Striking a Balance in HPLC. Choosing the Right Syringe Filter
Sample pre-filtration improves HPLC column life and data quality, but your filters must be matched to your application
January 13, 2022
In part one of this series, we discussed sample pre-filtration for HPLC and reviewed the problems that can arise over time in the absence of pre-filtration. In part two, we will look at filter selection and make sure you have the right filter for the job.
Finding a balance between speed and quality in HPLC
Analytical labs are often running large sample volumes daily, but still want the best possible results. That means the cleanest peaks, lowest background, and the clearest data from every sample. All of this requires finding the right balance between quality and speed to meet throughput requirements without sacrificing data quality. In this environment, any simple steps we can take that work to improve data quality, prolong the life of the HPLC equipment, and extend the time between services are worth considering, especially when they come with a very low cost and time overhead.
Pre-filtration of analytical samples prior to loading is just such a step that can greatly improve HPLC results. Pre-filtration not only impacts the sample being run, but by preserving the health of the column, can convey a higher level of quality on all the following samples to pass through the instrument as well. Sample pre-filtration ensures that your column stays in prime condition from run-to-run, and from sample-to-sample. However, it is not all plain sailing, using the wrong filtration membrane can result in contamination of the sample and a potentially deleterious effect on the column or other components of the HPLC system.
Considerations for syringe filter selection
Care needs to be taken during filtration not to influence the analytical results by subtly altering the sample, either by releasing extractable compounds into the sample, removing some of the analytes we wish to measure, or by removing solvent. There are three main considerations for filter selection:
1. Reducing extractables
Syringe filters need to have a very low level of extractables when challenged with the solvents in use. Consequently, it is very important to match the filter membrane to the application to avoid undesirable artifacts including false quantitation, coelution, and extraneous peaks. Membranes should be selected based on whether the protocol is using aqueous solvents, organic solvents, or some combination of the two.
2. Low binding
Syringe filters need very low levels of non-specific binding so that the syringe filter membrane does not reduce the concentration of the analytes in the sample influencing the results. This type of binding is a particular concern in applications such as pharmaceutical sample analysis where unwanted binding of the active pharmaceutical ingredient can cause out of specification results.
3. Correct pore size
Selecting filtration membranes with the correct pore size ensures effective particulate removal while maintaining flow rates and reducing filter blockage. The challenge for analytical methods is that we typically need to remove particles down to a very small size, around 0.2 mm, and syringe filter membranes of this pore size can quickly become blocked if the sample contains any quantity of larger particulate matter.
One solution is to use syringe filters that incorporate a larger pore size pre-filter that is capable of trapping larger particulate matter without blocking or backpressure. Ensuring the final filter membrane only needs to handle the smallest of the suspended particles.
Acrodisc® PSF GxF syringe filters incorporate serial glass fiber prefilters that progressively trap particulates all the way from >40 mm right down to 1 mm, maximizing flow and prolonging the life of the final filter membrane.
Syringe filter selection can be a complex process but finding the right filter for your specific application can have dramatic effects on the longevity of your analytical equipment and the quality of your data. Pall produces a wide range of syringe filters suitable for sample and mobile phase filtration in any HPLC application.
To help you navigate the requirements of different HPLC protocols and determine the best syringe filter membrane for your specific application you can download our poster: Considerations for Proper Syringe Filter Selection and our E-book that covers all aspects of Analytical Sample Preparation.