Hanna Phosphorus checker

Discussion in 'Reef Chemistry by Randy Holmes-Farley' started by Fudsey, Nov 10, 2017.

  1. Fudsey

    Fudsey Well-Known Member Build Thread Contributor Partner Member 2018

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    I have a question about running the Hanna Checker Phosphorus test:

    How many times do you run the test with the same sample?

    I ran the test and the 1st result was 17, then I decided to run it a couple more time just to see. I have 2 vials(one with sample and one with tank water) and just kept rerunning the test for a few times.

    Here are the results

    1. 17
    2. 7
    3. 5
    4. 4
    5. 7

    Which number should I use? Or do a avg of them all?
     
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  2. jsker

    jsker Reefing is all about the adventure R2R Supporter R2R Excellence Award Reef Squad Leader Build Thread Contributor Article Contributor Partner Member 2018

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    As many time as you need of the same sameple

    average 2 thru 5 =6. 17 is the only number that is off from the rest
     
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  3. Fudsey

    Fudsey Well-Known Member Build Thread Contributor Partner Member 2018

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    I used 7 just because it came up 2x but I understand where you're going. So running the sample multiple times is OK then? :)
     
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  4. jsker

    jsker Reefing is all about the adventure R2R Supporter R2R Excellence Award Reef Squad Leader Build Thread Contributor Article Contributor Partner Member 2018

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    Yes.
     
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  5. GoVols

    GoVols GRUMORS R2R Supporter R2R Excellence Award MTRCMember Build Thread Contributor Article Contributor Partner Member 2018

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    I had a bad vial one time that was driving me crazy ;Wacky
    I finally figured out that it was that one vial ;Wideyed

    So, I went outside and threw it as far away as I could and it felt, really good ;Woot ;Woot

    :)
     
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  6. billw

    billw Acroholic in Training R2R Supporter Big Blue Reef Member Partner Member 2018

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    If the reaction is time sensitive, only the first reading would be valid. I wouldn't run that test more than once without knowing the answer to that.
     
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  7. Skibum

    Skibum Well-Known Member

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    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.
     
  8. boozeman27

    boozeman27 Well-Known Member R2R Supporter Partner Member 2018

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  9. Waters

    Waters "...in perfect isolation, here behind my wall." R2R Supporter

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    Just to clarify (for myself :)), are you saying you ran those tests back to back just to verify the number and was getting different results?
     
  10. boozeman27

    boozeman27 Well-Known Member R2R Supporter Partner Member 2018

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    It sounds like the op did back to back tests with the SAME sample. I want to here from @Hanna Instruments to be sure time is not a factor.
     
  11. Fudsey

    Fudsey Well-Known Member Build Thread Contributor Partner Member 2018

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    That is exactly what I did, back to back tests with the same sample, and got 4 different readings out of 5.
     
  12. Alfrareef

    Alfrareef Well-Known Member

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    I don’t think time should be a issue if you do it 4-5 times sequentially without relevant pauses.
    On the other hand using different vials could be an issue...
     
  13. sghera64

    sghera64 Well-Known Member

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    I’ve done this many times. And see the same phenomena. I know the instructions say to wait 3 minutes before taking the reading. I believe this is to allow time for the micro bubbles to clear. If you take the sample at 1 minute, 2 minute and 3 minutes after mixing the solid reagent in, the numbers slowly decrease. They hold stead after about 5-7 minutes (which is what you are seeing).

    I made a phosphorous standard and did a check. The 5 minute reading was high and the 7-20 minute readings were low. So, I now use the average of the last 3 steady readings.
     
  14. Alfrareef

    Alfrareef Well-Known Member

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    I don’t think time should be a issue if you do it 4-5 times sequentially without relevant pauses.
    On the other hand using different vials could be an issue...
     
  15. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    No, you need to test a new water sample each time if you want comparative readings.

    From the Hanna manual:
    • Do not let the reacted sample stand for too long after reagent is added, or accuracy will be lost.
    • After the reading it is important to immediately discard the sample, otherwise the glass might become permanently stained.
     
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  16. sghera64

    sghera64 Well-Known Member

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    Here is an experiment to try:
    Clean two different cuvettes and fill them with tank water. “Zero” the meter with one of the cuvettes. Then insert the other cuvette and do a reading. You should get zero (no error, no positive reading). Repeat those steps, but switch the cuvettes (use the second one as the calibration cuvette). Again, you should get zero. Repeat this several times orienting the cuvettes (based on the “10 mL” mark) to different positions.

    I have done this several times with different Hanna checkers and I always get zero each time.

    For grins, one time I took a cuvette from a phosphate test when it gave me a 5ppm reading and used it to zero the meter. Then I tried to take a reading of a cuvette with RO/DI water in it. I got an error “- - “.


    What this tells me is that we can zero the instrument with one cuvette and measure the other (i.e. we don’t have to calibrate and measure the exact same cuvette with the same orientation).

    The manual says not to let the sample stay in the vial for “too long” or accuracy will be lost. How long is too long? Is the three minute timer for consistency? What about the mix for “up to two minutes”? If that is not kept consistent, then accuracy will (and does as I’ve proven) suffer.

    If one can get a repeatable (and reproducible) reading after a total of 7 minutes, then maybe that is how the instrument should be used. It is possible that this introduces a repeatable bias/error, but the value is that the user can more accurately see shifts in phosphate readings (even if the readings are all low/high by a consistent amount).

    The reason I wait 7 minutes is because I see micro bubbles in the vial after 5 minutes.
     
  17. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    Hach (which uses the same basic chemistry for phosphate detection) has more clear time limits. For the lowest range (0-0.8 ppm) of the PO-19, they say:

    "Wait 8 minutes. Read the result within 10 minutes"

    For higher ranges (say, 0-4 ppm), the give shorter times, since it presumably reacts faster at higher cocentration:

    "6. Wait 1 minute. Read the result within 5 minutes."
     
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  18. sghera64

    sghera64 Well-Known Member

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    Ah, this is a very important insight. Makes a lot of sense to me.

    Randy, if the Hach assay is similar, does the dissolution of the solid reagent also release/cause micro-bubbles in the sample?
     
  19. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    Each kit may have modified the ascorbic acid method slightly to fit their ranges, etc, so some things don't translate exactly, but the Hach also doesn't read as low. I never saw any microbubbles, but they may have been there.
     
  20. XNavyDiver

    XNavyDiver Well-Known Member R2R Supporter

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    How are others using the Hanna ULR conducting their test?

    My procedure:
    1. Wipe cuvette clear inside and out with micro fiber cloth.
    2. Tap reagent packet until reagent is gathered in one corner of packet, cut the packet open on right angle sides, fold half of the packet into a triangle pour spout and set aside.
    3. Fill cuvette with 10ml tank water.
    4. Zero the checker with the same cuvette.
    5. Take cuvette out, unscrew the lid and pour/tap reagent into sample water.
    6. Recap and shake for 2 minutes (timed on smartphone).
    7. Place cuvette back in checker in exactly the same orientation as before.
    8. Press and hold down the button until 3 minute countdown counter appears.
    9. Sip a cold one until final number appears.

    From the way I do it, the reagent is in solution for 5 minutes (give or take a few seconds) until final reading. Should I be waiting longer to take a reading?
     
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