In situ determination of adsorption kinetics of proteins in a finite bath

A method for fast in situ measurement of adsorption kinetics based on a finite bath was developed. We modified the conventional finite bath by replacing the external loop by a dip probe which enables in situ measurement of the concentration change in the contactor. Deposition of adsorbent particles on the reflection surface of the dip probe compromised measurements. Different membranes, a polyamide, a polypropylene and a nylon membrane were tested to protect the internal reflection surface of the dip probe from fouling with adsorbent particles. The nylon membrane provided efficient protection and high mass transfer evaluated by response time experiments. Unspecific adsorption of the model protein on the membrane could also be excluded. To corroborate the measurements of the dip probe the results were compared to a conventional finite bath and to a shallow-bed. The uptake curves for human polyclonal IgG at different concentrationes (0.1-3 g/l) on rProtein A Sepharose FF and MabSelect were used as model system. The effective diffusion coefficients were determined using a pore diffusion model. These values were in good agreement for all methods.     

Continuous desorption rate measurement from a shallow-bed of poly(styrene-divinylbenzene) particles with correction for experimental artifacts

A 0.50 mm high bed, containing ca. 3 mg of the nominally non-porous poly(styrene-divinylbenzene) (PS-DVB) sorbent Hamilton PRP-infinity, is located in a valve. After the bed is pre-equilibrated with a (7/3) methanol/water solution of naphthalene (NA), the valve is switched and (7/3) methanol/water solvent flows continuously through the bed at a high linear velocity. This causes NA to desorb into a constantly refreshed solvent, creating a "shallow-bed" contactor with an "infinite bath" kinetic condition. The effluent from the bed passes through a UV-absorbance detector which generates the observed instantaneous desorption rate curve for NA. The same experiment is performed using the solute phloroglucinol (PG), which is not sorbed by PRP-infinity and serves as an "impulse response function marker" (IRF-Marker). The resulting peak-shaped IRF curve is used in two ways (i.e. subtraction and deconvolution) in order to correct the observed instantaneous rate curve of NA for the following experimental artifacts: hold-up volume of the bed and valve, transit-delay time between the bed and the detector and instrument bandbroadening of the NA zone. The cumulative desorption rate curve, which is a plot of moles NA desorbed versus time, is obtained by integration. It is found to be accurately described by the theoretical equation for homogeneous spherical diffusion. The diffusion coefficient of NA inside the PRP-infinity particles (5.0+/-0.6) x 10(-11) cm2/s, agrees with the literature value that was obtained from the sorption rate of NA into the same particles. This constitutes virtually conclusive evidence for diffusion control of intra-particle kinetics of NA in the PS-DVB matrix of PRP-infinity and related polymers. The influence of both sorbent and solute properties on the method is evaluated.     

采用浅床技术测定亚铁氰化钛钾交换Cs+的传质特性

采用浅床技术分别研究了料液浓度、操作温度以及料液流速对用亚铁氰化钛钾无机离子交换剂从硝酸铯溶液中交换Cs+的总传质系数的影响.结果表明,随着料液浓度的上升,总传质系数变化不大,仅在q(交换剂相Cs+浓度)较高时呈微弱的下降趋势.在实验范围内,随着操作温度的升高,总传质系数相应升高.料液流速对亚铁氰化钛钾交换Cs+的总传质系数的影响最大,其影响分为两个阶段当q＜0.25mmol/ml时,对一定的料液流速,总传质系数随着q值增加而较快下降;对一定的q值,总传质系数随着料液流速增加而增加.当q≥0.25mmol/ml时,时一定的料液流速,总传质系数随着q值增加缓慢下降;对一定的q值,不同料液流速下的总传质系数几乎没有区别.总之,当q值较小时,传质过程由液膜扩散和交换剂粒内扩散共同控制;当q值较大时,液膜扩散阻力相对于交换剂粒内扩散阻力要小得多,传质过程由交换剂粒内扩散控制.