Hanna Phosphorus checker

[Cory]

2 minutes of shaking?

You only have to shake it until the powders dissolved. For me it's like 20 seconds. I put it in the checker and let the timer go for 3 mins. Results are repeatable.

Btw I use the same vial. Just makes more sense. But I used to use two vials.

 

[terri_ann]

Thank you I have "3 minutes for mixing" .......if I go the full 3 minutes, the checker will turn off so that's why I use 2 1/2 minutes for mixing/dissolving You say you have 2 minutes for mixing whereas I have 3 minutes. I try to use almost all of the 3 minutes when mixing so as to try to have any microbubbles disappear before I depress the button getting the 3 minute countdown. Timing is the key

 

[MnFish1]

2 minutes of shaking? You only have to shake it until the powders dissolved. For me it's like 20 seconds. I put it in the checker and let the timer go for 3 mins. Results are repeatable. Btw I use the same vial. Just makes more sense. But I used to use two vials.

Thank you I have "3 minutes for mixing" .......if I go the full 3 minutes, the checker will turn off so that's why I use 2 1/2 minutes for mixing/dissolving You say you have 2 minutes for mixing whereas I have 3 minutes. I try to use almost all of the 3 minutes when mixing so as to try to have any microbubbles disappear before I depress the button getting the 3 minute countdown. Timing is the key

I guess I dont understand why you both aren't just following the instructions in the manual:

*Remove the cuvette from the meter and unscrew the cap. Add the content of one packet of HI 713-25 reagent. Replace the cap and shake gently for 2 minutes until the powder is completely dissolved. Place the cuvette back into the meter.

*Press and hold the button until the timer is displayed on the LCD (the display will show the countdown prior to the measurement) or, alternatively, wait for 3 minutes and press the button.

This implies (to me) that you mix the sample for 2 minutes (To ensure the sample is dissolved), then put the cuvette in the machine and start the 3 minute timer - meaning the test is read at 5 minutes. I assume 5 minutes is the best time to read the test which is why they say to shake for 2 minutes and then the timer for 3.

 

[Cory]

I guess I dont understand why you both aren't just following the instructions in the manual:

*Remove the cuvette from the meter and unscrew the cap. Add the content of one packet of HI 713-25 reagent. Replace the cap and shake gently for 2 minutes until the powder is completely dissolved. Place the cuvette back into the meter.

*Press and hold the button until the timer is displayed on the LCD (the display will show the countdown prior to the measurement) or, alternatively, wait for 3 minutes and press the button.

This implies (to me) that you mix the sample for 2 minutes (To ensure the sample is dissolved), then put the cuvette in the machine and start the 3 minute timer - meaning the test is read at 5 minutes. I assume 5 minutes is the best time to read the test which is why they say to shake for 2 minutes and then the timer for 3.

Well just for the way it' worded. If it said shake for two minutes I would. But it says shake for 2 mins until the powder is dissolved. Suggesting having the powder dissolved is the main purpose. If it needs to react with air or something then that could be a problem not shaking for two minutes. That would be something Randy would know.

 

[sghera64]

Well just for the way it' worded. If it said shake for two minutes I would. But it says shake for 2 mins until the powder is dissolved. Suggesting having the powder dissolved is the main purpose. If it needs to react with air or something then that could be a problem not shaking for two minutes. That would be something Randy would know.

Thank you for sharing this.

Your interpretation of the instructions highlights a suspicion I shared earlier: The instructions are not worded precisely enough to ensure everyone will mix and assay such that 5 minutes is consistently used as the reaction time.

To MnFish’s point, many (maybe most, I don’t know) have presumed that Hanna wants us to hit the 5 minute mark. But, I don’t know if we “know” that, if we are inferring that, or even if it is necessary.

This might explain why some have begun to depart from the instructions a little to learn what happens. And those that have, share back data they can’t explain like the OP did (i.e. repeat assays that drop until the reaction is past the ~7 minute mark).

 

[MnFish1]

You only have to shake it until the powders dissolved. For me it's like 20 seconds. I put it in the checker and let the timer go for 3 mins. Results are repeatable.

As many time as you need of the same sameple

Does the reagent stay active in the water for more than one test? You may get bad readings the longer it stays in the vial. I don't know that for sure but probably something someone @Hanna could answer.

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 just called Hanna techincal support here are the answers:

1. The test is to be read 5 minutes +- 15 seconds (after the reagent is added to the vial.)
2. The vial needs to be mixed for "at least" 1 minute 45 seconds - preferably 2 minutes. (He said the 1:45 is for those who find it difficult to accomplish everything in the time allowed.). He also said they realize the shut off time is too short
3. Repeated testing - and tests done after longer than 5 minutes are not valid. The test is designed to be read at about 5 minutes.
4. If you want to do repeated testing, you have to obtain a new sample and repeat the entire test.
5. As mentioned earlier - its best to use the same cuvette for both the control and the test.

 

[MnFish1]

This might explain why some have begun to depart from the instructions a little to learn what happens. And those that have, share back data they can’t explain like the OP did (i.e. repeat assays that drop until the reaction is past the ~7 minute mark).

BTW I agree with everyone that the instructions aren't exactly clear. I based my thoughts on doing other scientific tests in college. Its always best to do each test exactly the same way each time - which is why I assumed mixing for 2 minutes was the 'best' way. I did a little test - I tested different samples with a new control each time. If you just mix for 2 minutes and do a reading without waiting the 3 minutes - the result is extremely low - its higher at 1, 2, and 3 minutes but seems to peak at 3 minutes (which is 5 minutes total)... Then drops off. I have to say I didnt repeat it 10 times - because its expensive. The other reason people may 'think' they have 'stable' readings at different times is that their Phosphorous is quite low. As the 'true' level of phosphorous increases, the 'variability' of the test will likely increase markedly - and make exact timing more important.

For example - if the true Phosphorous is 3 there isn't much opportunity for the test result to 'change' or be variable because of the accuracy/precision of the test. I,e, - using my experiment taking a reading just after the 2 minute mixing gives a result of 1 (lets say) at 5 minutes its 3 at 7 minutes its 2. All of those are within the variability of the test. (and it could lead a person to think that timing doesn't matter because all the results are 'the same'. If the true phosphorous is 100 lets say - my guess is that you well tend to see the results vary considerably at different times as the reaction progresses/degrades - which is why Hanna recommends reading at a particular time. (Im sure they tested the meter against known standards - and picked the time where it most consistently matched)

 

[jsker]

BTW I agree with everyone that the instructions aren't exactly clear. I based my thoughts on doing other scientific tests in college. Its always best to do each test exactly the same way each time - which is why I assumed mixing for 2 minutes was the 'best' way. I did a little test - I tested different samples with a new control each time. If you just mix for 2 minutes and do a reading without waiting the 3 minutes - the result is extremely low - its higher at 1, 2, and 3 minutes but seems to peak at 3 minutes (which is 5 minutes total)... Then drops off. I have to say I didnt repeat it 10 times - because its expensive. The other reason people may 'think' they have 'stable' readings at different times is that their Phosphorous is quite low. As the 'true' level of phosphorous increases, the 'variability' of the test will likely increase markedly - and make exact timing more important.

For example - if the true Phosphorous is 3 there isn't much opportunity for the test result to 'change' or be variable because of the accuracy/precision of the test. I,e, - using my experiment taking a reading just after the 2 minute mixing gives a result of 1 (lets say) at 5 minutes its 3 at 7 minutes its 2. All of those are within the variability of the test. (and it could lead a person to think that timing doesn't matter because all the results are 'the same'. If the true phosphorous is 100 lets say - my guess is that you well tend to see the results vary considerably at different times as the reaction progresses/degrades - which is why Hanna recommends reading at a particular time. (Im sure they tested the meter against known standards - and picked the time where it most consistently matched)

Thank you for taking the extra step and digging into to this

 

[sghera64]

Nice work, @MnFish1. Thank you!

You uncovered very important information about what Hanna knows regarding their assay.

It appears that the assay was designed to hit a maximum reacted concentration (5 min mark) and likely for maximum sensitivity reasons. This is understandable given it was designed for “Ultra Low Range” of ppB and designed to be affordable.

At the same time, in developing analytical methods where I work, my QC colleagues always strived to developed assays that were quantified during a stable point (-rate/dt = ~0) for reproducibility/repeatability reasons. And so engineers like me had the best chance of repeating their results so I would not have to pester them for analysis. .

 

[Cory]

Good info guess I'll be shaking it for 2 mins.

What I wonder is if the Hanna turns off during the shaking, and you turn it back on does it remember the previous empty vial in it? Or do we need to zero it again?

 

[sghera64]

Good info guess I'll be shaking it for 2 mins.

What I wonder is if the Hanna turns off during the shaking, and you turn it back on does it remember the previous empty vial in it? Or do we need to zero it again?

It does not remember. You do need to re-Zero

 

[Fudsey]

Good info guess I'll be shaking it for 2 mins.

What I wonder is if the Hanna turns off during the shaking, and you turn it back on does it remember the previous empty vial in it? Or do we need to zero it again?

This is the main reason I am using 2 cuvettes. I have FINALLY gotten my tester to register the 3 min timer but I missed the 2 minute shut off one time and had to re-zero the unit. I know Hanna says use the same cuvette but to me this seems pointless. Both came with the kit so why would I NOT use them both and both always test zero when testing plain tank water.

 

[rtparty]

This is the main reason I am using 2 cuvettes. I have FINALLY gotten my tester to register the 3 min timer but I missed the 2 minute shut off one time and had to re-zero the unit. I know Hanna says use the same cuvette but to me this seems pointless. Both came with the kit so why would I NOT use them both and both always test zero when testing plain tank water.

If I understand correctly, they don't TEST zero, they zero off the water you put in. The machine is simply looking at what "color" the water is to begin so it has a baseline. Then when you add the reagent, shake and place back in it looks at how much it changed.

I would bet if you put a mixed vial in to begin with, it will zero off that color and not care if it's slightly blue or not. It's just getting a baseline to work off

 

[sghera64]

If I understand correctly, they don't TEST zero, they zero off the water you put in. The machine is simply looking at what "color" the water is to begin so it has a baseline. Then when you add the reagent, shake and place back in it looks at how much it changed.

I would bet if you put a mixed vial in to begin with, it will zero off that color and not care if it's slightly blue or not. It's just getting a baseline to work off

That’s how I understand it.

 

[billw]

I try to use almost all of the 3 minutes when mixing so as to try to have any microbubbles disappear

The technique I use is vigorously shake the vial for 1m 45s and slowly rotate the vial on its side for another 15s - 20s. How is the rotating on the side effective? It exposes all the microbubbles to the shortest distance to the surface allowing them to combine with the air pocket in the vial quicker. I've only had one timeout while testing ... the first time I used it.

 

[sghera64]

The technique I use is vigorously shake the vial for 1m 45s and slowly rotate the vial on its side for another 15s - 20s. How is the rotating on the side effective? It exposes all the microbubbles to the shortest distance to the surface allowing them to combine with the air pocket in the vial quicker. I've only had one timeout while testing ... the first time I used it.

You don’t HAVE to put the vial in the checker during the 3 minute count down. So I leave it upright in the checker with the checker’s top open and spin the vial fast to cause the bubbles on the glass to release.

 

[MnFish1]

Thank you for taking the extra step and digging into to this

Np

 

[MnFish1]

Good info guess I'll be shaking it for 2 mins.

What I wonder is if the Hanna turns off during the shaking, and you turn it back on does it remember the previous empty vial in it? Or do we need to zero it again?

You need to do it agsin

 

[Scorpius]

The whole three minutes and the Checker shuts off silliness drives me nuts. Make it 10 minutes.

 

[MnFish1]

If I understand correctly, they don't TEST zero, they zero off the water you put in. The machine is simply looking at what "color" the water is to begin so it has a baseline. Then when you add the reagent, shake and place back in it looks at how much it changed.

I would bet if you put a mixed vial in to begin with, it will zero off that color and not care if it's slightly blue or not. It's just getting a baseline to work off

Dont understand whaat you mean - if you put in a mixed vial to begin with - the result will be zero when you do the test . (what do you mean by mixed vial)?