Elemental analysis dissolved organic matter

Advantages Simultaneous analysis for several elements per rim Disadvantages Prior photolytic decomposition of dissolved organic matter required from many types of sample including seawater... 

Ag, Cl, and N to six-figure accuracy.1 This Nobel Prize-winning research allowed the accurate determination of atomic masses of many elements. In combustion analysis, a sample is burned in excess oxygen and products are measured. Combustion is typically used to measure C, H, N, S, and halogens in organic compounds. To measure other elements in food, organic matter is burned in a closed system, the products and ash (unburned material) are dissolved in acid or base, and measured by inductively coupled plasma with atomic emission or mass spectrometry. 

Seawater contains dissolved organic matter that may complex trace metals. The possible effects in the analysis depend on the method of analysis and the element itself In methods using a complexation step (AAS, ADPCSV) the naturally present ligand may inhibit the complexation reaction or part of it, thus causing an underestimation of the total amount of the element. The method used should therefore be tested for the complexation efficiency of the complexants used, for each element. Several proven methods have been used in the certification. Natural ligands also interfere in... 

Marine chemists have had limited success in characterizing the molecular structure of organic matter, particularly for the dissolved compounds. Chemical analysis usually starts with the isolation of POM from DOM using a filter with a 0.2-p,m pore size. This is generally followed by elemental analysis. More sophisticated approaches involve structural analysis, but this is usually limited to detection of functional groups or broad classes of compounds. 

Probably the simplest of all decomposition systems involves the heating of the sample in a silica or porcelain crucible in a muffle furnace in the presence of air at 400-800°C. After decomposition, the residue is dissolved in acid and transferred to a volumetric flask prior to analysis. This allows organic matter to be destroyed. However, the method may also lead to the loss of volatile elements, e.g. Hg, Pb, Cd, Ca, As, Sb, Cr and Cu. Thus, while compounds can be added to retard the loss of volatiles, its use is limited. Due to the disadvantages of this method, namely ... 

Each different physico-chemical form of an element has a different toxicity, so analysis of a water sample for the total metal concentration alone, e.g. Sn, does not provide sufficient information to predict toxicity. If the main species of a river water containing 40 /xg/1 dissolved copper is ionic Cu(II) few organism will survive, while the same amount Cu adsorbed on colloidal particles will have no or only little effect on aquatic life. The toxicity of many substances is thus modified by water quality. For example, heavy metals are usually more toxic to fish in soft water than in hard water. The presence of suspended organic matter, can affect the observed toxicity when pollutants are adsorbed or form complexes. This has been noted for pesticides and for heavy metals. 

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