Hanna Phosphate Help

[CheifReeferNB]

I have recently battled inconsistent phosphate readings which were inexplicably fluctuating throughout the day. I suspected it may be my methods.

When I use a vial of tank water as the blank and follow the test procedure as normal. I get a reading of 0.16- 0.19ppm.

When I use the “blank” cuvette that comes with the phosphate standard kit as the C1 baseline and use a separate vial for the reaction with tank water, I get a phosphate reading of 0.09. It is very consistently 0.09 as well.

I would figure the latter reading should be higher since the blank has no cloudiness to set a baseline for light passing through.

Could my sample cuvette be damaged or stained causing the inconsistency and elevated readings? Let me know what you guys think and if you have any experience with this.

 

[Bucrob]

I have recently battled inconsistent phosphate readings which were inexplicably fluctuating throughout the day. I suspected it may be my methods.

When I use a vial of tank water as the blank and follow the test procedure as normal. I get a reading of 0.16- 0.19ppm.

When I use the “blank” cuvette that comes with the phosphate standard kit as the C1 baseline and use a separate vial for the reaction with tank water, I get a phosphate reading of 0.09. It is very consistently 0.09 as well.

I would figure the latter reading should be higher since the blank has no cloudiness to set a baseline for light passing through.

Could my sample cuvette be damaged or stained causing the inconsistency and elevated readings? Let me know what you guys think and if you have any experience with this.

Any fingerprints or markings on the glass of the cuvette?

 

[CheifReeferNB]

I have recently battled inconsistent phosphate readings which were inexplicably fluctuating throughout the day. I suspected it may be my methods.

When I use a vial of tank water as the blank and follow the test procedure as normal. I get a reading of 0.16- 0.19ppm.

When I use the “blank” cuvette that comes with the phosphate standard kit as the C1 baseline and use a separate vial for the reaction with tank water, I get a phosphate reading of 0.09. It is very consistently 0.09 as well.

I would figure the latter reading should be higher since the blank has no cloudiness to set a baseline for light passing through.

Could my sample cuvette be damaged or stained causing the inconsistency and elevated readings? Let me know what you guys think and if you have any experience with this.

There’s scratches for sure. Could be the source of the problem. No fingerprints. Still a little confused why the blank sample would induce a lower reading. I would figure the light diffraction from scratches would be normalized with using the same cuvette (to a certain extent).

 

[KrisReef]

Test should follow

Fill cuvette with tank water to be tested.

Zero the meter with that water, remove, add reagent, shake for 2 full minutes, replace in meter and start the three minute timer. The meter will read and report results after 5 minutes.

The vial needs to be aligned in the meter in the same location as the zero'ing was done to get best results.

 

[EnterName]

Have you tried using RO/DI instead of an empty vial for C.1? I would rely on the results but it would be an interesting test to see if the meter is broken.

Even though the photometer just measures light intensity, I could imagine the refractive index difference when using air vs. water in the vial can mess with the amount of light getting into the sensor.

 

[CheifReeferNB]

Have you tried using RO/DI instead of an empty vial for C.1? I would rely on the results but it would be an interesting test to see if the meter is broken.

Even though the photometer just measures light intensity, I could imagine the refractive index difference when using air vs. water in the vial can mess with the amount of light getting into the sensor.

I don’t use air. I use an unreacted sample of tank water. Using rodi water is essentially what I’m doing when I use the standards sample as that is a solution Hanna certified as a “zero”.

 

[Randy Holmes-Farley Verified Community Expert]

I would use the real vial test as directed, oriented the same way every time, not anything else. Switching vials may lead to oddities due, as you suspect, to differences in the vial itself or the contents. Even glass thickness differences might change the nature of light passing through a curved vial.

Real spectrometer’s nearly always use square cuvettes and would not have the odd scattering effects of a curved surface in the light path.