Hanna Phosphorus checker

[XNavyDiver]

I doubt the staining claim unless you leave a very dark blue sample sit in the vial for a very long time (e.g. forgot to take it out and discovered it was in there for a few days). Most of us have very low Phosphate/Phosphorous readings so there is very little blue color. Leaving that in the vial for 5-10 minutes is harmless. Also, you can simply soak your cuvette in diluted muriatic (HCl) acid to remove the staining. I do this periodically as a matter of habit.

One final note, a number of us have demonstrated that using 1 or 2 vials gives similar results (within sample/assay variation). Randy (RHF) has shared that the Hach test requires about 8 minutes to develop for low range phosphate. From my observation withe the Hanna I see a consistent "decrecendo" when I mix the reagent for 2 minutes and then try to make it do readings at minutes 2, 3, 4, 5, 6, 7. After that the reading holds fairly steady (repeatible) for minutes 8-20. I had to use two vials to do this. I switch vials filled with untested/unreacted tank water to verify that there was a zero difference in readings independent of the order of using the vials or their orientation in the checker. I just don't think these checker are that sensitive. They are not like the analytical lab grade UV-VIS spectraphotomers.

This is a new one for me. I have never detected any color at all in a Hanna ULR test. They've all been completely clear from the very first time I started using the checker some 6 months ago.

 

[Diazcm]

I doubt the staining claim unless you leave a very dark blue sample sit in the vial for a very long time (e.g. forgot to take it out and discovered it was in there for a few days). Most of us have very low Phosphate/Phosphorous readings so there is very little blue color. Leaving that in the vial for 5-10 minutes is harmless. Also, you can simply soak your cuvette in diluted muriatic (HCl) acid to remove the staining. I do this periodically as a matter of habit.

One final note, a number of us have demonstrated that using 1 or 2 vials gives similar results (within sample/assay variation). Randy (RHF) has shared that the Hach test requires about 8 minutes to develop for low range phosphate. From my observation withe the Hanna I see a consistent "decrecendo" when I mix the reagent for 2 minutes and then try to make it do readings at minutes 2, 3, 4, 5, 6, 7. After that the reading holds fairly steady (repeatible) for minutes 8-20. I had to use two vials to do this. I switch vials filled with untested/unreacted tank water to verify that there was a zero difference in readings independent of the order of using the vials or their orientation in the checker. I just don't think these checker are that sensitive. They are not like the analytical lab grade UV-VIS spectraphotomers.

you must be talking about the ALK checker not the ULR phosphrous checker .

 

[Diazcm]

you must be talking about the ALK checker not the ULR phosphrous checker. ALK checker is the only test that i know of that turns blue when testing.

 

[sghera64]

you must be talking about the ALK checker not the ULR phosphrous checker .

You won't see a blue color if your PPM reading is less than 100PPB. I've had spikes as high as 10,000 PPB (yeah, Oooops! 10PPM). I had to dilute my sample just to get it below 200PPB. Believe me when I saw that indigo blue color, I nearly passed out. When I realized I had accidentally confused grams for milligrams in my dosing, I realized my assay was fine, but my tank had been overdosed by 1000x what I was targeting.

All that is to explain why, I don't think there is anything to worry about when it comes to staining throwing off your future readings with the Hanna ULR checker.

 

[rtparty]

The human eye is absolutely terrible at detecting minute changes in color. If your checker is getting a reading, then the sample did change color to some degree. Your eye may/will never see this slight change. However, the sensor in the checker certainly knows the difference between a couple nm in color.

So to say you'll never stain the glass unless it is super blue is incorrect. If the checker can see the difference between a couple nm and your eye can't, your eye also can't see the stain if it does happen.

You also have to remember that BRS tested these testers directly against a hach machine and found them to be pretty darn accurate for our use.

 

[MnFish1]

I doubt the staining claim unless you leave a very dark blue sample sit in the vial for a very long time (e.g. forgot to take it out and discovered it was in there for a few days). Most of us have very low Phosphate/Phosphorous readings so there is very little blue color. Leaving that in the vial for 5-10 minutes is harmless. Also, you can simply soak your cuvette in diluted muriatic (HCl) acid to remove the staining. I do this periodically as a matter of habit.

The comment about the staining comes from the instructions for the Low range checker.
"After the reading it is important to immediately discard the sample, otherwise the glass might become permanently stained."

The Cuvettes are to be rinsed with water - not sure i would want to use muriatic acid - since it can etch glass itself (depending on the strength) - so who knows whether the wrong dilution would either cause imperfections in the glass or not clean the staining. But - since the company says 'permanent' I would take their word

One final note, a number of us have demonstrated that using 1 or 2 vials gives similar results (within sample/assay variation). Randy (RHF) has shared that the Hach test requires about 8 minutes to develop for low range phosphate. From my observation withe the Hanna I see a consistent "decrecendo" when I mix the reagent for 2 minutes and then try to make it do readings at minutes 2, 3, 4, 5, 6, 7. After that the reading holds fairly steady (repeatible) for minutes 8-20.

Also according to the instructions: "Do not let the reacted sample stand for too long after reagent is added, or accuracy will be lost"

Just because the Hach test says one thing does not mean it applies to this test. If you consistently see a decrescendo, it demonstrates that the 5 minute value (2 minutes mixing, 3 minutes in the machine) is the proper one to use. It means that testing beyond that period is potentially inaccurate. If it were not, Hanna would have set 4 or 5 minutes as the machine testing time.

I had to use two vials to do this. I switch vials filled with untested/unreacted tank water to verify that there was a zero difference in readings independent of the order of using the vials or their orientation in the checker. I just don't think these checker are that sensitive.

I decided to go to the source - and ask Hanna - per their technical support engineer (not the phone operator lol) - the cuvettes are designed to be as identical as possible and theoretically, one should be able to use 1 cuvette as the control and 1 cuvette as the test - but the recommended way is to use one cuvette per test. He did not recommend using 2 cuvettes for 1 test - but he said that 'many people do it' and 'it has not seemed to matter'. So - take it for what its worth.

 

[Randy Holmes-Farley]

If you consistently see a decrescendo,

That's my new word of the day.

 

[sghera64]

"Just because the Hach test says one thing does not mean it applies to this test."

I agree. However, both are using a form of the ascorbic acid method. I'm simply using the Hach as an insight to the reproducibility and repeatibility problem I see with the Hanna method.​

"If you consistently see a decrescendo, it demonstrates that the 5 minute value (2 minutes mixing, 3 minutes in the machine) is the proper one to use."

I tend to disagree. Seeing the results consistently decrease for the first 2-7 minutes means the reaction is continuing and has not hit a stable point. It is possible that Hanna did indeed calibrate the reading on the screen to coincide with the 5 minute mark, but that has many clear flaws:

1. The instructions do not give a specific mixing time. Therefore 5 minutes is not really 5 minutes in every case unless the user times their mixing.
   
   
2. One strives to develop an analytical method that is repeatable and reproducible. Meaning, the "reading" should be taken when the reaction has reached a stable point and not try to time the reading to hit a reaction in progress based on time.

• This may be necessary in some cases (no stable point, reduced assay discrimination at the stable point, impractically long time to reach a stable point and secondary reactions take place).
• Again, I don't know what the Hanna chemists goals or trade-offs were in developing their method.

It means that testing beyond that period is potentially inaccurate. If it were not, Hanna would have set 4 or 5 minutes as the machine testing time.

I guess I'm a skeptic of Hanna's method. I don't why then picked 4 or 5 minutes when the data clearly shows you get a different reading at 4 minutes versus 5 minutes. That is clearly a problem that I know I'm trying to figure out because I really like my ULR. From the writings of others, I'm not alone.

I believe the data also shows that you get better reproducibility/repeatibility if you take the reading 7-10 minutes after mixing has started. My concern with that is the instrument's digital display was probably not calibrated to show the true Pi reading at that stable point in the reaction. I've made several Pi standards and tested them to see that there is satisfactory discrimination (based on the instruments reported accuracy). But, I could not "calibrate" it because I don't have the exact concentration of my reference standard (commercial grade TSP).​

 

[rtparty]

Hanna gives a very specific mixing time: 2 minutes. Again, that's in the instructions. If the user isn't mixing for the 2 minutes, that's their problem, no?

 

[MnFish1]

I tend to disagree. Seeing the results consistently decrease for the first 2-7 minutes means the reaction is continuing and has not hit a stable point. It is possible that Hanna did indeed calibrate the reading on the screen to coincide with the 5 minute mark, but that has many clear flaws: The instructions do not give a specific mixing time. Therefore 5 minutes is not really 5 minutes in every case unless the user times their mixing One strives to develop an analytical method that is repeatable and reproducible. Meaning, the "reading" should be taken when the reaction has reached a stable point and not try to time the reading to hit a reaction in progress based on time.

1. The Instructions say: Remove the cuvette, open it and add the content of one packet of HI 736-25 reagent. Replace the cap and shake gently for 2 minutes until the powder is completely dissolved. Replace the cuvette into the meter.

2. I'm not sure why you would try to do your own quality control/modify the instructions of the test. Doing the test properly, per the instructions should give you the reported precision/accuracy/reproducibility that Hanna publishes on their site. You have no way of knowing whether waiting is better or not. (See below)

I believe the data also shows that you get better reproducibility/repeatibility if you take the reading 7-10 minutes after mixing has started. My concern with that is the instrument's digital display was probably not calibrated to show the true Pi reading at that stable point in the reaction. I've made several Pi standards and tested them to see that there is satisfactory discrimination (based on the instruments reported accuracy). But, I could not "calibrate" it because I don't have the exact concentration of my reference standard (commercial grade TSP).

Right - you just don't know - seems to me the proper way to do it is to send a sample of your tank water to a reference lab to use as a 'gold standard' to which to compare your results. Hanna does sell a calibration kit - at least that would check your monitor - it may also be your monitor that is the problem. It may also be that your samples were not mixed properly, there were bubbles or other problems with the way you did the test - as compared to a problem with the 'method' recommended by the company that designed the product. My guess is that if you aren't timing your mixing - that is the reason you're getting 'bad results'.. you're doing the test incorrectly.

 

[sghera64]

Hanna gives a very specific mixing time: 2 minutes. Again, that's in the instructions. If the user isn't mixing for the 2 minutes, that's their problem, no?

I believe the problem here is the instructions give two conditions for when to stop mixing: 1.) 2 Minutes and 2.) "until the powder is completely dissolved".

Perhaps this has led to some people starting the 3 minute timer as much as 1 minute early, and others having to mix a little longer to get a clear solution.

I use a stop watch and start the 3 minute timer right at 2 minutes after the display first reads C2. It takes me about 20 seconds to get the power into the vial and I'd say the solids are dissolved after about another 1 minute of mixing. However there are microbubbles that linger in the vial for at least another 2+ minutes (and may cause a problem with the reading at 5 minutes).

 

[sghera64]

@MnFish1 , have you experienced variation in Pi readings when doing repeat measurements with your Hanna ULR?

 

[MnFish1]

@MnFish1 , have you experienced variation in Pi readings when doing repeat measurements with your Hanna ULR?

No they have been literally within 1 or 2 ppm. I have not tried to analyze one sample over and over. I think the instructions mean shake until dissolved at least 2 minutes

 

[Victoria M]

I find that if you pre cut the packet and have that ready to pour before hand, it makes it easy to pour the reagent and shake for 2 minutes well before the timeout.

yeah, I agree but I figured that out later. Still a stoopid design flaw timing out after 3 minutes. love it anyway!

 

[Victoria M]

No they have been literally within 1 or 2 ppm. I have not tried to analyze one sample over and over. I think the instructions mean shake until dissolved at least 2 minutes

That is how I interpreted the instructions too.

 

[terri_ann]

Interesting, really. I talked with the son(Can't remember his name)about a year ago because I was thinking of buying their other phos unit( not the checker). He explained that the light that reads the solution is different,ie.better quality(naturally for a sale?) than the one in the checker. No matter what, these are not lab grade so I stick with the checker.

Also, my phosphorus checker does not time out at 2 minutes when dissolving the solution. It times out at 3 minutes.[emoji848]

 

[Sabellafella]

I retest my sample about 2 or 3 times after its initial result. There was plenty of times the beginning test checked out a couple ppb higher then the following tests. So i just chalked it up to micro bubbles. It takes just a few seconds to swap out the viles to complete another test. The results usually fall within the +/- detection accuracy on the checker.

 

[MnFish1]

Interesting, really. I talked with the son(Can't remember his name)about a year ago because I was thinking of buying their other phos unit( not the checker). He explained that the light that reads the solution is different,ie.better quality(naturally for a sale?) than the one in the checker. No matter what, these are not lab grade so I stick with the checker.

Also, my phosphorus checker does not time out at 2 minutes when dissolving the solution. It times out at 3 minutes.[emoji848]

You might be doing it wrong. Once you put the powder in the vial you mix for 2 minutes (there is no timer on the machine for the mixong). Then you put the vial in and hold the button until the 3 minute timer starts. Once that timer is done
The result is displayed

 

[terri_ann]

You might be doing it wrong. Once you put the powder in the vial you mix for 2 minutes (there is no timer on the machine for the mixong). Then you put the vial in and hold the button until the 3 minute timer starts. Once that timer is done
The result is displayed

Yes, after the solution is mixed and returned to the vial, hold the button until 3 minutes is displayed. I was saying that while "mixing" the solution, I have up to 3 minutes to return it to the vial. (The powder usually is fully dissolved at 2 1/2 minutes. I then place it back in the checker and at 3 seconds left on my timer, I press and hold the button until it reads 3:00

 

[MnFish1]

Yes, after the solution is mixed and returned to the vial, hold the button until 3 minutes is displayed. I was saying that while "mixing" the solution, I have up to 3 minutes to return it to the vial. (The powder usually is fully dissolved at 2 1/2 minutes. I then place it back in the checker and at 3 seconds left on my timer, I press and hold the button until it reads 3:00

Not sure what you are doing exactly - what I do - is take the water do the C1 part. Then add the powder to the vial - mix 2 minutes (timed separately) just by turning up and down not shaking. At 2 minutes I put the Cuvette back in the checker and hold the button until the timer reads 3 (then release the button) - and counts down to 0 - then it blinks a couple times and displays the results.

If you start the test - and at any time wait longer than 3 minutes (without going to the next step) - except the 3 minute timer at the end- the checker shuts off and you have to start over. If you dont read the result within (I think) 3 minutes at the end it shuts off - and the result is gone