Chromatographic Process Steps in Biopharmaceutical Manufacturing

Key Insight

Chromatographic processes typically transform dilute, impure solutions into concentrated, pure products. The strategy of first concentrating the product, then purifying it (path ACD), is generally preferred because processing costs for dilute solutions are directly proportional to volume. Reducing volume early through concentration, often on a high-capacity selective adsorbent, can also decrease product loss, for example, by separating proteases during the initial capture step.

A typical downstream process involves three major steps: Capture, Separation, and Polishing. The main goal of capture is product concentration on the stationary phase, separating it from unrelated impurities such as small molecules, DNA, endotoxin, and contaminant proteins, which have significantly different properties. High yield is critical, while resolution of related impurities is usually secondary. Capture steps commonly utilize stationary phases with high binding capacities, larger particles, shorter columns, and higher flow rates, often employing selective affinity adsorbents like Protein A for IgG capture and step or steep gradient elution.

Subsequent separation steps focus on resolving impurities closely related to the target product, including proteins with similar pI and hydrophobicity, or misfolded/altered isoforms. These require greater plate numbers, achieved with smaller particles, emphasizing selectivity over capacity, and using lower flow rates, longer columns, and shallow gradient operations. Polishing, the final step, removes process chemicals and process-generated impurities like dimers or aggregates; size exclusion chromatography (SEC) is often effective for this, despite its limited capacity, due to its mildness and ability to simultaneously remove aggregates and exchange buffers. Intermediate steps, such as buffer exchange via diafiltration or SEC, are also integrated, particularly when using orthogonal stationary phase chemistries, or by carefully arranging steps to avoid buffer exchange.