Chemical Compatibility

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Filter material must be compatible with the chemical nature of the liquid being filtered under the conditions that the filtration will be performed. This will minimize the risk of structural failure during filtration.

Although chemical compatibility usually deals with the liquid phase of the sample, dissolved solutes may interact with the membrane in an undesirable manner. The solute of interest should not be adsorbed onto the surface of the filter. Most polymers used to make filters are highly adsorptive for biomolecules and will bind them out of the sample stream until the polymer surface is saturated. If a low binding surface is required, this property should be specified during the selection process.

In venting applications, hydrophobicity of a filter is used to allow release of air bubbles from a liquid stream. The sample stream should not contain detergents or solvents that will wet out the surface of the filter.

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Organic liquids

Membranes used in the filtration of organic solvents must be resistant to those solvents. If the membrane dissolves in the filtration process, that membrane will be totally useless in filtering those solvents.

When selecting a filter, determine if constituents in the sample will chemically attack the filter. If the filter undergoes chemical degradation, it may release foulants into the sample stream.

Some solvents may be incapable of dissolving the filter, but could be absorbed into the polymer matrix causing it to swell over time and altering the effective pore size of the filter and changing its performance.

Aqueous liquids

The same is true of an aqueous stream. Care must be taken that the filter not be damaged by the aqueous stream. Most membrane polymers are resistant to standard water. Issues arise when the pH of the water is incorrect, or when additives chemically attack the polymer.

Determine if the filter is sensitive to extremes of pH and compatible with specific acids and bases. Chemical attack at extremes of pH may take time to appear and could be problematic well before filtration is completed.