Abstract
An improved gas sheathed cell for the cold-vapour determination of mercury by atomic fluorescence spectrometry is described. Mercury ions in aqueous solution are reduced by tin(II) chloride, and the mercury flushed from solution by argon is discharged from a tube situated adjacent to the spectrometer entrance slit and a mercury electrodeless discharge lamp. A second stream of argon is directed up small capillaries arranged around this outlet tube to provide a laminar sheath of argon around the atom cell. At optimised flow rates, the signal is about 10 times greater than when no laminar sheath is provided. Precision is also improved. The limit of detection (2σ) is 0.01 ng of mercury for a 0.5-ml aliquot of sample (i.e. 20 ng 1 -1). The accuracy of the system is demonstrated by the determination of mercury in NBS Orchard Leaves and in barley seeds. Typically relative standard deviations are in the range 0.6–3%.
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