Dissolved organic carbon (DOC), sometimes known as dissolved organic material (DOM), is a broad classification for organic molecules of varied origin and composition within aquatic systems. The "dissolved" fraction of organic carbon is an operational classification. Many researchers use the term "dissolved" for compounds below 0.45 micrometers, but 0.22 micrometers is also common, saving colloidal for higher concentrations. A practical definition of dissolved typically used in marine chemistry is all substances that pass through a GF/F filter. The recommended measure technique is the HTCO technique after filtration on precombusted glass fiber filters, typically GF/F filters.
Dissolved organic carbon in marine and freshwater systems is one of the greatest cycled reservoirs of organic matter on Earth, accounting for the same amount of carbon as the atmosphere and up to 20% of all organic carbon. The source of dissolved organic carbon depends on the body of water. In general, organic carbon compounds are a result of decomposition processes from dead organic matter such as plants or marine organisms. When water originates from land areas with a high proportion of organic soils, these components can drain into rivers and lakes as dissolved organic carbon.
Dissolved organic carbon is also extremely important in the transport of metals in aquatic systems. Metals form extremely strong complexes with dissolved organic carbon, enhancing metal solubility while also reducing metal bioavailability.
Determination of Fe (TDi) by flame AAS or ICP-OES or photometry
Potassium is a chemical element with symbol K (from Neo-Latin kalium) and atomic number 19. It was first isolated from potash, the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals. All of the alkali metals have a single valence electron in the outer electron shell, which is easily removed to create an ion with a positive charge – a cation, which combines with anions to form salts. Potassium in nature occurs only in ionic salts. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction and burning with a lilac-colored flame. It is found dissolved in sea water (which is 0.04% potassium by weight), and is part of many minerals.
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