Amines, adsorption

Hydrophilic interaction chromatography on Asahipak NH2P or Excel-pak CHA-P44 with pulsed amperometric detection has been used to fractionate malto-oligosaccharides.266 The Asahipak NH2P is a polyvinyl alcohol support with a polyamine bonded phase, and the Excelpak is a sulfonated polystyrene in the Zn+2 form. Amine adsorption of sialic acid-containing oligosaccharides was performed on a Micropak AX-5 column (Varian) using acetonitrile-water-acetic acid-triethylamine.267... 

In conclusion, the use of amines for the characterization of adsorption and active sites raises the same problems as ammonia. The interaction of the amines, saturated aliphatic amines in particular, with oxide surfaces is certainly still less specific than that of ammonia because of their higher basicity and their larger molecular size. The influence of steric effects on amine adsorption has been discussed (172, 201b). Thus, Medema et al. (172) came to the conclusion that the adsorbed amount of an amine on 7-Al2 03 primarily depends on its molec-... 

The heterogeneous catalysis process requires the formulation of a multifunctional catalyst which at a first approximation presents (i) acidic properties (amine adsorption, dehydration,...) and (ii) a hydro-dehydrogenating function (methanol dehydrogenation, hydrogenation of imine and enamine intermediates). 

System 11 Amine adsorption/ion suppression chromatography on Micropak AX-5 with UV monitoring (200 nm) at room temperature acetonitrile/water/0.25 M sodium dihydrogenphosphate (72 18 6, v/v/v) running time 21-24 min [283]. 

Anionic sulfonated polyacrylamide (PAMS) is also found to increase amine flotation of quartz. Although PAMS does not adsorb on the negatively charged quartz and cause no direct activation of amine adsorption, the polymer-surfactant electrostatic interaction can lead to the formation of complexes. This polymer-surfactant complex can reduce the armoring of bubbles and lead to flotation. The anionic polymer can also bridge the adsorbed amine to the amine on the bubble surface and enhance flotation under saturated adsorption conditions. The hydration effect of the polymer may also be responsible for the enhanced flotation in this case. 

The first term on the left-hand side occurs on account of diffusion of CF from compartment A to compartment B and kj is a constant, which would be related to diffusion coefficient and surface area. The second term is related to interaction of CF and NH4 ion, k2 is a constant which depends on the extent of NHj (amine) adsorption. It may be noted that Cl would be depleted with increase in (NH4) and consequently AC would increase. 

In general, when results obtained from titration methods are compared with the catalytic activity, the correlation is not necessarily good. One of the reasons is that only a small fraction of the total acid sites measured by titration are active for a given catalytic reaction. The low temperature at which amine adsorption is measured with the use of color indicators favors adsorption on aU sites, including the weakest ones. Thermal desorption methods may discriminate between sites of different strength but are unable to distinguish between Lewis and Bronsted sites. When coupled with vibrational spectroscopy data, the TPD technique may, indeed, be adequate for analysis of surface acidity [136]. However, it is almost... 

More recent studies of amine adsorption mechanisms at surfaces have been carried out using atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), and SFVS techniques (Bakshi et al. 2004 Castro et al. 1986 C hemyshova et al. 2000 Fuerstenau and Renhe 2004 Paruchuri et al. 2004 Schrodle and Richmond 2008 Subramanian and Ducker 2000 Velegol et al. 2000). AFM studies show that spherical micelles of cetyltrimethylammonium bromide/cetyltrimethylammonium chloride (CTAB/CTAC) surfactants form at silica surfaces near the critical micelle concentration (CMC) (Bakshi et al. 2004). Compared with tertiary and quaternary amines, primary amines, such as DDA, would have a different molecular structure at the silica surface. For example, AFM studies suggest that primary amine forms a featureless bilayer at mica surfaces. 

Amine adsorption in the active region of mild steel corrosion is based on chemisorp-tive interactions between the amine and the exposed metal atom (Li et al., 1997). 

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