July 12, 2017

Do's and don’ts when filtering viscous liquids

By Cytiva Scientific support team

Filtration of viscous liquids in preparation for analytical instrument analysis can be challenging. Save time and boost lab efficiency with this guide.

If you work in an analytical lab that performs filtration prior to analysis, then you’re probably used to processing many samples under a set time constraint.

Any way to save time in analytical sample preparation while still delivering accurate, consistent results can help get products released quickly and safely.

HPLC/UHPLC sample preparation

Sample filtration is a key step in the preparation of a sample for chromatographic analysis. Not filtering samples can lead to issues such as clogging of a chromatography column frit, resulting in back-pressure build-up and performance degradation. Ultimately, this increases the time spent on troubleshooting and preventive maintenance.

Filtration is relatively straightforward for most samples; however, you can run into problems with solutions that are viscous or heavily laden with particulate matter. These harder-to-filter samples are especially prevalent in the food and beverage industry—thick syrups, pulpy juices, and fatty oils are some common samples.

If your sample contains cornstarch, syrups, soy, sucrose, or fruit-based additives/ingredients, then you might find that using a standard syringe filter is a challenge.

What do I need to look out for when filtering viscous samples?

The biggest challenges when filtering viscous samples are:

  • Increased filter back pressure
  • Increased pump pressure required due to frit clogging
  • Shouldered or split chromatogram peaks

When pushing viscous samples through a syringe filter by hand, increased back pressure and membrane clogging might require you to exert a large force. This has ergonomic implications, because it brings with it an increased injury risk such as for repetitive strain injury.

Users often try to address this issue by either inefficiently using multiple syringe filters for a single sample, or applying as much pressure as possible to the syringe to force the sample through the filter. Both approaches are uncomfortable and take more time than necessary.

Find out more about ergonomic considerations for laboratory filtration from our previous blog post.

How can I filter viscous samples more effectively?

To filter challenging samples, we recommend using a syringe filter with a prefiltration stack, consisting of graded-density microfiber that traps larger particles before they reach the filter of specified pore size. This enables processing of larger sample volumes with less back-pressure build-up. Using an appropriate filter diameter will also ease the filtration of large volumes.

For example, in a recent study, our Whatman GD/X syringe filter showed the ability to process up to seven-fold more sample volume than comparable filters lacking a prefiltration stack. The GD/X syringe filters also have an increased loading capacity when compared to a single filtration syringe filter to accommodate high solids content.

It is important to choose a filter with the correct chemical compatibility. For example, using a hydrophobic material with an aqueous sample can cause back pressure build-up. And choosing the wrong membrane can cause other performance issues. If in doubt, consult a chemical compatibility table and test the material(s) in your application.

To help with your filtrations, we’ve compiled a brief checklist of some “Do’s and Don’ts” when filtering viscous samples:

  • Do exert even but moderate pressure on syringe filters to ensure that a consistent sample is produced. If back pressure begins to cause noticeable resistance, check whether your filter is optimized.
  • Do consider prefiltration stacks if you experience filtration back pressure, membrane clogging, or see high levels of chromatography column degradation due to unfiltered particles entering the injector.
  • Do conduct a review of your filtration processes to see if there are opportunities to streamline and boost efficiency.
  • X Don’t force liquid through the filter if you are encountering strong resistance from the filter. Doing so might cause unnecessary discomfort, hand strain, or potentially even filter leakage.
  • X Don’t automatically select a narrow diameter filter when you have a large sample volume. Select a diameter appropriate to the volume.

Try our Whatman filter selector to find out if you are using the most appropriate filtration solution for your samples. To discuss any challenges you are facing, please contact Cytiva.