Cascade impaction

SM Milosovich. Particle-size determination via cascade impaction. Pharm Technol 16 82-86, 1992. 

ONDOV Cascade Impact ors in the Characterization of Aerosol Particles... 

We have applied it to a determination of paraquat residues in air collected over 200 m from a spraying operation, both during and for several hours following treatment. Additionally, the method may be used to measure the quantity of paraquat associated with various particulate size fractions collected by cascade impaction. 

The impacted drug fractions are normally measured via a specific chemical assay, although mircoweighing the plates has also been investigated. A number of actuations are normally accumulated for each cascade impaction determination to collect sufficient drug for accurate assay. The United States Pharmacopoeia includes a test for MDIs, using a cascade impactor coupled to a throat of specified dimensions. ... 

Smart J, Berg E, Nerbrink O, Zuban R, Blakey D, New M. TouchSpray technology Comparison of the droplet size measured with cascade impaction and laser diffraction. In Respiratory Dmg Delivery V Dalby RN, Byron PR, Farr SJ, eds. Interpharm Press Phoenix, AZ, 2002 525-532. 

In the applications of gas-solid flows, measurements of particle mass fluxes, particle concentrations, gas and particle velocities, and particle aerodynamic size distributions are of utmost interest. The local particle mass flux is typically determined using the isokinetic sampling method as the first principle. With the particle velocity determined, the isokinetic sampling can also be used to directly measure the concentrations of airborne particles. For flows with extremely tiny particles such as aerosols, the particle velocity can be approximated as the same as the flow velocity. Otherwise, the particle velocity needs to be measured independently due to the slip effect between phases. In most applications of gas-solid flows, particles are polydispersed. Determination of particle size distribution hence becomes important. One typical instrument for the measurement of particle aerodynamic size distribution of particles is cascade impactor or cascade sampler. In this chapter, basic principles, applications, design and operation considerations of isokinetic sampling and cascade impaction are introduced. 

Classification of a particle cloud into discrete sizes using cascade impaction may be interpreted as measuring aerodynamic (equivalent spherical particle) diameter. Several impaction stages (cascade impactor) are used in the classification of a poly disperse cloud (see Figure 35). 

A series filter was used to separate atmospheric particulate iodine, HI and I2, HOI and organic iodine. The particulate iodine is usually separated and collected using micropore filters or glass microfiber. The distribution of iodine in the different sizes of particulates is collected by a multi-stage cascade impact collector. Wimschneider and Heumann (1995) used a six-stage slot cascade impactor to collect particulates... 

As described above, inertial cascade impaction is the gold standard for characterization of pharmaceutical aerosols. However, it is not the only method avail-... 

There are only two experimental strategies that have the potential to yield reliable predictive results for nebulized aerosols. The first is to measure the droplets in their fully hydrated state. This can be done either immediately as they exit the mouthpiece, using a real-time sizing instrument, or by reducing the evaporation kinetics sufficiently to allow measurement downstream with an offline techniqne snch as inertial cascade impaction. The second is to completely dry the aerosol, size the dry particles, and then calculate back to obtain the original size distribntion. Measuring the aerosol at intermediate hydration states between these two extremes is obviously problematic because the hydration state would have to be measured in order to correct the size distribution back to the original inhaled size. 

Cascade impaction has also been the method of choice for pMDI aerosols because they are generally multicomponent systems and drug assays are required if the drug size distributions are to be obtained. It is of course where the drug deposits and hence the drug size distribution that is of importance. 

Figure 6 represents an in vitro simulation of a patient breathing an aerosol from a nebulizer and measurement of inhaled mass. An important additional goal is the assessment of the distribution of nebulized particles in a manner that represents as closely as possible the aeresol as it is actually inhaled by a patient. To measme the particle distribution investigators often use cascade impaction, described in principle in Fig. 16. The aerosol, which consists of particles suspended in a gas, enters the cascade impactor at a constant volumetric...

Low-flow cascade impaction may have other technical advantages. The MMAD is often used to predict deposition in the human lung. However, many aerosols change their aerodynamic characteristics in real time after they are generated. For example, particles from MDIs may be nuxed with volatile com-... 

Figure 24 Diagram of neonatal ventilator circuit incorporating a nebulizer. This example illustrates an ultrasonic device. Cascade impaction can be performed at the distal tip of the endotracheal tube. (From Ref. 36.)...

A draft European Nebulizer Standard (30) has been submitted for formal approval to CEN (Comite Europeen de Normalisation European Committee for Standardization). CEN is responsible for European standardization in all fields except Electrotechnical (CENELEC) and Telecommunications (ETSl). Publication of the European Nebulizer Standard is expected during 2001. Included within the European standard are detailed descriptions of two test methods for (1) assessing nebulizer aerosol output inhaled using breath simulation similar to that described previously and (2) assessing nebulized aerosol droplet size using low-flow cascade impaction. Because this standard is expected to be adopted throughout Europe (and possibly more widely), a summary of its contents may be useful to readers. 

Aerosol Size Measurement Using Low-Flow Cascade Impaction... 

This low-flow cascade impaction method differs in a subtle but important manner from methods described earlier (Chap. 8, Fig. 7) in which the low-flow cascade is incorporated within a simulated breathing pattern. Here the cascade samples at a relatively low constant flow (2 L/min) within a sinus flow... 

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