Aerosols sampling

The simplest approach to sampling aerosols is to use filtration or an inertial device that traps all the airborne material. This would be useful for determining the total amount... 

The sample aerosol is introduced into the centre of the plasma, where it is exposed, for a few milliseconds, to the harsh conditions of the discharge, where discharge... 

The principle of inertial impaction is employed to sample aerosols aerodynamically for characterization of particle size and will be dealt with theoretically later in this chapter. 

Figure 5.21. Torch and sample aerosol generation system (QVAC 127 system). Source [510]...

Flames used in analytical measurements are similar to those produced by Bunsen burners with the added provision of a means of introducing the sample directly into the combustion zone. Support (oxidant) and fuel gases are fed to a nebulizer along with the sample solution. The mixed gases and sample aerosol then pass through the jets of the burner where ignition occurs. 

Flame atomization and excitation can be divided into a number of stages. Firstly, the heat of the flame evaporates solvent from the droplets of sample aerosol leaving a cloud of small particles of the solid compounds originally present in the solution. These are then vaporized and molecular associations broken down releasing free atoms (atomization) some of which... 

The digestion of solid samples to produce a solution is discussed in Section 13.2. For solution-based ICP MS analysis, the liquid is taken up through a thin tube via a peristaltic pump. This feeds directly into the instrument nebulizer, where argon gas is introduced into the liquid and a fine mist of droplets is expelled from the tip of the nebulizer. This sample aerosol is sprayed into the condenser to reduce the size of the droplets, ensuring an even sample loading and preventing cooling of the plasma. About 1% of the sample solution uptake is transported to the plasma torch, and any unused solution is drained away and may be recycled. 

Figure 5. Normalized S mass distribution, China Lake, CA—average of 8 samples. Aerosol segregated by LPl and analyzed by FVFPD. The solid histogram is the mass distribution with respect to the 50% aerodynamic cutoff diameter the dashed histogram is the inverted distribution obtained from LPl calibration data and Twomey (1975) inversion algorithm (a) July2-4, 1978 ("M = 0.765 fig/m ) (b) October 20-22, 1978 (M = 1.702 /ig/m ) (c) September 5-7, 1979 (M =...

The ability of currently used aircraft probes to accurately sample aerosols has been questioned. Huebert et al. (8) conducted a comparative study of several different types of aerosol probes, all mounted on the same aircraft. The results suggested that substantial losses of particles occurred in all of the inlet systems. Because of the limited nature of the study, however, the causes of the aerosol losses could not be identified. The results of the Huebert study prompted a workshop to reexamine the entire issue of aerosol sampling from aircraft (9). An important conclusion of the workshop was that currently there is insufficient knowledge to adequately describe important characteristics of airflow and particle trajectories at flight speeds of aerosol sampling probes used on aircraft. 

The role of the sample introduction system is to convert a sample into a form that can be effectively vaporized into free atoms and ions in the ICP. A peristaltic pump is typically used to deliver a constant flow or sample solution (independent of variations in solution viscosity) to the nebulizer. Several different kinds of nebulizers are available to generate the sample aerosol, and several different spray chamber designs have been used to modify the aerosol before it enters the ICP Gases can be directly introduced into the plasma, for example, after hydride generation. Solids can be introduced by using electrothermal vaporization or laser ablation. 

To a first approximation, this behavior can be understood by considering the processes that a drop of sample undergoes in the ICP (Fig. 3.2) and the main effects of a change in nebulizer gas flow rate on the plasma. After the sample aerosol exits the center tube of the torch, it travels a short distance (2 to 10 mm) before it enters the plasma s center channel. As the nebulizer gas flow rate is increased, the location where the plasma begins (and the temperature increases rapidly) in the center of the plasma moves downstream (Fig. 3.17). Therefore, for... 

It must be noted that increasing the amount of solvent in the ICP produces a higher load on the plasma and an increase in reflected powers, causing plasma instability. Desolvation of the sample aerosol may overcome this hurdle and is achieved by the use of a cooled spray chamber. In addition, Peltier coolers and membrane dryers [23] have been used for desolvating liquid aerosols and eliminate approximately 90% of the aerosol (Fig. 10.3). Spray chambers may also im-... 

Thermophoretic forces can be used in sampling aerosols the particles are passed through the dark space surrounding a hot body and are collected with nearly 100 percent efficiency on a cold surface placed nearby. To date, however, there has been no successful utilization of thermal forces for large-scale air cleaning. 

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