Selection Guide of Needle Filters's Material, Pore Size, Diameter

**Author:Orgian from HAMAG

Don’t you find yourself feeling a bit overwhelmed when you see all those colourful needle-type filters? There are so many colours, and each manufacturer uses different labelling conventions. For example, some manufacturers use a yellow casing to indicate that the material is nylon (NY), whilst others use purple for the same material; some manufacturers even use the same colour for the casings of all filter media (such as clear), relying entirely on the printed markings on the filter for identification. Therefore, when making a purchase, you must not ‘judge a book by its cover’; you must always refer to the material information marked on the filter casing.

Selecting the appropriate needle filter requires a comprehensive assessment based on three key factors: membrane material, filter diameter and membrane pore size.

The choice of membrane material is crucial to the success of the filtration process. To put it simply, filter membranes can be categorised into PES, Nylon, MCE, PVDF, PTFE and other materials; in simpler terms, they fall into two main categories: those suitable for aqueous phases and those suitable for organic phases, whilst some can be used universally following appropriate treatment. Choosing the wrong material can result in poor filtration at best, and at worst, membrane dissolution or sample contamination, rendering the entire analytical process futile.

In addition to the commonly used materials listed above, there are also some materials used for pre-filtration, such as glass fibre (GF) and quartz fibre (QF), which remove only large particles and are not used as final membranes in precision filtration.

The diameter of the filter determines the effective filtration area and the holding volume; it should be selected according to the volume of the sample to be filtered.

The pore size determines the minimum particle size that the filter can retain and must be selected according to the analytical requirements and sample characteristics.

Used for the pre-treatment filtration of mobile phases and samples to remove particulate impurities, protect the chromatographic column and extend its service life; this is the most common filtration application in liquid chromatography.

Used for the purification of organic samples to prevent particulate matter or non-volatile components from entering the injection port and chromatographic column, thereby preventing contamination and baseline interference.

Used for sterilising filtration and clarification of culture media, buffers, proteins and antibody solutions, covering the entire process from upstream cell culture to downstream formulation purification.

Used for sample preparation in microbiological limit testing and water quality microbiological analysis; retains microorganisms via membrane filtration whilst also serving as validation for sterilising filtration.

Used for the pre-treatment of surface water, groundwater and wastewater samples to remove suspended particulates, thereby providing clean samples for subsequent analytical instrumentation.

Used for the purification and filtration of food extracts to remove matrix interferences such as fats and proteins; suitable for testing for pesticide residues, veterinary drug residues and food additives.

Used for the clarification and sterilisation of cell culture supernatants, enzyme solutions and protein samples, whilst ensuring high sample recovery rates; a fundamental procedure in molecular and cell biology experiments.

1. Clarify intended use and requirements: Determine the material, pore size and diameter based on specific experimental requirements

2. Confirm sterilisation requirements: For biopharmaceutical and cell culture applications, select products in sterile packaging

3. Check connector specifications: The standard connector is the Luer-Lok connector, compatible with standard syringes

4. Select a reliable supplier: Give priority to brands and suppliers with qualifications such as ISO certification

5. Consider bulk purchasing: For routine experiments, bulk packs of 100 or 200 pieces are available; for applications with strict sterility requirements, we recommend choosing individually blister-packed products