Testing Nitrate Montior for accuracy?

[jamal-188]

Hey Randy,

I've read that you have one of the American Marine Nitrate Monitors but cannot comment on the accuracy. I'm intersted in purchasing one but would like to test the accuracy, any ideas on how I could go about doing this?

Even if it's not accurate but would at least pick up on increasea/decreases in a tank over time that would be benificial.

I"m thinking I could use the calibration solutions that come with it and try those on a few of the hobby test kits.

 

[Randy Holmes-Farley]

It clearly responds to nitrate levels, but it is not the type of thing that you can leave in the water like a pH meter. It is more like a kit in that you take a water sample and test it.

The calibration kits that come with it, if made properly, are a good way to test test kits, and I've recommended that to others.

To test the meter accuracy, you'd have to make standards independent of the Pinpoint standards, so will need access to some good quality nitrate compounds,like sodium nitrate.

 

[jamal-188]

You suggested before that you should probably calibrate these units at least once a day. Do you think it's necessary to calibrate if going from one tank to another?

 

[Randy Holmes-Farley]

Not if you do them all in a span of a few minutes. But hours, yes, I'd recalibrate.

 

[TandN]

Hey Randy just wondering your take on the monitor since you have one is it giving you a true reading or is it like test kits which give false readings?

 

[loudell]

Hi Guys. Let me jump in with a few comments about the nitrate monitor and the calibration fluids. The meter will display an accurate and reproducible value for NO3 in seawater. It will tell you if your nitrates are 4 or 6 ppm, or 67 or 68 ppm NO3, etc. and if you want to verify of the meter is reading correctly you can put the probe back into the appropriate nitrate calibration fluid to verify calibration (just like a pH meter). The nitrate calibtation fluids are in a seawater matrix and it is not easy to make your own. Definately not Deionized water and sodium nitrate. The meter comes with 3 different seawater matrix nitrate fluids: 1 ppm, 10 ppm and 100 ppm. If your objective was to determine how accurate the nitrate monitor (or your colormetric test kit) actually is then you should be testing the nitrate solutions. The accuracy of the 100 ppm fluid is +/- 1 ppm NO3 while the accuracy of the 10 ppm fluid is +/- .5 ppm NO3, the accuracy of the 1 ppm fluid is +/- 0.1 ppm NO3.
Hope this clears up a few things...Lou Dell/American Marine Inc.

 

[TandN]

Yes it does thank you Let me ask you are the calibration fliuds like the PH where you use it once and then throw it out ?

 

[loudell]

The nitrate calibration fluids are not subject to the oxidation that pH fluids suffer. Nitrate Calibration fluids are very robust and are limited by technique contamination which basicly means that are as accurate as you are careful not to mix other fluids with them. The fluids that come with the meter are expected to last the hobbyist 6-12 months.

 

[TandN]

Kewl thank you for the awnsers helps out alot

 

[Randy Holmes-Farley]

Hey Randy just wondering your take on the monitor since you have one is it giving you a true reading or is it like test kits which give false readings?

IMO, if the standard is made out of water close to the tank water, it is likely to be reasonably accurate. One concern with ion selective electrodes in general is what other ions may interfere with it. I do not know how close these solutions are to typical tank water, a d what variables really matter, but it has the potential to be very accurate.

 

[loudell]

Randy, The nitrate standards are painstakingly close to seawater and they were put together pretty much an element at a time. Some people may think it would be easy to mix deionized water, salt mix and sodium nitrate to create standards. Definately not true, trace nitrate can be found in salt mix and water supply as well. If you have the ability to accuraly measure the nitrate in the standards by another accurate method; please do so. The meter will be the most accurate method to precisely determine nitrate in a marine enviornment.

 

[Randy Holmes-Farley]

Thanks, Lou.

Do you know off hand how far folks would need to deviate from NSW in their tanks before any ions became a problem? Does the probe manufacturer describe which ions are most interfering? They probably list a bunch of things we won't have, but might list some we could. My old Orion catalog (1992) lists perchlorate, iodide, chlorate, cyanide, bromide, nitrite, HS-, carbonate, bicarbonate, chloride, phosphate, acetate, fluoride, and sulfate. The question is how interfering they (or others) might be to your probe at levels likely to vary from NSW.

What about salinity of 30 ppt?

 

[loudell]

Randy, the most interfering ion is definately sodium. The combination of the meters algorithm and calibration fluids counteract the impact down to about 21-22ppm with +/- about 2 ppm accuracy at the far end of that spectrum. Many people want to use the meter with fresh water and it will not be accurate there even if you formulate fresh water standards because the mathematical formula is optimized for marine saltwater.

 

[Randy Holmes-Farley]

combination of the meters algorithm and calibration fluids counteract the impact down to about 21-22ppm with +/- about 2 ppm accuracy at the far end of that spectrum.

Do you mean 21-22 ppt?

 

[loudell]

Sorry, you're right. I meant ppt.
Regarding electrode interference if you look at potential interference for pH electrodes the list is also long. But essentially if you look at the conditions that each ion will interfere and the concentration range and you carefully create calibration medium that takes these factors into proper account the result is a highly accurate measurement.
Expample: pH is highly temperature dependant however in the range of an average aquarium between 68 and 86 F the resulting interference is negligable.

 

[mwitten]

<a href=showthread.php?s=&postid=9112477#post9112477 target=_blank>Originally posted</a> by loudell
Randy, The nitrate standards are painstakingly close to seawater and they were put together pretty much an element at a time. Some people may think it would be easy to mix deionized water, salt mix and sodium nitrate to create standards. Definately not true, trace nitrate can be found in salt mix and water supply as well. If you have the ability to accuraly measure the nitrate in the standards by another accurate method; please do so. The meter will be the most accurate method to precisely determine nitrate in a marine enviornment.

Loudell,

Reading this, I am not quite sure... Should the standard work with test kits? I just got the monitor, but I would love to see how my kits compare against the standards, if that will work. So far, against the tank water, my Lamotte kit is reading quite close to the monitor.

Thanks!

-Mike

 

[Randy Holmes-Farley]

Yes, they should.

 

[loudell]

The Nitrate standards should definately work with all colormetric nitrate test kits. Check the standards with your LaMotte Kit to see how 1 ppm, 10, ppm and 100 ppm will look relativel to color chart. If you are very precise on your measurement. You can combine 10 ppm nitrate standard with 1 ppm standard to create a standard that is 5.5 ppm NO3. I would suggest adding say 15 drops of each standard to a measurement vial...

 

[mwitten]

Randy & Loudell,

Thanks! I'll give it a try tonight (at least the simple test).

-Mike

 

[jamal-188]

I"m anxious to see how some of my test kits compare as well. Going to try an instant ocean, salifer, and aq pharm this week. I'll report back with the findings.