FAQ - Frequently Asked Questions

Here you'll find answers to our most asked questions. Still can't find quite what you're looking for, or have something we should know? Send us an email, we're happy to help!

• Q1: What is ultrafiltration?

  A1: Historically, laboratory ultrafiltration was a technique used to concentrate proteins. Therefore, expressing pore sizes as MWCOs in units of kilo Daltons (kDa) was a convenient way to understand a membrane’s ability to retain a protein of known molecular weight. Today, research scientists use ultrafiltration and diafiltration to process a much wider variety of molecules, including viruses, nucleic acids, and nanoparticles. Therefore, Sartorius provides selection guides with convenient conversion tables to help you determine which MWCO to use when the size of your target molecule is not expressed in kDa.

• Q2: Why choose PES membranes for ultratfiltration?

  A2: For most ultrafiltration and diafiltration applications, both PES and RC are good choices. PES can provide higher recoveries for negatively charged molecules, while RC typically supports higher recoveries for linear molecules, including oligonucleotides and peptides.

• Q3: Which applications can I use ultrafilters for?

  A3: Ultrafilters are versatile consumables that can be used for ultrafiltration applications, such as macromolecule concentration and enrichment, clarification and particle removal, and sample volume reduction. They can also be used for diafiltration, which is an efficient alternative to gel filtration and dialysis for buffer exchange and desalting. Diafiltration can also be used for polishing, binding studies, and screening buffers to assess molecular stability.

• Q4: Why choose Hydrosart membranes?

  A4: The horizontal Hydrosart® RC membranes and option of PCR-grade ultrafilters provide worry-free, contamination-free processing, especially in critical applications such as crime scene sample concentration prior to DNA sequencing. Vivaflow®️ is ideal for concentrating pDNA, purifying mRNA and processing other nucleic acids when working with larger feed volumes.

• Q5: How should I concentrate virus sample?

  A5: Many viruses can be processed in a similar manner to proteins, but typically with MWCOs ≥100 kDa. For enveloped viruses and similar molecules with lipid membranes, such as lipid nanoparticles (LNPs) and extracellular vesicles (EVs) and particles (EPs), reducing the operating pressure and shear stress on the sample by using a lower centrifugal force or pump flow rate may result in improved recoveries.

• Q6: How can I concentrate my protein?

  A6: Proteins are commonly concentrated using ultrafiltration. Product design of ultrafiltration devices for laboratory use consists of ultrafiltration membranes placed within housings specially designed to enable concentration through centrifugal, positive pressure, solvent adsorption and tangential flow separation methods. These methods use controlled forces to pass solutes and non-targeted molecules through a semi-permeable ultrafiltration membrane, into the permeate - while retaining the larger molecule(s) of interest in the retentate.

• Q7: How can I maximize recovery of my target molecule?

  A7: The same membrane material, MWCO, feed flow direction and operating method may not be ideal for every sample. Therefore, optimizing your ultrafiltration and diafiltration processes for each target molecule should be a priority. Start by selecting a MWCO up to 1/3 or 1/2 the size of the molecule to be retained. If possible, it is also recommended to test different membrane materials and operating methods. Finally, refining your process by using, for example, reduced differential pressures, membrane passivation, or a buffer rinse after retentate collection can also help maximize target recoveries.

• Q8: Can ultrafilters be reused?

  A8:The performance of ultrafiltration membranes degrades with repeated use, so most ultrafilters are designed for single use. This helps to reduce hands-on time, improve laboratory safety, and eliminate the risk of carryover. However, cleaning and storage procedures are provided for Vivaspin® 100 and selected Vivaflow® ultrafilters, so that they can be used multiple times.