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.

We measured daily dietary Cr intake in southern Spain by sampling duplicate diets for seven consecutive days in different population groups. Cr was determined by electrothermal atomization±atomic absorption spectrometry. The samples were mineralized in a digestion block with HNO 3 , HClO 4 and V 2 O 5 . A total of 161 duplicate diets from twenty-three subjects were analysed, and mean levels of Cr intake ranged from 9´39 to 205´16 mg/d. Mean Cr intake (100 mg/d) was similar to levels found for most other countries, and was within the range recommended by the National Research Council for a safe and adequate daily intake (50±200 mg/d). Chromium intake correlated significantly with energy, protein and carbohydrate intake, and with the daily intake of Zn, Fe, Mg, K, Na, Ca and nicotinic acid in the diets analysed.

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An in vitro method was used to study the dialysable fraction of chromium (Cr) from the diet which simulates human gastric and intestinal digestion. The percentage of dialysed Cr was used to assess the bioavailability. The duplicate diet approach was used to obtain ten different sets of samples each representative of the normal diet consumed in southern Spain. In each case triplicate analysis of Cr was carried out by electrothermal atomization-atomic absorption spectrometry in acid-mineralized samples. The Cr dietary intake ranged from 16 to 117 microg/day, and the dialysable Cr fraction ranged from 0.4% to 1.6%. The Cr absorption was higher for low levels of daily dietary intake of Cr (< 40 microg) than for levels of 40-80 microg; for high levels (> 80 microg) there was an increase in the dialysable fraction. The energy and nutrient intake of these diets was also evaluated.