Mechanism of size-exclusion chromatography

Utilization of a precolumn with size exclusion and reversed-phase modes for size-exclusion chromatographic analysis of polysorbate-containing protein aggregates

Size-exclusion chromatography (SEC) is a useful method for quantification of protein aggregates because of its high throughput capacity and highly quantitative performance. One of the problems in this method concerns polysorbates, which are well-known additives for protein-containing products to prevent protein aggregation, but frequently interfere with the photometric detection of protein aggregates. We developed a new SEC method that can separate polysorbates from protein sample solutions in an on-line mode with a precolumn with size exclusion and reversed-phase mixed modes. The precolumn can effectively trap polysorbates in aqueous mobile phase, and the trapped polysorbates are easily eluted with acetonitrile-containing aqueous mobile phase to clean the precolumn. Small parts of protein aggregates may be also trapped on the precolumn depending on temperature and proteins. Setting appropriate column temperature can minimize such inconvenient trapping of aggregates.

How much does band broadening adulterate results deduced from chromatograms measured by size-exclusion chromatography really?

A number of polystyrene samples and standards were measured with several column combinations which differed in their extent of band broadening, sigma(BB). Comparison of the derived chain length distributions showed in some cases good agreement even despite strong distinctions in the determined sigma(BB) values. The calculated number and weight averages of the samples were almost identical in most cases for the column combinations used. Furthermore, the points of inflection of the standards and of multimodale distributions composed of narrow (Poisson like) peaks in microemulsion were examined. When conferred with the theoretical values which were calculated for assumed Poisson distributions the respective deviations from the "true" ones were as high as 10% (almost reaching 20% in unfavorable cases). Simple (correction) procedures were tested in order to obtain the actual average values as well as the effective points of inflection of narrow distributions.

Estimation of band broadening in size-exclusion chromatography. I. A method based on analyzing narrow standards with a molar mass-sensitive detector

A method is proposed for estimating the (asymmetrical and non-uniform) band broadening function (BBF) in size-exclusion chromatography (SEC). The following data are required: the molar mass calibration and the concentration- and molar mass chromatograms of a set of narrow standards. In the narrow range of each standard, the BBF is uniform but skewed. Each uniform BBF is estimated through a nonlinear optimization procedure that compares one (of the two) measured chromatograms with its theoretical prediction based on the other chromatogram. The method is validated with numerical examples that simulate the analyses of narrow standards exhibiting log-normal and Poisson weight chain length distributions. The BBF can be assumed of arbitrary shape, or represented by an exponentially-modified Gaussian (EMG). From the uniform BBF estimate, the true polydispersity of the standard can be determined. The global non-uniform BBF is obtained by interpolation between a set of uniform BBFs covering a wide range of elution volumes.

Direct determination of band broadening in size exclusion chromatography

A simple method to correct the measured extent of band broadening in size exclusion chromatography for the contribution of narrow (polydisperse) standards is presented. It is based on the assumptions that commercial polymer standards can be described by a Poisson distribution and the additivity of peak variances. Two sets of standards (polystyrene from two suppliers) were investigated under normal working conditions, i.e. a combination of four columns with different porosities and a flow rate of 1 ml/min. Furthermore, the polystyrene standards were used to determine the extent of band broadening for four additional combinations of columns (varying in their separation range and porosities) as a function of the elution volume. The assumption of a constant peak variance for band broadening turned out to be a (very) rough approximation for some combinations of columns, but all results taken together demonstrate that this assumption is not generally applicable. Qualitative agreement between theory and experiment was found with a rearranged van Deemter equation.

Removal of NOM in the different stages of the water treatment process

Natural organic matter (NOM) is abundant in natural waters in Finland and in many ways affects the unit operations in water purification. In this study, the organic matter content in water in different stages of a full-scale treatment process over 1 year was measured. The full-scale treatment sequence, studied at the Rusko water treatment plant in Tampere, Finland, consisted of coagulation, flocculation, clarification by sedimentation or flotation, activated carbon (AC) filtration, and disinfection. High-performance size exclusion chromatography (HPSEC) was used for separation to determine changes in the humic substances content during the purification process. In addition, total organic carbon (TOC), KMnO4-number, and UV-absorbance at wavelength 254 nm (UV254) were measured. High molecular weight (HMW) matter was clearly easier to remove in coagulation and clarification than low molecular weight (LMW) matter. Furthermore, depending on the regeneration of the activated carbon filters, activated carbon filtration was effective to a degree but did not remove most of the lowest molecular weight compounds. Significant correlation was established among HPSEC, KMnO4, UV254 absorbance, and TOC. HPSEC proved to be a fast and relatively easy method to estimate NOM content in water and, in fact, gave more information than traditional methods on the type of NOM in a water sample. It also helped the process performance follow-up.

Non-ideal behaviour of free vanadate on a Superose 12 size-exclusion column. Application to in vivo 48V-labelled rat spleen homogenate

Seven chromatographic columns were evaluated for the recovery of 48V-radiolabelled vanadate. Further, the behaviour of vanadate (H2VO4-) was studied on a size-exclusion column Superose 12 as a function of (a) buffer salt molarity, (b) different buffer salts, (c) different buffers and (d) organic solvents added to the buffer. As opposed to the unsatisfactory recovery of V-compounds on other columns, we recovered the vanadium quantitatively. We observed that in most cases vanadate eluted after the total volume of the Superose 12 column. This indicates a non-ideal behaviour of vanadate. However, through this non-ideal behaviour it was possible to separate low-molecular-mass bound (Mr<5000) and unbound vanadium which would not be possible under normal behaviour. A possible explanation for this non-ideal behaviour of vanadium is put forward. The method has been successfully applied for the fractionation of different vanadium species in rat spleen homogenate.

Size-exclusion electrochromatography with controlled pore flow

In size-exclusion electrochromatography (SEEC) there exists an optimum in pore-to-interstitial flow ratio with respect to the resolution. Two methods for finding and controlling the optimal pore-to-interstitial flow ratio in SEEC have been studied: (i) varying the ionic strength of the mobile phase and (ii) the application of a hydrodynamic flow in addition to the electrco-driven flow. Both methodologies have been evaluated in terms of efficiency and applicability with columns packed with silica particles containing pores of either 10 or 50 nm in diameter, and with different ionic strength mobile phases. Using the first method with the 10-nm pore particles, the flow ratio could be adjusted within an appropriate range. However, with the wide-pore (50 nm) particles it appeared that the pore-to-interstitial flow ratio was too high at all conditions tested to obtain proper selectivity. In the second approach, the desired pore flow was generated by the electric field and the pore-to-interstitial flow ratio could then be adjusted by an applied pressure over the column. This method was applicable with both particle types studied. The application of a (low) voltage gradient in addition to a pressure-driven flow resulted in a sharply improved separation efficiency as a result of a strongly improved mass transfer due to intra-particle electroosmotic flow. When optimized, pressurized SEEC generates identical separation efficiencies for polystyrene standards as are obtained with pure SEEC, while the reduction in selectivity, in comparison to pressure-driven SEC, is kept minimal.

Ion-exclusion controlled size-exclusion chromatography of methacrylic acid-methyl methacrylate copolymers

Controlled ion-exclusion allows compensation of hydrophobic adsorption in size-exclusion chromatography of negatively charged methacrylic acid-methyl methacrylate (Eudragit) polymers using methanol as a mobile phase. Properly selected low-ionic-strength conditions below 5 mM LiCl provide correct separation in the size-exclusion mode. Possible disturbing effects, mainly related to light scattering, under low-salt conditions are discussed and shown to be negligible if on-line concentration-light scattering detection is used. The absence of these disturbances is checked by a comparison of experiments performed in methanol containing 1.25 mM and 2.5 mM LiCl. Molecular mass averages and distributions identical within the experimental error are obtained.

Refolding and purification of a urokinase plasminogen activator fragment by chromatography

A fragment of recombinant urokinase plasminogen activator (u-PA), was expressed in E. coli in the form of inclusion bodies. Purification and renaturation was achieved in a three-stage process. Capture of the inclusion bodies was achieved by coupling wash steps in Triton X-100 and urea with centrifugation. Solubilised inclusion bodies were then renatured by buffer exchange performed by size-exclusion chromatography (SEPROS). Use of size-exclusion media with higher fractionation ranges resulted in an increase in the recovery of u-PA activity, to a maximum fractionation range of Mr 10000-1500000 after which recovery is reduced, due to a low resolution between the refolded u-PA and denaturant. Fractions of refolded u-PA were concentrated using cation ion-exchange chromatography, which selectively binds correctly folded u-PA. The result is concentrated, active, homogeneous u-PA.

Considerations of sample application and elution during size-exclusion chromatography-based protein refolding

A mechanism for size-exclusion chromatography-based protein refolding is described. The model considers the steps of loading the denatured protein onto a gel filtration column, and protein elution. The model predictions are compared with results of refolding lysozyme (10 and 20 mg/ml) using Superdex 75 HR. The main collapse in protein structure occurred immediately after loading, where the partition coefficient of unfolded lysozyme increased from 0.1 to 0.48 for the partially folded molecule. Use of a refolding buffer as the mobile phase resulted in complete refolding of lysozyme; this eluted at an elution volume of 15.6 ml with a final partition coefficient of 0.54. The model predicted the elution volume of refolded lysozyme at 19.3 ml.