Page 169 - Analytical method for food addtives

114 Analytical methods for food additives

Calculation of nitrate or nitrite content
Convert the result given by the recorder for the test portion to µg nitrate or nitrite
per mL read from the calibration curve of the standard solutions.
Calculate the nitrate or nitrite contents of the sample by using one of the
following equations:
For dried milk products: W = W × d × f [9.7]
n t d
For liquid milk products: W = W × 5 × f [9.8]
n t l
For cheese: W = W × 20.5 × f [9.9]
n t c
where:
W is the numerical value of the nitrate or nitrite content of the test sample, in
n
micrograms per kilograms
W is the numerical value of the amount of the nitrate or nitrite content of the
t
test portion read from the calibration curve, in micrograms per mL
d is the numerical value of the dilution factor
f is the multiplying factor for dried milk obtained by the following formula
d
(f = 20.6)
d

50 × 1.03 × 400
f = ––––––––––––
d 1000

f is the multiplying factor for liquid milk obtained by the following formula
1
(f = 5):
1

50 × 100
f = –––––––
l 1000

f is the multiplying factor for cheese obtained by the following formula
c
(f = 20.5):
c

50 × 1.025 × 400
f = –––––––––––––
c 1000

where:
50 is the conversion value to change the expression from mg per mL to mg per
50 mL
1.03 is the ratio of the volume of the test portion (2.5 g + 50 mL) and the volume
of the standard solutions (50 mL)
1.025 is the correction value for the moisture content of cheese (average moisture
content: 50 %)
400 is the conversion value to change the expression from 2.5 g to 1 kg
1000 is the conversion value to change the expression from µg to mg

Expression of results
Express the results for nitrite to 1 decimal place.