Kinetics desorption, flowing protein solution

Application of a quantity of solution, in this case protein solution, to a column filled with appropriate substrate, leads to an exchange between the solute and the surface, and movement with the solvent front such that the emerging solute profile contains complete information concerning the kinetics of adsorption/desorption. Apart from the interaction of solute with surface, concurrent three-dimensional diffusion often occurs, and perhaps occlusion, if the substrate is porous. Nevertheless, the option of deducing interfacial kinetics from the elution profile in a flowing system has a certain elegance and relevance to the performance of blood plasma proteins in vivo. 

Protein Adsorption and Desorption Rates and Kinetics. The TIRF flow cell was designed to investigate protein adsorption under well-defined hydrodynamic conditions. Therefore, the adsorption process in this apparatus can be described by a mathematical convection-diffusion model (17). The rate of protein adsorption is determined by both transport of protein to the surface and intrinsic kinetics of adsorption at the surface. In general, where transport and kinetics are comparable, the model must be solved numerically to yield protein adsorption kinetics. The solution can be simplified in two limiting cases 1) In the kinetic limit, the initial rate of protein adsorption is equal to the intrinsic kinetic adsorption rate. 2) In the transport limit, the initial protein adsorption rate, as predicted by Ldveque s analysis (23), is proportional to the wall shear rate raised to the 1/3 power. In the transport-limited adsorption case, intrinsic protein adsorption kinetics are unobservable. 

Although ATR has been used to quantify the variation in composition at the surface in TPEs (Sung and Hu, 1980), a related utility is its ability to monitor in situ processes such as reaction injection molding (RIM) (Ishida and Scott, 1986) and protein adsorption onto a polyurethane substrate (Pitt and Cooper, 1986). In the latter, the effect of shear rate on the kinetics of protein adsorption and desorption from phosphate-buffered saline (PBS) was studied in a specially designed flow cell. A very thin film of the commercial MDI-ED-PTMO polyurethane Biomer was cast from solution onto a Ge ATR prism. The thickness of the film was less than the penetration depth so the protein concentration could be monitored after the infrared absorption of the polymer... 

Under HPLAC conditions, similar elution curves for AT III and Heparin were observed on PAOM and PSSO stationary phases. Antithrombin III was immediately eluted by 0.1 M sodium chloride solution and no detectable protein desorption was observed at 2 M ionic strength (Figure 3A). Thus the inhibitor was not retained by either PAOM or PSSO, Compared with the findings mentioned above, thi s can be explained in terms of kinetic effects. By decreasing the elution flow-rate and simultaneously overloading the columms, retention of a small amount of AT III ( 1%) was observed at the same ionic strength, i.e. 0.1 M NaCl. 

Figure 6. Kinetic plot for protein and polysaccharide adsorption and desorption as a function of time of flow of gum arabic solutions at pH 6.5. Key 0.1% (w v) gum arabic, 0 1549 cm ol035 cm" , 1.0% (w v) gum arabic, + 1549 cm x 1035 cm (All data not shown for clarity.)...

---