Filter breakthrough is a critical issue in syringe filtration that can lead to sample contamination and damage to analytical instruments such as HPLC. To avoid filter breakthrough, it is important to select the right syringe filter and follow best practices during the filtration process. Here are some key tips:

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Select the Appropriate Filter Material and Pore Size

The choice of filter material and pore size depends on the nature of your sample:

For aqueous solutions and most organic solvents, hydrophilic regenerated cellulose (RC) filters are a good option.

Avoid filters containing PFAS (per- and polyfluoroalkyl substances) which can leach into the sample.

Consider the active ingredients in your sample and choose a filter material that is compatible and free of extractables.

For most applications, a 0.45 μm pore size is sufficient to remove particles. Smaller pore sizes like 0.2 μm may be needed for UHPLC or to remove fine particles and bacteria.

Use a Prefilter for Challenging Samples

Prefilters placed upstream of the sterilizing filter can help prevent breakthrough by reducing the microbial burden and removing particulates that could cause pressure fluctuations:

Adsorptive depth filters are effective prefilters for virus filters, removing small aggregates that could plug the downstream filter.

Using a 0.5 μm prefilter prevented breakthrough of S. marcescens through 0.2 μm filters in one experiment.

However, prefilters add cost and complexity, so their use should be justified based on the specific application.

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Optimize the Filtration Process

Proper technique is key to avoiding breakthrough:

Filter samples immediately before analysis to minimize microbial growth.

Use a gentle filtration method like pressure rather than vacuum to avoid shearing cells.

Filter sufficient volumes to detect low levels of contamination - at least 100 mL in one study. The USP recommends testing 10% of the batch volume.

Avoid storing filtered samples for extended periods which could allow microbial growth.

Validate the Filtration Process

Experimental validation is essential to ensure the filtration process is effective for each specific application:

Challenge filters with the actual sample matrix and relevant microbes, not just standard test organisms.

Starved cultures may be more representative of real-world conditions than nutrient-rich cultures.

Evaluate the entire filtration process, not just the filter itself.

Ensure sufficient microbial challenge levels and sample volumes to detect breakthrough.

Use High-quality Syringe Filters

Choosing syringe filters from a reputable manufacturer can provide further assurance that filter breakthrough will not occur:

Look for filters with features such as heat-seal membranes that prevent particle release.

Sufficient headspace within the filter housing to accommodate larger filter cakes before plugging.

Qualification of filter performance (e.g., HPLC) verifies quality.

By following these best practices for filter selection, process optimization, and experimental validation, you can minimize the risk of filter breakthrough and ensure the integrity of your samples and analytical results. Investing in high-quality syringe filters from a trusted manufacturer is also an important safeguard.

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