Overload Effects in Reversed Phase Protein Separations using Capillary-Channeled Polymer Fiber Columns.

In preparative chromatography, overloading effects are a fact of life. However, peak distortion is problematic in analytical scale chromatography, especially in the case of bio-macromolecule separations. Capillary-channeled polymer fibers have been employed for fast protein separations in reversed phase, ion exchange, and hydrophobic interaction liquid chromatography. Although the primary advantage of the phase is operation at high linear velocities (~100 mm s-1 ) without van Deemter C-term limitations, the limited specific surface area (<5 m2 g-1 ) suggests that a thorough understanding of overloading effects is needed. We evaluate important factors (injected mass and volume) affecting overload in terms of peak height, width and shape (asymmetry). Overload conditions readily apparent as the peak shape changes from a Gaussian distribution to a left-triangle with slight tailing; more-or-less classical overload behavior. Three methods were used to compute column efficiency in terms of plate counts (N), including the area height, half-height, and the Dorsey-Foley approaches. The half-height method is best-suited for describing column overload, accounting for peak distortion and achieving high levels of consistency. The limiting plate count (N0 ) and the column sample loading capacity (ω0.5 ) were key metrics to characterize overall column performance. Peak capacity (P) was used to assess gradient elution separation performance. Increased flow rates and column length result in enhanced loading capacity. pH mismatch between the sample matrix and the mobile phase, a common cause of protein overload with other phases, was not responsible for distorted peak shapes unless the solvent pH is close to the pI of protein samples.