HI782 Reagent Issue

[JinWu]

I wanted to see if my HI782 was accurate, so I conducted a small experiment, and the results were quite interesting.
I used 9.5 mL of the ASTM D1141 standard solution and added 0.5 mL of a 100 mg/L NO3-N standard solution; the theoretical NO3 concentration of the resulting mixture should be 22.13 ppm.However, the HI782 yielded a reading of only 16.3. Is this reading normal? It looks like it far exceeds the margin of error allowed for the HI782.

 

[Randy Holmes-Farley Verified Community Expert]

I think perhaps your expectations of accuracy exceed what we usually get. lol

The Hanna estimates of accuracy assume, IMO, everything is perfect.

 

[JinWu]

I conducted another experiment afterwards, replacing 9.5ML of artificial seawater with RO water, and the reading soared directly to 33.5ppm. This reagent seems to be significantly affected by chloride ions in water

 

[Randy Holmes-Farley Verified Community Expert]

I conducted another experiment afterwards, replacing 9.5ML of artificial seawater with RO water, and the reading soared directly to 33.5ppm. This reagent seems to be significantly affected by chloride ions in water

Why think it is chloride and not things like alkalinity impacting the pH? Chloride should not react with the reducing agents in a nitrate test.