Hanna Phosphorus checker jumps around

[Robert Binz]

I’ve been told that the phosphorus ULR (HI 736)‘s results jump around with the same samples.

Mine just gave me the following results in order within 3 minutes:

109
79
57
75

Is this normal jumping around? I figure I’ll assume an average of the bottom three numbers is the most accurate because they’re the closest together

 

[JumboShrimp]

I would say user error. Things like fingerprints, air bubbles, not having the cuvette facing the same way each time; as with any science experiment, try to be completely consistent so that only one (1) variable is being tested. (That's my 2-cents.) Best wishes! ;Happy

 

[zuri]

its has to be used within the timeframe as its stated this is how long it takes for the soltion to work to short or long will impact

 

[Reef.]

Within 3 minutes?

How can you perform 4 tests within 3 minutes?

I think it may be something you are doing incorrectly.

I love mine, very consistent.

 

[Robert Binz]

Within 3 minutes?

How can you perform 4 tests within 3 minutes?

I think it may be something you are doing incorrectly.

I love mine, very consistent.

it happens very quick.

put a tube in, push the button, change the tubes, push a betton, have a result in 3 seconds

 

[BostonReefer300]

Within 3 minutes?

How can you perform 4 tests within 3 minutes?

I think it may be something you are doing incorrectly.

I love mine, very consistent.

Same question. Anyway, if you want to see how precise it is, have two vials ready. One just with tank water for your "blank". Use other for the "sample" (tank water and the reagent). Mix the latter thoroughly for a couple minutes, wipe it down thoroughly with a microfiber cloth or a tissue damp with RODI water then dry it, make sure there aren't air bubbles inside (if so, gently swirl), then let it sit for 3 minutes. Now do multiple tests. Power up the tester. Put the blank vial (also cleaned carefully) in when it says C1. Make sure the tester lid is closed tightly. Press the button to zero the tester. When it says C2, remove the blank and replace with the sample. Press the button once. Don't hold it which will set the timer for 3 minutes---the sample has already sat for three minutes. This will give you a reading. Cycle the power on the tester and repeat the blank zeroing and sample measurement again. Then do it a third time. You should have very similar if not exactly the same results from all three tests. If you're doing the three tests in quick succession, the longer time the sample vial has sat between measurements shouldn't matter much (as long as you shook the vial for 2 minutes and then let sit for 3 minutes at the beginning). The above method isn't meant to replace the standard testing protocol. Instead, it's meant to gauge the precision of the checker as it eliminates most of the variability that could be attributed to user error.
[BTW, in my experience, you don't need to align the test vial the same way in the checker every time. Also, once you clean the vials, try to only touch them by the cap to avoid smudges on the glass.]

 

[Robert Binz]

it happens very quick.

put a tube in, push the button, change the tubes, push a betton, have a result in 3 seconds

EDIT: just learned that there’s a timer if you hold down the button rather than just clicking it lol

That could mean the chemical reaction needed to take place longer resulting more the sequence of much lower results.... still jumping around but all within the same tenth decimal

 

[canadianeh]

EDIT: just learned that there’s a timer if you hold down the button rather than just clicking it lol

That could mean the chemical reaction needed to take place longer resulting more the sequence of much lower results.... still jumping around but all within the same tenth decimal

Yep user error

 

[Robert Binz]

Thanks everyone!! This is what happens when you skip the directions

y’all are the best

 

[Lasse]

Same question. Anyway, if you want to see how precise it is, have two vials ready. One just with tank water for your "blank". Use other for the "sample" (tank water and the reagent). Mix the latter thoroughly for a couple minutes, wipe it down thoroughly with a microfiber cloth or a tissue damp with RODI water then dry it, make sure there aren't air bubbles inside (if so, gently swirl), then let it sit for 3 minutes. Now do multiple tests. Power up the tester. Put the blank vial (also cleaned carefully) in when it says C1. Make sure the tester lid is closed tightly. Press the button to zero the tester. When it says C2, remove the blank and replace with the sample. Press the button once. Don't hold it which will set the timer for 3 minutes---the sample has already sat for three minutes. This will give you a reading. Cycle the power on the tester and repeat the blank zeroing and sample measurement again. Then do it a third time. You should have very similar if not exactly the same results from all three tests. If you're doing the three tests in quick succession, the longer time the sample vial has sat between measurements shouldn't matter much (as long as you shook the vial for 2 minutes and then let sit for 3 minutes at the beginning). The above method isn't meant to replace the standard testing protocol. Instead, it's meant to gauge the precision of the checker as it eliminates most of the variability that could be attributed to user error.
[BTW, in my experience, you don't need to align the test vial the same way in the checker every time. Also, once you clean the vials, try to only touch them by the cap to avoid smudges on the glass.]

I use this method - but 10 readings in a raw. It is clearly that way that the result jump around especially with ULR P and ULR PO4 checkers. Mostly it following the specification ± x ppm

Sincerely Lasse

 

[Dennis Cartier]

I use a similar method to BostonReefer300 and Lasse. Basically use 2 vials and allow the 3 minute timer to count down for the initial test and then do n instant tests following the counted down test. I find that the instant tests come out ~10 ppb under the counted down one normally.

Things that I have found affect accuracy are:

• Store the vials wet: After using the vials, I drain the contents and re-fill with RODI water. This helps to prevent any buildup on the inside of the vials over time.
• Rinse the vials under the tap after being filled: To remove smudges I rinse the vials under the tap and dry with a paper towel. I find the caps on the vials never seal particularly well, and get worse over time. So shaking the vials can cause saltwater to seep out and dribble down the side. Rinsing the vials exterior and holding them by their cap helps to remove this and prevent smudges.
• Rotate the vials for each test: Some would argue that this will cause less accuracy, but I use it to help determine if a test is suspect. By rotating the vial, if there is surface contamination on the vial, the reading will jump. This helps to alert me that the test(s) are impacted and should be examined/redone after cleaning the vial.

Dennis

 

[Lasse]

I also clean with citric acid now and than

Sincerely Lasse

 

[BostonReefer300]

I wish there was another reliable test so I can double-check the results of my HI736 ULR Phosphorus checker. That's the only test I regularly do where I don't have a confirmatory test in case I get a squirrelly result. I also wish that I had done more research before I dropped $50 on the ULR phosphate checker! Speaking of which, anyone want a barely used Hanna HI776 for $49 (plus $14.99 S&H)?

 

[BCSreef]

You can compare your result to an ICP result from the same sample. My ULR P values align well with the ATI ICP P values.

Also, wipe the vials with an alcohol based eyeglass wipe before zeroing and reading.

 

[BostonReefer300]

You can compare your result to an ICP result from the same sample. My ULR P values align well with the ATI ICP P values.

Also, wipe the vials with an alcohol based eyeglass wipe before zeroing and reading.

Ahh, great point. I can't believe that I forgot about this!;Eggonface;Facepalm

 

[Dennis Cartier]

I wish there was another reliable test so I can double-check the results of my HI736 ULR Phosphorus checker. That's the only test I regularly do where I don't have a confirmatory test in case I get a squirrelly result. I also wish that I had done more research before I dropped $50 on the ULR phosphate checker! Speaking of which, anyone want a barely used Hanna HI776 for $49 (plus $14.99 S&H)?

This reminds me of when I accidentally purchased the ULR Phosphate reagents instead of the Phosphorus reagent. I had been lax and testing my phosphate and when I got a much higher result than I was expecting, so I was perplexed until I noticed I was using the wrong reagent for the checker. I exchanged an unopened box of reagent and gave away the remaining portion of the open, but incorrect reagent. When I tested with the correct matching reagent for the HI736, I got the exact same readings as when I was using the mismatched reagent. So the high result, though unexpected, was correct and the 2 testers appeared to use similar, if not identical reagents.

Dennis

 

[jmichaelh7]

EDIT: just learned that there’s a timer if you hold down the button rather than just clicking it lol

That could mean the chemical reaction needed to take place longer resulting more the sequence of much lower results.... still jumping around but all within the same tenth decimal

I didn’t know there wasn’t a 3 minute mode. Lol I just learned today

 

[jmichaelh7]

Same question. Anyway, if you want to see how precise it is, have two vials ready. One just with tank water for your "blank". Use other for the "sample" (tank water and the reagent). Mix the latter thoroughly for a couple minutes, wipe it down thoroughly with a microfiber cloth or a tissue damp with RODI water then dry it, make sure there aren't air bubbles inside (if so, gently swirl), then let it sit for 3 minutes. Now do multiple tests. Power up the tester. Put the blank vial (also cleaned carefully) in when it says C1. Make sure the tester lid is closed tightly. Press the button to zero the tester. When it says C2, remove the blank and replace with the sample. Press the button once. Don't hold it which will set the timer for 3 minutes---the sample has already sat for three minutes. This will give you a reading. Cycle the power on the tester and repeat the blank zeroing and sample measurement again. Then do it a third time. You should have very similar if not exactly the same results from all three tests. If you're doing the three tests in quick succession, the longer time the sample vial has sat between measurements shouldn't matter much (as long as you shook the vial for 2 minutes and then let sit for 3 minutes at the beginning). The above method isn't meant to replace the standard testing protocol. Instead, it's meant to gauge the precision of the checker as it eliminates most of the variability that could be attributed to user error.
[BTW, in my experience, you don't need to align the test vial the same way in the checker every time. Also, once you clean the vials, try to only touch them by the cap to avoid smudges on the glass.]

I always thought you had to hold it during c2 to do the 3 minute test. So there is a quick method without waiting 3 minutes....

 

[BostonReefer300]

I always thought you had to hold it during c2 to do the 3 minute test. So there is a quick method without waiting 3 minutes....

You do need to wait for 3 minutes whether you time it yourself or use the checker timer. Hanna undoubtedly did a bunch of analytics and determined that 2 minutes of shaking plus three minutes of additional reaction time were needed for an accurate measurement.

 

[jmichaelh7]

You do need to wait for 3 minutes whether you time it yourself or use the checker timer. Hanna undoubtedly did a bunch of analytics and determined that 2 minutes of shaking plus three minutes of additional reaction time were needed for an accurate measurement.

That’s good to know . That defeats the quick method even