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Re: NO3 testing
<<Nitrate test kits do not measure nitrate directly. The first step is to
reduce nitrate to nitrite. It is the nitrite that actually forms the color.
The 10-20 minute waiting period is to allow sufficient time for the nitrate
in your sample to be fully reduced. --Bill >>
Yes, in fact LaMotte tells you that you would first have to perform a step
to get rid of any nitrite before measuring the nitrate. Of course we plant
folks (correctly) assume there isn't appreciable nitrite around. From the
LaMotte site about their various nitrate kits: "The nitrate is reduced to
nitrite by cadmium or zinc and this undergoes diazotization/coupling to
form a pink color. All kits below use cadmium except #3354, which uses zinc
and which also contains a reagent that eliminates nitrite interference. Kit
#3519 tests both nitrate and nitrite"