Sediment Samples Used in the Interlaboratory Studies

The sediment sample used in the first interlaboratory trial was collected in Yrseke, The Netherlands, with grab samplers, wet sieved at 2 mm and air dried at room temperature (ca. 20 °C). The air-dried material was then ground, sieved at 90 pm and homogenized before bottling. The bulk homogeneity of the sediment was tested by X-ray fluorescence (XRF) by determining the major components. 

The sediment sample used in the second interlaboratory trial was collected in the River Besos, Spain. The material was sampled with a grab, air-dried, then sieved at 63 pm, homogenized and bottled. Homogeneity and stability studies of extractable trace metals were carried out and the material was found to be homogeneous and stable enough to be used in the intercomparison exercise [196]. 

The techniques used to determine metal concentration in extracts were generally FAAS (flame atomic absorption spectrometry) or ETAAS (electrothermal atomic absorption spectrometry). ICP-OES (inductively coupled plasma optical emission spectrometry) and ICP-MS (inductively coupled plasma mass spectrometry) were also used by some laboratories. 

Copper. A high spread of results was observed in both steps 1 and 2 for copper, which was suspected to be due to the final determination rather than to the extraction procedure itself. Ca interferences were suspected to occur at the emission line used in ICP (324.8 nm) by one laboratory however, two other laboratories used the same emission line and did not observe such interferences. The University of Barcelona tested the likelihood for such interferences at the emission line of 324.754 nm and the presence of a high background signal was observed, which was confirmed by the addition of Ca to the calibrant solutions. The copper content was actually considered to be close to the determination limits for a number of laboratories, and the accepted sets of results (6 ETAAS, 1 ICP and 1 ICP-MS) were too low to draw any firm conclusions on the state of the art of steps 1 and 2 in this material. 

In the case of step 3, the effects of shaking type and speed or room temperature on the spread of results were thoroughly discussed. Changes due 

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