Estuarine reference material for trace elements: effect of flocculation upon homogeneity and stability

Abstract

Abstract In the course of a feasibility study to produce a reference material for trace metals in organic matter-rich estuarine water, particulate matter was formed after the originally 0.45 μm filtered water was stored for several months. This material, that was formed after acidification of the sample, does not contain substantial amounts of Fe or Mn, and is therefore attributed to precipitated humic acids. Although they do not interfere with the trace-metal analyses, these particulates are undesirable for the production of a reference material because of potential inhomogeneity. An operational scheme is proposed to minimize the flocculates in the reference material. The estuarine water samples collected proved to be satisfactorily homogeneous and stable with time for use as a potential reference material. Due to the organic matter in the estuarine water, an intercomparison exercise was less successful than a previous one in open seawater. These factors may hamper the analyses in any stored estuarine or coastal seawater.