Surface group concentration measurement

The processes classified in the third group are of primary importance in elucidating the significance of electric variables in electrosorption and in the double layer structure at solid electrodes. These processes encompass interactions of ionic components of supporting electrolytes with electrode surfaces and adsorption of some organic molecules such as saturated carboxylic acids and their derivatives (except for formic acid). The species that are concerned here are weakly adsorbed on platinum and rhodium electrodes and their heat of adsorption is well below 20 kcal/mole (25). Due to the reversibility and significant mobility of such weakly adsorbed ions or molecules, the application of the i n situ methods for the surface concentration measurements is more appropriate than that of the vacuum... 

Takahashi et al.67) prepared ionene-tetrahydrofuran-ionene (ITI) triblock copolymers and investigated their surface activities. Surface tension-concentration curves for salt-free aqueous solutions of ITI showed that the critical micelle concentration (CMC) decreased with increasing mole fraction of tetrahydrofuran units in the copolymer. This behavior is due to an increase in hydrophobicity. The adsorbance and the thickness of the adsorbed layer for various ITI at the air-water interface were measured by ellipsometry. The adsorbance was also estimated from the Gibbs adsorption equation extended to aqueous polyelectrolyte solutions. The measured and calculated adsorbances were of the same order of magnitude. The thickness of the adsorbed layer was almost equal to the contour length of the ionene blocks. The intramolecular electrostatic repulsion between charged groups in the ionene blocks is probably responsible for the full extension of the... 

Many attempts have been made to measure silanol surface density (aon)-Her [7] estimated Ooh to be equal to 8 groups/nm on the basis of the [100] face of P-cristobalite. However, most porous amorphous silicas show surface silanol concentration on the level of 4.6 to 5 groups/nm [6]. 

Iron is the only nutrient element for which particulate concentrations are typically higher than dissolved levels (de Baar and de Jong, 2001). Despite this, considerably more research attention has focused on measuring dissolved pools than on the particulate fraction. The literature on total dissolved Fe concentrations is now far too extensive to comprehensively review here, but most analysts report oceanic surface concentrations of <0.1—0.5 nM (de Baar and de Jong, 2001 Johnson et al., 1997), and deep-water levels ranging from 0.3 to 0.7 nM (Parekh etal., 2005). Some differences in reported dissolved Fe levels could be due to analytical artifacts, since various methods used by different groups may measure different fractions of dissolved and/or colloidal and particulate pools. Methods intercomparisons are currently underway that could help to clarify these issues. 

The acid-base properties of DOM are of intrinsic interest because acidic functional groups contribute to the acid-base balance of natural waters, affect complexation and transport of dissolved metals, and interact with mineral surfaces. The concentrations of carboxyl and phenolic functional groups are among the most widely measured and reported properties of DOM. Methodologically, there are two basic approaches for measuring acidic group content—indirect titrations and direct titrations (Perdue et al., 1980 Perdue, 1985 Ritchie and Perdue, 2003). 

The oxygen-containing surface groups are responsible for the potential response of carbon electrodes to hydrogen ion concentration in. solution. Potential measurements of carbon materials in buffer solutions show that the relationship E = /(pH) is linear in the pH range 2.0-7.0 and can be de.scribed by a linear equation with a slope between 20 and 60 mV/pH. depending on the nature of the electrode material [160,161]. 

Although passive samplers (and particularly the DGT) have been used by many different research groups to measure concentrations of metals in surface waters, and the work has been widely published, they have yet to be adopted within a regulatory context. 

US with changing salt concentration, indicating the presence of relatively thick adsorbed layers on the sulfur particles (see Fig. 4). This, as well as surface charge density measurements showing values comparable to surface charge densities of bacterial cell walls and humic acids, support the suggestion of proteins adsorbed on the particles. In addition, electrophoretic mobility experiments showed an iso-electric point comparable to the pKa-value of carboxylic acid groups in proteins (pKa=2.3) [45]. 

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