We have studied the contents of trace elements of nutritional or
toxicological interest in 90 samples of whole, low-fat, skim, condensed, evaporated
and powdered milks. Slurries of the samples were prepared with Triton X-100 and
analysed using electrothermal atomic absorption spectrometry. The temperature–time
programme of the graphite oven was optimized for each element, and the
accuracy, precision, selectivity and sensitivity of the method were verified.
Concentrations of the trace elements we investigated were: Pb 0–0·211 μg/g, Cd
0–28·985 ng/g, Al 0·528–4·025 μg/g,
Cu 0·041–0·370 μg/g, Cr 0–0·177 μg/g, Mn
0·024–0·145 μg/g, Se 0–237·333 ng/g,
Zn 0·297–0·827 μg/g and Ni 0·058–1·750 μg/g.
(A value of zero indicates that the element was undetectable by our methods.)
Concentrations of the pairs of elements Cu–Cd, Mn–Cd, Mn–Cu,
Zn–Mn, Ni–Cu, Ni–Mn and Ni–Zn were significantly
correlated (P<0·001). Linear discriminant
analysis confirmed the separation between the six types of milk analysed.