Biomedical Engineering Reference
In-Depth Information
Table 1.1
Classifi cation of size-analysis methods for OIPs
Aerodynamic methods
Non-aerodynamic methods
Multistage CI and multistage liquid
impinger:
• Full-resolution CIs provide complete
APSDs but are slow and labor intensive
• Abbreviated impactors increase speed
and throughput and decrease labor and
time requirements. They provide
simplifi ed APSD metrics such as coarse,
fi ne, and extra-fi ne particles (potentially
relevant for relating to HRT deposition)
or based on large and small particles (for
product QC)
Laser diffractometry (LD):
• Rapid with high size resolution
• Can be made noninvasive (no need to extract
a sample of the aerosol from that created by
the OIP for measurement)
• No API specifi city, hence inapplicable to
mixtures of APIs or API + excipient(s)
• The most useful technique for size-analyzing
the large droplets from nasal sprays
Phase (laser) Doppler particle size analysis
(PDPA):
• Similar to LD in terms of resolution and
rapidity
• No API specifi city, hence may be inappli-
cable to mixtures of APIs or
API + excipient(s)
• Complex signal rejection criteria can make
representative sampling diffi cult
Single particle light scattering [optical particle
counting (OPC)]:
• Similar to LD in terms of resolution and
rapidity
• No API specifi city, hence may be inappli-
cable to mixtures of APIs or
API + excipient(s)
• A sampling system is needed to allow the
aerosol to pass through the measurement
zone at a defi ned velocity
Time-of-fl ight (TOF) methods:
• Measure APSD directly with high size
resolution, but weighting in the
distribution is particle count rather than
mass-based
• Rapid compared with cascade impaction
• No API specifi city—hence may be
inapplicable to mixtures of APIs or
API + excipient(s)
-
-
Microscopy-automated image analysis:
• Moderately fast with automated image
analysis, but care is needed to defi ne particle
boundaries
• When combined with Raman Chemical
Imaging may provide specifi city to API
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