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A new coincidence model for single particle counters, Part I: Theory and experimental verification
1R & D Associates, Inc, Somerset, New Jersey.
Journal of Pharmaceutical Science and Technology : the Official Journal of PDA
|May 1, 1994
Summary
This study defines prerequisites for accurate particle counting in pharmaceutical assays, developing a new model to minimize undercounting and false counts from signal coincidence. Empirical verification ensures reliable results for contamination testing.
Area of Science:
- Pharmaceutical analysis
- Particle counting technology
- Metrology
Background:
- Accurate particle counting is crucial for U.S.P. 788 contaminating particle assays.
- Signal coincidence in light extinction counters can lead to undercounting and false counts.
- Existing methods lack comprehensive models for coincidence effects.
Purpose of the Study:
- To define prerequisites for estimating signal coincidence effects in particle counting.
- To develop a new model for the particle counting process.
- To verify empirical prerequisites and establish a protocol for operating limits.
Main Methods:
- Defined particle concentration measures varying with particle size.
- Developed a new model for the particle counting process.
- Empirically verified a single normalized equation for coincidence effects across single particle counters.
- Utilized a Poisson model to estimate and control false counts.
Main Results:
- A single normalized equation accurately describes coincidence effects in all single particle counters.
- A maximum undercount limit of 5% is proposed.
- Undercount errors were estimated for various container sizes based on U.S.P. limits.
- The new model and measures enable standard instrument specifications for pharmacopeial testing.
Conclusions:
- The developed model and measures provide a robust framework for accurate particle counting in pharmaceutical contamination testing.
- Understanding particle counter capabilities and employing dilution techniques are key to achieving acceptable counting accuracy.
- This work facilitates the establishment of conservative instrument specifications for regulatory compliance.
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