Page 160 - Analytical method for food addtives

E249–50: Nitrites 105

Mobile phase Buffered acetonitrile at pH 6.5
UV 205 nm
Injection volume 40 µL (minimum)
Flow rate 1 mL/min
If other columns are used, adjust chromatographic conditions.

IC measurement
Inject the standard solutions first and then the blank and the sample test solutions
under the conditions as described above. One of the standard solutions should be
injected every five sample test solutions when performing a series of analyses. If
the peak obtained for the sample falls outside the range of the calibration graph,
dilute the sample test solution in the mobile phase and repeat the measurement step.
Identify the nitrate or nitrite peak by comparing the retention times for the standard
solutions and the sample test solutions. Read off the content of nitrate or nitrite of
the sample test solution from the calibration graph. Check the blank value to ensure
that there was no nitrate and/or nitrite contamination during the sample preparation.

Expression of results
–
Calculate the mass fraction of nitrite, W NO , expressed in milligrams of ion per
2
kilogram with equation [9.4]:
–
200 × A NO
2
–
W NO = ––––––––– × F [9.4]
2
m
where:
–
A NO is the value for nitrite, read off the calibration graph, in milligrams per litre
2
200 is the volume of the diluted test portion, in millilitres
m is the initial mass of the test portion, in grams
F is the dilution factor
Round the results without any decimals.
Calculate the mass fraction of nitrate, W – expressed in milligrams of ion per
NO
kilogram with equation [9.5]: 3
–
200 × A NO
3
–
W NO = ––––––––– × F [9.5]
3
m
where:
–
A NO is the value for nitrate, read off the calibration graph, in milligrams per litre;
3
200, m, F, see equation [9.4].
Round the result to the nearest whole number.
Precision: general
Details of the interlaboratory test of the method are summarised in Table 9.3. The
values derived from the interlaboratory test may not be applicable to analyte
concentration ranges and matrices other than those given in Table 9.3.