Biphasic desorption

Finally, it is possible that the analyte and the sorbent may be chemically reactive toward each other such that the analyte becomes covalently bonded to the solid-phase sorbent. This type of sorption is generally detrimental to analytical recovery and may lead to slow or reduced recovery, also termed biphasic desorption. All of these interactions have the potential of operating simultaneously during sorption [8,54,55],... 

In a series of papers, Gupta et al. (109-112) studied the in vitro release properties of heat-stabilized BSA microspheres containing adriamycin. The biphasic release of drug was attributed to its location in the microsphere. The initial release results from surface desorption and diffusion through pores, while the later release arises from drug within the microsphere, which becomes available as the microsphere hydrates. 

CO oxidation, 38 236 differential heat of adsorption, 38 217 Biphasic systems, catalysis see Multiphase homogeneous catalysis BiPMo catalysts, 34 39 in formamide to nitrile reaction, 34 39 Bi-postdosing thermal desorption spectroscopy cyclohexene, 42 240... 

We observed that only a small fraction of the adsorbed mass would desorb even after a number of successive desorption steps. The investigation on laboratory contaminated soil showed a biphasic behavior, namely an easily desorbed fraction and a desorption resistant fraction. Both field contaminated and aged soils also showed the same behavior. The first stage involved a loosely bound fraction and the second stage involved a tightly bound fraction. The desorption constants calculated or estimated for the two fractions were em-... 

An empirical model was used by Opdyke and Loehr [17] to describe the contaminant rate of release (ROR) similar to what we observed a relatively rapid release of the chemical followed by a much slower release of the remaining chemical. The non-linear equation used to describe this biphasic behavior during desorption was given by... 

Slow sorption has also been ascribed to conversion of the sorbate from a high-energy state to a low-energy state. For example, sorption-desorption of Cu from soil was observed to be biphasic, which was attributed to high- and low-energy bonding sites (Lehman and Harter, 1984). Incubations for up to 4 days showed continued uptake of Cu and a decrease in the fraction released within the first 3 minutes, which was referred to as the low-energy sorbed fraction. 

In contrast to sorption studies, relatively little information is available on the desorption of trace elements from soils or soil components as affected by organic and inorganic ligands. Desorption studies have showed biphasic reaction processes for sorption and desorption of trace elements (Sparks, 1990) a fast reaction followed by a slow reaction. 

Other, more direct evidence for co-existing populations of adsorbed proteins with very different rates of removal is provided by the behavior of IgG on silica and n-pentyl silanized silica (22.) The desorption of this protein from silica, when it had been allowed to reside on the surface less than 100 min, was linear with the square root of time, suggesting a single state existed. However, after longer residence times on silica (1000 min), the desorption curves were distinctly biphasic. Diphasic desorption was observed for IgG adsorbed to n-pentyl silanized silica but in this case it was observed even after short residence times. Thus, under these conditions some of the IgG desorbed much more rapidly than the remainder. It is difficult to attribute... 

The sorption of mono-CB on marine sediment required 3 hours to reach a sorp-tion/desorption equiUbration (Zhao et al, 2001). Compared with sediment organic carbon content, surface and microporosity of the sediment might have a more important effect on the sorption of mono-CB (Zhao et al, 2001). Temperature does not have great influence on the adsorption behavior of mono-CB in seawater, but the saturate sorption capacity decreases as the temperature increases. The Tenax-mediated desorption of HCB from four freshly spiked, artificial sediments exhibited biphasic kinetics the first-order rate constants of the fast desorbing phase and slow desorbing phase were 9.6 x 10 and 7.2 x lO h respectively (Chai et al, 2007). The fast desorption fractions for the four sediments varied from 41.2 to 68.8% (Chai et al, 2007). 

However, it should be pointed out that some of these systems are really miniemulsions that is, biphasic systems with extremely small droplets in the same 100-A range as microemuisions. These are made, thanks to a physico-chemical transition trick, by quenching a desorption-nucleation mechanism or by forcing an inversion to take place [158,159]. Such miniemulsions are not thermodynamically stable, but they can be stabilized against Brownian coalescence for extremely long periods by the formation of a liquid-crystal layer [160]. 

The distributed reactivity model explanation for the biphasic rate behavior commonly observed for desorption of HOCs from soils is that the soft-carbon sorbed, or labile fraction of the contaminant desorbs readily and reversibly, whereas the hard-carbon sorbed, or resistant component is released much more slowly. The slow desorption step has been attributed to non-Fickian diffusion into a tightly-knit SOM, polymerization, or entrapment within the SOM matrix. The rate model found in comparative analyses to be the most appropriate for description of such behavior (17) is a two-phase release model which couples first-order rate equations for both the slow, resistant, and rapid, labile fractions, < >r (= 1- (j) ... 

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