Aerosol efficiency

Dautrebande, L. (1962a). Importance of particle size for therapeutic aerosol efficiency. In Microaerosols. Academic Press, New York, pp. 37-57. 

MIPs have been used widely in gas chromatography (GC) detection. Low-power MIPs (50-150 W) do not accept liquid aerosols efficiently. One way of overcoming this disadvantage is to desolvate the sample solution or to employ electrothermal vaporization. A commercial system is available consisting of a... 

Concentric nebulizers date back more than a century, to Gouy [75], and in principle are selfaspirating. They can be made of metal, plastic, or glass. In atomic absorption spectrometry. Pt-lr capillaries are often used to allow the aspiration of highly acid solutions. In plasma atomic spectrometry, concentric glass nebulizers (Meinhard) 74] are well known. They use a rather lower gas flow (1-2 L/min) than atomic absorption types (up to 5 L/min). In both cases, aspiration rates are 1-2 mL/min and aerosol efficiencies 2-5%. Direct injection nebulizers are a useful alternative for the introduction of small-volume samples [76]. 

Regardless of the method used to generate the aerosol, efficient pulmonary deposition of the active agent is critically dependent on the aerodynamic diameter of the inhaled particle. Aerodynamic diameter is the physical property of a particle, which defines how it will behave in an airstream, and depends on the particle geometric size, density, and shape. An in-depth discnssion of how particle shape affects aerodynamic diameter is beyond the scope of this review therefore, the cited examples will assume a spherical particle. 

Samples to be examined by inductively coupled plasma and mass spectrometry (ICP/MS) are commonly in the form of a solution that is transported into the plasma flame. The thermal mass of the flame is small, and ingress of excessive quantities of extraneous matter, such as solvent, would cool the flame and might even extinguish it. Even cooling the flame reduces its ionization efficiency, with concomitant effects on the accuracy and detection limits of the ICP/MS method. Consequently, it is necessary to remove as much solvent as possible which can be done by evaporation off-line or done on-line by spraying the solution as an aerosol into the plasma flame. 

This arrangement provides a thin film of liquid sample solution flowing down to a narrow orifice (0.007-cm diameter) through which argon flows at high linear velocity (volume flow is about 0.5-1 1/min). A fine aerosol is produced. This particular nebulizer is efficient for solutions having a high concentration of analyte constituents. 

Depending on the type of nebulizer used and its efficiency, there may be initially a significant proportion of large droplets in the aerosol. Heavier than the very fine droplets, the larger droplets are affected by gravity and by turbulent flow in the argon sweep gas, which cause them to deposit onto the walls of the transfer tube. 

Verification of the microbial retention efficiency of the membrane filters may be undertaken using either Hquid or aerosol challenge tests. A Hquid challenge test is more stringent. Furthermore, this test can provide retention information for process conditions such as extreme moisture after sterilization or air entrained with water drops. A Hquid challenge is performed using a protocol similar to that described for Hquid filtration. 

Aerosol products are hermetically sealed, ensuring that the contents caimot leak, spill, or be contaminated. The packages can be considered to be tamper-proof. They deUver the product in an efficient manner generating Httie waste, often to sites of difficult access. By control of particle size, spray pattern, and volume deUvered per second, the product can be appHed directiy without contact by the user. For example, use of aerosol pesticides can minimize user exposure and aerosol first-aid products can soothe without applying painful pressure to a wound. Spray contact lens solutions can be appHed directiy and aerosol lubricants (qv) can be used on machinery in operation. Some preparations, such as stable foams, can only be packaged as aerosols. 

Plutonium solutions that have a low activity (<3.7 x 10 Bq (1 mCi) or 10 mg of Pu) and that do not produce aerosols can be handled safely by a trained radiochemist in a laboratory fume hood with face velocity 125—150 linear feet per minute (38—45 m/min). Larger amounts of solutions, solutions that may produce aerosols, and plutonium compounds that are not air-sensitive are handled in glove boxes that ate maintained at a slight negative pressure, ca 0.1 kPa (0.001 atm, more precisely measured as 1.0—1.2 cm (0.35—0.50 in.) differential pressure on a water column) with respect to the surrounding laboratory pressure (176,179—181). This air is exhausted through high efficiency particulate (HEPA) filters. 

The AeroSizer, manufactured by Amherst Process Instmments Inc. (Hadley, Massachusetts), is equipped with a special device called the AeroDisperser for ensuring efficient dispersal of the powders to be inspected. The disperser and the measurement instmment are shown schematically in Figure 13. The aerosol particles to be characterized are sucked into the inspection zone which operates at a partial vacuum. As the air leaves the nozzle at near sonic velocities, the particles in the stream are accelerated across an inspection zone where they cross two laser beams. The time of flight between the two laser beams is used to deduce the size of the particles. The instmment is caUbrated with latex particles of known size. A stream of clean air confines the aerosol stream to the measurement zone. This technique is known as hydrodynamic focusing. A computer correlation estabUshes which peak in the second laser inspection matches the initiation of action from the first laser beam. The equipment can measure particles at a rate of 10,000/s. The output from the AeroSizer can either be displayed as a number count or a volume percentage count. 

Collective protection enclosures are required for groups of personnel. Such enclosures must be airtight to prevent inward seepage of contamination. They can be independent units or can be formed by adequately treating the interior walls of stmctures, tents, airplanes, or vehicles. A supply of uncontaminated air, provided by passing ambient air through high efficiency aerosol and carbon filters, must be provided. 

FIG. 22-36 Efficiency of an electrofilter as a function of gas flow rate at 5 different voltages. Experimental materials l- im aerosol of dioctyl phthalate glass-fiher filter. Symbols O, no voltage applied A, 2 kV , 3.5 kV , 5 kV , 7 kV. After Fielting et ah, Dielectrophoretic Filtration of Solid and Liquid Aerosol Particulates, Prepr. 75-32.2, 68th ann. meet., AirPollut. Conttol Assoc., Boston, June 1975.)... 

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