Chloride conservative element

S04 see Conservative Elements). The analytical results reported by W. Dittmar in 1884 for waters collected during the British RMS Challenger Expedition (1872-1876) from the world s oceans were almost the same as today s values. The constancy of major chemical composition has led oceanographers to define salinity as a fundamental property together with temperature to calculate the density of sea water. It was routine for classic physical oceanographers to titrate sea water for chloride (plus bromide) ion with silver nitrate standard solution, until the mid 1960s when salinity could be determined more practically by measurement of conductivity. 

An element that is relatively conservative through water-rock reaction is chlorine in the form of the anion chloride. Chloride is key in hydrothermal fluids, because with the precipitation and/or reduction of SO4 and the titration of HC03"/C03, chloride becomes the overwhelming and almost only anion (Br is usually present in the seawater proportion to chloride). Chloride becomes a key component, therefore, because almost all of the cations in hydrothermal fluids are present as chloro-complexes thus, the levels of chloride in a fluid efiectively determine the total concentration of cationic species that can be present. A fundamental aspect of seawater is that the major ions are present in relatively constant ratios—this forms the basis of the definition of salinity (see Volume Editor s Introduction). Because these constant proportions are not maintained in vent fluids and because chloride is the predominant anion, discussions of vent fluids are best discussed in terms of their chlorinity, not their salinity. 

Conservative, non-labile parameters such as toxic metals, chloride, water soluble boron, elemental sulfur are analysed on the air-dried sample (30 5°C) after crushing and grinding, whilst labile and more volatile substances are analysed on the as received sample and the results converted to an air-dried basis after air drying a representative separate aliquot of the sample. The sampling for these labile and more volatile substances in the as received sample is more prone to error (i.e. lower precision) than sampling an air-dried, crushed and ground sample but ensures that the analyses are fit for purpose with respect to bias. 

Only 11 elements can be considered major components of seasalt the cations sodium, potassium, magnesium, calcium and strontium, and the anions chloride, sulphate, bromide, hydrogen carbonate (carbonate), borate (borid acid) and fluoride. These major dissolved constituents (concentrations > 1 mg/kg in ocean waters) make up > 99 % of the soluble ionic species of seawater. The elemental ratios are relatively constant throughout the world ocean, and their concentrations change due to the addition or substruction of water only (concept of conservatism ). Therefore, it is possible to characterize the composition by determining only one constituent that is easy to measure and is conservative in its behaviour. An example is chlorinity (Cl, as defined in Section 11.2.4). 

Sodium and chloride are the major osmotic constituents of glomerular filtrate that need to be conserved by reabsorptive transport across the renal tubular epithelium. Double-barreled Cl -selective liquid ion-exchange microelectrodes were used to measure intracellular Cl concentration in single cellular elements of the proximal tubular epithelium. 

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