Chemical Reference Materials Setting the Standards for Ocean Science (2002) / Chapter Skim
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From page 47... ...
47 4 Chemical Reference Materials for the Analysis of Particulate and Sediment Samples RATIONALE FOR SEDIMENT AND PARTICULATE MATTER ANALYSES Many of the analytes of interest for solid phase chemical reference materials are the same as those in seawater, but the need for and the preparation of reference materials for suspended particulate matter and sediments is quite different. The low concentrations of many seawater species and the presence of the salt matrix create particular difficulties for seawater analyses.
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From page 48... ...
48 CHEMICAL REFERENCE MATERIALS oxygen, nitrogen, sulfur, and phosphorus) make up essentially all the mass of marine organic matter and largely govern the processes by which these elements are cycled in the ocean.
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ANALYSIS OF PARTICULATE AND SEDIMENT SAMPLES 49 produces terrestrial matter with a δ13C value near –12‰, and other plants use both pathways (CAM plants) 1 (Deines, 1980)
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50 CHEMICAL REFERENCE MATERIALS tighter constraints on ocean mixing in global carbon cycle models (Guilderson et al., 1998, 2000)
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ANALYSIS OF PARTICULATE AND SEDIMENT SAMPLES 51 change in redox state during photosynthesis and remineralization and thus does not affect respiration demand. This revised formula corresponds to much lower hydrogen (8 wt percent)
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52 CHEMICAL REFERENCE MATERIALS tivity of higher trophic levels (e.g., micronekton and fish) in coastal, pelagic, and benthic habitats.
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ANALYSIS OF PARTICULATE AND SEDIMENT SAMPLES 53 TABLE 4.1 Examples of Microbial Biomarkers and Potential Source Organisms (Volkman, 1986; Ourisson et al., 1987; Ratledge and Wilkinson, 1988; Mayer et al., 1989; Conte et al., 1994; Jeffrey et al., 1997; Béjà, et al., 2000: Kolber et al., 2000; Madigan et al., 2000) Biomarker Potential Source Organism(s)
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54 CHEMICAL REFERENCE MATERIALS zooplankton grazing activity. Global maps of Chl a distribution are now available daily from satellite-based ocean color sensors such as SeaWiFS and MODIS.
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56 CHEMICAL REFERENCE MATERIALS 1984) indicate relatively undegraded organic matter.
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ANALYSIS OF PARTICULATE AND SEDIMENT SAMPLES 57 Radionuclides Measurements of radionuclides and metals in marine sediments and particulate matter are conducted for a variety of purposes, including the determination of sedimentation rates, trace metal and radionuclide fluxes through the water column, enrichment of metals in specific phases of the sediments, and examination of new sedimentary phases produced after sediment deposition. Such studies address fundamental questions concerning the chronology of deep-sea and near-shore sedimentary deposits, removal mechanisms and cycling of metals in the ocean, and diagenesis within deep-sea sediments.
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58 CHEMICAL REFERENCE MATERIALS Major Bio-organic Elements The organic carbon, hydrogen, and nitrogen content of marine samples is usually measured by quantitative combustion of a weighed amount of solid (or liquid) material into volatile gases whose concentration can then be measured in a CHN analyzer, equipped with a nonspecific thermal-conductivity detector.
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ANALYSIS OF PARTICULATE AND SEDIMENT SAMPLES 59 Carbon Organic carbon is by far the most commonly quantified organic element in marine samples, for which CaCO3 is the most typically encountered interference. This problem occurs because carbonates decompose upon heating, releasing CO2, the same gas that CHN analyzers measure after the oxidation of organic matter.
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60 CHEMICAL REFERENCE MATERIALS now be measured accurately for all major sample matrix types. Whether this is in fact the case across the oceanographic community is unknown because no intercomparisons have been reported for different mineral matrix types.
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ANALYSIS OF PARTICULATE AND SEDIMENT SAMPLES 61 different sediment types are preferably done on untreated samples (Gélinas et al., 2001b)
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62 CHEMICAL REFERENCE MATERIALS evolved oxygen compounds are converted over an activated carbon bed to CO, which is then measured with a thermal conductivity detector. In practice, this direct oxygen method is seldom used.
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ANALYSIS OF PARTICULATE AND SEDIMENT SAMPLES 63 Finally, but critically, the matrix of a sample can have a profound effect on measurements of individual organic molecules within it. Such matrix effects can take many forms and be complexly interrelated.
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64 CHEMICAL REFERENCE MATERIALS logue fingerprints) and of quantitative parameters (e.g., amounts, ages, and fluxes)
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ANALYSIS OF PARTICULATE AND SEDIMENT SAMPLES 65 Amino Acids Amino acids are generally considered to be labile and easily analyzed in most marine matrices. However, recent studies have shown that a significant percentage of the proteinaceous component of marine particulate matter is not accessible using traditional methods (Hedges et al., 2001)
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66 CHEMICAL REFERENCE MATERIALS technique involves direct measurement of gamma rays emitted during radionuclide decay. The interaction of these gamma rays with the sample is a function of the energy of the gamma-ray and the composition of the sample; low energy gamma rays are strongly absorbed by sedimentary minerals.
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From page 67... ...
ANALYSIS OF PARTICULATE AND SEDIMENT SAMPLES 67 however, lack precise measurements of the major bio-organic element compositions of the materials. The trace organic components that are certified, such as PAH, PCBs, pesticides, and hydrocarbons, do not constrain the concentrations of the organic elements.
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68 CHEMICAL REFERENCE MATERIALS TABLE 4.2 Selected Solid Reference Materials Currently Available from Canadian, U.S., and European Sources with Potential Utility for Marine Organic Studies (See Appendix E for information about obtaining these materials.) Identifier Type Matrix Source Selected materials distributed by the National Research Council of Canada (NRC)
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ANALYSIS OF PARTICULATE AND SEDIMENT SAMPLES 69 le from Marine g these Source Form Analyte %OC NRC) Beaufort Sea dry powder TE ~2 Esquimalt BC harbor dry powder TE ~3.3 Hibernia shelf, NFL dry powder TE ND Nova Scotia harbor dry powder PAH ND Nova Scotia harbor dry powder PAH ND Nova Scotia harbor dry powder PAH ND Nova Scotia harbor dry powder PAH ND U dry powder PAH ND Lake Huron water slurry PCB ND U dry powder TE ND U dry powder TE ND U water slurry TE ND U dry powder TE ND d Technology (NIST)
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70 CHEMICAL REFERENCE MATERIALS TABLE 4.3 Carbon Isotopic Composition of Selected Carbon–bearing Isotopic Reference Materials (Coplen et al., 2001) Identifier Substance δ13C Reference NBS 18 CaCO3 (carbonate)
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ANALYSIS OF PARTICULATE AND SEDIMENT SAMPLES 71 ter-comparisons, and help resolve inter-method variability during oceanographic expeditions. A variety of high quality, non-certified organic chemical standards are commercially available, e.g., from Alltech (fatty acids)
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72 CHEMICAL REFERENCE MATERIALS which 230Th, 226Ra, 232Th, 228Th, and numerous artificial radionuclides are certified, and which give non-certified activities of uranium isotopes, 210Pb, 228Ra, and additional artificial radionuclides. This reference material is a blend of sediments collected from both the Chesapeake Bay and from the seafloor off of the British Nuclear Fuels Sellafield facility in the United Kingdom.
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ANALYSIS OF PARTICULATE AND SEDIMENT SAMPLES 73 constituents, the greatest value will be derived by producing stable, homogeneous materials that can be used to derive community consensus values for many specific analytes. Further certification could then be accomplished as needed.
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74 CHEMICAL REFERENCE MATERIALS TABLE 4.5 Distribution of Mineral, Trace Metal, and Organic Analytes in the Target Biological Matrices Recommended as Reference Materials (+ = present and – = absent)
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ANALYSIS OF PARTICULATE AND SEDIMENT SAMPLES 75 Table 4.6 (opal, carbonate and aluminosilicate) were chosen to provide end members for matrix analysis.
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76 CHEMICAL REFERENCE MATERIALS 241Am, 90Sr, 239Pu, 240Pu, 137Cs, 129I, or 14C, which also lack solution standards. NIST has an active program to address the development of all of these radionuclide standards except 14C.
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