DIY NITRATE TEST METER

Randy Holmes-Farley · Oct 18, 2017

Rick Mathew said:
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

I'm not sure how sensitive it is to chloride levels, and whether it is a fixed offset (e.g., always 2 ppm low with a given chloride difference) or percentage offset (always 98% of the actual value with a given chloride difference).

Rick Mathew · Oct 18, 2017

Randy Holmes-Farley said:
I'm not sure how sensitive it is to chloride levels, and whether it is a fixed offset (e.g., always 2 ppm low with a given chloride difference) or percentage offset (always 98% of the actual value with a given chloride difference).

Might be worth my time to check that out by running the same test at different salinity levels...also here are my results comparing RODI and saltwater as the diluent...looks as if they both have the same issue below 3ppm...this might be an issue with the measurement instruments at that low level and the slope of the adsorption curves. the measurement wavelength might be the problem...the Hanna Nitrate meter measures at 525 the same as the Iron Checker (HI-721) but the checker is most likely less sensitive than the Nitrate Spectrometer...Interestingly the raw data in the RODI samples appears to be less repeatable than the saltwater...have not had a change to really take a hard look and analyze the data statistically but will explore this later..will keep you posted...in the mean time I am going to proceed with my best model and do measurements and validate as I can...I will work on tweaking the model mathmatically...might consider two models...one for 0-4 ppm and another for > 4 ppm

Thanks again for your help

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kecked · Jun 7, 2018

Any new news on this? I just picked up an ocean optics hr2000 and was going to try this out. I figured to just measure the absorbance and plot it out with a known salt concentration and then run my samples. I'm looking for gross 0, 1, 5, 10 ppm levels. I can't tell by eye the color change so for me it's a ballpark test to confirm what I THINK I see. Would be nice if someone could make this work to the 1ppm level. That's good enough for what we do. Heck 2ppm is good enough.

Since I have 200-1100nm I'll see if I see a less affected absorption band fresh vs salt. I also wonder if we can scavenge the chloride out by using one more step but what ion to replace it with that will not also affect the test. Lead would work to pull the chloride but I would not suggest it as a hobby reagent and you would have to filter. AND dispose as haz waste.

Rick Mathew · Jun 7, 2018

kecked said:
Any new news on this? I just picked up an ocean optics hr2000 and was going to try this out. I figured to just measure the absorbance and plot it out with a known salt concentration and then run my samples. I'm looking for gross 0, 1, 5, 10 ppm levels. I can't tell by eye the color change so for me it's a ballpark test to confirm what I THINK I see. Would be nice if someone could make this work to the 1ppm level. That's good enough for what we do. Heck 2ppm is good enough.

Since I have 200-1100nm I'll see if I see a less affected absorption band fresh vs salt. I also wonder if we can scavenge the chloride out by using one more step but what ion to replace it with that will not also affect the test. Lead would work to pull the chloride but I would not suggest it as a hobby reagent and you would have to filter. AND dispose as haz waste.