Sampling salinity

In addition to the chemical effects of varying salinity, there are optical interferences in colorimetric analysis which are peculiar to estuarine samples. Saline waters and river waters have, in the absence of colorimetric reagents, an apparent absorbance arising from ... 

Earle and Drever (1983) found He concentrations of 0.05-236 pL/L in groundwaters from various depths (up to 500 m) in the Athabasca Basin, Saskatchewan. They claimed there to be a moderate correlation between the occurrence of He anomalies and known U mineralisation, provided the He concentrations were divided by sample salinity in a rough correction for groundwater residence time. 

A typical experiment then consists of preparing the surface and placing the probes on the surface (often not in the experimenter s lab) followed by placing the sample saline solution containing the target on the spots. The kinetics of hybridization may then proceed. Once sufficient time has elapsed, saline solution is used to wash the remaining unhybridized nucleic acid away. At this point the fluorophores can be excited and the area normalized intensity of fluorescence at each spot is then related to the affinity and the concentration of duplex nucleic acid. 

In a pioneering publication, a feedback mechanism was exploited to minimise matrix effects in the determination of metals in seawater by ICP-OES [396]. Direct analysis was not feasible, as variations in salinity affected the nebuliser efficiency and the intensity of the sodium spectral interference. For matrix matching, the sample salinity was estimated by a prior determination of sodium and the salinity of the standard solution used was selected by matching as closely as possible the salinity to that of the sample. This was done by modifying the tzs value in the sampling zone process (see 7.2.1), thus selecting a different amount of sodium chloride to be added to the working standard solutions. 

Only lAPSO recognized SSW provides a reliable standard for conductivity ratio measurements. It should be used to standardize each bench salinometer before being used for sample salinity measurements and to detect and eventually trace any drift. The use of so-called substandards for standardization is not recommended, as it will significantly decrease accuracy (see Section 3.5.7 for exceptions if a decrease in accuracy is acceptable). 

Immediately after the salinometer has been standardized with SSW (see Sections 3.5.3 and 3.5.4 for the AUTOSAL and the RSIO, respectively), the saUnities of three substandard bottles are measured successively. If each salinity differs from their average by less than the accuracy that is required for individual samples during the cruise, the substandard is accepted, with the average as the salinity of the substandard and the maximum difference between the three individual substandard sample salinities as its uncertainty. 

A sodium chloride solution of a g/kg concentration equal to the sample salinity usually satisfies the first and second requirements. Problems encountered with potential impurities in the chemicals used for the preparation of artificial seawater according to the protocol in the Appendix of this book are likely to introduce errors rather than improve the analysis. In flow-analysis of nitrate, nitrite, phosphate and silicate we could not detect analytical differences between using ASW or sodium chloride solutions Hansen, unpublished). 

To compensate for matrix effects either LNSW (preferable), ASW or a sodium chloride solution is recommended with a salinity equal to the mean of the (expected) sample salinities Hansen, 1994). For all components showing salt effects for the expected salinity range, correction functions have to be established. In most cases simple linear corrections are sufficient. 

Prepare a series of five dilutions of a basic matrix (LNSW, ASW or NaO) from lowest to highest expected sample salinities. Spike aliquots of the zero matrix with individual or mixed nutrient standard solutions to give five concentrations of each series from 0 to a high standard concentration (just above the expected maximum sample concentration). 

The salinity error of a nutrient determination (A unc) is corrected by a linear correction equation including terms for the differences in the sample salinity S and the standard salinity Sstd which is used as the blank, wash and standard matrix. 

Prepare an adequate supply of zero water (ZW), Le., LNSW, ASW or a sodium chloride solution of medium sample salinity (see Section 10.2.2). If the expected variation of salinity is < 2, salinity corrections are generally not required. 

Samples fi om brackish waters, with a wide salinity range, have to be corrected with respect to the salt error. Standards are prepared using a zero water (ZW) of medium sample salinity ( o). 

The salt error is < 3 % for salinities from 25 to 35 if sodium chloride solutions or LNSW of medium sample salinities are used as ZW. The linear salinity correction (see Section 10.2.11.3) may be applied if required. 

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. 

Ocean sea water is roughly equivalent in strength to a 3 j % w/v solution of sodium chloride, but it has a much more complex composition, embodying a number of major constituents, and traces at least of almost all naturally occurring elements. For convenience, however, the concentration of salts in any sample of sea water is expressed in terms of the chloride content, either as chlorinity or as salinity. Both these units are again subject to arbitrary definition and do not conform simply to the chemical composition. 

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 thermal gradients vary considerably within boilers, a typical BW sample, which is essentially representative of average internal bulk water conditions, is unlikely to provide sufficient valid information necessary for the critical assessment of conditions at boiler surfaces. This makes fine-tune control of coordinated phosphate programs within the areas they are most needed very difficult, if not impossible, especially because caustic and saline concentrations may be much higher under deposits than in the bulk water as a result of localized effects. 

From this material, samples are cut and swelled to constant weight in a buffered saline solution prepared from 8.43 g sodium chloride (NaCl), 9.26 g boric acid (H3BO3), 1.0 g sodium borate (Na3B03), and 0.1 g of the disodium salt of the dihydrate of ethylenediaminetetraacetic acid [Na2 EDTA -(/ 0)21 ini L of distilled water. 

Effect of Aqueous Phase Salinity and pH on Interfacial Tension. Comparison of the first two entries in Table 14 shows that an increase in AOS 2024 solvent salinity from 0 to 3% NaCl results in a significant decrease in IFT. This suggests that the optimum salinity of this AOS 2024 sample is closer to 3% NaCl than to 0%. 

The second valve controls a sample loop, 5 cm long and 1 mm in diameter, packed with dimethyloctadecyl reverse phase comprising of fairly coarse particles 100-120 im in diameter to reduce flow impedance. The sample pump is supplied via a two-way tap from either of two reservoirs, one containing pure water and the other, normal saline. The output of the pump can be used to either force the contents of the open loop sample tube through the packed loop, or to permit washing with an appropriate solvent. The separate pump is necessary to overcome the impedance of the packed loop. 

A sample loop, having a capacity of 400 pi, was filled with the serum which was displaced by 2 ml of normal saline onto the packed sample loop. The loop was then washed with a further 2 ml of saline followed by 2 ml of water and the placed in line with the solvent flow and the program initiated. The chromatogram obtained is shown in figure 6. 

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