Bubble point test

The bubble point test (also: bubble pressure test or bubble point measurement ) is used to test the quality of membranes . It is particularly important in sterile filtration .

In addition to the burst pressure and the water value, the blow point is one of the simplest and most reliable ways to characterize the properties of a filter element.

execution

In preparation, the pores of the membrane (with sterile filtration usually have a diameter of 0.22 µm) are filled with a solvent , which is most easily achieved by flushing the filter system under pressure.

For the actual test, the membrane housing (depending on the design) is best pressurized slowly from the permeate side (for hollow fiber modules ). In order to displace the solvent from the pore, a force ( pressure difference between the two filter sides) is necessary, which depends on the pore diameter:

${\displaystyle \Delta p={\frac {4\,\sigma \cdot \cos \theta }{D}}}$

With

• Δp = pressure difference
• σ = surface tension of the liquid (water = 72.75 mN / m; 2-propanol = 21.7 mN / m)
• θ = wetting angle of the membrane material ( CTA : 50 - 55 °; PAN : 52 - 58 °; PESU : 65 - 70 °, each for water as a liquid)
• D = pore diameter.

The pressure and thus the pressure difference on the filter is increased. As soon as a continuous discharge of air bubbles can be seen, the pressure is read on the manometer .

By rearranging the equation, the largest pore of the membrane can be calculated from the remaining sizes.

${\displaystyle D={\frac {4\,\sigma \cdot \cos \theta }{\Delta p}}}$

literature

• K. Bauer, K. Frömming, C. Führer and B. Lippold: Textbook of Pharmaceutical Technology , Wissenschaftliche Verlagsgesellschaft mbH, Stuttgart, 8th edition 2006, ISBN 3-8047-2222-9
• Munir Cheryan: Handbuch Ultrafiltration , B. Behr's Verlag GmbH & Co, Hamburg 1990, ISBN 3-925673-87-3
• DIN ISO 4003, Beuth Verlag, Burggrafenstrasse 6, 10787 Berlin, www.beuth.de