W
ATER DISPLACEMENT METHOD (QUANTITATIVE)
The first step is to thoroughly wet the membrane with water
assuring that each pore is filled with liquid. Once the membrane
is thoroughly wetted, the feed/retentate flow path is drained.
A graduated cylinder is filled with water and carefully turned
upside down in a beaker full of water. The end of the filtrate
tube is placed inside the graduated cylinder. The retentate
port is then closed off. The system is pressurized to about
10 psig (0.7 bar) through the device feed port. Air will
diffuse through the membrane, exiting through the filtrate
tubing and into the graduated cylinder. The amount of air
displaced over time is measured in mL/min. This is the air
diffusion (forward flow) integrity test value.
Initially water in the filtrate line will be displaced. Wait until air
starts to flow before taking any measurement, as any water
left in the feed channel will first pass across the membrane.
The membrane creates a barrier to air flow, not water flow.
Figure 2
Set-up for Air Integrity Testing of Minimate TFF Capsule
This protocol describes performing the procedure using a
peristaltic pump to generate airflow. For more accurate testing,
a regulated, compressed air or nitrogen supply should be used.
Forward Flow Air Integrity Test Procedure:
1. Empty the feed reservoir.
2. Open retentate and filtrate screw clamps and pump out
liquid from feed and retentate tubing.
3. Fill a 400 mL or larger beaker and a 25 mL graduated
cylinder with water.
4. Invert the full graduated cylinder into the large beaker.
(Place a piece of paper or Parafilm over the mouth of
the cylinder. Turn the cylinder over and remove the
piece of paper after the mouth of the cylinder is below
the water level in the beaker.) The cylinder should
remain filled with water.
5. Place the end of the filtrate tubing into the beaker.
The filtrate tube should be open.
6. Slowly turn up the pump speed to give a retentate flow
rate of 40 mL/min. Tighten the retentate screw clamp to
apply a feed pressure of 10 psi.
7. Watch for bubbles emerging at the end of the filtrate
tube. When the flow seems to be consistent, place the
end of the filtrate tubing into the inverted cylinder. The
cylinder can now rest on the bottom of the beaker.
Make sure that the filtrate tubing is not crimped under
the cylinder mouth.
8. Measure the amount of air entering the graduated
cylinder for sixty seconds (mL/min). Compare to integrity
specifications for the Minimate TFF capsule
9. If no air bubble reaches the cylinder within 3-5 minute,
the device is most likely within specifications. (Calculate
the volume in the filtrate tubing and compare to the
allowable airflow rate to see if sufficient waiting time has
been allowed.)
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