Employing constant rate filtration to assess active pharmaceutical ingredient washing efficiency

Muhid Shahid, Chloé Faure, Sara Ottoboni, Leo Lue, Chris Price

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)
31 Downloads (Pure)


Washing is a key step in pharmaceutical isolation to remove unwanted crystallization solvents and dissolved impurities (mother liquor) from the active pharmaceutical ingredient (API) filter cake to ensure the purity of the product whilst maximizing yield. It is therefore essential to avoid both product dissolution and impurity precipitation during washing, especially precipitation of impurities caused by the wash solvent acting as an antisolvent, affecting purity and causing agglomerate formation. This work investigates the wash solvent flow through a saturated filter cake to optimize washing by displacement, taking account of diffusional mechanisms and manipulating the wash contact time. Constant rate filtration/washing is employed in this study using readily available laboratory equipment. One advantage of using constant rate filtration in this work is that it allows for the collection of separate aliquots during all stages of filtration, washing, and deliquoring of the API cake. This enables a wash profile to be obtained, as well as providing an overall picture on the mass of API lost during isolation and so can assist in optimizing the washing strategy. Particle size analysis of damp cake obtained straight after washing is also performed using laser diffraction. This allowed for agglomerate formation caused during washing to be distinguished from agglomeration that would be caused by subsequent drying of the wet filter cake. This work aims at improving pharmaceutical product quality, increasing sustainability, and reducing manufacturing cost.
Original languageEnglish
Pages (from-to)97-110
Number of pages14
JournalOrganic Process Research and Development
Issue number1
Early online date21 Dec 2021
Publication statusPublished - 21 Jan 2022


  • constant rate filtration
  • washing
  • impurity precipitation
  • anti-solvent crystallisation
  • agglomeration


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