Question about Hannah phosphorous checker readings

[Sabellafella]

I can't remember what the margin of error is out of the box, but you might want to check that. Unfortunately the Hanna ulr is not a lab grade checker.

Think its +/-5 ppb. @TRPlacek i use 2 phosphorus checkers and theyre usually always 3 ppb withen reach of eachother. Also the slightest bit of micro bubbles or undissolved reagent will usually alter the reading so this may be what you experienced

 

[bif24701]

If you notice I'm using 3 decimal places. The readings correspond with yours. Yours are just rounded to two decimal points.

Ops, you are right. Details, its all in the details.

 

[TRPlacek]

I guess I just need to do it a few more times to get the hang of it. I better order a couple cases of reagents.

 

[TRPlacek]

But just for clarification for my initial question wouldn't it make sense that the lower reading would be the correct one since it seems the only way you would get an error is if the vial was dirty or scratched, undissolved reagent, bubbles or detritus in the water sample which would all cause a higher reading correct?

 

[Myka]

But just for clarification for my initial question wouldn't it make sense that the lower reading would be the correct one since it seems the only way you would get an error is if the vial was dirty or scratched, undissolved reagent, bubbles or detritus in the water sample which would all cause a higher reading correct?

I'm not sure if the reading would be higher or lower, but I wouldn't assume that it would be higher.

Almost exactly my procedure. The only thing I do different is make sure all bubbles are out of the vial before I put it in the checker so I don't disturb the vial right before the reading is taken. My reasoning for that is the 3 minute countdown allows any precipitate/undisolved reagent to settle to the bottom of the vial so it isn't affecting the photometer.

That's what I do as well, except I do it at the 1 minute left mark because it seems bubbles form in the vial during the first part of the 3 minute wait. After these bubbles are removed the vial is inserted into the checker with about 45 seconds remaining which gives enough time for any particulates to settle, though it's rare that I see any particulates (not to say they aren't there).

 

[TRPlacek]

@Myka I did the exact same procedure you mentioned and am now getting a reading of 0 on the two tests I've performed so far this morning.
Just to be clear, after you mix the reagent you start the 3 minute timer but do not put the vial in the checker until about 45 sec left on the clock right?

 

[Randy Holmes-Farley]

But just for clarification for my initial question wouldn't it make sense that the lower reading would be the correct one since it seems the only way you would get an error is if the vial was dirty or scratched, undissolved reagent, bubbles or detritus in the water sample which would all cause a higher reading correct?

Nope. Those are not the only reasons for errors. In fact, scratches and dirt are probably not part of the standard error determinations which would use good clean vials. If you allowed for such errors, the deviations can obviously get much worse if the defects are bad.

 

[Kungpaoshizi]

Uhhh, I believe 713 is +/- 5ppm. The 736 is the ULR phosphorous, which has an accuracy in the ppb.
Also the conversion number is 'reading x 3.0661 divided by 1000'.

I have rock solid, repeatable results that do not vary too much with the 736. The 713 of course inherently is less accurate.

 

[Myka]

@Myka I did the exact same procedure you mentioned and am now getting a reading of 0 on the two tests I've performed so far this morning.
Just to be clear, after you mix the reagent you start the 3 minute timer but do not put the vial in the checker until about 45 sec left on the clock right?

Yes, that's how I do it. As Randy mentioned too, once the vials get scratched, you'll need to buy new ones, so try not to scratch them (eg. don't rinse two at the same time, they'll scratch each other).

 

[TRPlacek]

I do appreciate the help ya'll. But after doing about 20 tests I've decided the hannah checker isn't for me and I'd be better off judging phosphates by the looks of my coral and algae on the glass than wondering which of the readings I received are the correct ones.