(312c) Use of Particle Size Analysis to Characterize Bed Stability Over Multiple Cycles in a Packed Chromatography Column

Particle size analysis by laser diffraction was used to correlate the in-situ (batch mode) bead diameter of chromatography media to bed stability of a packed chromatography column. An empirical method was developed to predict the performance of a packed chromatography bed during extended use. For a selected Hydrophobic Charge Induction Chromatography (HCIC) medium (pKa 4.8), the median bead diameter was measured in buffer under a variety of conditions of pH and conductivity. Particle size analysis indicated a significant increase in bead diameter after equilibration in a low pH (<4) buffer. An increased pressure drop across a packed bed at production scale (45 cm diameter) was also observed under this low pH condition. To further investigate this observation, a scale down column (3.2 cm diameter), using a constant diameter-to-height aspect ratio instead of a conventional fixed bed height, was employed to characterize bed stability over multiple cycles. In-situ bead size data was correlated to a measure of breakthrough volume and calculated HETP values when the medium was exposed to repeated cycles of swelling and compression in a packed bed. The analysis indicated that the low pH buffer accelerated bed deterioration. This trend was further supported by qualitative overlays of rate of change of conductivity versus totalized volume. When the low pH buffer was omitted from the process, increased bed stability was observed over multiple cycles. Thus, the trends determined by particle size analysis, that the bead diameter should not change significantly if buffer pH remains above a threshold level (pKa 4.8) throughout the process step, were confirmed. This suggests that changes in bead size could be attributed to induced electrostatic repulsion at low pH and could be modulated to increase usable column lifetime. When correlated with packed-bed performance, particle size analysis can be a valuable tool to better characterize column lifetime at increased scale. This technique can also be used as a predictive tool for screening new chromatography media and developing robust process operations.