Why the labels are not equivalent
MF often uses nominal pore size; UF/NF also use molecular-weight cut-off derived from test molecules and a defined rejection criterion. Solute shape, charge and affinity, pH and concentration change actual separation. Two molecules of equal mass need not transport identically.
Inopor's published ceramic range includes nominal NF down to 200 Da. This helps catalogue selection; it does not itself define rejection of each component or availability of every historical geometry.
| Term | Typical unit | Question answered |
|---|---|---|
| Pore size | nm or µm | What physical scale does the datasheet state? |
| MWCO | Da or kDa | What reference test does the supplier use? |
| Observed rejection | % | How much solute passes on this water and duty? |
A verifiable specification
Describe the target molecule or fraction, concentration, feed matrix, temperature, pH, flow and required permeate and retentate composition. Request the maker's MWCO method, layer material, support, geometry, operating conditions and assembly limits.
For whey, for example, protein, lactose and minerals need separate measurements. Do not infer that a 200 Da MWCO always rejects a heavier molecule or passes every salt.
- Request a rejection curve or trial with representative solutes.
- Measure flux and selectivity at initial and final concentration.
- Record material balance for both outlets.
Procurement decision
Compare options at the same quality and net production target. A tighter cut-off may improve separation but can increase pressure, fouling or loss of useful component. Let the trial choose the membrane, not a nominal unit conversion.
For a rejection test, report feed and permeate concentration, recovery, temperature and sampling time together. Concentration polarisation and changing feed during a batch trial can distort a simple inlet/outlet percentage. Repeat at the intended final concentration before committing to a production separation.
Common questions
Does 200 Da equal a particular pore size in nanometres?
There is no general conversion. Material, molecular geometry, interactions and test method all matter.