EPA lists 38 approved nitrate methods in its EPA 815-B-16-014 Methods document. Most are overlapping.  I have no idea which Evirolyzer uses. If they won't help you get another one.

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EPA lists 38 approved nitrate methods in its EPA 815-B-16-014 Methods document. Most are overlapping.  I have no idea which Evirolyzer uses. If they won't help you get another one.