To measure total nitrate/nitrite concentration of the sample,
after proportional dilution of
filtrate (if needed), VCl3 and Griess
reagents were added to
filtrate; the volumetric
flask was incubated
at 37 C for 180 min and then the absorbance was read at 538 nm
using ELISA reader. To optimize the reaction of nitrate to nitrite
reduction, different amounts of VCl3, and a range of various time
and temperature conditions were evaluated. To consider maximum
reduction, color stability and reaction time simultaneously, a
temperature of 37 C and a duration of 180 min, respectively were
selected