Hanna low range nitrate accuracy, nitrite interference

[Randy Holmes-Farley Verified Community Expert]

Back to the title topic, I probably missed it, but do we know if nitrite impacts the Hanna nitrate kit, and if so, but how much?

 

[Randy Holmes-Farley Verified Community Expert]

isn't valid - it should always be "AND" , or the +-2% is meaningless window dressing.

OK, I see that. The 2% is a useless add on. It is probably just their standard way to report error, and in this case, the zero point error is big, where sometimes it is very small.

That probably is meant to account for the things that impact values unrelated to nitrate, like salinity. Those usually are not a big source of error.

 

[Rick Mathew]

My understanding too, with the caveat that a meter reading of 0.25 and below means 0 ppm Is a possibility right? That’s why I am thinking in terms of LOQ.

If I get a little free time, I will look at the spectra of a Hanna test and see if there is detectable color when Hanna reads zero.

@taricha did quite a detailed look at the response of one of the Checkers and thought it look “strange” near zero.

That is my interpretation... .25 or below could be zero

 

[Dan_P]

Back to the title topic, I probably missed it, but do we know if nitrite impacts the Hanna nitrate kit, and if so, but how much?

Back in post #24 I compared how the same amount of nitrite registers as nitrate with the Hanna and Red Sea kit, assuming nitrite survives the zinc reduction step. It has a smaller impact for the Hanna test. But now I am not sure this is a valid test because of the assumption.

Since doing the above experiment I have learned that Zn metal will reduce nitrite. To correctly answer the question, I must go back and process a nitrite containing sample with the zinc reduction step intact to determine how much nitrite survives to produce a color.

 

[Randy Holmes-Farley Verified Community Expert]

Back in post #24 I compared how the same amount of nitrite registers as nitrate with the Hanna and Red Sea kit, assuming nitrite survives the zinc reduction step. It has a smaller impact for the Hanna test. But now I am not sure this is a valid test because of the assumption.

Since doing the above experiment I have learned that Zn metal will reduce nitrite. To correctly answer the question, I must go back and process a nitrite containing sample with the zinc reduction step intact to determine how much nitrite survives to produce a color.

OK, thanks.

 

[Dan_P]

Back to the title topic, I probably missed it, but do we know if nitrite impacts the Hanna nitrate kit, and if so, but how much?

Here are the results for nitrite interference for Hanna Marine Nitrate and Red Sea Nitrate Pro.

Nitrite interference is smaller for Hanna than Red Sea. You will note that all slopes are much less than 100.

 

[Rick Mathew]

Here are the results for nitrite interference for Hanna Marine Nitrate and Red Sea Nitrate Pro.

Nitrite interference is smaller for Hanna than Red Sea. You will note that all slopes are much less than 100.

Nice work Dan...looks like the measurements we take on NO3 in an established system would be very close give the additional nitrite available should be low...if I am reading this right...and it seems the Hanna method does a better job of conversion..

Thanks for the work...very helpful

Rick

 

[Courtney Aldrich]

Here are the results for nitrite interference for Hanna Marine Nitrate and Red Sea Nitrate Pro.

Nitrite interference is smaller for Hanna than Red Sea. You will note that all slopes are much less than 100.

Very nice. FYI, Hanna uses a copper-cadmium reducing agent (from their MSDS), which has been shown to quantitatively reduces nitrate to nitrite. Your experimental observations confirm this.

 

[Dan_P]

Nice work Dan...looks like the measurements we take on NO3 in an established system would be very close give the additional nitrite available should be low...if I am reading this right...and it seems the Hanna method does a better job of conversion..

Thanks for the work...very helpful

Rick

Thanks Rick!

I agree with your interpretations.

 

[Dan_P]

Very nice. FYI, Hanna uses a copper-cadmium reducing agent (from their MSDS), which has been shown to quantitatively reduces nitrate to nitrite. Your experimental observations confirm this.

Aha, I was wondering when a kit maker was going to move from zinc to cadmium.

Thanks for pointing this out!

 

[Righteous]

Very nice. FYI, Hanna uses a copper-cadmium reducing agent (from their MSDS), which has been shown to quantitatively reduces nitrate to nitrite. Your experimental observations confirm this.

This is not correct. Here’s the actual SDS for the HI781B-0 reagent which indicates it’s zinc.

http://www.revbase.com/tt/sl.ashx?z=506c2f61&dataid=4765254

Back to the title topic, I probably missed it, but do we know if nitrite impacts the Hanna nitrate kit, and if so, but how much?

Is it perhaps as simple as Hanna is using a lot of zinc to reduce the nitrate? Other tests use a lot less since theres no filtering step. With the Hanna there’s so much zinc the sample just looks grey prior to filtering.

I pretty consistently get readings of 2ppm on Salifert while Hanna reads only 0.10ppm, so that’s an order of magnitude. This is with regular ammonia dosing.

 

[Randy Holmes-Farley Verified Community Expert]

Is it perhaps as simple as Hanna is using a lot of zinc to reduce the nitrate? Other tests use a lot less since theres no filtering step. With the Hanna there’s so much zinc the sample just looks grey prior to filtering.

I do not believe that the degree of interference of nitrite with a nitrate kit like Salifert or Tropic Marin is inherent only to the nature of the reductant, but rather to what fraction of the nitrate is intended to be reduced in the time allowed for the test. That is where the multiplier on the more easily reduced nitrite comes from, since it will probably be 100% reduced instead of, say, 1% or 5%.

Thus, the exact times and concentrations of the various components that alter the fraction of nitrate reduced should be what drives the interference ratio.

I do not know exactly what factors are most important, but as you suggest, the amount of reducing agent certainly seems likely to be a big part of it.

 

[Courtney Aldrich]

This is not correct. Here’s the actual SDS for the HI781B-0 reagent which indicates it’s zinc.

http://www.revbase.com/tt/sl.ashx?z=506c2f61&dataid=4765254

Is it perhaps as simple as Hanna is using a lot of zinc to reduce the nitrate? Other tests use a lot less since theres no filtering step. With the Hanna there’s so much zinc the sample just looks grey prior to filtering.

I pretty consistently get readings of 2ppm on Salifert while Hanna reads only 0.10ppm, so that’s an order of magnitude. This is with regular ammonia dosing.

Hanna also uses the cadmium reduction method in their 100 pack refills for their photometers (https://www.hannainst.com/hi93728-0...R0nn0VoauY50jLOeetYsD9WUU0cI060waApq5EALw_wcB). MSDS is attached.

 

[Courtney Aldrich]

I do not believe that the degree of interference of nitrite with a nitrate kit like Salifert or Tropic Marin is inherent only to the nature of the reductant, but rather to what fraction of the nitrate is intended to be reduced in the time allowed for the test. That is where the multiplier on the more easily reduced nitrite comes from, since it will probably be 100% reduced instead of, say, 1% or 5%.

Thus, the exact times and concentrations of the various components that alter the fraction of nitrate reduced should be what drives the interference ratio.

I do not know exactly what factors are most important, but as you suggest, the amount of reducing agent certainly seems likely to be a big part of it.

Yes, the reductant and reduction time are both important. I think Hanna uses a longer incubation time than most tests (I thought it was 8 minutes) to ensure more complete reduction. I have attached a really nice review of assays for determination of nitrate and nitrite that goes over several dozen different assays and compares their limits of detection and interference.

 

[Righteous]

Yes, the reductant and reduction time are both important. I think Hanna uses a longer incubation time than most tests (I thought it was 8 minutes) to ensure more complete reduction. I have attached a really nice review of assays for determination of nitrate and nitrite that goes over several dozen different assays and compares their limits of detection and interference. The review notes that among all the reductants, cadmium-copper is close to 100% efficient. The Hanna nitrate reagent 100 pack refills use cadmium-copper (HI93728-0) whereas the Hanna 25 pack refills use zinc (HI781B-0).

Just to be clear, this thread has been discussing the HI781 Hanna LR Nitrate Colorimeter. This test only uses zinc.

You are referring to the HI96728 Nitrate-Nitrogen Portable Photometer which uses that cadmium based reagent you linked. It’s a different machine and measuring procedure, so the reagents are not going to be swappable.

 

[Courtney Aldrich]

Just to be clear, this thread has been discussing the HI781 Hanna LR Nitrate Colorimeter. This test only uses zinc.

You are referring to the HI96728 Nitrate-Nitrogen Portable Photometer which uses that cadmium based reagent you linked. It’s a different machine and measuring procedure, so the reagents are not going to be swappable.

You're right. I had saved the MSDS a while back out of curiosity, but this is for their more advanced instrument.

 

[Righteous]

You're right. I had saved the MSDS a while back out of curiosity, but this is for their more advanced instrument.

And now I’m curious (maybe in another thread) how the two test compare. Anyone got the photometer? The sensitivity and accuracy of this test makes me think it’s on par... but maybe the photometer is an easier procedure.

 

[Lasse]

I´m sorry @Dan_P - but I not understand your graphs. The Hana graph more or less say that the interference is 1:1 - it means that if you have 1 ppm nitrite in the water, 0 ppm nitrate in the water and you test for nitrate - you will read 1 ppm nitrate. That´s not my experiences.

Tropic marine normal nitrite/nitrate test kit have the ratio 1:50 and the Pro version 1:100. The tests I have done indicate that Salifert is in the 1:50 range - also the Hanna checker - but I will do more tests with Hanna Checker

Sincerely Lasse

 

[Dan_P]

I´m sorry @Dan_P - but I not understand your graphs. The Hana graph more or less say that the interference is 1:1 - it means that if you have 1 ppm nitrite in the water, 0 ppm nitrate in the water and you test for nitrate - you will read 1 ppm nitrate. That´s not my experiences.

Tropic marine normal nitrite/nitrate test kit have the ratio 1:50 and the Pro version 1:100. The tests I have done indicate that Salifert is in the 1:50 range - also the Hanna checker - but I will do more tests with Hanna Checker

Sincerely Lasse

Hi @Lasse

I will run through the information and maybe the trends will make more sense. First some chemistry background.

When a nitrate test kit step requires vigorous shaking for one minute, a metal, typically zinc, is being used to reduce nitrate to nitrite. If there is any nitrite present it too can be reduced to a certain extent to ammonia and nitrogen gas. This means when a nitrite solution which is free of nitrate is subjected to the zinc reduction step in a nitrate test, the concentration of nitrite is reduced.

Odd you might think. Isn’t nitrate reduced to nitrite and wouldn’t the nitrite then go on to be destroyed by zinc reduction, thus rendering nitrate test useless? The nitrite reduction might take more than one minute to reach completion, leaving behind plenty of the nitrite. Nitrite is also being removed from “harms way” by reacting with sulfanilic acid. By the way, the above reductions are known as parallel competitive reactions: nitrate and nitrite react with zinc at the same time.

The consequence of parallel reactions is that the yields are linked. One reaction determines the extent of the other reaction by using up the common reactant, in this case zinc metal. For example, in a mixture of nitrate and nitrite, the higher the nitrate concentration, the less zinc is available to reduce nitrite and more nitrite survives to go on to the Griess reaction where the pink color is formed. And this means nitrite will interfere more at higher nitrate concentrations. This interaction can be seen in both nitrate test results in the plots I posted earlier in this thread.

For both the Red Sea and Hanna Marine nitrate tests, the effect of nitrite on the nitrate result is greater for the sample with the higher nitrate concentration (compare the slopes of the lines. The slope is the “conversion factor” for that particular test and nitrate concentration). Interestingly, this nitrate concentration effect is almost eliminated in the Hanna Marine nitrate test, presumably because of the large excess of zinc that is employed.

Quite a complex situation, right? Lasse I hope you find time to post your study results that show Salifert to have a 50:1 conversion factor (at what nitrate concentration?)

 

[Lasse]

Is this really true?

For the salifert - see this

https://en.oceamo.com/post/tröpfchentests-nitrat-nitrit

Sincerely Lasse