Bioreactor Product Charge Variant Profile Assessment by the A2P2 System
To evaluate charge variant profile in a cell culture sample, the sample must undergo affinity purification and buffer exchange to reduce the salt content of the sample matrix before injection into an ion exchange column. As shown in Figure 8b , the autosampler needle takes manually collected or online samples from the vial or FTV and directs them through an affinity capture column for cleanup. The column captures the protein of interest, flushing the sample matrix to waste via the FTV. The protein of interest is then eluted from the affinity capture column and accumulates in the FTV as an affinity-purified sample. The sample is subsequently diluted with the mobile phase of the charge variant assay inside intermediate vials to lower the salt concentration before injection into the analytical ion exchange column. If dilution doesn’t sufficiently reduce the sample’s salt concentration, a desalting column can perform a buffer exchange on the sample before injection for analysis. However, samples that are free from cell culture medium and meet the assay requirements for salt content require no affinity capture/cleanup, dilution, or buffer exchange. These samples can be directly injected into the ion exchange column for analysis.