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How to Deal with Difficult to Filter Dissolution Samples?

Often, filters get selected based on what’s available in the laboratory or past experiences with other samples, rather than considering their actual suitability.

Regardless of its simplicity, filtration is a crucial step in dissolution testing. It’s the filter’s job to pause the dissolution process at a specific sampling time point. Essentially, it keeps the undissolved particles and other excipients out of the filtrate.

Choosing the wrong filter might lead to poor filtration, low recovery of the drug substance being tested, compatibility issues with the solvent or extractables, affecting the accuracy and consistency.

It is not recommended to use a single filter for a dissolution test! That can cause problems like carryover and analyte-binding.

Some filters may be reused for more than one point for the same sample considering the flushing volume needed to saturate the filter and number of samples that can be filtered before clogging have been optimized during method development. 

Hard-to-filter samples due to clogged membrane pores of the filter might need lots of manual effort, take more time per sample, and result in low drug recovery – definitely not good for lab productivity.

Avoiding excessive force while filtering is crucial too. Too much pressure can mess with automated systems or even force undissolved drug particles through the filter, giving incorrect results.

Plus, some drug product formulations release high levels of excipients during dissolution testing, which can quickly clog filters and mess up the analysis accuracy.

One option to deal with difficult-to-filter samples is to switch to filters with larger membrane pore sizes, but make sure they still retain the undissolved drug particles.

Another solution involves stacked filters, using a glass fiber (GF) pre-filter attached to the membrane filter. The GF traps coarse particles, keeping them from clogging up the final membrane. 

Let’s swap insights! Share your ideas on dealing with difficult-to-filter samples! Because the best learning often comes from shared experiences.

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Resource Person: Pearl Pereira Nambiar

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