Speciation curves

Figure 6.3a shows the plot of log S versus pH of an ampholyte (ciprofloxacin, pKa values 8.62 and 6.16, log So — 3.72 [pION]). In Figs. 6.1b, 6.2b, and 6.3b are the log-log speciation profiles, analogous to those shown in Figs. 4.2b, 4.3b, and 4.4b. Note the discontinuities shown for the solubility speciation curves. These are the transition points between a solution containing some precipitate and a solution where the sample is completely dissolved. These log-log solubility curves are important components of the absorption model described in Section 2.1 and illustrated in Fig. 2.2. 

Vertical concentration profiles of (a) temperature, (b) potential density, (c) salinity, (d) O2, (e) % saturation of O2, (f) bicarbonate and TDIC, (g) carbonate alkalinity and total alkalinity, (h) pH, (i) carbonate, ( ) carbon dioxide and carbonic acid concentrations, and (k) carbonate-to-bicarbonate ion concentration ratio. Curves labeled f,p have been corrected for the effects of in-situ temperature and pressure on equilibrium speciation. Curves labeled t, 1 atm have been corrected for the in-situ temperature effect, but not for that caused by pressure. Data from 50°27.5 N, 176°13.8 W in the North Pacific Ocean on June 1966. Source From Culberson, C., and R. M. Pytkowicz (1968). Limnology and Oceanography, 13, 403-417. 

Figure 1. Speciation curves for the activities of free copper ion and the hydroxo complexes of copper vs. pH...

If the carbonato complexes are accepted as being non-toxic, a set of experiments are needed in which the toxicity of copper to Daphnia magna is measured at equal intervals over the pH range 6.0-8.0. The speciation curves shown in Figure 1 would predict that this set of experiments plus inclusion of all copper complexes involved in the speciation calculations should allo separation of the species of concern into four groups, (Cu ),... 

The ratios of carbonate containing species in aqueous solution are a function of pH value as depicted by the weU-known carbonate speciation curve (Figure 6.13). Aqueous carbon takes on three different forms depending on the acidic or basic nature of the water. At pH 4.3, the concentration of bicarbonate (HCOs ) is 1% of the dissolved CO2, and neutralisation of carbonate (COs ) is virtually complete. Alkalinity is, thus, related to... 

Figure 6.13 Carbonate speciation curve. Aqueous carbon takes on three forms depending on the acidic or basic nature (pH) of water.

We can also examine the case (Figure 8) where a 100 mV shift changes the affinity from /fa = 10 to a moderate value of /f edox = 2 x 10 M. In this instance, the speciation curve (Figure 8a) shows that, upon reduction to G , only 50% is complexed as H G (blue trace) upon addition of 1 equivalent of guest with the other half present... 

Figure 8 Complex shows some dethreading upon reduction, (a) Simulated speciation curves for the binding affinity of the host-guest complex before K — 10 M ) and after reduction ( redox 2 X 10 M-1). (b) Simulated CV titration (0, 0.25, 0.5, 0.75, 1, 2, and 5 equivalents) of host into redox-active guest under conditions where the complex is destabilized to a small extent upon reduction to (0.1 V s ).

Figure 12 Simulated speciation curves showing the fraction of complex formed under various conditions as noted in the panels, (a) Dilution effects with A" = 1 x ltf M . (b and c) Effects of the K value, (d) Effect of the K value at lower concentrations of guest and host...

Fig. 21.40 Speciation curves for complexes formed in an aqueous solution of vanadium(IV) and maltol (HL) with a metal ligand ratio of 1 2. [Redrawn with permission from T. Kiss et al. (2000) J. Inorg. Biochem., vol. 80, p. 65, Elsevier.]...

Fig. 15-11 Effects of strong complexation on metal ion toxicity, (a) Increasing concentration of NTA, a strong multi-dentate complexing agent, decreases the toxicity of Cd to grass shrimp. All systems have equal concentrations of total Cd. (b) When the results are replotted showing survival as a function of Cd concentration, the data for all concentrations of NTA collapse to a single curve. (Reprinted with permission from W. G. Sunda et al. (1978). Effect of chemical speciation on toxicity of cadmium to grass shrimp, Palaemonetes pugio importance of free cadmium ions. Environ. Sci. Technol. 12,409-413, American Chemical Society.)...

R. Tauler, A.K. Smilde, J.M. Henshaw, L.W. Burgess and B.R. Kowalski, Multicomponent determination of chlorinated hydrocarbons using a reaction-based chemical sensor. 2 Chemical speciation using multivariate curve resolution. Anal. Chem., 66 (1994) 3337-3344. 

Figures 4.2b, 4.3b, and 4.4b are log-log speciation plots, indicating the concentrations of species in units of the total aqueous sample concentration. (Similar plots were described by Scherrer [280].) The uppermost curve in Fig. 4.2b shows the concentration of the uncharged species in octanol, as a function of pH. If only uncharged species permeate across lipid membranes, as the pH-partition hypothesis...

Tauler R., Smilde A.K., Hemshaw J.M., Burgess L.W., Kowalski B.R., Multicomponent Determination of Chlorinated Hydrocarbons Using a Reaction-based Chemical Sensor. Part 2. Chemical Speciation Using Multivariate Curve Resolution, Anal. Chem. 1994 66 3337-3344. 

Detailed speciation calculations for the fluid coupled with mineralogical investigation of the solid paragenesis generally allow a sufficiently precise estimate of the T of equilibrium. As figure 8.30A shows, the chemistry of the fluid is buffered by wall-rock minerals, so that the saturation curves of other phases not pertaining to the system of interest are scattered (figure 8.28B). 

Figure 2.3 Speciation of arsenious acid with pH. Curves calculated from acid dissociation constants listed in Table 2.10.

Eh-pH diagram showing the predominance fields for oxidized (upper right) and reduced (lower left) forms of selected redox-active species. Note that the curves represent totals for each species i.e., further speciation is not shown. Curves are drawn from variations on Equation (18) for 25°C, using values of E° from Table 16.6 and additional constants from various sources (5, 8, 23). Dashed diagonal lines are for the H2/H20 (lower) and H20 / 02 (upper) couples and together they enclose the conditions over which water is stable. 

Fig. 15.5. Calculated metal sorption curves for Pb, Cu and Cd onto the bacterium Bacillus subtilis, shown as a function of pH versus the concentration of sorbed metal. Curves are calculated based on experimental metal sorption data of Fein et al. (1997), and were computed using the geochemical speciation programme JCHESS. The solution depicted contains 1 g 1 bacteria dry wt (155 m g surface area, 8.0 Cm electrical double layer capacitance), 1 mM dissolved CaC03 and 1 iM dissolved lead, copper and cadmium. Adsorption was calculated using a CCM treatment.

Beryllium is an alkaline-earth elements whose behavior drastically differs from that of the other alkaline-earth elements. Its low mobility in natural waters is attributed to its affinity for surfaces. Laboratory experiments have been performed to examine the partitioning of Be between sediments from natural systems and water (You et al, 1989). The partition coefficient depends strongly on pH in the range 2-7. The curve of as a function of pH (Figure 24) can be explained by a thermodynamic model by taking into account beryllium speciation in freshwater and the... 

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