Most of the time our preparation of the sample is what causes the problems we face during filtration. This article covers some tips and tricks that will help you troubleshoot filtration samples to some of the issues that you might be overlooking as you use PVDF syringe filters and any other filters you might be applying.

Sample filtration is ubiquitous when preparing samples for your work since it is designed to eliminate particulates before injection. Most of us will ignore this fact. The filter body is constructed by use of various materials and the solvent to be used together with the application will decide which one you will select for your use.

Chemical Compatibility

Your supplier will help you select a filter material that is chemically compatible with your application since there are only a few subset materials. For instance, when applying organic solvents or others with extreme levels of pH, you should ensure that filter membrane disintegration does not happen.

Allowing any leachates can be the reason for interference within the chromatogram adversely affecting the quality and quantity aspects of your analysis particularly when employing spectrometric detectors. If you doubt whether there is the presence of leachates, you need to rinse using 1 ml of aliquot which is typically enough for most filters — which will pre-clean it.

Analyte Binding

Analyte binding/adsorption is another problem that you might encounter. It is capable of having an impact on the quantitative performance of the procedure. Adsorption degree varies with filter types and the sample matrix will determine the changes.

Glass fiber and nylon show bond highly with peptides and proteins while polyethersulfone (PES) and polyvinylidene (PVDF) fluoride are generally ideal. Hydrophilic membranes like polytetrafluoroethylene (PTFE) and PVDF tend to produce minimal nonspecific binding for molecular analytes with lower weight. Because of this, you should always do some investigations on the binding of these filters as you develop your method. This can be made possible by trying out how your instrument reacts to each analyte with unfiltered and filtered sample.

Prefilters

There are those analytes that are packed with particulates. In this case, processing that is facile will need a prefilter to enable continuous flow in porosity membrane that is under it. Such syringes are known as multilayer syringes with the ability to allow the sample to pass through five times more. Take note that a big number of pre-filters are actually glass fibers, which will make protein filtration an impossibility. You should, therefore, pick on filters with PES or PVDF prefilter construction material.

Selecting a filter size that suits your application is also vital. Filters with large diameters will allow the quick flow of the sample without needing too much pressure and with less clogging. However, be ready for possibilities of higher extractable levels, hold-up volumes that are large and higher analyte binding that is nonspecific. It is critical to choose PVDF syringe filters or any other filter with proper porosity and the right filter pore size (2um for UHPLC analysis).