2 mL Sample for Hanna P ULR

Dan_P · 11/05/2016, 10:46 AM

I needed to perform a number of tests on small aquarium water samples. Recently, I found a way to use a 2 instead of a 10 mL sample in the Hanna ULR Phosphorous Checker. The test vial needed to be raised about 24 mm which was accomplished with a five mL syringe barrel cut down with an Xacto saw and placed in the Checker sample compartment. Because the test vial was now too high for the Checker lid to close, an opaque medicine bottle served as a cover during the test. For the normal 10 mL sample, 0.16 mL of powder reagent is used. Using a 1 mL syringe with the end cut off just below the "0" mark, 0.03 mL, a little less than 1/5 the amount used for a 10 mL sample, was dosed to the sample. The plot below of the Hanna reading versus the phosphate standard validates the use of a 2 mL sample.

bertoni · 11/05/2016, 09:52 PM

Hmm, most of those points are quite close. I wonder what happened at around 100 ppm P-PO₄. That's not bad for the cost!

Dan_P · 11/06/2016, 08:16 AM

Quote:

Originally Posted by bertoni

Hmm, most of those points are quite close. I wonder what happened at around 100 ppm P-PO₄. That's not bad for the cost!

Had the same thoughts. I speculate that consistent reagent dosing still needs improvement, but I typically run 2-3 tests to cover this. I am thinking that I should deliberately vary the amount of reagent dosed to see how important the exact amount is to the test results. It seems other users have the same question.

bertoni · 11/06/2016, 03:54 PM

I agree that checking the sensitivity to the quantity of reagent would be a good next step.

Dan_P · 01/29/2017, 05:56 AM

A quick update. I did extensive testing of the 2 mL sample protocol and found it gave variable results and PO4 values much lower than the same sample tested at 10 mL. I don't know what's going on, so, I am suspending use of this approach until I can solve these issues. Sorry about the misleading information.

Dan

bertoni · 01/29/2017, 09:28 PM

Oh, well, it's an interesting idea. It might require a precision scale to get it working, though.

Dan_P · 01/30/2017, 05:22 PM

Quote:

Originally Posted by bertoni

Oh, well, it's an interesting idea. It might require a precision scale to get it working, though.

Jonathan, you are probably right, but I was hoping for a cheaper "hack". I will probably sit on this idea awhile before studying this further.

11/05/2016, 10:46 AM	#1
Dan_P Registered Member Join Date: Aug 2014 Posts: 1,432	2 mL Sample for Hanna P ULR I needed to perform a number of tests on small aquarium water samples. Recently, I found a way to use a 2 instead of a 10 mL sample in the Hanna ULR Phosphorous Checker. The test vial needed to be raised about 24 mm which was accomplished with a five mL syringe barrel cut down with an Xacto saw and placed in the Checker sample compartment. Because the test vial was now too high for the Checker lid to close, an opaque medicine bottle served as a cover during the test. For the normal 10 mL sample, 0.16 mL of powder reagent is used. Using a 1 mL syringe with the end cut off just below the "0" mark, 0.03 mL, a little less than 1/5 the amount used for a 10 mL sample, was dosed to the sample. The plot below of the Hanna reading versus the phosphate standard validates the use of a 2 mL sample.

11/05/2016, 09:52 PM	#2
bertoni RC Mod Join Date: Mar 2002 Location: Mountain View, CA, USA Posts: 88,616	Hmm, most of those points are quite close. I wonder what happened at around 100 ppm P-PO₄. That's not bad for the cost! __________________ Jonathan Bertoni

11/06/2016, 03:54 PM	#4
bertoni RC Mod Join Date: Mar 2002 Location: Mountain View, CA, USA Posts: 88,616	I agree that checking the sensitivity to the quantity of reagent would be a good next step. __________________ Jonathan Bertoni

01/29/2017, 09:28 PM	#6
bertoni RC Mod Join Date: Mar 2002 Location: Mountain View, CA, USA Posts: 88,616	Oh, well, it's an interesting idea. It might require a precision scale to get it working, though. __________________ Jonathan Bertoni

01/29/2017, 05:56 AM	#5
Dan_P Registered Member Join Date: Aug 2014 Posts: 1,432	A quick update. I did extensive testing of the 2 mL sample protocol and found it gave variable results and PO4 values much lower than the same sample tested at 10 mL. I don't know what's going on, so, I am suspending use of this approach until I can solve these issues. Sorry about the misleading information. Dan