During dissolution test, in most cases it’s very important to filter the sample immediately after withdrawal. If not filtered two things may happen:

- Undissolved API may continue to dissolve even after specified time which may cause the result to be higher than the actual value.

and/or

- Undissolved excipient may continue to dissolve and cause interference in method.


While choosing filter, few things to be considered:

  • Material should be compatible with each of API & Dissolution Medium.
  • Pore size should be appropriate for the API particle size so that undissolved API doesn’t pass through.
  • Filter type which is convenient and compatible (e.g., disk, whatman, cannula filter etc.)
  • Filter size should be appropriate with the withdrawn sample volume (i.e., using very large size filter for small amount of sample may lead to inadequate filtrate or small filter for large amount of sample may cause quick clogging).

  • Also adsorption is a very common phenomena in filtration. To avoid decreased concentration, first few amount of filtrate should be discarded so that saturation is achieved.



Reference:

  • 𝑼𝑺𝑷 𝑮𝒆𝒏𝒆𝒓𝒂𝒍 𝑪𝒉𝒂𝒑𝒕𝒆𝒓 <1092>