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The homogeneity and stability study of the candidate reference material is essential for the quality of reference material(certified reference material)used in quality control and quality assurance activities.In this presentation,homogeneity of four reference materials,more precisely,a candidate reference materials,and preliminary stability for total mercury content were carried out.The samples used in the study(a candidate reference materials)are part of the project MODAS.Final results of this project will be obtain a "package" certified reference materials,which can be regarded as a response to the needs of Polish analytical laboratories in the field of broader environmental analysis.Four of them(bottom sediment,herring tissue,codfish tissue,cormorant tissue)select characteristic for trophic chain of Polish marine ecosystem.The most important feature of the production is to be representative of the composition of both the matrix and the levels of total mercury in comparison to typical environmental samples tested in the Polish analytical laboratories.Cold Vapour Atomic Absorption Spectrometry technique has been used for mercury determination.This method has the advantage of achieving excellent precision under repeatability and reproducibility conditions.The experimental design and study using one way ANOVA showed no significant difference within and between bottle homogeneity and the material was found homogeneous.Total expanded uncertainty(k=2)due to heterogeneity for mercury does not exceed10%.The candidate reference material was found to be homogeneous up to the minimum sample size of 100 mg for total mercury content and is suitable for certification.