Quality Control and Advanced Characterization of Membranes - Size-exclusion chromatography (SEC) — also known as gel permeation chromatography (GPC) — is the standard technique used to cha
Quality Control and Advanced Characterization of Membranes
Size-exclusion chromatography (SEC) — also known as gel permeation chromatography (GPC) — is the standard technique used to characterize macromolecules in solution. In this article GPC is employed to measure membrane performance parameters such as retention behaviour, pore size and molar mass cut-off. This method relies on the filtration behaviour of the membranes. The applicability to different kinds of membranes is described.
Membrane technologies have emerged in recent years as a viable and cost-effective alternative to various purification and
separation methods. Membrane processes can provide
a barrier against microbes and pathogens
an effective way to disinfect by-products
fewer treatment unit processes
higher process efficiency at lower costs
application to a broad range of water qualities.
Table 1: Sales of membrane industry.
Membranes play an important role in many aspects of life (Figure 1 and Table 1).1,2 Biological membranes control our body's metabolism, artificial phospholipid membranes can be used for drug delivery and
synthetic membranes allow kidney patients to live until a transplant is available. Membranes with special adsorption properties
are used for selective removal of unwanted compounds in pharmaceutical and fine chemical production processes. Synthetic membranes
are used for sterile filtration, water treatment, energy-efficient purification of solvents and many more processes (Table
2).
Table 2: Sales of membranes and modules in various membrane processes.
The membranes can only meet the requirements in such important processes if they show the proper membrane properties (Table
3). Consequently, the characterization of membrane properties and quality parameters is very important.3–6 Quality testing should also be fast, efficient, reliable and reflecting the application (i.e., not in a vacuum or dry state).
Table 3: Important membranes properties.
Most of the listed properties can be assessed by the proposed SEC method; only the last two properties cannot be measured
by SEC methods easily. In contrast, traditional characterization methods by latex particles and proteins, for example, are
slow and tedious, reflect only a single parameter (such as bubble point) or cannot be used in the final product (the membrane
is analysed separately in an early stage that doesn't reflect the product properties). This article shows how liquid chromatography
(LC) can be used to overcome several of the disadvantages of traditional methods. The authors employed SEC to characterize
either the membrane itself or the membrane in the final product in both a comprehensive and simple way. Standard chromatography
equipment can be used as it is readily available in most laboratories. No special staff training is necessary to perform the
tests. This technique can be a cost-effective alternative or addition to the more traditional membrane characterization methods.
Description of Membrane Characterization Technique
Figure 2
This membrane characterization method is based on the filtration of a probe molecule of known size or molecular weight.7 The probe molecule (e.g., a broad molar mass dextran sample) is dissolved in water (stock solution) and filtered through
the membrane (Figure 2).
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