Compound nonpolar surfaces

Schwarzenbach, R. P., Westall, J. (1981) Transport of nonpolar compounds from surface water to groundwater. Laboratory sorption studies. Environ. Sci. Technol. 11, 1360-1367. 

Schwartzenbach, R. P. and Westhall, H., 1981, Transport of Nonpolar Organic Compounds from Surface Water to Groundwater, Laboratory Sorption Studies Environmental Science and Technology, Vol. 15, pp. 1350-1367. 

Schwarzenbach, R.P., Giger, W., Schaffner, C., Wanner, O. (1985) Groundwater contamination by volatile halogenated alkanes Abiotic formation of volatile sulfur compounds under anaerobic conditions. Environ. Sci. Technol. 19(4), 322-327. Schwarzenbach, R.P., Westall, J. (1981) Transport of nonpolar compounds from surface water to groundwater. Laboratory sorption studies. Environ. Sci. Technol. 11,1360-1367. 

Healy et al. (134) studied experimentally the heats of adsorption of many polar and nonpolar gases on polar and nonpolar surfaces by means of their heats of immersion. It was found that the heat of immersion of rutile on a series of straight-chain compounds was a linear function of the dipole moment of the wetting liquid. In a later article (135)- this work was extended and it is shown that nearly the entire heat effect on immersion of the clean solid surface is due to adsorption of molecules in the first layer. From the slope of the line, giving the values found for the net heat of adsorption as a function of the dipole moments, the average field strength, F, of rutile can be found by means of Eq. (22). The experimental value found by these investigators is... 

Figure 13.6 shows a schematic for IGC operation. Inverse, in this instance, refers to the observation that the powder is the unknown material, and the vapor that is injected into the column is known, which is inverse to the conditions that exist in traditional gas chromatography. After the initial injection of the known gas probe, the retention time and volume of the probe are measured as it passes through the packed powder bed. The gas probes range from a series of alkanes, which are nonpolar in nature, to polar probes such as chloroform and water. Using these different probes, the acid-base nature of the compound, specific surface energies of adsorption, and other thermodynamic properties are calculated. The governing equations for these calculations are based upon fundamental thermodynamic principles, and reveal a great deal of information about the surface of powder with a relatively simple experimental setup (Fig. 13.6). This technique has been applied to a number of different applications. IGC has been used to detect the following scenarios ...

To help clarify the nature of the site we have determined systematically its affinity for many different structurally related compounds. Thus, in the case of simple aliphatic carboxylate ions, affinities vary in proportion to their nonpolar surface areas as shown in Figure 14 (29,47). The straight line is drawn for the unbranched carboxylates, butyrate through... 

Amphiphilic compounds with surface-active properties, such as surfactants or ten-sides, assemble in water to form spherical aggregates. The size and shape of these aggregates depends on the structure of the amphiphile. As a general rule amphi-philes with one polar head group and one nonpolar alkyl chain form micelles. 

HP-RPC separates compounds according to their relative nonpolarity or hydrophobicity. In RPC, the polarity of the stationary and mobile phase is to the reverse of that used in NPC. HP-RPC is performed on porous or nonporous stationary phases with immobilized nonpolar polymers (i.e., -alkylsilicas) or nonpolymer polymers (i.e., microparticulate polystyrenes). The most commonly accepted retention mechanism in RPC is based on the solvophobic theory, which describes the hydrophobic interaction between the nonpolar surface regions of the analytes and the nonpolar ligands/surfaces of the stationary phase.15 16... 

Both dehydrogenation and dehydration were observed on these surfaces. On the three surfaces studied, the acetone peak, which was a product of dehydrogenation, always appeared at the same temperature as the propene peak, which was a product of dehydration. The H2 peak also appeared at the same temperature as acetone on the (0001) and the (OOOl) surface, but was at a lower temperature on the nonpolar surface. The water peaks were small, and appeared at temperatures different from the peaks of the carbon compounds. 

This technique, in its most popular application, is a modification of reversed phase liquid-solid chromatography. It is based entirely on concentration equilibrium and can be used to separate highly polar materials with a nonpolar surface. A counter ion to the ion desired to be separated is added to the mobile phase along with a buffer to maintain ionic strength and pH. A "paired ion" is formed that is neutral and can be separated from other similar compounds by a normal reversed phase column. A diagram of how this is done is shown in Figure 19-6. 

Because the high voltages required for ESI and plasma-APCI are independently applied and controlled, the dual ion source can be operated in ESl-only, APCI-only, or ESI + APCI modes to characterize polar, nonpolar, or both polar and nonpolar compounds, respectively. Laser systems, inclnding a CW laser and a pulsed laser, have been combined with the dual-ion sonrce to characterize chemical compounds on surfaces, where the desorbed analytes are introduced into the ESI and/or APCI plumes for postionization. In addition, analytes on sample snrfaces can also be directly desorbed and ionized by directing the ESI -H APCI plume toward the sampling area, an approach also known as desorption ESI -t APCI [47]. Chemical compounds including PAHs, peptides, drugs, diesel oils, and essential oils on stainless-steel and paper surfaces have been characterized by the dual ionization source. 

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