The U.S. Geological Survey (USGS), American Society for Testing and Materials (ASTM), and U.S. Environmental Protection Agency (EPA) have validated the enzymatic nitrate analysis method to be used in certified laboratories. This method has been simplified into various kits, providing accurate and reliable nitrate results.


Enzyme-Based Reductase Could Replace Cadmium in Nitrate Testing, WaterWorld, March 7, 2015, viewed by visiting: 
http://www.waterworld.com/articles/print/volume-22/issue-3/product-focus/enzyme-based-reductase-could-replace-cadmium-in-nitrate-testing.html


Enzymatic method for nitrate-nitrite determination by nitrate reductase is now an ASTM standard method.  This active standard, ASTM D7781 is now available for purchase directly from ASTM.  This method replaces Test Methods D1254 (Nitrite) and D992 (Nitrate), which use "a reagent that is considered to be a potential carcinogen" (ASTM Significance and Use 5.1).  This information may also be viewed by visiting:: http://www.astm.org/Standards/D7781.htm


Enzymatic Method for Determining Nitrate in Wastewater Reaches First Step Toward EPA Approval, Environmental Protection, May 05, 2014, viewed by visiting: http://eponline.com/articles/2014/05/05/enzyme-based-nitrate-analysis.aspx


Above information is courtesy of NECi (The Nitrate Elimination Company, Inc.)