Bubble Point Test (Only Valid For The Sartocheck ® 4 Plus Filter Tester) - Sartorius Stedim Biotech Sartocheck 4 plus Betriebsanleitung

12.1.2 Bubble Point Test (Only valid for
the Sartocheck
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In wet membranes, the wetting liquid is held inside the porous structure by
®
4 plus Filter tester) capillary force. This force increases as the pore size decreases. A specific gas pressure
dependent on the pore size of the membrane is necessary to force out the liquid
from the pores. This pressure is generally designated as the "Bubble Point," or B.P. for
short. It indicates the largest pores of a filter since, liquid is first expelled through
them. An overproportional increase in the diffusion rate is characteristic for this
process. If the B.P. is below a defined limit, it can no longer be ensured that a filtra-
tion process will do the job intended (e.g., remove all bacteria in sterile filtration).
For an ideal capillary system, the Bubble Point can be calculated as follows:
B.P. = – – – – – – – – – – – –
B.P. =
cos =
r
Hence, it follows that the Bubble Point of a filter depends both on the filter material
(the contact angle varies from material to material) and, in particular, on the surface
tension of the wetting fluid.
Low surface tensions, as are present in organic solvents, detergents and emulsifiers,
yield low B.P.s.
If the test pressure required for the diffusion or the Pressure Drop Test is attained,
or even if the pressure goes below this level, it is no longer possible to perform
the Bubble Point Test under standard conditions. In this case, the test parameters
must be changed. This must be kept in mind when the test parameters are entered.
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2 · cos
r
Bubble Point
= Surface tension of the
wetting liquid (sigma)
Contact angle between
the wetting liquid and
the filter surface (theta)
= Pore radius.
Appendix 73