title: State of the art in the determination of trace elements in seawater: a worldwide proficiency test.
abstract: This manuscript presents the results of the International Measurement Evaluation Programme 40 (IMEP-40) study, a proficiency test (PT) which was organised to assess the worldwide performance of laboratories for the determination of trace elements in seawater. This PT supports the implementation of the European Union Water Framework Directive 2000/60/EC, which aims at achieving a long-term high level protection of the aquatic environment, covering lakes, ground water and coastal waters. Forty-six participants reported results. The test item was seawater containing the trace elements As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Se and Zn. The trace elements in the test item were present in very low concentrations to mimic natural levels. The results of the participants were rated with z and zeta (ζ) scores in accordance with ISO 13528 and ISO 17043. The standard deviation for proficiency assessment, σ̂, was set at 25% of the respective assigned values for the 12 measured elements based on previous experience with similar PTs. The low levels of the trace elements combined with the high salt concentration of the seawater made the measurements challenging. Many laboratories were unable to detect or quantify the elements and reported "lower than X" values. The percentage of satisfactory performances (expressed as z scores) ranged from 41% (Cr, Fe) to 86% (Mo). The PT study showed that the use of proper standard methods, like ISO 17294-2, and sensitive techniques, like inductively coupled plasma mass spectrometry (ICP-MS), contributed to performing well in this PT round.
authors.affiliation: European Commission, Directorate General Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg 111, 2440, Geel, Belgium. pieter.dehouck@ec.europa.eu.
authors.forename: Pieter
authors.initials: P
authors.lastname: Dehouck
authors.affiliation: European Commission, Directorate General Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg 111, 2440, Geel, Belgium.
authors.forename: Fernando
authors.initials: F
authors.lastname: Cordeiro
authors.affiliation: European Commission, Directorate General Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg 111, 2440, Geel, Belgium.
authors.forename: James
authors.initials: J
authors.lastname: Snell
authors.affiliation: European Commission, Directorate General Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg 111, 2440, Geel, Belgium.
authors.forename: Beatriz
authors.initials: B
authors.lastname: de la Calle
keywords: Atomic absorption spectroscopy; Inductively coupled plasma mass spectrometry; Inductively coupled plasma optical emission spectrometry; Proficiency test; Seawater; Trace elements