Concentration in sea water

The quantitative determination of surfactant concentration in solution is an essential part of any experimental work on surfactant adsorption or phase behaviour. In the field of experimental enhanced oil recovery the technique employed should be capable of determining surfactant concentrations in sea water, and in the presence of oil and alcohols, the latter being frequently added as a co-surfactant. 

The conditions for reliable cyclic voltametry determination of trace Sn concentrations in sea water were investigated. All organotin compounds should be converted to Sn(II) by UV-photolysis adsorption on mercury drop in the presence of 40 pM of tropolone (1) cyclic voltametry stripping shows two cathodic peaks, corresponding to the two-step process Sn(IV) — Sn(II) -> Sn(0)29. A complex of Sn ions with catechol can be accumulated in a glassy carbon mercury film electrode, followed by stripping voltametry measurement in the cathodic direction, at pH 4.2-4.7. Interference occurs when Cu, Cd and Cr are present LOD 0.5 pg/L for 300 s accumulation30. 

According to this equation an 0 increase of 0.26%c in carbonate represents a 1°C temperature decrease. Bemis et al. (1998) have re-evaluated the different temperature equations and demonstrated that they can differ as much as 2°C in the temperature range between 5 and 25°C. The reason for these differences is that in addition to temperature and water isotopic composition, the 5 0 of a shell may be affected by the carbonate ion concentration in sea water and by photosynthetic activity of algal symbionts. 

Calcium chloride may be found in nature as the mineral tachhydrite, CaCb 2MgCl2 I2H2O. It also is found in other minerals. Its concentration in sea water is about 0.15%. 

The element was discovered by Klaproth in 1803 and also in the same year by Berzelius and Hisinger. It is named after the asteroid Ceres. Cerium is found in several minerals often associated with thorium and lanthanum. Some important minerals are monazite, aUanite, cerite, bastnasite, and samarskite. It is the most abundant element among aU rare-earth metals. Its abundance in the earth s crust is estimated to be 66 mg/kg, while its concentration in sea water is approximately 0.0012 microgram/L. 

Chromium occurs in the minerals chromite, Fe0 Cr203 and crocoite, PbCr04. The element is never found free in nature. Its abundance in earth s crust is estimated in the range 0.01% and its concentration in sea water is 0.3 qg/L. The element was discovered by Vaquelin in 1797. 

Gadolinum is found in minerals bastnasite and monazite, always associated with other rare earth metals. It was isolated from yttria in 1880 by the Swiss chemist Marignac, and discovered independently in 1885 by Boisbaudran. It was named in honor of the Swedish chemist Gadolin. Its abundance in the earth s crust is 6.2 mg/kg and concentration in sea water is 0.7 ng/L. 

GaUium is widely distributed in nature, mostly found in trace amounts in many minerals including sphalerite, diaspore, bauxite, and germanite. It is found in aU aluminum ores. Gallium sulfide occurs in several zinc and germanium ores in trace amounts. It also is often found in flue dusts from burning coal. Abundance of this element in the earth s crust is about 19 mg/kg. Its average concentration in sea water is 30 ng/L. 

Hafnium was discovered in 1922 by Coster and deHevesy. They named it for Hafnia, the Latin word for Copenhagen. It is found in aU zirconium ores, such as zircon, (ZrSi04) and baddeleyite (Zr02). It occurs in the earth s crust at about 3 mg/kg. Its average concentration in sea water is 7 ng/L. 

The element does not occur in nature in native form. Its principal mineral is cinnabar, the red mercuric sulfide, HgS. Black mercuric sulfide, metacinnabar, also is found in nature. Other ores are hvingstonite, HgSh4S coloradite, HgTe tiemannite, HgSe and calomel, HgCl. Its concentration in the earth s crust is estimated to be 0.08 mg/kg. The average concentration in sea water is about 0.03 ag/L. 

The abundance of niobium in the earth s crust is estimated to be in the range 20 mg/kg and its average concentration in sea water is 0.01 mg/L. The metal also is found in the solar system including the lunar surface. Radionucleides niobium-94 and -95 occur in the fission products of uranium-235. 

Zinc occurs in nature, widely distributed. The principal ores are sphalerite (and wurtzite) known as zinc blende, ZnS gahnite, ZnAl204 calamine smith-sonite, ZnCOs franklinite, ZnFe204 and zincite, ZnO. Abundance in earth s crust is about 70 mg/kg and average concentration in sea water is about 10 pg/L. 

Bromine from Sea Water. Balard recognized in 1826 that bromine is present in low concentration in sea water. Professor Gmelin of Tubingen detected it in water from the Dead Sea, a discovery which was promptly confirmed by S. F. Hermbstadt of Berlin (149). In 1934 the Dow Chemical Company successfully extracted bromine commercially from raw ocean water at Kure Beach, North Carolina (150). 

There is another immense reservoir of the precious metal the oceans. Sea water contains a tiny ten parts per trillion of gold, hundreds of times less than the crust. Even so, this implies that an awesome ten million tonnes are dispersed through the world s oceans a prize worth over 1,500 trillion to anyone who can claim it. But it would be easier to risk the hazards of Jason s mythic quest, for it is hard to imagine how such low concentrations could ever be harvested at a profit. The German chemist Fritz Haber once believed that he could do so, and that the rewards would pay off the reparations imposed on his country after the First World War. Haber turned out to be just another of those dazzled by gold s bright charms, for he had overestimated its concentration in sea water a thousandfold. 

In the past three decades, it has become clear that a rather large amount of surface-active organic material ends up in each tiny droplet ejected into the air by bursting bubbles. Some of these materials may reach concentrations in (or on) the droplets well over a thousand times their bulk concentrations in sea water (ref. 46,85,92). The water in the droplets that remain airborne eventually evaporates, leaving the nonvolatile materials to float around in the atmosphere (ref. 46) and ultimately settle out and, as a result, contribute appreciably to soil nutrients (ref. 93-95). 

Turner, S.M., Nightingale, P.D., Spokes, L.J., Liddicoat, M.I. and Liss, PS. (1996) Increased dimethyl sulfide concentrations in sea-water from in-situ iron enrichment. 

Figure 4.5 A section of 3He concentrations in sea water over the East Pacific Rise at 15°S. The contour labels are 3He ratio anomalies [Equation (4.7)] in percent. Reproduced from Lupton and Craig (1981).

The procedure used was to determine the concentration of dissolved oxygen (02) with an 02-electrode63. A (linear) calibration curve was prepared of current (due to the response of the 02-electrode) vs. oxygen concentration in sea water ranging from fully deaerated to saturation at an 02 pressure of one atmosphere. 

Samples were collected from the FRV Walther Herwig at one control site and at four locations in the area of the two main subsites. The results show enhancements of 5-7 times in the Pu concentrations in sea water collected at the dumpsites relative to those at the control site. " Am, Cs and C are also higher in some dumpsite... 

In practice, W is directly inferred from heat flow and chemical mass balances. Warm hydro-thermal flow is a major sink for dissolved oceanic The Mg + in the warm hydrothermal fluid is removed quantitatively by reaction with basalt. Because the flux of Mg + into the ocean in river waters and the competing sinks (e.g. clays) can be estimated, the known Mg + concentration in sea water can be used to determine W. This argument is independent of CO2. 

The lithium concentration in sea water is almost constant according to Table 1 the concentration amounts to 0.173 mg/1, however, the total quantity occuring in sea water is trehiendous and estimated to be 2.4 x 1011 tons. 

The oceans contain about 4.5 billion tons of dissolved uranium, almost a thousandfold of the reasonably assured and estimated terrestrial uranium resources in the western world 101). The concentration of uranium in sea water appears to be remarkably constant at about 3.3 pg/liter 120-122). Very recent measurements of uranium concentrations in sea water samples taken in the Arctic and South Pacific Ocean down to depths of more than 5000 m confirm this mean value 123). However, with increasing salinity of sea water a slight increase of uranium concentration is observed 124). The molar concentration of uranium in sea water is nearly 8 orders of magnitude lower than the total concentration of the major ions 125). Marine uranium displays no detactable deviation from the normal terrestrial U-235/U-238 isotope ratio, 03>126). 

Sea water is actually a very low grade uranium source, however, the advantage of the dissolved state and the almost inexhaustible quantities of uranium should be kept in mind. Moreover, it should be emphasized that the uranium concentration in sea water is relatively high compared to other heavy metals as for instance gold or thorium. Common metals like chromium, manganese, copper, or cobalt occur in sea water in lower molar concentrations than uranium (Table 1). 

Here the discussion focuses on the analytical procedure adopted to determine trace metals concentration in sea water in the dissolved phase. Particular attention will be given to the procedures preceding the analytical measurement (sampling, sample treatment and storage), the analytieal determination of total concentration by DPASV and Inductively Coupled Plasma Mass Speetrometry (ICP-MS) the contamination control procedure will also be discussed. The direct DPASV procedure for determining metal complexation in sea water is reported in detail and after a discussion of theoretical aspects an outline of the experimental procedure is presented. Finally, an overview of the distribution in the Southern Ocean of some metals of particular interest is examined and the evaluation of traee metals distribution is carried out also by comparison with results obtained in different geographical areas. 

DPASV equipped with the Thin Mercury Film Electrode (TMFE) plated onto a Rotating Glassy Carbon Disc Electrode (RGCDE), is one of the most sensitive and powerful techniques at present available for the determination of ultra-trace metals in real time samples (59, 60). Cadmium, Cu, Pb and Zn are the most frequently determined metals at subnanomolar or even picomolar concentration in sea water, without any preconcentration step (17, 61, 62), but other elements can also be determined (63-66). Detection limits lower than 0.5 ng/1 are normally reached (17, 60). 

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