Lait 71 (1991) 87-97
DOI: 10.1051/lait:199117

Méthodes de dosage du zinc dans le lait humain

J. Arnaud^a, A. Favier^a and J. Alary<sup>b

a</sup>  CHRUG, Laboratoire de biochimie C, BP 217X, 38043 Grenoble Cedex
^b  Université Joseph Fourier, Faculté de pharmacie, laboratoire de chimie analytique, Domaine de la Merci, 38700 La Tronche, France

(Reçu le 26 août 1990; accepté le 16 novembre 1990)

Abstract - Zinc determination in human milk: comparison of different methods
Three flameless atomic absorption spectrometric methods for zinc determination in human milk, have been examined. Optimum analytical conditions were selected. The first was a direct method, using 1:99 milk dilution in Triton X 100 0.1% (w / v). Within-run and between-run precision were found to be 4.5% and 6%, respectively. Recovery of standard addition was found to be 103 ± 9%. Linear range was between 0.052 and 3 μmol.l^-1. In the second method, milk was submitted to wet ashing with concentrated nitric acid at 180 °C, prior to dilution in Triton X 100 0.1% (final dilution: 1:199, final nitric acid concentration: 0.3 mol.l^-1). Within-run and between-run precision were found to be 6%. Recovery of standard addition was 111 ± 5%. Linear range was between 0.017 and 1.5 μmol.l^-1. In the third method, milk was submitted to dry ashing at 400 °C; then ash was dissolved in nitric acid 0.1 mol.l^-1 (final dilution 1:99). Within-run and between-run precision were found to be 8 and 5%, respectively. Recovery of standard addition was 104.5 ± 5%. Linear range was found to be between 0.122 and 2 μmol.l^-1. Zinc content in different milks was determined by these 3 methods. Correlation coefficients were found to be 0.98 (methods 1 and 2) and 0.96 (methods 1 and 3). Linear regressions were Y = 0.93 X + 17 (Y = method 2, X = method 1) and Z = 0.79 X+ 4 (Z = method 3, X = method 1) (figs 5 and 6). Differences in milk zinc concentrations obtained with the 3 methods were not statistically significant (match Student's t-test). In conclusion, the authors found that the direct method was the most efficient for zinc determination in milk.

Résumé - Les auteurs ont optimisé et comparé 3 méthodes de dosage du zinc dans le lait humain par spectrométrie d'absorption atomique électrothermique. La première méthode est une méthode directe utilisant une simple dilution du lait humain dans une solution de Triton x 100 à 0,1% (p / v). La seconde utilise une minéralisation par voie humide en présence d'acide nitrique concentré, le minéralisat étant dilué dans la solution de Triton x 100 avant injection dans le four graphite. La troisième technique fait appel à une minéralisation par voie sèche à 400 °C, les cendres étant reprises par de l'acide nitrique 0,1 mol.l^-1. Ces 3 méthodes conduisent à des résultats comparables. La méthode directe, de praticabilité supérieure, est recommandée par les auteurs.

Key words: zinc / flame atomic absorption spectrometry / flameless atomic absorption spectrometry / milk / determination

Mots clés : zinc / spectrométrie d'absorption atomique en flamme / spectrométrie d'absorption atomique électrothermique / lait / dosage