Study of the stability of extractable phosphate content in a candidate reference material using a modified Williams extraction procedure

Extraction schemes have been widely used to study the environmental behavio ur of phosphate in soils and sediments. Owing to the variety of extraction methods, the results are not comparable, as they are highly dependent on th e procedure. Moreover, the lack of suitable reference materials for this ty pe of analysis makes it difficult to monitor the quality of measurements. I n 1996, the European Commission, within the Standards, Measurements and Tes ting Programme (formerly Community Bureau of Reference, BCR), started a pro ject to harmonise the methodology and to produce certified reference materi als. This paper presents the work carried out to prepare a sediment sample to be analysed using a modified Williams extraction procedure adopted by a group of European experts. The studies of homogeneity and stability with ti me of the extractable phosphate content in the sample are also reported.