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A multicommutated flow system was designed and evaluated for the determination of selenium by hydride generation atomic absorption spectrometry (HG-AAS). It was applied to the determination of total selenium in samples of cow's milk (fluid and powder) and infant formulae. Linearity was satisfactory in the range up to 27.5 mg L À1 (h ¼ 0.082 C + 0.0033, h ¼ peak-height, absorbance, C ¼ concentration in mg L À1 , r 2 ¼ 0.999). Detection (3s) and quantification (10s) limits in solution were LD ¼ 0.08 mg L À1 and LQ ¼ 0.27 mg L À1 , corresponding to LD ¼ 3.2 mg kg À1 and LQ ¼ 10.8 mg kg À1 in solid samples, and to LD ¼ 0.8 mg L À1 , LQ ¼ 2.7 mg L À1 in fluid milk samples. Trueness was verified by analysis (n ¼ 5) of two reference materials (NIST 1549, Non-fat Milk Powder and NIST 1846 Infant Formula). At the 95% significance level, results were statistically equivalent to the certified values. Instrumental precision (s r (%), n ¼ 5) was in the range 1.4% to 11.7%, analytical precision (s r (%), n ¼ 5) being 4.2 and 9.3% respectively for the determination of the above mentioned reference materials. The sampling frequency of the system was 160 hour À1 .

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