Evidence is presented to support the theory that the formation of atoms of noble metals during carbon furnace atomisation proceeds via direct evaporation of the metal. The evidence includes (i) thermogravimetric investigation of noble metal salts and their aqueous solutions in an argon atmosphere, (ii) X-ray diffraction studies of the residues formed on heating aqueous solutions of some noble metal salts in a carbon furnace atomiser and in the microfurnace of a thermobalance, (iii) measurements of the appearance temperatures of noble metals in a carbon furnace atomiser using aqueous solutions and vacuum-deposited metal films and (iv) activation energies, Eg, and vapour pressure data relating to noble metals at elevated temperatures.Experimental conditions giving the best sensitivity for the determination of seven noble metals (osmium was not detected) in the Perkin-Elmer HGA-74 carbon furnace atomiser are presented. On the basis of a 20-p1 sample volume these gave sensitivities (1% absorption) of 0.019, 0.0058, 0.0045, 0.00021, 0.038, 0.023 and 0.00089 pg ml-l for ruthenium, rhodium, palladium, silver, indium, platinum and gold, respectively.

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An investigation of interferences in the determination of iron by atomicabsorption spectrophotometry in an airacetylene flame is reported. It has been found that three elements, cobalt, nickel and copper, exhibit serious depressive effects, the magnitude of which is strongly dependent on the flame conditions, with respect to both fuel-to-air ratio and the height of the optical path above the burner, and is also dependent on the anion present in the sample solution. The optimisation of the flame for both pure iron solutions and those containing the interfering elements, and means of suppressing these interferences, are discussed. The use of 8-hydroxyquinoline a t a concentration equal to or greater than the total concentration of cobalt, nickel and copper is recommended as an effective releasing agent.

It has been suggested that, for injected solutions prepared in the absence of halides, i.e., in oxyanion media, metal atoms are formed during carbon furnace atomisation by thermal dissociation or carbon reduction of metal ~x i d e s . l -~ In some instances, a solid or liquid metal phase may occur as an intermediate on the surface of the atomiser before volatilisation of the metal

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