How important is it to get /all/ of the Hanna dry reagent in the sample?

[BrettDS]

I've been using the Hanna LR phosphate checker for a couple of months now, but each time it use it I get a bit concerned about not being able to get all of the powder into the solution. I've gotten pretty good at opening the packet and folding a spout into one of the sides, but sometimes a bit of powder will miss the test tube or sometimes some of it will be stuck in the edges of the packet. I've also noticed that the inside of the packet is usually coated with a fine powder that is obviously impossible to get into the test tube.

Will I get a significantly different reading if, say, I'm super careful and get 99% of the power into the tube vs just going quickly and only getting 95% of it in?

 

[robbous]

.

 

[scar79]

following this as well!

I really dislike those little packets, as powder is either getting stuck in the corners or comes flying out a million mph. I figure if I'm testing fairly regularly and any particular sample is only off by 5-10%, I'm not going to do anything about it anyways. If the true value is .030 but your test reads 0.033 are you really going to be running to your supply closet to grab some fresh GFO? Probably not.

 

[Darth_Tater]

I have a tiny funnel (came with my acrylic glue I never used) I use that helps me get 99% in, but I agree it's impossible to not spill a little.

 

[Potatohead]

IME if you don't get it all in, the result actually reads higher. I could be wrong but I believe I have noticed that pattern.

 

[BlackTip]

Hanna Instrument should provide best answer and takes the guess work out of it.
Send them and email, they are very good at responding in timely manner.

 

[Dan_P]

This easily answered. Carefully pour out the entire contents of a packet onto a piece of wax paper. Using a razor blade carefully gather the powder into a shallow pile and then form a square, while trying to keep the depth about the same across the square. With the razor blade divide the square into two unequal piles, say 1/4 and 3/4 the original size. Run two separate phosphate tests using these quantities. Compare these two results to your usual full packet results. Post the results so we know what happened. Thanks!

 

[BrettDS]

This easily answered.

interesting idea. Other than the fact that someone might think I had a drug problem if they walked in on me

But unfortunately my phosphate levels are usually quite low (Usually 0.00 and I typically change my gfo when it gets up to 0.04) so if less powder would cause it to read low (which seems logical) then I'm not sure there is enough phosphate in the system to make a noticeable difference.

I did see the BRS sells a phosphate calibration standard solution, so it might not be a bad idea to get that and try your suggestion... especially since we know what the reading should be.

I'll try contacting Hanna as well and see if they have any input.

 

[BrettDS]

Well, I went to Hanna's website looking for their email address and I found a phone number as well, so I called and spoke with one of their technicians. He said that it is definitely best to get all of the powder in. He said it's OK if you miss a speck or two, but getting 95% of it in vs 99% may affect the reading.

 

[LeslieP]

To get as much reagent as possible into the vial, I take a small square of wax paper, fold it diagonally to get a crease in the middle, then dump the contents of the packet onto it. Hold it folded, with the wax paper corner over the top of the vial and gently slide the reagent into the vial. Tap it gently to make sure that all reagent has come off of the wax paper. That's usually good enough for me, but if you want to be extra anal, then take a plastic pipet or syringe, suck up some of the water from the vial, rinse the packet and then suck the water out of the packet and squirt it back into the vial.

I work in a lab and this is how we have always weighed out reagents. I even have a nice box of "weighing paper" which is basically wax paper pre-cut into 3.5" squares.

 

[Reefer40b]

To get as much reagent as possible into the vial, I take a small square of wax paper, fold it diagonally to get a crease in the middle, then dump the contents of the packet onto it. Hold it folded, with the wax paper corner over the top of the vial and gently slide the reagent into the vial. Tap it gently to make sure that all reagent has come off of the wax paper. That's usually good enough for me, but if you want to be extra anal, then take a plastic pipet or syringe, suck up some of the water from the vial, rinse the packet and then suck the water out of the packet and squirt it back into the vial.

I work in a lab and this is how we have always weighed out reagents. I even have a nice box of "weighing paper" which is basically wax paper pre-cut into 3.5" squares.

100%. I think this wax paper idea really is probably the best way to do these tests.

 

[Potatohead]

Well, I went to Hanna's website looking for their email address and I found a phone number as well, so I called and spoke with one of their technicians. He said that it is definitely best to get all of the powder in. He said it's OK if you miss a speck or two, but getting 95% of it in vs 99% may affect the reading.

Ugh. They really should package it differently then, maybe in little vials.

 

[Brieninsac]

I'm sure Hanna took into account the residual still remaining in the packet when filling them to the designated level. What I do is hold the packet by a corner and flick the two top sides with my finger to loosen anything caught in the top creases of the packet. I then cut the two side as indicated on the packaging and then pull the two remaining seams to the edges. I'll then tap the sides with scissors to loosen anything still in the crease. Then fold a nice crease and pour it in.

Only once did I spill some of the Ca powder, which threw my results off. The Ca reagent is more course and pours out better then the super fine Ph reagent. But if you're careful I think you're getting all that's needed to conduct the test.

 

[xCry0x]

I don't understand why they don't sell it like the salifert reagent for calcium/nitrate/magnesium where you get a little bottle and a little scooper.

The individually packed powder seems more expensive to produce and it is ridiculously dumb to use in practice.

I just assume I am always going to be a bit off -- having them say 95% vs 99% affects the reading isn't helpful. Helpful would be knowing if it meaningfully impacts the reading..

 

[642642]

I guess Ill throw this in here. How long should it sit before testing? I flip vial for two minutes to mix then test a few seconds later. I notice that if I test the same vial more then once, every test gets lower and lower. Like today I test the same water five times. 22ppb, 15ppb, 12ppb,10ppb then 11ppb. So I just say its 11.

 

[BrettDS]

I guess Ill throw this in here. How long should it sit before testing? I flip vial for two minutes to mix then test a few seconds later. I notice that if I test the same vial more then once, every test gets lower and lower. Like today I test the same water five times. 22ppb, 15ppb, 12ppb,10ppb then 11ppb. So I just say its 11.

The directions that came with my meter say to mix for 2 minutes, then let it sit for 3 minutes before taking the reading. You can mix for two minutes, then put the sample in the meter and press and hold the button and it will start a 3 minute timer and then take the final reading when the timer expires.

The only downside is that there is no beep or anything to let you know when it takes the final reading and I forgot about it once and waited so long that it had already shut off. Now I usually set a 3 minute timer on my phone or microwave at the same time I start the timer on the meter so I'm sure to notice when it finishes.

 

[scar79]

I do the same thing with the timer. Nothing worse than going through the effort of running the test and then remembering 10 minutes later and the unit had already powered off

 

[Focal]

Hannah should produce the reagents in a tablet form. Just drop the tablet in the vial and you are good to go.

 

[toothybugs]

Or you could reduce your testing noise by testing in triplicate and averaging the results...

 

[BrettDS]

Or you could reduce your testing noise by testing in triplicate and averaging the results...

I think the concern here is that by not being able to get enough of the reagent into the sample the test results will be too low. Averaging the results might not be ideal in this situation since there wouldn't be any case where a little too much reagent got in to the sample to balance it out. It might be better to test three times and then take the highest reading.