title: Assessment of relative accuracy in the determination of organic matter concentrations in aquatic systems.
abstract: Accurate determinations of total (TOC), dissolved (DOC) and particulate (POC) organic carbon concentrations are critical for understanding the geochemical, environmental, and ecological roles of aquatic organic matter. Of particular significance for the drinking water industry, TOC measurements are the basis for compliance with US EPA regulations. The results of an interlaboratory comparison designed to identify problems associated with the determination of organic matter concentrations in drinking water supplies are presented. The study involved 31 laboratories and a variety of commercially available analytical instruments. All participating laboratories performed well on samples of potassium hydrogen phthalate (KHP), a compound commonly used as a standard in carbon analysis. However, problems associated with the oxidation of difficult to oxidize compounds, such as dodecylbenzene sulfonic acid and caffeine, were noted. Humic substances posed fewer problems for analysts. Particulate organic matter (POM) in the form of polystyrene beads, freeze-dried bacteria and pulverized leaf material were the most difficult for all analysts, with a wide range of performances reported. The POM results indicate that the methods surveyed in this study are inappropriate for the accurate determination of POC and TOC concentration. Finally, several analysts had difficulty in efficiently separating inorganic carbon from KHP solutions, thereby biasing DOC results.
authors.affiliation: US Geological Survey, Boulder, CO 80303, USA. graiken@usgs.gov
authors.forename: George
authors.initials: G
authors.lastname: Aiken
authors.forename: Louis A
authors.initials: LA
authors.lastname: Kaplan
authors.forename: James
authors.initials: J
authors.lastname: Weishaa
mesh_terms: D004784:Environmental Monitoring / Q000379:methods*; D019983:Guideline Adherence; D006812:Humic Substances / Q000032:analysis; D009930:Organic Chemicals / Q000032:analysis*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis; D010316:Particle Size; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012995:Solubility; D014871:Water Microbiology; D014881:Water Supply
chemical_list: D006812:Humic Substances; D009930:Organic Chemicals; D010100:Oxygen