Salinity determination

Figure 8,12 Salting-out phenomenon for aqueous CO2. Activity coefficient of neutral species increases with increasing salinity, determining decreased solubility of aqueous CO2 in water, T and P conditions being equal. Reprinted from Garrels and Christ (1965), with kind permission from Jones and Bartlett Publishers Inc., copyright 1990.

In natural systems therefore part of the complexation capacity might be caused by colloidal material. This was demonstrated in experiments on the complexation capacity of samples from the Scheldt estuary at different salinities, determined as function of several concentration steps, using a hollow fiber ultrafiltration set up with a theoretical cut off of MW 5000 (Kramer and Duinker, 1984a). 

The major constituents in seawater are conventionally taken to be those elements present in typical oceanic water of salinity 35 that have a concentration greater than 1 mg kg excluding Si, which is an important nutrient in the marine environment. The concentrations and main species of these elements are presented in Table 1. One of the most significant observations from the Challenger expedition of 1872-1876 was that these major components existed in constant relative amounts. As already explained, this feature was exploited for salinity determinations. Inter-element ratios are generally constant, and often expressed as a ratio to Cl%o as shown in Table 1. This implies conservative behaviour, with concentrations depending solely upon mixing processes, and indeed, salinity itself is a conservative index. 

The salinity determined from this equation (e.g., S = 35.00 at Cl = 19.374) is lower than the value... 

Variation of Solubility with Salinity. Determination of the solubility of PAHs in water is of both thermodynamic interest and practical relevance in assessing the environmental fate and effects of oil present in rivers, lakes, groundwater, and oceans. Although the aqueous solubilities of a large number of specific PAHs have been measured and correlated, few data exist on the solubility in the presence of a third component such as an electrolyte. The practical implications are that the presence of this third compound may substantially change the solubility an example of this is the salting-out effect of sodium chloride and other salts present in seawater. 

Until the development of the conductivity method for salinity determination considerable time and effort had to be expended in ensuring the precision and accuracy of the salinity titration until the automatic analyzers, and more recently, the microchip controllers, nutrient analyses, even if actually performed by biologists or biological technicians, were often under the watchful eye of the resident chemist. 

To achieve the accuracy of 0.02 %o in salinity for a single determination with the above method, and also to make salinity determinations from different institutions comparable, Knudsen required frequent comparison with an internationally accepted standard of known chlorinity. On behalf of the International Council for the Exploration of the Sea (ICES), standard seawater (SSW), later often called Copenhagen Water as it was prepared in Copenhagen for a long time, served this purpose. Each batch was numbered and distributed to oceanographers in sealed ampoules with the chlorinity indicated. For a detailed description of the history of standard seawater see Culkin and Smed (1979). 

In addition to the determination of the traditional nutrients, flow methods have been reported for a number of other components using either flow spectrophotometers or other types of detectors. Flow methods can be easily combined in multi-variable systems. Despite the occasionally low accuracy, they can provide useful additional information about the analysed samples. As an example, consider conventional water sampling in an estuary using a small vessel and sample bottles on a hydrographic wire. To confirm that a sample has really been taken at the depth indicated by the cable length and sampler position on the cable, it is necessary to measure the salinity. Instead of using sample water for separate salinity determinations with a salinometer (increasing the required sampler size), a small conductivity cell in the flow analyser would provide this information. 

Hirschfeld, T., Salinity determination using NIRA, Appl. Spectrosc., 39, 740-743, 1985. 

Experience indicates that any delicate weighing operation or highly precise titration work (such as is necessary for the best salinity determinations) is unsuited to routine shipboard use. It is also very inconvenient to undertake the evaporation and fuming of solutions in most ship laboratories. The methods in this manual have been designed with these considerations in mind and, whenever possible, substances are determined by light absorptiometry. 

When these bottles, or the containers of Eau de Mer Normale, are opened the salinity determination must be carried out within a few minutes. Repeat determinations on re-corked bottles should not be delayed for more than about 1 hr. 

The previous sections have shown that pore-water extraction and solute leaching procedures can provide useful information concerning the general chemical characteristics of pore-waters from low-permeability media. In particular, it is possible to establish levels of total salinity, determine whether systems are chloride dominated and provide useful information concerning chemical gradients. 

Data gathering in the water column should not be overlooked at the appraisal stage of the field life. Assessing the size and flow properties of the aquifer are essential in predicting the pressure support which may be provided. Sampling of the formation water is necessary to assess the salinity of the water for use in the determination of hydrocarbon saturations. 

One of the primary objectives of production operations is to deliver product at the required rate and quality. Therefore the product quality specification and any agreed contract terms will drive the activities of the production operations department, and will be a starting point for determining the preferred mode of operation. The specifications, such as delivery of stabilised crude with a BS W of less than 0.5%, and a salinity of 70 g/m, ... 

Hydrocarbon-water contact movement in the reservoir may be determined from the open hole logs of new wells drilled after the beginning of production, or from a thermal decay time (TDT) log run in an existing cased production well. The TDT is able to differentiate between hydrocarbons and saline water by measuring the thermal decay time of neutrons pulsed into the formation from a source in the tool. By running the TDT tool in the same well at intervals of say one or two years (time lapse TDTs), the rate of movement of the hydrocarbon-water contact can be tracked. This is useful in determining the displacement in the reservoir, as well as the encroachment of an aquifer. 

Minimal Energy Requirements. The relative effect of the cost of the energy on the cost of the freshwater produced depends on local conditions, and is up to one-half of the total. In attempting to reduce this cost, it is of interest to determine the minimal energy amount thermodynamically needed for separating the water from the saline solution. The physical background to this will be introduced in a simple example. Because of the negligible... 

Figure 4 Measurements of (A) uranium aetivity ratios, UARs ( U U) and U eoneentrations (B) aeross a salinity gradient off the Amazon River mouth (1996). UARs were determined by thermal ionization mass speetrometry (TIMS) at Calteeh (D. Poreelli) U eoneentrations by ICPMS...

Determination of total mud salinity. The total pounds of soluble salts per barrel of mud are calculated as... 

Determination of water phase salinity. By entering the graph in Figure 4-110 with total soluble salts, Ib/bbl of mud, at the correct volume percent of water line, the water phase salinity can be read from the left-hand scale. 

Salinity This term is intended to denote the total proportion of dissolved salts in sea water. As it is inconvenient to determine directly, it is norm.ally derived from the chlorinity, defined and determined as above, using the empirical relationship ... 

Saline and acid waters are particularly aggressive to mild steel, so the composition of the water is clearly important in determining the rate of rusting of steel exposed to it. Some of the main factors here are the nature and... 

Theory. Conventional anion and cation exchange resins appear to be of limited use for concentrating trace metals from saline solutions such as sea water. The introduction of chelating resins, particularly those based on iminodiacetic acid, makes it possible to concentrate trace metals from brine solutions and separate them from the major components of the solution. Thus the elements cadmium, copper, cobalt, nickel and zinc are selectively retained by the resin Chelex-100 and can be recovered subsequently for determination by atomic absorption spectrophotometry.45 To enhance the sensitivity of the AAS procedure the eluate is evaporated to dryness and the residue dissolved in 90 per cent aqueous acetone. The use of the chelating resin offers the advantage over concentration by solvent extraction that, in principle, there is no limit to the volume of sample which can be used. 

Because seawater signatures of temperature and salinity are acquired by processes occurring at the air-sea interface we can also state that the density characteristics of a parcel of seawater are determined when it is at the sea surface. This density signature is locked into the water when it sinks. The density will be modified by mixing with other parcels of water but if the density signatures of all the end member water masses are known, this mixing can be unraveled and the proportions of the different source waters to a given parcel can be determined. 

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