Membrane Characterization and Sieve Curve Analysis
- Solutions for membrane characterization and sieve curve analysis
- PSS products and services for membrane characterization and sieve curve analysis
- Theoretical background membrane characterization and sieve curve analysis
Solutions for membrane characterization and sieve curve analysis
Filtration experiment: The membrane is used to filter a stock solution (Dextran solution). Afterwards the stock solution and the filtrate (optional also retentate) are analyzed on a conventional GPC/SEC system with RI detection.Membranes are characterized by several characteristics:
- Average pore size and pore size distribution
- Molar mass cut-off
- Size selectivity
- Filtration behaviour
- Sieve curve and retention efficiency
- Binding or non-binding efficiency
- Pore accessibility
- Chemical, physical and biological stability
- Hydrophobic properties
- Fouling
All of the listed properties (with the exception of the last two) can be determined easily by a filtration experiment with following GPC/SEC characterization of the filtrate and the stock solution used for the filtration experiment.
Filtration experiment:
The stock solution is made from a water soluble macromolecule (e.g. Dextran) with a broad molecular weight distribution. Plane and hollow-fibre membranes require different filtration set-ups. In the situation of plane membranes a commercial dialysis cell can be used (see Figure). For hollow-fibre membranes a dedicated filtration tester can be used (see P. Kilz, Polym. Sci. Mat .Eng.77, 56 (1997)).
GPC/SEC experiment:
A conventional GPC/SEC system with RI detection can be used to measure the stock solution, the filtrate and the retentate (optional).
Calculations:
The GPC/SEC traces are used to calculate the characteristic sieve curve for the membrane. A GPC/SEC calibration curve allows to determine molar mass information, molar mass cut-off, average pore size and pore size distribution.
PSS products and services for membrane characterization and sieve curve analysis
PSS offers complete turn-key systems for sieve curve determination with GPC/SEC as well as GPC/SEC membrane characterization service analysis in our analytical service department. Please contact us for a quote.
The turn-key system is based on the modular SECcurity GPC System with WinGPC UniChrom GPC/SEC software. WinGPC UniChrom offers a dedicated tool for sieve curve analysis that allows convenient determination and comparison of sieve curves.
PSS has made available three lines of reference membrane characterization standards to prepare stock solutions for the filtering experiment. Aqueous (Dextran or Pullulan) or organic (Poly(styrene)) stock solutions can be made. Recommended columns for the analyis of the Dextran and Pullulan membrane standards are the PSS SUPREMA columns. For the Poly(styrene) line PSS SDV columns are the columns of choice.
Theoretical background membrane characterization and sieve curve analysis
How does a sieve curve look like and what are the parameters obrained from the sieve curve?
The figure shows an overlay of the sieve curves of three different membranes. The sieve curve shows the membrane pore size diameters (in nm) and the amount of retention for this pore. Often besides the average pore size of the membrane one or more cut-off points, defined e.g. as 90% and/or 95% retention, are given to describe the membrane properties.