Testing Nitrate Montior for accuracy?

[mwitten]

<a href=showthread.php?s=&postid=9113610#post9113610 target=_blank>Originally posted</a> by 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...

OK, well... Something ain't right, but I am not sure exactly what.

On the Lamotte kit, tried twice, I used the 10 ppm standard solution. The kit I have (low range) is SUPPOSED to give me a reading in Nitrate-N... thus I would have expected a reading of 10/4.4 or a bit over 2. It comes out well above 10... the highest range I can read on this kit.

I had ordered some additional solutions, so I did the second test with the it and had the same result (in case I had done something brilliant, like pouring the leftover 100 into the 10 bottle).

I also tried it with a HACH kit, but messed it up (was reading from the 0-1ppm Nitrate-N instructions, not 1-10), however with some basic dilution, it looked pretty close (very close, actually). I'll try both again this weekend, as well as the 1ppm solution to see how it goes. The Lamotte kit only has one set of instructions, so I don't think I could make the same mistake... especially twice.

I'll also verify my reagents, but I believe I replaced them just a few months ago.

If anyone sees a mistake I made, please let me know. I'd love to find out my Lamotte is reading way too high...javascript:smilie('')


-Mike

 

[loudell]

Mike, FWIW you can not dilute the nitrate calibration matrix and use it with the nitrate meter. You may be able to use the diluted matrix with a color test kit, I can't say for sure, you may want to inquire with the manufacturer of the colormetric kit.

 

[mwitten]

<a href=showthread.php?s=&postid=9136857#post9136857 target=_blank>Originally posted</a> by loudell
Mike, FWIW you can not dilute the nitrate calibration matrix and use it with the nitrate meter. You may be able to use the diluted matrix with a color test kit, I can't say for sure, you may want to inquire with the manufacturer of the colormetric kit.

Good to know for sure... and makes sense. I was going to ask, since the refills come in 3 bottle sets, and (with luck) I won't be doing much in the high range, making the 100ppm "spare".

That Hach kit has separate instructions for the 1-10 range, which I'll follow when I re-try: I totally messed that one up, and was just trying to salvage it to some degree. My only point was that the Hach kit had the potential to agree better than the LaMotte kit did and, as I understand it, the methods they use are similar. I did not dilute the sample for the LaMotte kit test.

Thanks!

-Mike

 

[Randy Holmes-Farley]

The Hach kit should work diluted or not, as it is not intended only for salt water anyway, and the fact that it does work is good to hear, although not surprising.