**Assay ** |
**Purpose ** |

Field flow fractionation multiangle light scattering (FFF-MALS) |
Determine particle number and aggregation state |

Atomic force microscopy (AFM) |
Determine particle number and aggregation state |

Transmission electron microscopy (TEM) |
Determine particle number |

Size exclusion chromatography multi - angle light scattering (SEC-MALS) |
Determine particle number and aggregation state |

TCID, FFA, plaque, or other assays |
Determine proportion of defective particles based on the difference between total particles and infectious particles |

Polymerase chain reaction (PCR) |
Determine proportion of nucleic acid containing particles |

Density gradient centrifugation |
Determine proportion of defective particles based on relative densities of particle populations |

Analytical ultracentrifugation (AUC) |
Determine proportion of defective and aggregated particles based on hydrodynamic properties of particle populations |

Capillary electrophoresis (CE) |
Determine proportion of defective and aggregated particles based on particle mass and charge |

Reversed-phase HPLC (RPHPLC) |
Determine proportion of defective and aggregated particles based on hydrophobic interaction properties |

Ion-exchange chromatography (IEC) |
Determine proportion of defective and aggregated particles based on charge state of the particles |

Size exclusion chromatography (SEC) |
Determine proportion of defective and aggregated particles based on hydrodynamic sieving properties of particle populations |

SDS-PAGE (or equivalent) |
Determine composition of proteins contained in preparation based on polypeptide chain sizes |

Western blot |
Determine composition of immunoreactive proteins contained in preparation |

Process residuals (BSA, benzonase, polysorbate, etc.) |
Quantify process-related impurities |