1 on my Hanna PO4 meter.

The sample that I am testing is being drawn from the output of the DI units directly to the Cuvet for the hanna meter. The Cuvet is always rinsed with sample water before the test is run.

I consistently get a reading of .02 po4 from my RO/DI water. I also get the same reading after I have mixed salt for water changes. I use RC salt and after mixing to 1.026 I get .02 PO4 on my Hanna meter.

eins

[Randy Holmes-Farley]

I expect that is background noise in the phosphate testing. Phosphate is well bound by a DI resin that is functioning properly, and 0 TDS suggests it is. :)

[einsteins]

Thanks Randy

Is that "background noise" something that I need to compensate for in my regular testing with this meter?

eins

[Randy Holmes-Farley]

Maybe. I can't really be sure. The background may be higher or lower with tank water in the mix, but as a first approximation, subtracting 0.02 may be in order, with the recognition that it may not read accurately below that level.

How do you make a blank?

[einsteins]

The meter has you put the sample of water into the meter to ZERO it out....
Then you remove the sample add the reagent, dissolve it and then put it in the meter for a reading....also before it takes a reading with the reagent it lets the sample sit for 3 minutes to let particles settle.

eins

[garymcgrath]

There should be no particles to settle. You should gently swirl it for about 2 to 3 minutes until all of the powder is disolved, then put it in the meter for the timed 3 minutes. If you don't dissolve all of the powder first, you will get a high reading that may not be repeatable IME.

[einsteins]

Yes...When testing RO/DI there really are no particles to settle, however when you test tank water there can be fine particles.

I always try to ensure that I dissolve all of the particles.

eins

[Boomer]

I also agree with Randy and there is something not yet brought up on this meter or any meter. Resolution is not Accuracy and this meters Accuracy is..

Resolution = 0.01 mg / L

Accuracy = ±0.04 mg/L, ±4% of reading

That means they are only guaranteeing an Accuracy. If for example, the sample was tested in a know solution of 0 ppm PO4 the meter may read - 0.04 ppm to 0.04 ppm. And if it does the meter is with its guide lines for Accuracy.

One can make the argument about making a black and "zeroing" it out.

[einsteins]

<a href=showthread.php?s=&postid=11771930#post11771930 target=_blank>Originally posted</a> by Boomer
One can make the argument about making a black and "zeroing" it out.

Thanks Boomer....but what does the above statement mean?

thanks
eins

[Randy Holmes-Farley]

He meant "blank". That is, how you set the zero with RO/DI, and then subtracting the value, either be using the machine to reset that value to zero, or doing it manually.

[einsteins]

Sorry but I guess I dont understand what you are saying....
Do I need to reset or recalibrate my meter?

thanks for you patience....
eins

[Boomer]

The meter has you put the sample of water into the meter to ZERO it out....

It means that if you do the above and zero it out it may not really be zero, only close to it zero, thus there may be a slight error or "noise" in the reading.


I guess I don't understand what you are saying

We mean that if we think or know there is 0.00 ppm PO4 in the water and the meter reads 0.02 ppm, an error reading, we subtract that from the reading. So, if the meter read 0.06 ppm, then 0.06 - 0.02 = 0.04 ppm PO4 is what we *may have as a more real value. What Randy is calling "manual". Or we could zero the meter not to zero but so it reads - 0.02 instead of zero. And - 0.02 - 0.06 = 0.04 ppm. With this last method we have corrected the meter to give us a more real value. What Randy is calling true "zero'

I want to be sure you understand this

The Accuracy of this meter is +/ - 0.04 ppm

Pretend the meter reads 0.02 ppm PO4

This means that the actual value may be 0.04 ppm above that reading or 0.04 ppm below that reading. Meaning, the actual PO4 in the sample is somewhere between..


- 0.02 to 0.06 ppm.

So, the actual amount in the sample may be 0.00 ppm or 0.01 ppm, or 05 ppm, etc. We do not know what it really is as the meter is not that accurate.

With all this being said, in general, that +/- 0.04 becomes less that 0.04 as the PO4 gets closer to 0.00 ppm. So, if you are near 0.00 pm in the sample the accuracy may really be +/- 0.01 ppm and not +/-0.04 ppm but the manufactures just do not give this kind of info. One could get this kind of info by having the meter NIST certified. The meter comes with a signed piece of paper showing the real PO4 readings vs. what the meter says. That meter would now cost you maybe ~ $1,000

When ever you buy a test kit or a meter you need to look at the Accuracy. Resolution is very misleading and is a bad habit of many to go by this and not Accuracy. If your meter had an Accuracy of +/- 0.01 ppm rather than +/- 0.04 ppm it would be much more expensive. And the expensive meter may have the same resolution as yours of 0.01 ppm.

[einsteins]

So can this meter be checked for accuracy with a calibration solution that is at a set amount of PO4.
Does anyone make a po4 calibration solution?

Thanks so much for the help!

eins

[Boomer]

Yes and no :) There are PO4 stds as you are asking for FW but you are testing seawater. There are no such std for seawater. However, from what I have been able to find out there is no difference between the two for PO4 measurement. But some meters, such as those that measure Nitrate, need a seawater std. I'll see if I can find one tomorrow.

[einsteins]

Thanks Boomer...your awesome!

eins

[slug]

Using a hach DR/890 colorimeter I was getting a reading of 0.14ppm po4 from 0 tds ro/di water. It's accuracy is listed as 0.05. So most likely I contaminated the sample. For best results the directions say to clean the test vial with hydrochloric acid, which I didn't do, I don't keep it sitting around my house :P Maybe with any colorimeter this step is necessary when testing po4 to get the best results?

Why people think they can accurately know their water's po4 to 0.01ppm is a mystery to me though.

[Boomer]

ein

Phosphate Standard Solutions as PO4 (NIST), 1 mg/L, Bottle/500 mL

http://www.hach.com/hc/search.product.details.invoker/VendorProductCode=256949/View=PRODUCT_OVERVIEW/NewLinkLabel=Phosphate+Standard+Solutions+as+PO4+(NIST)%2C+1+mg%26frasl%3BL%2C+Bottle%26frasl%3B500+ mL/PREVIOUS_BREADCRUMB_ID=HC_SEARCH_PRODUCT2106069/SESSIONID|B3lNREkxTXpRMk56RTNNRFltWjNWbGMzUlZTQT09QWtwYVNqRQ==|

[jdieck]

<a href=showthread.php?s=&postid=11776875#post11776875 target=_blank>Originally posted</a> by Randy Holmes-Farley
He meant "blank". That is, how you set the zero with RO/DI, and then subtracting the value, either be using the machine to reset that value to zero, or doing it manually.
I tried to develop a compensation graph for my Hanna and just wasted $600.00 in reference samples, cleaning solution and calibrated precisin measuring pipetes and cylinders.

Same reference sample on equipment cleaned with UHP nitric acid test 5 different times, 5 different measurements.
I got somehow consistent results in the range of 0.1 to 1 ppm, below 0.1 it was all over the place.
Basically I use it as a reference only, in other words I replace my GFO as soon as it detects anything, even 0.01.

[Billybeau1]

Yup, thats what I do with my Salifert PO4 kit.

I change my GFO at the first hint of a bluish tint. A couple days later, it's back to clear. :)

So I'm not the only testing fool, huh jd :lol:

[jdieck]

<a href=showthread.php?s=&postid=11803765#post11803765 target=_blank>Originally posted</a> by Billybeau1
Yup, thats what I do with my Salifert PO4 kit.

I change my GFO at the first hint of a bluish tint. A couple days later, it's back to clear. :)

So I'm not the only testing fool, huh jd :lol:
Nope, not the only one... but there are different degrees! :D








I think I got a master's ...!

[Boomer]

I think I got a master's ...!

Yes a Masters = Master of Sh__T.

Randy has a Ph.D. = Piled Higher and Deeper.

And some have a BS Bull S__t degree :).

I don't have none of those so I don't fit in :lol:

[jdieck]

<a href=showthread.php?s=&postid=11805811#post11805811 target=_blank>Originally posted</a> by Boomer
I think I got a master's ...!

Yes a Masters = Master of Sh__T.

Randy has a Ph.D. = Piled Higher and Deeper.

And some have a BS Bull S__t degree :).

I don't have none of those so I don't fit in :lol:

I tought you got a spreader to do it more efficiently covering a larger territory :lol:

Nice to see you around boom!

[Billybeau1]

No, but you have a degree on how to blow things up. :blown:

If I see you running, I will keep up. :D

BTW, they shut down I-94 tonight in Upper Minn.

I'll bet you're glad you are still in Tejas. :lol:

[Boomer]

Yes Billy still kinda warm here in Texarkana :lol:

I-94, Ok just went for a look WOW lots of snow landing on the tarmac. The other day they shut-down down some in Kansas and Nebraska. They got like 20 "

These links keep me informed

http://www.wunderground.com/US/Region/US/2xSnowDepth.html

and

http://www.intellicast.com/National/Radar/Current.aspx?location=USMN0208&animate=true


Right now it is - 18 F Below zero

Jd

Don't be giving out my secrets about spreading things around. I seem to get in enough trouble as it is ;)