Artificial seawater, solution

It is appropriate at this point to discuss the "apparent" pH, which results from the sad fact that electrodes do not truly measure hydrogen ion activity. Influences such as the surface chemistry of the glass electrode and liquid junction potential between the reference electrode filling solution and seawater contribute to this complexity (see for example Bates, 1973). Also, commonly used NBS buffer standards have a much lower ionic strength than seawater, which further complicates the problem. One way in which this last problem has been attacked is to make up buffered artificial seawater solutions and very carefully determine the relation between measurements and actual hydrogen ion activities or concentrations. The most widely accepted approach is based on the work of Hansson (1973). pH values measured in seawater on his scale are generally close to 0.15 pH units lower than those based on NBS standards. These two different pH scales also demand their own sets of apparent constants. It is now clear that for very precise work in seawater the Hansson approach is best. 

Artificial seawater Prepare an artificial seawater solution, but without sodium fluoride (see Tables 1 and 2 in the Appendix). 

MicrobiologicaHy influenced corrosion, which results from the interaction of microorganisms and a metal, is receiving increased emphasis (1,3,9). The action of microorganisms is at least one of the reasons why natural seawater is more corrosive than either artificial seawater or sodium chloride solutions. Microorganisms attach to the surfaces of metals and can, for example, act as diffusion barriers produce metaboHtes that enhance or initiate... 

Working solutions (1 litre) which were 10 7 mol/1 in one of the elements to be studied were prepared by appropriate addition of the radioactive stock solutions to pH-adjusted artificial seawater. After the pH had been checked, 100 ml portions were transferred to the bottles to be tested. The filled bottles were shaken continuously and gently in an upright position, at room temperature and in the dark. At certain time intervals, ranging from 1 min to 28 d, 0.1 ml aliquots were taken. These aliquots were counted in a 3 x 3 in Nal (TI) well-type scintillation detector, coupled to a single-channel analyser with a window setting corresponding to the rays to be measured. 

Stein et al. [673] have described a simplified, sensitive, and rapid method for determining low concentrations of cadmium, lead, and chromium in estuarine waters. To minimise matrix interferences, nitric acid and ammonium nitrate are added for cadmium and lead only nitric acid is added for chromium. Then 10,20, or 50 pi of the sample or standard (the amount depending on the sensitivity required) is injected into a heated graphite atomiser, and specific atomic absorbance is measured. Analyte concentrations are calculated from calibration curves for standard solutions in demineralised water for chromium, or an artificial seawater medium for lead and cadmium. 

Hiraide et al. [737] developed a multielement preconcentration technique for chromium (III), manganese (II), cobalt, nickel, copper (II), cadmium, and lead in artificial seawater using coprecipitation and flotation with indium hydroxide followed by ICP-AES. The metals are simultaneously coprecipitated with indium hydroxide adjusted to pH 9.5, with sodium hydroxide, ethano-lic solutions of sodium oleate and dodecyl sulfate added, and then floated to... 

C. 1. The figure shows that coprecipitation occurs in distilled water, so it should first be shown that coprecipitation occurs in seawater, which has a high salt concentration. This can be done by adding standard Pb2+ to real seawater and to artificial seawater (NaCl solution) and repeating the experiment in the figure. 

For example, the concentrations of ore metals in most natural waters are quite low, particularly so in normal seawater. Measuring these low concentrations has been a problem of marine chemistry for many years. It is interesting to note that when artificial seawater, made up from pure reagent chemicals, is exposed to metallic elements, the ultimate solutions produced will contain from 100 lo 1000 limes the concentrations of these metals as compared with natural seawater. 

McCubbin, D. and Leonard, K.S. (1997) Laboratory studies to investigate short-term oxidation and sorption behaviour of Np in artificial and natural seawater solutions. Mar. Chem., 56, 107-121. 

To experimentally validate the Gitterman model, we prepared an artificial seawater sample that had the composition of seawater s liquid partially frozen down to — 23 °C (Marion et al. 1999). To this sample we added an excess of mirabilite crystals to ensure an adequate sulfate source. The sample was then placed in a — 26 °C temperature-controlled bath and allowed to equilibrate with periodic sampling and analyses over a 12-week period. The precipitation of hydrohalite between — 23 °C and — 26 °C (Fig. 3.16) led to an initial decrease in the sodium molality. Magnesium, on the other hand, was conserved in the solution phase, as ice formed and hydrohalite precipi-... 

Figure 5, Recorder signals obtained with the manifold shown in Figure 4. The blank solution is artificial seawate (7). The remaining solutions were natural seawater containing —0.9 /xM PO4 to which phosphate standard solution...

Five series of solutions were prepared in artificial seawater. The solutions were hydrochloric acid, an acetate buffer solution (mHAc/ NaAc = 1), and three equimolal buffer solutions (mBHci/ B = l) prepared from the following bases (B) tris, 2-amino-2-methylpropanediol (bis), and the N-bis(hydroxyethyl) derivative of tris, bis-tris. The pKa values of the protonated bases in water at 25°C are, respectively, 8.075 (16), 8.801 (17), and 6.483 (18). When hydrochloric acid or buffer was added to the seawater solvent, the ionic strength and chloride molality were kept constant by reducing the molalities of sodium chloride or sodium perchlorate as necessary. 

Measurements of the emf (E) of cell A were made at 5°, 15°, 25°, and 35°C, and the data are summarized in Tables II and III. The results for solutions of hydrochloric acid were used to calculate the mean activity coeflBcient y of hydrochloric acid at three low molalities (m) in artificial seawater (without sulfate) ... 

We now turn to emf measurements of cell A containing equimolal buffer solutions (macid = ait = ) in artificial seawater of the two compositions given in Table I. The emf data are given in Tables II and III. One can write formally ... 

The emf data for cell A can be used to establish standard reference values of (pMh)s in the buffer solutions studied, where the unit of Mh is moles of free H" /kg of seawater. With the use of these standards in a form of Equation 6 (with pMn written in place of pmn), experimental values of (pMn)x in artificial seawater of about 35%o salinity (and hopefully also in natural seawater of the same salinity) can be obtained. These standard values are Hsted in Table VII. 

Figure 2 shows data for addition of Pu(Vl) to artificial seawater with different amounts of humic acid. In all solutions, the Pu(Vl) was reduced rapidly to Pu(V) + Pu(lV) with the ratio of the V/IV decreasing with humic acid concentration. The Pu(lV) is not found in solution but can be recovered quantitatively from the walls... 

Above a pH of 3 and in the absence of chelators dissolved iron is only present as ferrous iron under natural conditions. Therefore, the colored complex that results from the reaction between ferrous iron and a reagent can be analysed colorimetrically and correlates with the concentration of total dissolved iron. Most conveniently, one can mix a drop of Ferrozine solution (Stookey 1970), one drop of H SO (diluted 1 4) and 1 ml of pore water in the glove box, wait until complex formation is completed (20-30 minutes) and quantify the iron concentration by the intensity of the color at a wavelength of 562 nm. To avoid matrix effects standards should be prepared with artificial seawater. 

Fukushi K, Watanabe K, Takeda S, Wakida SI, Yamane M, Higashi K and Hiiro K (1998) Determination of bromide ions in seawater by capillary zone electrophoresis using diluted artificial seawater as the buffer solution. J Chromatogr A 802 211-217. 

An electrostatic ion chromatographic method was developed for the direct determination of iodide, bromide and nitrate in seawater (Hu et ai, 1999). An octadecylsifica column modified with a zwitterionic surfactant 3- NJV-dimethylmyristylammonio)propane-suifonate was used as the stationary phase, and an electrolytic solution was used as the eluent. The matrix species (such as chloride and sulfate) were retained weakly, and showed iitde or no interference. The method was applied to the determination of iodide, bromide, and nitrate in artificial seawater, giving detection fimits of 0.8 p,g 1 for iodide, 0.75 p.g 1 for bromide, and 0.52 p,g 1 for nitrate, and relative standard deviations of <1.2%. The real seawater samples were also analyzed successfully. Later, another electrostatic ion chromatographic method was developed for the determination of iodide in seawater by the same research group (Hu et ai, 2002). A reversed-phase ODS column was... 

The solubility data points in Figure 1 were obtained in several different solutions, including artificial seawater ( 3, in Figure... 

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