Drugs and the pharmaceutical sciences

Filter Sizing: The Requirements and Their Attainment 181
Differential pressure (pH)
50
45
40
35
30
25
20
15
10
5
X
X
X
Acroflow 121 0.45 with 1 micron prefilter (prefilter too right prefilter plugged)
X
X
X
X
Acroflow 121 0.45 (no prefilter)
Acroflow 121 0.45 with to micron prefilter (prefilter too loose)
Acroflow 121 0.45 with 2.5 micron prefilter (correct prefilter)
X
X
1 2 3 4 5 6
Time (minutes)
X
FIGURE 12 Throughput of trypticase soy broth (1.25%) effects of prefiltration. Source: From
Lukaszewicz, Johnston, and Meltzer, 1981.
stock to pleated membranes due to influences inherent in the pleating process. The
measurement of the EFAs of flat disc filters is uncomplicated. That of pleated filters is
appreciably more complex. The flow rate scale-up using 47-mm flat discs reflects only
the influences of the membrane thickness and its porosity. The modifications in EFA
resulting from pleat-pack constructions must not be neglected. These derive from the
flow-attenuating influences of the cartridge’s support and drainage layers. To this must be
added the reduction in flow caused by the occurrence of pleat compaction. The utmost
caution has to be exercised when filter choices are made by evaluating flow rates using
47-mm flat disc filters. The flow data will not extrapolate well from flat stock to pleated
filter cartridges.
A more responsible action is to follow the “indicator trials” using 47-mm discs with
“verification trials” wherein the total throughput and flow rate measurements are
X
X
X