Effect of background electrolytes

It can be seen that calcium chloride and sodium chloride (at a much higher concentration) contribute to a similar extent to flux decline. This flux decline in the presence of FA is most likely caused by concentration polarisation due to an increased concentration in the stirred cell (the concentration increases by a factor of up to 3 during the experiment) and the resulting osmotic pressure increase. The deposit values show that calcium increases deposition of DOC and UV (see 2.5 mM CaCl 2), but no significant difference in deposition is visible for the other solutions (see Table 7.23). 

Salt After Recycle 3 J/J After Experiment J v/J o After Water Rinse DOC Loss l%] ([ ng]) HV 2 nm Loss r/o]([cm- ]) Calcium Loss rojcM) 

As can be seen from Table 7.24, very small amounts of material are deposited on the membranes (close to the measurable limit of this method). Relatively large values of calcium losses (in mg) are measured for the TFC membranes. 

The lack of stirring indeed showed that concentration polarisation (which is increased in the absence of stirring) increases flux decline tremendously, even though the membrane appeared less sensitive to osmotic pressure effects. With the flux decline at unstirred conditions, a very significant deposit was 

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Fillet M., Servais A.C., Crommen J., Effects of background electrolyte composition and addition of selectors on separation selectivity in nonaqueous capillary electrophoresis. Electrophoresis, 24, 1499-1507 (2003). 

Kadish et al. (1989) have described the effect of axially bound anions on the electroreduction of tris(IV) porphyrins in THF. Cyclic voltammetric investigations of zinc tetraphenylporphyrin in dichloromethane in the presence of background electrolyte anions reveal significant perturbations of the met-alloporphyrin s first one-electron oxidation, ranging from 0.86 V for TBAPF6 to 0.50 V for TBAC1 (Seely et al., 1994). 

Shibukawa et al. [109] published a new liquid chromatographic method for the determination of acid dissociation constants. On the basis of theoretical equations regarding the effect of background mobile phase ions on the retention of ionic analytes on a non-ionic polymer packing, they could determine simultaneously the dissociation constants (p/fa) and the charges of analyte molecules. They used chloride and perchlorate ions in the mobile phase as they exhibit large differences in the retention on the hydrophilic polymer packings used, so that the effect of the mobile phase electrolyte on the retention factor of an ionic analyte could be clearly evaluated. 

Between the simplicity of the model and the complexity of the TLM, there are several other sorption models. These include various forms of isotherm equations (e.g., Langmuir and Freundlich isotherms) and models that include kinetic effects. The generalized two-layer model (Dzombak and Morel, 1990) (also referred to as the DLM) recently has been used to model radionuclide sorption by several research groups (Langmuir, 1997a Jenne, 1998 Davis, 2001). Constants used in this model are dependent upon the concentration of background electrolytes and... 

AH+ and complex A1 ions. In their studies, soil scientists have tended to use electrolyte solutions which they see as relevant. Often the solution used is a dilute solution of calcium chloride. This contrasts with those who have studied oxides. Their choice of background electrolyte has been motivated by a desire to use electrolytes which are close to indifferent . Ideally, this means that neither the cation nor the anion has any affinity for the surface. In practice, it means that the affinity of both ions is small and similar. These differences in the choice of background electrolyte mean that the observed effects of pH differ. Fig. 8 shows that the decline in phosphate sorption by a soil with increasing pH is steeper when the background electrolyte is sodium chloride than when it is calcium chloride. This is because the presence of the divalent cation compresses the distribution of ions near the surface and the change with pH in the electric potential is less steep. 

The electrostatic repulsion between dispersed particles can be diminished by increasing the concentration of background electrolyte (e.g. NaCl, CaCl2)- Polyvalent ions are more effective than monovalent. There is a critical electrolyte concentration for every system at which flocculation or coalescence takes place. These principles must be taken into account when emulsions have to form in very hard water. 

Le Gall, M., Lelievre, J., Loppinet-Serani, A., LeteUier, P. Thermodynamic and kinetic approach of the reactivity in micellar media — reaction of hydroxide ion with 1,3,5-trinitrobenzene in aqueous solutions of neutral nonionic surfactant effect of the concentration of background electrolyte. J. Phys. Chem. B 2003, 707(13), 8454-8461. 

Reed, B. and Nonavinakere, S., Metal adsorption by activated carbon—effect of complexing ligands, competing adsorbates, ionic strength, and background electrolyte, Sep Sci Technol, 27 (14), 1985-2000, 1992. 

Fig. 3.161. (A) Zone electrophoresis patterns of FITC-labelled transferrin samples by fluorescence detection. The unbound dye (providing a main peak and several minor ones) was not removed from the samples. Experimental conditions background electrolyte, 100 mM borate buffer, pH 8.3 voltage, 20 kV capillary 59 cm (effective length 41 cm) X 75 pm i.d. injection of samples 100 mbar x s 20°C detection with fluorescence detector (240 - 400 nm, broadband excitation filter and a 495 nm cut-off emmision filter). The reaction was left to continue for 20 h, and the reaction mixtures contained 13 pm (1 mg/ml) Tf and (a) 0.01 mM FITC, (b) 0.1 mM FITC, and 1 mM FITC. (B) Zone electrophoresis patterns of an FITC-labelled transferrin sample by simultaneous fluorescence (upper trace, left axis) and UV detection (lower trace, right axis). The unbound dye shows several peaks with both detections. Experimental conditions background electrolyte, 100 mM borate buffer, pH 8.3 voltage, 20 kV capillary 59 cm (effective length fluorescence 41 cm, UV 50.5 cm) X 75 pm i.d. injection of samples 100 mbar X s 20°C detection with fluorescence detector (240 - 400 nm, broadband excitation filter and a 495 nm cut off emmision filter). The reaction was left to continue for 20 h, and the reaction mixtures contained 6.5 pm (0.5 mg/ml) Tf and 0.1 mM FITC. Reprinted with permission from T. Konecsni et al. [199].

Matrix effects in the analysis of nutrients in seawater are caused by differences in background electrolyte composition and concentration (salinity) between the standard solutions and samples. This effect causes several methodological difficulties. First, the effect of ionic strength on the kinetics of colorimetric reactions results in color intensity changes with matrix composition and electrolyte concentration. In practice, analytical sensitivity depends upon the actual sample matrix. This effect is most serious in silicate analysis using the molybdenum blue method. Second, matrix differences can also cause refractive index interference in automated continuous flow analysis, the most popular technique for routine nutrient measurement. To deal with these matrix effects, seawater of... 

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