Nebulizers particle size distribution

Denyer J. Breathing patterns in adult patients. J Aerosol Med 1997 10(1) 99. Stapleton KW, Finlay WH. Errors in characterizing nebulized particle size Distributions with cascade impactors. J Aerosol Med 1998 ll(Suppl l) 80-83. 

Water samples deserve some special attention despite of the apparent simplicity of their analysis. One reason is that, depending upon the source, water samples will have varying degrees of particulates. Most pollution surveys require filtration through a 0.45 M Millipore filter. In the event that filtration is omitted deliberately or unknowin gly, such particulates are entrained into the plasma, dissociated, and excited in the intense heat of the source. The efficiency of entrainment and nebulization depends on the specific nebulizer used, as well as the particle-size distribution. These in turn effect the degree of dissociation in the plasma. Thus, it is important to ensure that water samples are properly prepared. 

This was developed by Aerometrics in 1983, in collaboration with Lewis Research center, for research into pollution reduction from gas turbines. It is particularly relevent to measurements of small, spherical particles such as are found in fuel injection systems, medical nebulizers and bubbles in water. Aerometrics was later acquired by TSI who currently produce the TSI/Aerometrics PDPA 2D System. This instrument measures sizes in the 0.5 to 10,000 pm range using various optical configurations. The optical transmitter and receiver can be traversed together to move the location of the optical probe for spatial mapping of the flow field and the particle size distributions. 

Recently, a comparison study of deposition pattern of aqueous nasal spray pumps and non-portable nebulizers was published. The obtained controversial results showed a relative standard deviation of 35-80%. This demonstrates the variations in nasal anatomy and physiology from individual to individual. Other stud-ies indicate that differences in the spray performance, i.e., spray angle and particle size distribution, of delivery systems do not necessarily result in different in vivo deposition. 

Table 4 Particle size distribution of different nebulizers...

Table 1 Design features of ultrasonic nebulizers determining particle size distribution and mass output...

Fig. 49. Particle size distributions of pneumatic nebulizers for ICP. MAK, high-pressure cross-flow nebulizer CGN, concentric glass nebulizer JAB, Jarrell—Ash Babington nebulizer JAC, Jarrell—.Ash fixed cross-flow nebulizer (Reprinted with permission from Ref. [139].)...

If the drug is insoluble, it is important that for a suspension formulation the drug be micronized to a size of less than 2 p.m (Dahlback 1994). The particle size distribution of nebulized droplets can be measured using, e.g, laser diffraction (Clark 1995). Validation experiments showed that laser diffraction was robust and reliable and that the diffraction data were a good measure of the particle size of the aerosolized droplets. 

Others have investigated the effect of changing the compressor flow on the particle size distribution of various nebulizers. Using a Cirrhus nebuliser, Everard et al. increased compressor flow from 4 to 8 L/min. This resulted in decreasing the MMAD from 7 to 3.7 pm, whereas the percentage of the droplet mass <5 pm increased from 26.8 to 70.8% (95). These data are similar to those reported by... 

Riedler J, Robertson CF. Effect of tidal volume on the output and particle size distribution of hypertonic sahne from an ultrasonic nebulizer. Fur Resp J 1994 7 998-1002. 

Viscosity is a force that opposes the nebulization process it is the tendency for a liquid to resist flow. Thus a highly viscous liquid would be almost impossible to force through a small capillary. Viscosity is inversely related to temperature thus a highly viscous sample could be processed through a capillary if the temperature of the sample were raised. It is important that standard solutions and sample solutions have approximately the same viscosity since it is necessary that these solutions have the same sample uptake rate and produce the same particle size distribution. 

The response factor of an ELSD largely depends on the size of analyte particles entering the detection chamber. After exiting from the HPLC column, the eluent stream is nebulized, and a scavenger gas stream carries the effluent cloud through a hot drift tube where the solvent vaporizes. The droplet shrinks to the volume of the non-volatile material contained in the eluent. The average particle size in the cloud at a given time and the particle size distribution can be derived from the elution profile of the analyte and... 

Aerosol droplet size di.stributions can be determined by stray-light measurements [87], [88]. Data obtained from sampling with cascade impac-tors may suffer from evaporation of the droplets on their way through the device, especially as sampling may require the application of underpressure [89]. Data for different nebulizers are available [90]. Particle size distributions depend on the nebulizer and its working conditions, on the liquid nebulized, and on the nebulization chamber. These relations have been studied in depth for organic solutions [91], [92], for which, at low gas flow, pneumatic nebulizers often... 

Ultrasonic nebulization has two advantages over pneumatic nebulization. The aerosol particles have a lower diameter and a narrower particle size distribution compared with pneumatic nebulization (< 5 compared with 10-25 pm). Therefore, aerosol production efficiency may be up to 30%, and analyte introduction efficiency is high. No gas flow is required for aerosol production, the trans-... 

Inhaled aerosols are widely nsed as nonspecific provocation tests with histamine and methacholine and with specific provocation tests for different allergens. Comparison of data between research centers is hampered by differences in the methods used. Results are often given as concentration of the test snbstance in the nebulizer, giving rise to an effect such as 15 or 20% decrease in FEVi (PC 20) or 100% increase in specific airway resistance from baseline. The use of the corresponding provocation dose gives information on dose to the mouth, but without information on the nebnlizer used or of particle size distribution, comparability cannot be ascertained. Aerosols of hypertonic saline have been used in induction of sputum for test of bronchial responsiveness (3,4). Analysis of sputum... 

Specific advancements ia the chemical synthesis of coUoidal materials are noteworthy. Many types of genera ting devices have been used to produce coUoidal Hquid aerosols (qv) and emulsions (qv) (39—43) among them are atomizers and nebulizers of various designs (30,44—50). A unique feature of produciag Hquid or soHd coUoids via aerosol processes (Table 3) is that material with a relatively narrow size distribution can be routinely prepared. These monosized coUoids are often produced by relying on an electrostatic classifier to select desired particle sizes ia the final stage of aerosol production. 

These compressed air nebulizers produce polydisperse aerosols. After the aerosol is produced, the size distribution may change due to evaporation of liquid from the droplets. In addition, the particles may be electrically charged due to an ion imbalance in the droplets as they form if such charges become further concentrated due to evaporation, the particle may break up into smaller particles. Thus electrical neutralization of the aerosol, for example, by exposure to a radioactive source, is usually necessary to prevent electrostatic effects from dominating the particle motion, coagulation, and other behavior. 

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