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Atomic fluorescence (AFS) is used for determination of mercury after cold evaporation, and of selenium and arsenic after hydride generation. While fluorescence spectrometry uses light emission from atoms as in ICP-AES, this is not obtained by heat, but by light of a wavelength characteristic of the element. This light is absorbed by the atom and subsequently re-emitted. The technique is highly sensitive and achieves a detection limit at the ng/L level for mercury in water.
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GOLD TRAP
By means of an accessory the sensitivity of the fluorescence instrument can be further increased. Following cold vapour generation, the mercury vapour is collected in a gold trap, where it is amalgamated with gold. In the measurement step the gold trap is heated and the mercury vapour is transported to the AFS detector in a stream of argon.
AFS with gold trap is recommended when mercury is to be determined at or close to natural background levels in surface water, ground water, and sea water. We have experimentally determined the limit of quantitation (10s) to 0.27 ng/l.
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