How to Choose the Right MWCO for 15 mL Centrifugal Filter Tubes

An MWCO centrifugal filter tube is a spin-column device rated by molecular weight cut-off, the nominal molecular weight limit at which a membrane retains ≥90% of a reference globular protein during ultrafiltration. Sigma-Aldrich and other suppliers typically define MWCO as the smallest molecular weight at which at least 90% of the solute is retained under standardized test conditions. A 10 kDa membrane usually retains molecules above roughly 3–5 nm in hydrodynamic diameter, while typical 15 mL tubes spin at 3,000–5,000 × g in swing-bucket rotors according to common lab protocols.

What exactly does MWCO mean, and how is it rated? How does pore size relate to the specific molecules you are working with?

Which membrane material is compatible with your buffer and solvent conditions? What centrifuge speed and g-force are appropriate for 15 mL tubes? And how do you avoid the most common sizing mistakes that researchers tend to make?

Quick Answer: For a 15 mL PES MWCO centrifugal filter tube, first determine your target’s molecular weight and whether your goal is protein concentration, buffer exchange, or desalting. For concentration, choose an MWCO about 3–5× smaller than the target (for example, a 10–15 kDa MWCO for a 50 kDa protein) to achieve ≥90% retention while keeping spin times reasonable. For desalting mid‑size proteins (20–50 kDa), a 5–10 kDa MWCO balances salt removal and recovery. Stick to 3,000–5,000 × g and verify PES compatibility with your buffer system.

Quick Takeaways

• MWCO rates the molecular weight where membranes typically retain around 90% of reference globular proteins, based on manufacturer specifications and test solutes such as dextran or PEG.
• A 10 kDa membrane retains molecules above roughly 3–5 nm diameter in hydrodynamic radius, depending on molecular shape and conformation.
• Choose PES membranes for aqueous protein work in 15 mL tubes; PES combines low protein binding with broad pH and buffer compatibility.
• Spin standard 15 mL filter tubes at 3,000–5,000 × g for 15–30 minutes for typical concentration factors, following the tube manufacturer’s maximum g rating.
• Pick an MWCO one-half to one-third (about 3–5× smaller) than your target to prevent loss while maintaining reasonable filtration speed.

What Does MWCO Mean on a Centrifugal Filter Tube?

MWCO stands for Molecular Weight Cut-Off and describes the nominal molecular weight of a globular solute that a membrane retains by approximately 90% during ultrafiltration. In other words, it is a statistical, performance-based rating rather than an absolute pore-size threshold. Manufacturers like Sigma-Aldrich, Pall, Sartorius, and Cobetter define MWCO using standardized test proteins or polymers, and explicitly state that ≥90% of molecules above the MWCO are retained under test conditions.

That said, MWCO is not a hard, binary cutoff. It represents a threshold where retention efficiency is quite high, but not absolute. Molecules slightly below the MWCO can be partially retained, and those slightly above it might not be fully captured either. The actual separation performance depends heavily on the molecular shape, compactness, and hydration shell of your specific sample rather than molecular weight alone.

A globular protein like albumin (66.5 kDa) will be retained very effectively by a 30 kDa MWCO filter, whereas an elongated polysaccharide or denatured protein with a similar molecular weight can partially pass through because its effective hydrodynamic radius is smaller. This behavior aligns with the concept of the Stokes radius, which better correlates with membrane sieving than molecular weight alone and is widely discussed in membrane science literature.

Understanding this nuance is fundamental to choosing the right filter. For reliable concentration of proteins and other macromolecules, a commonly cited rule of thumb from suppliers such as Pall, Sartorius, and Sigma-Aldrich is to select an MWCO that is around one-half to one-third the size of your target molecule (roughly 2–3× smaller in MW). Nanolab supplies 15 mL PES membrane centrifugal ultrafiltration tubes across this spectrum, offering 5 kDa, 10 kDa, 30 kDa, 50 kDa, and 100 kDa MWCO options to match diverse research needs in protein, peptide, and nucleic acid workflows.

Diagram explaining MWCO centrifugal filter tube membrane retention mechanism

Why Does Choosing the Wrong MWCO Wreck Your Experiment?

Choosing an incorrect Molecular Weight Cut-Off for your centrifugal filter tube can dramatically reduce recovery, compromise purity, and waste precious sample. If the MWCO is too large, your target partially passes into the filtrate and yields drop well below the ≥90% recovery expected when the MWCO is 2–3× smaller than the solute. If it is too tight, spin times increase, non-specific binding rises, and sensitive proteins can denature or aggregate during extended centrifugation.

To give you a concrete estimate based on common lab experience: using a 30 kDa MWCO tube to concentrate a 30 kDa globular protein often recovers only about 50–approximately 70% of the starting material, whereas switching to a 10 kDa tube (3× smaller) can increase recovery above approximately 90% when spin conditions are optimized. This mismatch essentially turns what should be a simple concentration step into a major source of variability and irreproducible results across replicates or batches.

What happens if the MWCO is too large for my target molecule?

If the MWCO is too large relative to the target, your molecule passes more readily through the membrane into the filtrate, resulting in low recovery and a diluted retentate. Because MWCO is defined as the approximate molecular weight at which approximately 90% of a globular solute is retained, a molecule that is close to or slightly smaller than the listed MWCO will not be reliably kept on the concentrate side. For example, a 30 kDa protein used with a 30 kDa MWCO tube can exhibit substantial losses since the protein’s effective hydrodynamic size may allow it to slither through the pores.

Suppliers and application notes generally recommend choosing an MWCO that is 2–3× smaller than the target molecular weight to avoid this issue. This means a 30 kDa protein should be concentrated using a 10–15 kDa MWCO filter rather than a 30 kDa filter, especially when sample quantity is limited or when high recovery is critical for downstream assays such as mass spectrometry or activity measurements.

Why does a too-tight MWCO make concentration painfully slow?

A membrane with an MWCO that is much smaller than what you actually need severely restricts the flow of water and small molecules, dramatically increasing centrifugation times. Prolonged spinning at 3,000–5,000 × g can expose sensitive proteins to mechanical stress and elevated local concentrations, increasing the risk of denaturation, aggregation, or surface adsorption. It also elevates the risk of membrane fouling as retained contaminants accumulate at the surface.

In practice, using an excessively tight 3 kDa MWCO for a 50 kDa protein may more than double the spin time compared with a 10 kDa MWCO, without proportionally improving recovery. For rapid buffer exchange of large proteins or complexes above 100 kDa, a 50–100 kDa MWCO is often chosen because it minimizes spin time while still providing high retention, which is consistent with manufacturer selection guides for centrifugal ultrafilters.

Can the wrong MWCO cause membrane fouling?

Yes, an oversized mismatch between sample properties and membrane rating can promote membrane fouling. If your sample contains aggregates or particulates that are similar in size to or larger than the membrane pores, these species rapidly clog the surface and internal pores, blocking flow and reducing effective membrane area. This can permanently damage the filter and significantly lower recovery for subsequent runs.

A 5 kDa tube used with a viscous, aggregate-prone cell lysate or crude serum will foul much faster than a 30 kDa tube under the same conditions because the tighter membrane must retain a broader range of contaminants. Understanding your sample’s viscosity, aggregate content, and particulate load is just as critical as knowing your target’s molecular weight when selecting an MWCO centrifugal filter tube. Nanolab supplies 15 mL PES membrane centrifugal ultrafiltration tubes in a full range of 5, 10, 30, 50, and 100 kDa MWCO options, allowing you to tailor both retention and fouling risk to the specific characteristics of your sample.

MWCO selection diagram showing protein retention vs. loss in centrifugal filter tubes

How Do You Match MWCO to Your Target Molecule Size?

To match MWCO to target size, choose a membrane rated about 3–5× smaller than the molecular weight of the molecule you want to retain. For a 50 kDa protein, this translates to using a 10–15 kDa MWCO centrifugal filter tube to guarantee reliable retention above approximately 90% under standard spin conditions. Supplier selection guides from companies such as Pall, Sartorius, Cobetter, and Sigma-Aldrich consistently recommend selecting an MWCO that is about one-half to one-third of the target molecular weight for most protein concentration tasks.

Why not just match MWCO to molecular weight directly?

The pores in ultrafiltration membranes do not behave like perfectly uniform sieves with sharp size thresholds; they follow a sigmoidal retention curve. Molecules well below the MWCO pass freely, molecules well above it are retained with high probability, and species near the MWCO exhibit a rapid transition from almost complete retention to substantial passage. In this transition zone, small differences in molecular conformation can lead to large differences in retention.

The Stokes radius, which reflects how a molecule moves through solution and interacts with pores, is more predictive than raw molecular weight alone. A compact 30 kDa globular protein behaves very differently from a 30 kDa elongated chain or glycoprotein. Because of this, matching MWCO directly to molecular weight typically underestimates the fraction of molecules that will pass through, so experienced users and vendor protocols generally recommend MWCO values 2–3× smaller than the target MW for concentration and ≥3× smaller when maximal recovery is required.

When does the 3–5× rule break down?

The 3–5× rule works well for most globular proteins and many nucleoprotein complexes, but it can break down for extremely elongated, flexible, or heavily glycosylated molecules. Elongated proteins such as fibronectin (~440 kDa) behave as if they are considerably larger than their molecular weight suggests because their extended conformation increases the effective Stokes radius. Glycoproteins with large carbohydrate moieties and membrane proteins with detergent micelles also occupy more volume than their core protein mass would indicate.

Nucleic acids represent a special case: a single-stranded 10 kDa oligonucleotide can behave hydrodynamically like a 50+ kDa globular protein because of its rod-like conformation and hydration shell. For these atypical molecules, you should consider using an even smaller MWCO than the 3–5× rule suggests and verify retention empirically by measuring concentration in both retentate and filtrate during trial runs.

Quick-reference MWCO lookup

Nanolab's 15 mL PES membrane centrifugal ultrafiltration tubes cover the five most common MWCO values—5, 10, 30, 50, and 100 kDa—giving you practical flexibility to match nearly any protein or peptide target that falls in the 5–300 kDa range without changing tube format or rotor configuration.

MWCO centrifugal filter tube selection guide matching molecular weight to recommended cutoff

Which MWCO Should You Use for Concentrating Proteins in a 15 mL Tube?

For protein concentration in a 15 mL tube, select an MWCO centrifugal filter tube whose nominal cutoff is approximately 3–5× smaller than your target protein’s molecular weight. This approach, recommended in selection guides from major ultrafiltration suppliers such as Pall and Sartorius, typically achieves ≥90% retention for globular proteins while avoiding excessively long spin times. In the context of 15 mL formats, this MWCO choice exerts a direct influence on both final recovery and the total centrifugation time required to reach your desired concentration factor.

How Do You Map Protein Size to a Specific MWCO?

Mapping protein size to MWCO starts with the molecular weight and oligomeric state of your target. Small proteins and peptides under 20 kDa often require a 3–5 kDa MWCO to prevent significant loss during concentration. Medium-sized proteins such as BSA (66 kDa) or IgG antibodies (~150 kDa) are commonly processed with 10–30 kDa MWCO filters, aligning with the 3–5× smaller rule. Large proteins or complexes above 100 kDa may be concentrated efficiently using 50–100 kDa MWCO devices, which allow faster filtrate flow without sacrificing acceptable recovery.

Why Does the 15 mL Volume Affect Your Spin Time?

The larger geometry and membrane area of a 15 mL centrifugal filter tube, compared with 0.5–4 mL devices, increase both sample path length and membrane load. As a result, a typical spin to concentrate 15 mL down to 200–500 µL can take approximately 15–30 minutes at 3,000–4,000 × g, depending on MWCO, protein concentration, and solution viscosity. Using an MWCO that is tighter than necessary—such as a 3 kDa filter for a 50 kDa protein—can further extend spin time and require multiple spin–mix cycles, whereas a 10 or 30 kDa MWCO for a medium-sized protein offers a better balance between process time and retentate recovery.

Nanolab supplies 15 mL PES membrane centrifugal ultrafiltration filter tubes in the key MWCO values of 5, 10, 30, 50, and 100 kDa. This range covers standard protein concentration applications—from short peptides around 5–10 kDa to large antibodies and complexes above 150 kDa—using low-binding PES membranes that help minimize sample loss while maintaining robust flow rates in swing-bucket or fixed-angle rotors.

15 mL centrifugal filter tubes with different MWCO markings for protein concentration

How Do You Choose MWCO for Buffer Exchange and Desalting?

For buffer exchange and desalting with a 15 mL centrifugal filter tube, you still need an MWCO smaller than your target, but you prioritize rapid passage of salts and small molecules over maximal tightness. The goal is to retain the protein while allowing low-molecular-weight components (typically <1 kDa) to pass quickly, so an MWCO of 5–10 kDa is often preferred for mid-size proteins such as a 25 kDa enzyme. For such a 25 kDa protein, a 10 kDa MWCO usually provides a better balance of salt clearance, spin time, and recovery than an ultra-tight 3 kDa membrane.

Why Is Desalting Different from Protein Concentration?

In desalting, the primary objective is efficient removal of low-molecular-weight components such as salts, imidazole, glycerol, or reducing agents while retaining the macromolecule. The membrane must have pores large enough to allow these small species to pass through freely into the filtrate during centrifugation, which means an MWCO that is too small can slow clearance without adding meaningful retention benefit for the protein.

Using a 3 kDa MWCO for a 25 kDa protein, for example, can increase spin time and the number of required buffer-exchange cycles, elevating the risk of protein loss via non-specific binding and aggregation. Industry application notes and supplier protocols frequently recommend 5–10 kDa MWCO devices for desalting proteins in the 20–50 kDa range, because this range efficiently passes sub‑1 kDa solutes while maintaining high protein retention.

How Does Buffer Exchange Work with Centrifugal Filters?

Buffer exchange via centrifugal ultrafiltration uses repeated dilute-and-spin cycles. You add your new buffer to the sample in the filter device, centrifuge to reduce the volume, and repeat the process until the original buffer components are diluted to acceptable levels. Each cycle typically reduces the concentration of the original buffer by a factor related to the volume reduction (for example, a 10-fold concentration step yields roughly a 10-fold dilution of the original buffer.

Choosing a slightly larger MWCO, such as 10 kDa for a 25 kDa protein, can reduce the number of cycles required to reach >95% buffer exchange, because filtrate flows faster and low-molecular-weight species diffuse more rapidly. For instance, exchanging buffer for a 25 kDa protein might require 3–4 cycles with a 10 kDa MWCO tube but 5–6 cycles with a 3 kDa tube due to slower filtration. This trade-off between cycle count and marginal gains in retention efficiency should guide your MWCO selection for desalting.

3 kDa vs. 10 kDa: Which Is Better for Desalting a 25 kDa Protein?

The choice between a 3 kDa and 10 kDa MWCO for a 25 kDa protein reflects a direct trade-off between ultimate retention, speed, and ease of handling. A 3 kDa MWCO tube provides near-absolute retention for a 25 kDa globular protein but requires longer spin times, more buffer-exchange cycles, and carries a higher risk of non-specific binding over prolonged contact with the membrane. A 10 kDa MWCO tube, by contrast, still effectively retains molecules above ~20 kDa while permitting faster filtrate flow and shorter total processing time.

Based on typical ultrafiltration performance data, a 10 kDa filter can achieve >95% salt removal in approximately two cycles for a 25 kDa protein while maintaining protein recovery often around 85–90%, whereas a 3 kDa filter may reach >99% salt removal but with recovery that can drop to roughly 75–80% in practice. Major suppliers offer both 3 and 10 kDa MWCO options to cover these different priorities, and Nanolab’s 10 kDa PES centrifugal filter tubes present a versatile choice for routine desalting where both recovery and throughput are important.

For researchers performing routine desalting of 20–50 kDa proteins in 15 mL volumes, Nanolab's 10 kDa MWCO PES centrifugal filter tubes offer an effective compromise between high salt clearance, high protein recovery, and manageable spin times in the 3,000–4,000 × g range.

5 vs 10 vs 30 vs 50 vs 100 kDa — Which MWCO Fits Your Application?

When you are selecting a 15 mL centrifugal filter tube, you will typically encounter five standard MWCO ratings: 5, 10, 30, 50, and 100 kDa. Each rating targets a specific molecule size range and set of applications, from concentrating small peptides to rapidly desalting large protein complexes. The optimal choice depends on both the molecular weight distribution of your target and whether your main goal is concentration, buffer exchange, clean-up of small solutes, or removal of aggregates. These five MWCO values are widely offered by major suppliers, underscoring their status as the de facto standard set for protein and nucleic acid workflows.

What are the specific differences between each MWCO rating?

The table below summarizes the key characteristics and typical performance expectations for each MWCO value in 15 mL PES centrifugal devices. For proteins at least twofold larger than the nominal MWCO, typical recovery rates exceed 90% when recommended spin conditions are followed. This aligns with product information sheets for PES centrifugal filters that specify >90% recovery for solutes at least 2× above the MWCO under standard conditions.

How do you decide using a simple decision matrix?

You can approach MWCO selection systematically by considering target size and workflow goal. If your molecule is around 5–15 kDa and the aim is to concentrate or desalt it without loss, a 5 kDa tube is usually the safest choice. For proteins between roughly 20 and 50 kDa, 10 or 30 kDa devices generally provide a good compromise between retention and processing time, with the tighter choice favored when recovery is paramount.

If your molecule is larger than 100 kDa, or you primarily need to process large complexes or viral particles quickly, 50 or 100 kDa tubes are appropriate. Nanolab provides the full set of these 15 mL PES membrane ultrafiltration tubes, giving you all five MWCO ratings to handle applications ranging from peptide enrichment to rapid clean-up of multi-hundred-kDa complexes in a consistent tube format.

What Common Mistakes Do Researchers Make When Selecting MWCO?

Researchers frequently make several recurring mistakes when selecting an MWCO centrifugal filter tube, and the most impactful is choosing an MWCO that is too close to the molecular weight of the target molecule. This single error is the primary reason for unexpected sample loss, because molecules near the stated cut-off can partially penetrate the membrane’s pore size distribution. Internal support data from Nanolab, based on interactions with more than 300 research labs worldwide, consistently identify this mismatch as the leading cause of low recovery calls about “disappearing proteins.”

Why is matching MWCO directly to molecule size a mistake?

Matching MWCO directly to the molecular weight of your target (for example, using a 50 kDa MWCO for a 50 kDa protein) virtually guarantees suboptimal retention because of the probabilistic nature of MWCO. By definition, MWCO is the molecular weight at which only about 90% of a standard globular solute is retained, meaning a significant minority can still pass through even under test conditions. For real-world proteins with diverse shapes, this leakage can be substantially higher.

Best practice, reflected in guidance from manufacturers such as Sigma-Aldrich and Sartorius, is to choose an MWCO that is about one-half to one-third of the target’s molecular weight (roughly 2–3× smaller). This shift out of the transition zone of the retention curve ensures that more than 90% of your macromolecule is retained in typical 15 mL spin protocols, especially for globular proteins and antibody domains.

How does sample viscosity affect filtration?

Sample viscosity dramatically influences filtration behavior. Highly viscous samples such as concentrated cell lysates, serum, or high-protein formulations increase hydraulic resistance across the membrane and can trigger rapid fouling as particulates accumulate at the surface. Ignoring viscosity leads to extended spin times, unexpected heat generation in the rotor, and potential degradation of labile proteins.

To mitigate these issues, you should pre-clear viscous samples by low-speed centrifugation to remove debris, consider diluting to reduce viscosity, and use moderate g-forces rather than the maximum allowed by the tube. For 15 mL PES ultrafilters, staying within 3,000–5,000 × g and inspecting the membrane after each run can help maintain performance and reduce the risk of clogging that cannot be reversed.

Can over-centrifuging damage the filter?

Yes, over-centrifuging can permanently damage the filter device. Spinning at speeds higher than the manufacturer’s maximum g rating, or extending spin time far beyond recommended intervals, compresses the polyethersulfone membrane and support structure. This compaction reduces effective pore size, slows future filtrations, and can deform the plastic housing, compromising the integrity of the tube and cap.

To protect your centrifugal filters, always consult the product insert or online specification sheet for the maximum allowable g-force and spin time, and design your protocol with staged spins and intermittent mixing rather than a single, prolonged high-speed run. This approach preserves the membrane’s structure and improves long-term reproducibility when using multiple tubes from the same lot.

Do all membranes with the same MWCO perform identically?

No, membranes with identical MWCO ratings can behave differently because performance depends on polymer chemistry, pore size distribution, surface charge, and manufacturing method. Two nominally 10 kDa filters from different suppliers can exhibit different levels of non-specific binding, fouling propensity, and effective retention for the same protein sample, especially if the protein is hydrophobic or carries a net charge near the membrane’s isoelectric point.

This variability means you should examine vendor data for protein recovery, binding characteristics, and chemical compatibility rather than assuming that all 10 kDa PES or regenerated cellulose filters are interchangeable. Running a small pilot experiment comparing two membrane types with your specific sample is often worthwhile before committing to a bulk purchase for critical production workflows.

Should you always check the flow-through?

Absolutely, you should. Throwing away the flow-through, which is the liquid that passed through the filter, without looking at it means you're throwing away useful information. If your target molecule is missing from the part that was kept by the filter, checking the flow-through will tell you if it passed through because you picked the wrong MWCO or if something else is going on. This simple check can save you a lot of time trying to figure out what went wrong.

Why Does PES Membrane Material Matter Alongside MWCO Selection?

Choosing the right MWCO is only half the battle; the membrane polymer dictates sample recovery, chemical compatibility, and leachable risks. Polyethersulfone (PES) is the dominant material for most life-science MWCO centrifugal filter tubes because it offers a unique combination of low non-specific protein binding and broad chemical resistance. For instance, PES membranes typically maintain stability across a pH range of 2 to 13 and show good compatibility with common biological buffers, mild detergents, and low concentrations of organic solvents like ethanol or DMSO.

How Does PES Compare to Regenerated Cellulose and PVDF?

PES, regenerated cellulose, and PVDF (polyvinylidene fluoride) each serve different needs. The key differentiator is protein binding. PES exhibits significantly lower non-specific binding, meaning less of your precious target protein sticks to the membrane and is lost. Regenerated cellulose membranes, like those in some Amicon Ultra filters, can achieve retentate recoveries greater than 90%[9] but may bind more hydrophobic proteins. PVDF is highly chemical-resistant but often has higher protein binding than PES. For most aqueous biological samples, PES provides the best balance of recovery and compatibility.

Why Is PES the Default Choice for Most 15 mL Tubes?

PES has become the standard for 15 mL centrifugal concentrators in life science labs due to its optimal performance profile. Major suppliers, including Sigma-Aldrich, offer their low-binding PES centrifugal filters in the five common MWCO values (5 kDa, 10 kDa, 30 kDa, 50 kDa, 100 kDa). This low-binding characteristic is critical when concentrating dilute proteins or working with limited samples, as it maximizes final yield. Nanolab's PES membrane 15 mL tubes follow this industry-standard approach, providing researchers with a reliable, low-loss platform for concentration and desalting.

When Should You Choose Regenerated Cellulose Over PES?

Opt for regenerated cellulose when your primary concern is maximizing recovery of very hydrophobic proteins or peptides that might adsorb to PES. While PES handles most common buffers well, regenerated cellulose can sometimes offer superior performance with certain viscous or detergent-heavy samples. However, for the vast majority of standard protein work, DNA cleanup, and buffer exchange, PES remains the recommended choice for its consistent low-binding performance and broad compatibility.

Frequently Asked Questions About MWCO and 15 mL Centrifugal Filter Tubes

Can I use a 10 kDa MWCO tube for a 12 kDa protein? No, this isn't recommended. The general rule is to select an MWCO that is 3 to 5 times smaller than your target molecule's molecular weight to ensure >90% retention. A 10 kDa tube would likely allow significant loss of a 12 kDa protein during centrifugation, as the protein's effective size is too close to the membrane's nominal pore size.

What happens if I spin the sample too long? Over-centrifugation can force smaller molecules through the membrane, reducing recovery of your target analyte. It may also lead to excessive sample concentration, increasing viscosity and potentially causing protein aggregation or precipitation, which clogs the membrane and reduces filtration efficiency.

How many times can I reuse a centrifugal filter tube? Most centrifugal filter tubes, including those with PES membranes, are designed for single use. Reuse isn't advised due to the risk of cross-contamination, membrane degradation, and inconsistent results. For cost-sensitive, high-throughput labs, single-use devices provide the most reliable and reproducible data.

What's the maximum sample volume for a 15 mL tube? The nominal capacity is 15 mL, but the actual recommended working volume is typically lower, around 12,14 mL. This headspace is crucial to allow for proper mixing and to prevent sample from contacting the cap, which can cause leakage or loss during centrifugation. Always check the manufacturer's specifications for the exact fill line.

Is PES better than regenerated cellulose for my application? It depends on your sample. PES (polyethersulfone) membranes offer very low protein binding and high flow rates, making them ideal for concentrating proteins and nucleic acids. Regenerated cellulose can provide slightly higher recovery for some sensitive proteins but may have higher non-specific binding. For most standard biological applications, low-binding PES filters are the versatile choice, which is why Nanolab offers its 15 mL centrifugal ultrafiltration tubes with PES membranes.

How do I calculate final concentration from starting volume? Use the formula: Final Concentration = (Starting Volume / Final Volume) × Starting Concentration. For example, concentrating 10 mL of a 1 mg/mL protein solution to 1 mL yields a final concentration of 10 mg/mL. Remember that actual recovery may be less than 100% due to membrane binding and dead volume.

Conclusion — How to Pick the Right MWCO for Your Next Experiment

Choosing the right MWCO for a 15 mL centrifugal filter tube is a straightforward process with three main steps. First, you need to know the molecular weight and shape of your target molecule. Second, you follow the 3.5-times rule for concentration, or you adjust the logic if you are doing desalting. Third, you check that the membrane material works well with your specific buffer system. This approach helps you get high recovery and avoids losing valuable sample.

You should start by finding the exact molecular weight, measured in kDa or Da, of the protein, antibody, or nucleic acid you are working with. For concentrating, you generally pick an MWCO that is about one-half to one-third the size of your target molecule to make sure it stays in the retentate.

For instance, a 50 kDa protein would typically need a 10 kDa or 15 kDa MWCO tube. This guideline is based on industry standards that aim for reliable retention while keeping filtration time practical.

You should always make sure that the membrane polymer, which is usually low-binding PES, is chemically compatible with the pH, solvents, and detergents in your sample.

The table below provides a quick-reference guide for the most common 15 mL tube options:

Nanolab's 15 mL PES centrifugal filter tubes are available in all five of these standard MWCO ratings. For application-specific guidance on selecting the right MWCO centrifugal filter tube, the technical team at Nanolab is available to help you match your protocol to the optimal product.