Nebulizers pneumatic

In flame AAS the sample solutions are usually nebulized pneumatically into a spray chamber and the aerosol produced is lead together with a mixture of a burning gas and an oxidant into a suitable burner. 

Atmospheric pressure chemical ionization (APCI) [15] involves the primary formation of ions by corona discharge in a solvent spray under atmospheric pressure. A solution of the sample is nebulized pneumatically and the droplets formed are vaporized by heating (120 °C). The resulting sample gas is chemically ionized by the transfer of protons from the primary reactant ions.The APCI technique is widely used in the analysis of drugs or metabolic studies. Detection is limited to a molecular mass of about 1000 Da. 

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Nebulizers. The nebulizer converts a liquid into an aerosol of small droplets that can be transported to the plasma. Two approaches for aerosol formation are used commercially for ICPs, pneumatic nebulization, and ultrasonic nebulization. Pneumatic nebulizers use high-speed gas flows to create the aerosol. There are three commonly used pneumatic nebulizers the concentric nebulizer, the cross-flow nebulizer, and the Babington nebulizer. Pneumatic nebulizers produce a range of aerosol droplet sizes. Large droplets cannot be efficiently desolvated, so the aerosol is passed through a spray chamber to remove large droplets. As is the case with AAS, less than 5% of the original sample liquid actually reaches the plasma. 

Pneumatic Nebulization. Pneumatic nebulizers are of two basic types concentric nebulizer and cross-flow nebulizer. The viscosity and surface tension of the sample solution affect the carrier gas flow rate and the liquid uptake. In order to ensure steady sample uptake, peristaltic pumps are used for sample introduction. 

The sample is nebulized pneumatically at the orifice. It is then mixed with fuel and oxidant. Spoilers render the fuel-air-sample droplet mixture uniform before the mixture enters the burner. The large droplets fall to the bottom of the mixing chamber and exit through the drain. This method produces a more uniform droplet size to enter the flame than does the total-consumption type of burner. Almost all commercial nebulizers for liquid samples use modifications of the two systems described, i.e., total consumption as illustrated with the Beckman burner (Figure 9-4), or the separate nebulizing-gas mixing chamber illustrated in Figure 10-12. 

As shown in the schematic of the particle-beam interface (Figure 5.7), three steps, nebulization, desolvation, and momentum separation, are involved in the conversion of analytes from LC effluents into gas-phase species. First, the LC effluent is nebulized pneumatically by forcing the liquid and helium carrier gas through a small orifice. Desolvation of the droplets in the mist occurs when they travel at very high velocity through the desolvation chamber. The temperature of this chamber is maintained a few degrees above ambient temperature to provide thermal energy just sufficient to compensate for the latent heat of vaporization of the solvent. The third step is momentum separation of the solute particles fi om... 

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ICP-AES Nebulization pneumatic or ultrasonic High- temperature argon plasma Emission measured by spectrophotometer ppm-ppb Multielemental High throughput Low interferences Refractory clem. High dissolved solids tolerance Relatively expensive Limited sensitivity Spectral interferences... 

ICP-MS Nebulization pneumatic or ultrasonic High- temperature argon plasma Ion separation, m/z measured by mass spectrometer ppt with few exceptions, ppq for some elements High sensitivity— better than GFAAS Multielemental High sample throughput Expensive Matrix interferences Low dissolved solids tolerance... 

Organic. solutions (methyl isobulyl ketone, xylene, kerosene) can be nebulized pneumatically and determinations in these. solvents can be performed directly with ICP-AES [250]. The addition of oxygen or the use of higher power is help-... 

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