Hanna Phosphate Checker results are inconsistent

[chrisl10]

I have been using my Hanna Phosphate Checker pretty regularly and the least couple of times I ran the Checker 2 times with the same samples, the plain tank water in one test vile and the reagent in the second one, shaken about a minute and a half to two mins. The results are very inconsistent. The first time results were.18 the second time .10 how is this possible?? Which is the correct reading?
The high levels are another topic

 

[NY_Caveman]

I would use the same cuvette for the clean and the reagent sample as Hanna recommends. I would also orient the cuvette in the same position. Say with the 10ml text facing you. The light reading the sample should be testing the same cuvette and same cuvette position for the best possible reading. If, for example the cuvette becomes discolored over time, or gets a smudge, the difference between the two readings would still be apples to apples.

 

[NY_Caveman]

Also, if you are testing the same reagent sample after it has been sitting for say 10-20 minutes, that may also affect the reading. However, I would ask Hanna directly if you want to know for sure how the time sitting in the cuvette affects the sample.

 

[bubbaque]

Also remember the accuracy range is .04. With a reading of .10 and .18, if you include the error range, it's possible to be .14

 

[chrisl10]

Also, if you are testing the same reagent sample after it has been sitting for say 10-20 minutes, that may also affect the reading. However, I would ask Hanna directly if you want to know for sure how the time sitting in the cuvette affects the sample.

I retested it back to back. I may post to Hanna. TY

 

[madweazl]

I use a syringe to add the water sample as I found it hard to consistently eyeball the meniscus. I also orient the 10ml label on the cuvette forward (facing me) each time I place it in the checker. I'm not sure why you're waiting 1.5-2 minutes, you should be shaking for two minutes per the instructions. Wipe the cuvette down with a clean rag prior to inserting it into the checker after handling (do this for each step).

Doing the above has provided pretty consistent results for me. With that said, Triton results have been roughly 33% of these for the three samples I've submitted (I have no explanation for that).

 

[Acuario]

Applying the Hanna Antistatic Solution for Cuvette Cleaning HI 93703-50 with a lint-free antistatic cloth after each step in the test has been helpful in eliminating finger or salt smudges that would throw the test.

 

[IslandLifeReef]

Also remember the accuracy range is .04. With a reading of .10 and .18, if you include the error range, it's possible to be .14

I agree with this. Hanna says that the accuracy is +/- 4%, +/- 4ppm. Your results are in this range.

 

[pfoxgrover]

Storing the cuvettes in RO/DI water has made the biggest inprovement in the consistentcy of my results. Makes it much easier to keep them clean.