The use of sodium dithionite as the reducing agent to produce the radical cation of methyl viologen cofactor for the nitrate reductase-catalyzed reduction of nitrate to nitrite causes a negative interference in the diazonium salt azo dye determination of nitrite. The interference results from bisulfite, a reaction product of dithionite, reacting with the diazonium salt formed from nitrite and sulfanilamide. Addition of formaldehyde before the diazotization reaction masks this interference but at low acidity introduces a nonlinearity in the nitrite calibration curve. This nonlinearity is due to a competing reaction of formaldehyde with sulfanilamide to yield a Schiff base and can be eliminated by increasing the HCL content of the sulfanilamide reagent.
Bibliographical noteFunding Information:
This work was supported in part by Grant R-800858 of the Environmental Protection Agency and by Grant GM17913 of the National Institute of Health. It was taken in part from the Ph.D. dissertation of David R. Senn submitted to the Graduate School, University of Georgia. The use of facilities at the University of Georgia Fermentation Laboratory is gratefully acknowledged.