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A Practical Guide on Coupling a Scanning Mobility Sizer and Inductively Coupled Plasma Mass Spectrometer (SMPS-ICPMS)
Published on: July 11, 2017
Good Cascade Impactor Practice (GCIP) and considerations for "in-use" specifications
S C Nichols1, J P Mitchell, C M Shelton
1OINDP Consultancy, Rugby, UK.
AAPS Pharmscitech
|January 25, 2013
Summary
Cascade impactors (CI) measure aerodynamic particle size distributions for inhaled products. Stage nozzle dimensions (effective diameter) are critical for accuracy, with variations causing shifts in cut-point size.
Area of Science:
- Pharmaceutical technology
- Aerodynamics
- Metrology
Background:
- Multi-stage cascade impactors (CI) are essential for determining aerodynamic particle size distributions (APSDs) of orally inhaled products.
- The accuracy of APSD measurements relies on the precise dimensions of CI nozzles, specifically their effective diameter (Deff).
- Good Cascade Impactor Practice (GCIP) mandates linking these critical dimensions to measurement accuracy traceable to international standards.
Purpose of the Study:
- To evaluate the impact of nozzle dimension variations on the accuracy of APSD measurements.
- To explore the feasibility of using stage flow resistance (pressure drop) as a surrogate for effective diameter measurement.
- To assess if flow resistance measurements can ensure CI stage fitness for use before each APSD determination.
Main Methods:
- Analysis of the relationship between effective diameter (Deff) and stage cut-point size (d50).
- Assessment of potential shifts in d50 due to Deff variations within manufacturer tolerances.
- Investigation into measuring stage flow resistance (ΔPstage) as a proxy for Deff.
Main Results:
- Variations in Deff within typical tolerances can lead to shifts in d50 of less than ±10%.
- Stage mensuration (measurement of dimensions) provides satisfactory control over measurement accuracy.
- Measuring stage flow resistance shows potential for real-time assessment of CI stage fitness, but requires further data on wear and blockage effects.
Conclusions:
- Stage mensuration is a reliable method for ensuring CI accuracy for APSD determination.
- Flow resistance measurement is a promising, but not yet fully validated, method for routine checks of CI stage performance.
- Further research is needed to incorporate flow resistance measurements into Good Cascade Impactor Practice (GCIP).
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