DIY NITRATE TEST METER

[Rick Mathew]

Would love to hear your feedback and any ideas you might have for this project

Rick

 

[Randy Holmes-Farley]

One issue with nitrate checkers in seawater is interference by chloride. That's what Hanna says limits their coming out with a marine nitrate checker.

So if you develop a method, it would be worth seeing how much (if at all) salinity impacts your results.

 

[rkpetersen]

Really interesting results. It's unfortunate that the Hanna iron checker isn't better in the most relevant range (I had a brief hope here that mine might be of some actual use.)

Also interesting that you are using the Red Sea and Nyos nitrate test kits; I also thought those were the best hobbyist kits currently available after comparing them directly to various others.

Another testing service you might try is from ATI. I've used them a few times and the results are quite similar to Triton; however, they provide a paid mailer, they also include alkalinity and nitrate measurements in addition to elemental spectroscopy, and they also analyze a sample of your RODI water at no additional charge.

AWT is AquaMedic Water Testing; not spectroscopic but a good service nonetheless, and very fast results. I've also noticed that their nitrate values run higher than the Red Sea on concurrent samples.

 

[Rick Mathew]

One issue with nitrate checkers in seawater is interference by chloride. That's what Hanna says limits their coming out with a marine nitrate checker.

So if you develop a method, it would be worth seeing how much (if at all) salinity impacts your results.

That is an excellent point sir. I could repeat selected test making up the known solutions with RODI water as the diluent and not Saltwater. Then see if my results are ,different, better, more consistent or no difference...will add it to my list of future actions.

By the way do you happen to know in what way the chloride interferes with the test?

Thank you for your input it is appreciated.

 

[Rick Mathew]

Really interesting results. It's unfortunate that the Hanna iron checker isn't better in the most relevant range (I had a brief hope here that mine might be of some actual use.)

Also interesting that you are using the Red Sea and Nyos nitrate test kits; I also thought those were the best hobbyist kits currently available after comparing them directly to various others.

Another testing service you might try is from ATI. I've used them a few times and the results are quite similar to Triton; however, they provide a paid mailer, they also include alkalinity and nitrate measurements in addition to elemental spectroscopy, and they also analyze a sample of your RODI water at no additional charge.

AWT is AquaMedic Water Testing; not spectroscopic but a good service nonetheless, and very fast results. I've also noticed that their nitrate values run higher than the Red Sea on concurrent samples.

Thanks for the info on ATI....I will check it out.

I have not given up on the Hanna Iron Checker. As I was posting I had another idea to work the data to see if a relevant correction might be made to the regression model...worth a try...will update as things develop

Rick

 

[Dennis Cartier]

There are some hobbyist level colorimeters that may be able to be used for testing similar to the Hanna ones. The one I am thinking of is the http://public.iorodeo.com/docs/colorimeter/index.html, however I am not sure if it is sensitive enough. It would be interesting to see though as they have posted some nitrate and phosphate results obtained using test kits that we commonly use.

Dennis

 

[Dennis Cartier]

This is the part of that site that would have the most application to our purposes https://sites.google.com/iorodeo.com/colorimeter/aquarium-tests

Dennis

 

[Rick Mathew]

Really interesting results. It's unfortunate that the Hanna iron checker isn't better in the most relevant range (I had a brief hope here that mine might be of some actual use.)

Also interesting that you are using the Red Sea and Nyos nitrate test kits; I also thought those were the best hobbyist kits currently available after comparing them directly to various others.

Another testing service you might try is from ATI. I've used them a few times and the results are quite similar to Triton; however, they provide a paid mailer, they also include alkalinity and nitrate measurements in addition to elemental spectroscopy, and they also analyze a sample of your RODI water at no additional charge.

AWT is AquaMedic Water Testing; not spectroscopic but a good service nonetheless, and very fast results. I've also noticed that their nitrate values run higher than the Red Sea on concurrent samples.

I ordered an ATI analysis kit for trial...thanks for the lead

 

[Rick Mathew]

There are some hobbyist level colorimeters that may be able to be used for testing similar to the Hanna ones. The one I am thinking of is the http://public.iorodeo.com/docs/colorimeter/index.html, however I am not sure if it is sensitive enough. It would be interesting to see though as they have posted some nitrate and phosphate results obtained using test kits that we commonly use.

Dennis

I will check it out...thanks

Rick

 

[Rick Mathew]

This is the part of that site that would have the most application to our purposes https://sites.google.com/iorodeo.com/colorimeter/aquarium-tests

Dennis

Thanks

 

[Stigigemla]

@ Randy: Do you know anything of how the chloride interference works?
Is it possible to get around it using longer reaction time? Or shorter?
Is it possible to inhibit it by adding an extra chemical before or after the normal test procedure?
Is it linear so one can have a conversion table for different salinitys?
Does it have anything with temperature to do?

 

[Dennis Cartier]

This is a bit off topic, but related. This morning while I was doing a phosphate test, and after having the Hanna reagent fall out, missing the vial and hitting my fingers, I thought there has to be a better way. I have been having a problem with elevated PO4 on this particular tank, but due to an expired set of Hanna reagents, I had not realized it. After going out yesterday and buying all new Salifert kits and Hanna reagents, I set about to find out what was out of whack. The PO4 was high enough that the new Hanna reagents tinged the vial light blue that was visible to my eye while resting on the paper towel. Seeing that light blue tint gave me an idea. It looked a lot like the colour shift of the Salifert test, that I clearly had been miss reading for awhile due to the shades being so close to each other at the low range part. What if you could use the Hanna ULR tester to read the shades of blue in the Salifert test?

After completing the Phosphorus test on the Hanna (Yep, really high ~0.21), I performed another Salifert PO4 test. When the Salifert test was complete, I placed the reacted sample in a Hanna cuvette and using a second cuvette for the blank, I tested it through the ULR Hanna. It read 151 ppb. Not surprising as the shades of blue on the Salifert card looked to my eye to be darker than the shade of blue (when I was using the Hanna reagent in the initial test). So I performed another test using the Salifert reagents, but with my sample diluted by 50% with RODI water. The ULR tester now read 40 ppb. So not a linear decrease, but heading in the right direction.

The conclusion I draw from this is that a calibration curve may be able to be created to use the Hanna ULR Phosphors tester to read the Salifert PO4 test. For people who struggle with identifying the correct matching shade of blue on the Salifert card, this might be a viable alternative.

Dennis

 

[Dennis Cartier]

While searching around to see if I could find anyone that had used the ULR tester with Salifert reagents, I stumbled across a post where the poster had posted how to use the ULR tester with an API Nitrate test to read low range nitrate. See: http://www.reefcentral.com/forums/showthread.php?t=2460022

Dennis

 

[Randy Holmes-Farley]

That is an excellent point sir. I could repeat selected test making up the known solutions with RODI water as the diluent and not Saltwater. Then see if my results are ,different, better, more consistent or no difference...will add it to my list of future actions.

By the way do you happen to know in what way the chloride interferes with the test?

Thank you for your input it is appreciated.

This is what Hach says about their nitrate test:

Chloride concentrations above 100 mg/L cause low results. The test can be used at high chloride
concentrations (seawater) if a calibration is made with standards that have the same chloride
concentration as the samples (refer to Seawater calibration on page 6).

 

[Rick Mathew]

While searching around to see if I could find anyone that had used the ULR tester with Salifert reagents, I stumbled across a post where the poster had posted how to use the ULR tester with an API Nitrate test to read low range nitrate. See: http://www.reefcentral.com/forums/showthread.php?t=2460022

Dennis

Dennis; Thanks for the link...looks like they were attacking the problem in the same way....very valuable information...thank you

 

[Rick Mathew]

This is what Hach says about their nitrate test:

Chloride concentrations above 100 mg/L cause low results. The test can be used at high chloride
concentrations (seawater) if a calibration is made with standards that have the same chloride
concentration as the samples (refer to Seawater calibration on page 6).

Thank you for the reply. Based on Hanna's comments, it seems as if I proceed using SeaWater as my calibration solution that this might yield some usable results. I am in the process of completing the calibration levels in RODI to see what the difference is and what kind of regression formula it generates...Will post results as soon as I am done.

Can you tell me what document you are referencing from Hanna...I have not been able to find one that goes into any detail about the Chloride interference...Thank for your help


Rick

 

[Rick Mathew]

This is what Hach says about their nitrate test:

Chloride concentrations above 100 mg/L cause low results. The test can be used at high chloride
concentrations (seawater) if a calibration is made with standards that have the same chloride
concentration as the samples (refer to Seawater calibration on page 6).

Sorry...just saw you were referring to a Hach document not a Hanna Document...will search there...thanks again

 

[Randy Holmes-Farley]

Hanna posted the comment on chloride interference in a discussion at Reef2Reef on why they did not have a seawater nitrate kit.

The Hach comment is here (page 4):

https://www.hach.com/asset-get.download.jsa?id=7639983737

 

[Randy Holmes-Farley]

The same article from Hach also says this:

Seawater calibration
Chloride concentrations above 100 mg/L cause low results. To use this method for
samples with high chloride concentrations, calibrate the instrument with nitrate standard
solutions that contain the same amount of chloride as the samples.
Prepare calibration standards that contain chloride and 1.0, 3.0, 5.0 and 10.0 mg/L nitrate
(as NO3
––N) as follows:
1. Prepare 1 liter of chloride water that has the same chloride concentration as the
samples.
a. Weigh the applicable amount of ACS-grade sodium chloride: (chloride
concentration of samples in g/L) x (1.6485) = g of NaCl per liter.
Note: 18.8 g/L is the typical chloride concentration of seawater.
b. Add the sodium chloride to a 1-liter volumetric flask.
c. Dilute to the mark with deionized water. Mix thoroughly. Use this water as the
dilution water to prepare the nitrate standard solutions.
2. Use a pipet to add 1.0, 3.0, 5.0 and 10.0 mL of a 100 mg/L nitrate-nitrogen (NO3
––N)
standard solution into four different 100-mL Class A volumetric flasks.
3. Dilute to the mark with the prepared chloride water. Mix thoroughly.
4. Complete the test procedure for each of the standard solutions and for the prepared
chloride water (for a 0-mg/L standard solution).
5. Measure the absorbance of the standard solutions and enter a user calibration into
the instrument.
6. Use the user program to measure samples that contain high concentrations of
chloride.

 

[Rick Mathew]

The same article from Hach also says this:

Seawater calibration
Chloride concentrations above 100 mg/L cause low results. To use this method for
samples with high chloride concentrations, calibrate the instrument with nitrate standard
solutions that contain the same amount of chloride as the samples.
Prepare calibration standards that contain chloride and 1.0, 3.0, 5.0 and 10.0 mg/L nitrate
(as NO3
––N) as follows:
1. Prepare 1 liter of chloride water that has the same chloride concentration as the
samples.
a. Weigh the applicable amount of ACS-grade sodium chloride: (chloride
concentration of samples in g/L) x (1.6485) = g of NaCl per liter.
Note: 18.8 g/L is the typical chloride concentration of seawater.
b. Add the sodium chloride to a 1-liter volumetric flask.
c. Dilute to the mark with deionized water. Mix thoroughly. Use this water as the
dilution water to prepare the nitrate standard solutions.
2. Use a pipet to add 1.0, 3.0, 5.0 and 10.0 mL of a 100 mg/L nitrate-nitrogen (NO3
––N)
standard solution into four different 100-mL Class A volumetric flasks.
3. Dilute to the mark with the prepared chloride water. Mix thoroughly.
4. Complete the test procedure for each of the standard solutions and for the prepared
chloride water (for a 0-mg/L standard solution).
5. Measure the absorbance of the standard solutions and enter a user calibration into
the instrument.
6. Use the user program to measure samples that contain high concentrations of
chloride.

Wow...thanks. I actually used a fresh batch of Reef Crystals at 35 ppt as my chloride solution...Do you think this would close enough.....according to the literature this would be about 19,400mg/L a bit higher than the above article states