PubMed · 14861067
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1951-09-15. ELECTRESTEEM vaporizers accepted.. https://pubmed.ncbi.nlm.nih.gov/14861067/
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The performance of Andersen Mark II impactors was investigated theoretically and experimentally. Theoretical calculations were made to assess the impact that differences in jet diameters among Mark II impactors have on size distribution measurements of metered dose inhalers (MDIs). A previous investigation indicated that the jet diameter for stages on Mark II impactors often do not conform to the manufacturer's specifications (Stein and Olson, 1997). For the calculations reported in this paper, only jet diameters that conform to the manufacturer's specifications were considered. The calculations indicate that large differences in the amount of drug collecting on a given stage should be expected among Mark II impactors sampling an identical aerosol-even for Mark II impactors that conform to the manufacturer's specifications. These calculations suggest that it is impractical to analyze size distribution data generated with cascade impactors, such as the Mark II, on a stage-by-stage basis. Experimental measurements of three MDI products were made using three different Andersen Mark II cascade impactors. Measurements of the same product were very consistent for a given impactor, but large differences were observed in measurements of the same product with different impactors. For measurements of QVAR HFA beclomethasone dipropionate MDIs using three Mark II impactors, the amount of drug that collected on Stage 6 ranged from 28.7 to 41.3% of the sampled mass depending on which impactor was used. The theoretical calculations and experimental measurements reported in this paper demonstrate that it is important to consider the limited precision of cascade impactors, such as the Andersen Mark II, when analyzing the size distribution measurements that they provide.
Given the rapid sizing capability and high sensitivity, the quartz crystal microbalance (QCM) cascade impactor has been evaluated for the size determination of metered-dose inhaler (MDI) aerosols. The effects of surfactants present in MDI formulations, crystal coating, particle bounce and crystal overloading on the QCM cascade impactor are investigated. To reduce particle bounce, it is necessary to coat the crystals and use new coated surfaces for each measurement. Mass median aerodynamic diameters (MMADs) obtained from the QCM cascade impactor are compared to those from the commonly used Andersen cascade impactor. For MDI formulations containing little or no surfactants, MMADs obtained from the QCM and Andersen cascade impactors are comparable. For MDI formulations containing a significant amount of surfactant (or any non-volatile excipients), the QCM cascade impactor measures the combined size distribution of the drug and non-volatile excipients. A technique is devised in this study to deduce the drug-only size distribution from the QCM impactor for surfactant-containing MDI formulations and show comparable results to the Andersen cascade impactor except for high drug load Intal. The QCM impactor has proved to be a useful tool for rapid size measurement of MDI formulations.
The purpose of this study was to analyze atomizer performance in the production of respirable spray-dried particles. An ultrasonic nebulizer and a plain-jet airblast atomizer were evaluated in an open cycle, cocurrent spray-drying tower using a 0.5% w/v disodium fluorescein solution. The plain-jet airblast atomizer produced smaller initial droplet sizes (D32 = 4.5-4.8 microns) relative to the ultrasonic nebulizer (D32 = 20-48 microns) over a range of atomizer operating conditions. The airblast atomizer was selected for further analysis in two spray-drying tower configurations: grounded and electrostatically charged. The spray-dried particles produced by the airblast atomizer were of a size range (mass median aerodynamic diameter [MMAD] < 1.6 microns) suitable for inhalation. Significant differences were observed for the grounded and electrostatically charged tower configurations, the latter producing the smaller median particle size at the expense of decreased collection efficiency. The electrostatically charged tower was size selective because of diffusion charging, retaining particles with an aerodynamic diameter (Dae) in the range 1 < Dae < 2 microns. The particle size was reduced with decreasing ambient relative humidity, although a controlled study of this parameter would be required to explicitly define its effects.