LC impurity analysis: filtration versus centrifugation

[mojo]

Qualification of a filter for use in an assay is straightforward as you can compare the peak response between a filtered and an unfiltered portion of your test solution. However, if your test solution is to be used to determine the level of impurities in a drug product containnig insoluble excipients, can the filter truely be qualified if impurity stds do not exist? Retention of the drug substance on the filter may not be representative of the adsorption of impurities on the filter. Should such solutions be centrifuged instead of being filtered?

[carnie]

You could prepare one sample solution by filtration and another by centrifugation for comparison using samples after forced degradation.