Page 158 - Analytical method for food addtives

E249–50: Nitrites 103

nitrate, (in 200 mL solution), in milligrams of nitrite ion.

Determination of nitrite content
Mix 2.0 mL of the sample solution in a cell with 1.0 mL of water and 3.0 mL of the
colour reagent mixture and allow to stand in the dark at room temperature. After 30
in a spectrometer at a wavelength of 540 nm
min, measure the absorption A NO 2
against water.
Determination of the total nitrite/nitrate content
Introduce 0.2 mL of the NADPH solution, 2.0 mL of sample solution and 0.8 mL
of nitrate reductase buffer solution into a test tube, mix thoroughly and allow to
stand for 1 h at room temperature. Then add 3.0 mL of the colour reagent mixture,
shake and store the solution in the dark at room temperature. After 30 min, measure
at a wavelength of 540 nm in a spectrometer against water.
the absorption A NO 2 +NO 3
Calculation of the nitrite content
Read off the absolute amount of nitrite, X NO , corresponding to the absorption
2
value A NO determining nitrite without reduction step from the nitrite calibration
2
graph.
Calculate the mass fraction, W NO , in milligrams per kilogram of nitrite ion in
2
the sample using equation [9.1]:

X NO 2 × 1000
W NO = ––––––––––– [9.1]
2 m

where:
is the absolute amount of nitrite (in 200 mL solution) without reduction
X NO
2
step, in milligrams, read off from the calibration graph
m is the mass of the test portion, in 200 mL of the sample test solution, in
grams
Calculation of the total nitrite/nitrate content
Read off the amount of the absorption value A NO +NO determining total nitrite/
2 3
nitrate with reduction step from the nitrate calibration graph as nitrite ion.
Calculate the mass fraction, W NO +NO , in milligrams per kilogram, of total
2 3
nitrite/nitrate as nitrite ion in the sample using equation [9.2]:

X NO +NO × 1000
2
3
W NO +NO = –––––––––––––– [9.2]
2 3 m

where:
is the absolute amount of total nitrite/nitrate (in 200 mL solution)
X NO +NO
2 3
expressed as nitrite ion after the reduction step, in milligrams, read off
from the calibration graph
m is the mass of the test portion, in 200 mL of the sample test solution, in
grams