Biomedical Engineering Reference
In-Depth Information
a
Pre-separator body
Nozzle diameter
Catch
Central cup
Pre-separator insert
Pre-separator base
Fig. 10.29
Fast screening impactor (FSI). (
a
) Components. (
b
) Assembly (
Courtesy of MSP
Corp., St. Paul, MN
)
Table 10.11
Design and calibration data for the FSI at different flow rates with inserts having a
nominal stage
d
50
of 5.0
m
(
From
[
34
]—
courtesy of D.L. Roberts
)
μ
Nozzle-to-nozzle circum-
ferential distance/nozzle
diameter (dimensionless)
STK
1/2
(critical
Stokes number
for impaction)
Flow rate
(L/min)
Number
of nozzles
Size of
nozzles (mm)
GSD
stage
30
6
4.08
11.0
0.49
1.07
35
7
4.08
9.4
0.49
1.10
a
60
12
3.94
5.7
0.51
1.12
90
9
5.00
5.9
0.51
1.12
a
Measured subsequent to publication of [
34
]
from 30 to 100 L/min [
37
], primarily for DPI testing in accordance with the method
given in monograph 2.9.18 of the Ph. Eur.
If greater control of cut point is required and the sampling flow rate from the
inhaler can be varied, the use of a fixed insert at different volumetric flow rates (
Q
)
can allow fine adjustment of the boundary for the coarse/fine fraction, as cut-off
diameters (
d
50
) shift in accordance with Marple-Liu theory [Eq. (10.2)]. Other inserts
can therefore be manufactured to order, providing any desired cut point in the range
1.0-10
m aerodynamic diameter for measurements at a given flow rate (Roberts
DL (2012) MSP Corporation, St. Paul, MN, USA, personal communication).
The first reports issued in late 2009 by a group from Pfizer (Sandwich, UK) [
38
,
39
] described the use of an FSI for DPI studies. To begin with, a commercially
available DPI was measured at 70 L/min using a FSI with a 5
μ
m insert. The NGI
APSD measurements were made in accordance with the compendial DPI methodol-
ogy, which was adapted, in the case of the FSI evaluation, to reflect the simplified
information obtainable from this abbreviated system. Results were gathered for the
uncoated FSI and again following collection surface coating with a very fine layer
of silicone fluid applied as a 1% v/v solution in cyclohexane. Their metrics,
CPF
>5.0μm
,
FPF
<5.0μm,
and total impactor recovery (equivalent to
IM
) were compared
with data from a full-resolution NGI, with data from the full-resolution APSD
μ
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