Statistical analysis was used to select internal standards in order t o improve the precision and accuracy of multi-element atomic emission spectrometry (AES) under various matrix conditions. The process of sample vaporisation f r o m a carbon arc electrode was investigated. The similarity in behaviour of the analyte elements was found to be reduced at the late vaporisation stages. Model calculations of vapour diffusion and experimental measurements of element accumulation in the electrode body (walls and base) were used to explain this effect. The investigations showed that a possible cause of the reduced effectiveness of an internal standard was sorption in the electrode. A criterion for selecting internal standards, based o n measurement of the average signal delay of curve I(t), was proposed for increasing the efficiency of internal standardisation. It was applied to techniques used for the determination of trace elements in rocks and environmental samples. Keywords : M ulti-elem en t a tom ic emission spec from e tric analysis; in te rna I standard; average signal delay; diffusion into carbon arc electrode Internal standardisation is an often used technique for

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