Adsorption columns, residence time

Figure 9. Plutonium Adsorption on Bone Char for Various Column Residence Times...

HPLC is ideally suited to examine adsorption kinetics in the working conditions of column immunoassays. In this technique, high flow rates and minimized column volumes are required to perform rapid on-line immunodetections. The column capacities and residence times in the column are parameters that influence the efficiency of the immunoreactor. Kinetic studies using the chromatographic format will be useful to understand the process better and optimize the methodology. 

There are four unknown parameters in the theoretical impulse response for porous particles, h(t) the pellet diffusion time, tdif (which contains the effective diffusion coefficient of the pair T-C, Dtc, td.fs R p/D.f( , R is the radius of the pellet equivalent sphere), the mean residence time of the carrier-gas in the interparticle space, tc (tc = v/L with the carrier gas linear interstitial velocity, v, and column length, L), Peclet number, Pe (Pe = L.v/E, with E the effective axial dispersion coefficient) and the adsorption parameter, 5q (see below). Because matching with four unknown parameters would give highly correlated parameters, it is better to determine some parameters independently,... 

When trace elements are introduced into a lake by riverine and atmospheric input, they interact (1) with solutes (complex formation) and (2) with inorganic and organic (phytoplankton) particles (adsorption and assimilation). The affinity of the reactive elements for the particles, which settle through the water column, determines essentially the relative residence time of these elements and their residual concentrations and ultimate fate (Figure 10.20). 

The required size of the process bone char columns for PFP wastewater can be estimated from adsorption rate measurements. Values of C/Co are plotted in Figure 9 for the 26 mL bone char columns as a function of residence time. TTie required C/Co value is defined as follows ... 

There have been many investigations on surfactant foams, foam films. Plateau border, foam drainage and their physical chemistry. The application of these results to protein foams is only partly possible. Proteins are macromolecules, their adsorption is coupled with a change in conformation at the gas/liquid interface which is a slow process. It takes 15 to 20 h to obtain the equilibrium surface tension. The residence time of the protein molecules in a flotation column is too short to attain the equilibrium surface tension during this time. Therefore, the transport of proteins to the interface and their adsorption at the interface are dynamical processes which are far from equilibrium. Surfactants have well-defined hydrophilic and hydrophobic domains. Thus it is relatively easy to calculate their interaction with the interface. Protein molecules have several hydrophilic and hydrophobic domains, and their interaction with the interface depends on the hydrophilic/hydrophobic character of their surface... 

Pulsed splitless Reduction of the residence time in the liner resulting in the decreased analyte degradation/adsorption and reduced matrix-induced response enhancement Larger injection volumes (limited by the liner size and solvent expansion volume) Potential transfer of nonvolatile matrix cx)mponents further into the column... 

Instantaneous adsorption. During the flow of polymer solutions through porous media, the hydrodynamic convection of macromolecules brings them into contact with solid surface in a mean time t which is of the order of a few seconds under our experimental conditions. Since the probability for a macromolecule to be adsorbed during the first contact with the pore surface free of adsorbed pol3mier is very high, the polymer adsorption can be considered as instantaneous. Indeed, this mean time is negligible compared to the residence time of macromolecules t inside the column. 

Any chromatographic technique is based on the flow through a porous medium— the stationary phase. The flow in the pores is very slow and the transport of solutes and particles is mainly diffusive. Adsorption/desorption, hydrodynamic or steric effects specifically influence the residence time of the different species and, thus, facilitate their separation. In SEC, one employs stationary media with very hroad pore size distributions. Since the particles can only move into those pores that exceed their geometric dimensions, the penetrable pore volume decreases with increasing particle size. Coarse particles, therefore, pass the column more quickly than fine ones (Fedotov et al. 2011). SEC was originally developed for the separation of polymer... 

Two types of techniques are commonly used for the determination of the internal void fraction and the tortuosity. The first uses a column packed with the catalyst and having a djdp ratio such that the flow approximates the ideal plug flow pattern, it is conveniently inserted in the furnace of a gas chromatograph that has all the parts for detecting the feed and response signals, besides temperature- and flow controls and six way valves. A narrow tracer pulse is injected in the carrier gas flow and the response is measured at the exit of the column. The pulse widens as a consequence of the dispersion in the bed, adsorption on the catalyst surface and effective diffusion inside the catalyst particle. The tracer does not have to be the component A itself The injected pulse should have an adequate residence time in the column and sufficient widening. Preference is given to transient measurements because steady state operation would not measure the effect of the dead end pores. 

When a protein is adsorbed to a hydrophobic surface, denaturation is often not an instantaneous phenomenon. Thus, the extent of unfolding will increase with increasing time of adsorption. Both Karger and Hearn et al. [40] have monitored this residency effect on reversed-phase and hydrophobic interaction columns using a combination of techniques including derivative spectroscopy. The Hearn group also studied denaturation kinetics in size exclusion chromatography in the presence of the powerful denaturant urea. 

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