Page 166 - Analytical method for food addtives

E249–50: Nitrites 111

Preparation of calibration graph
Pipette 0 mL (zero member), then 2, 4, 6, 8, 12 and 20 mL of the sodium nitrite
standard solution into separate 100 mL volumetric flasks. Add water to each of the
flasks to obtain volumes of about 60 mL.
Proceed as specified under ‘Colour development and measurement’.
Measure the absorbances of the blank test solutions against that of the zero
member at a wavelength of 538 nm within 15 min. Plot the absorbances obtained
against the nitrite concentrations, in micrograms per millilitre, calculated from the
amounts of standard sodium nitrite solution added.

Calculation of the nitrite content
Calculate the nitrite content of the sample, W , using the following equation:
Ni

20 000×c
W = –––––––––– 1 [9.6]
Ni
m× V
where:
W is the nitrite content of the sample, in milligrams of NO per kilogram
Ni 2
c is the numerical value of the concentration read from the calibration graph,
1
corresponding to the measured absorbance of the test portion solution in
micrograms of nitrite ion per millilitre
m is the mass of the test portion in grams
V is the volume of the aliquot portion taken from the filtrate, in millilitres

Expression of results
Express the results to 1 decimal place.

Repeatability
The absolute difference between two single test results, obtained out simultaneously
or in rapid succession by the same operator under the same conditions on identical
test material, will in not more than 95 % of cases be greater than 1.0 mg/kg.
(For further information on this method see BS EN ISO 14673-1:2001.)

Method using segmented flow analyses 18

Preparation of test sample: cheese
Prior to analysis, remove the rind or mouldy surface layer of the test sample so as
to obtain a sample representative of the cheese as it is usually consumed. Grind the
test sample by means of an appropriate grinding device. Mix the ground mass
quickly and, if possible, grind it a second time and again mix thoroughly. Clean the
device after grinding each sample. If the sample cannot be ground, mix thoroughly
by intensive kneading. Transfer the test sample as soon as possible after grinding
into an airtight sample container. Close the container until the time of analysis. If
a delay after grinding is unavoidable, take every precaution to ensure proper