Page 154 - Analytical method for food addtives

E249–50: Nitrites 99

1 Nitrates and nitrites in meat, xylenol method. 3
4
2 Nitrites in cured meat, colorimetric method, and
3 Nitrate and nitrite in cheese, modified Jones reduction method. 5
These methods were developed in the early 1980s and there are no performance
characteristics available for them.
The European Standard specifies two methods for the determination of nitrite in
meat products:
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1 Spectrometric determination: Treatment in an aqueous extract of the analyti-
cal sample with sulphanilamide and N-(1-naphthyl)ethylenediammonium
dichloride to produce a red compound with spectrometric measurement of the
colour intensity of this red compound at 540 nm.
15
2 An ion-exchange chromatographic (IC) method: The extraction of nitrate
and nitrite is carried out with hot water. Any interfering substance is removed
by clarification with acetonitrile and subsequent filtration. The determination
is carried out by ion-exchange high performance liquid chromatography (IC)
and ultraviolet (UV) detection at a wavelength of 205 nm.
A summary of the procedure for these methods is given in Appendix 1 and the
performance characteristics are given in Table 9.3. NMKL have carried out
collaborative studies which show that the European Standard ENV 12014-4 is well
suited for the determination of nitrite and nitrate in different foods (e.g., meat
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products, vegetables, baby food and cheese). The performance characteristics are
given in Table 9.4.
The International Standard specifies three methods for the determination of
nitrite in milk and milk products.

2
1 Cadmium reduction and spectrometric determination: Test portion dispersed
in warm water, followed by precipitation of the fat and proteins, and filtration.
Reduction of the nitrate to nitrite in a portion of the filtrate by means of
copperised cadmium. Development of a red colour in portions of both unre-
duced filtrate and of the reduced solution, by addition of sulphanilamide and
N-1-naphthyl ethylenediamine dihydrochloride, and spectrometric measure-
ment at a wavelength of 538 nm. Calculation of the nitrite content of the
sample and of the total nitrite content after reduction of nitrate, by comparing
the measured absorbances with those of a set of sodium nitrite calibration
solutions.
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2 Segmented flow analysis method: Test portion suspended in an ammonium-
and sodium chloride solution. Transference of a part of this suspension to the
analyser. Dialysis of this suspension. Determination of the nitrite by a
spectrometric method. Determination of the standard nitrite solutions by the
same procedure. Calculation of the nitrite content by comparing the reading
obtained from the test portion with the readings of the standard solution.
3 Flow injection analysis with in-line dialysis: Test sample suspended in warm
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extraction buffer. Separation of fat by centrifugation and rapid cooling.
Analyses of small portions of the de-fatted suspension by flow injection