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A multicommutated flow system was designed and evaluated for the determination of total arsenic and selenium by Hydride Generation Atomic Absorption Spectrometry (HG-AAS). It was applied to the determination of arsenic and selenium in samples of natural and drinking water. Detection limits were 0.46 and 0.08 μg l(-1) for arsenic and selenium, respectively; sampling frequency was 120 samples h(-1) for arsenic and 160 samples h(-1) for selenium. Linear ranges found were 1.54-10 μg l(-1) (R = 0.999) for arsenic and 0.27-27 μg l(-1) (R = 0.999) for selenium. Accuracy was evaluated by spiking various water samples and using a reference material. Recoveries were in the range 95-116%. Analytical precision (s ( r ) (%), n = 10) was 6% for both elements. Compared with the Standard Methods, APHA, 3114B manual method, the system consumes at least 10 times less sample per determination, and the quantities of acid and reducing agent used are significantly lower with a reduction in the generation of pollutants and waste. As an additional advantage, the system is very fast, efficient and environmentally friendly for monitoring total arsenic and selenium levels in waters.

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The use of zero-order and first-derivative flame emission spectrometry has been investigated for the determination of basal concentrations of lithium in serum and urine at the microgram dm-3 level. No significant matrix effect was observed; however, it was necessary to make use of background correction techniques. Two or three wavelength measurements and first-derivative spectrometry were used for this purpose; both methods gave similar results. Detection limits for serum of approximately 0.09 micrograms dm-3 were found by both zero-order and first-derivative emission measurements, while normal lithium levels were found to be 29.3 and 1.17 micrograms dm-3 for urine and serum, respectively.