Atomizing device

Because of the diverse appHcatioas involving Hquid atomizers, a large vocabulary of terms has evolved ia the spray community. The American Society for Testing and Materials, ASTM Subcommittee E29.04 on Liquid Particle Characterization, has attempted to standardize the terminology relating to atomizing devices (1). The definitions adopted by ASTM are used herein. 

The scope of this review Is limited to electrothermal atomic absorption spectrometry, with emphasis upon Its clinical applications. This article Is Intended to supplement the recent treatises on the basic technique which have been written by Aggett and Sprott ( ) > Ingle ( ), Klrkbrlght (34), Price (63), and Woodrlff (83). This resume does not consider various related topics, such as (a) atomic fluorescence or emission spectrometry (b) non-flame atomization devices which employ direct current... 

A comprehensive review of electrothermal atomization devices has been published (94). The review includes a discussion of commonly encountered problems such as atom loss through non-pyrolytic graphite, non-isothermal conditions, differences in peak height and peak area measurement, etc. 

In Refs 2 3 it is suggested that for blasting hard rock, tunnels can be dug deep underground and the charges are uranium-plutonium atomic devices instead of conventional explosives... 

The flame spectnmteter. used in emission spectrometry, consists til (I) die pressure regulators and llow meters for Ihe fuel gases (2) the atomizing device (3) the flame source (4) the optical system ... 

As an alternative to the motor-driven syringe, an atomizer device was developed (Fig. 4). The sample is atomized in a stream of air or nitrogen, depending on the nature of the sample and its tendency to become oxidized. The atomizer is mounted on a mechanical arm that can sweep from side to side while directing the atomized sample onto the surface of a TLC plate. The range and the number of sweeps are usually under microprocessor control the speed of movement is adjusted so that the solvent can be evaporated from a given area of the sample before it receives a subsequent dose. 

In all atomic spectroscopic techniques, we must atomize the sample, converting it into gas-phase atoms and ions. Samples are most commonly presented to the atomizer in solution form, although we sometimes introduce gases and solids. Hence, the atomization device must perform the complex task of converting analyte species in solution into gas-phase free atoms or elementary ions, or both. 

Atomization devices fall into two classes continuous atomizers and discrete atomizers. With continuous atomizers, such as plasmas and flames, samples are introduced in a continuous manner. With discrete atomizers, samples are introduced in a discrete manner with a device such as a syringe or an autosampler. The most common discrete atomizer is the electrothermal atomizer. 

Many other types of atomization devices have been used in atomic spectroscopy. Gas discharges operated at reduced pressure have been investigated as sources of atomic emission and as ion sources for mass spectrometry. The glow discharge is generated between two planar electrodes in a cylindrical glass tube filled with gas to a pressure of a few torr. High-powered lasers have been employed to ablate samples and to cause laser-induced breakdown. In the latter technique, dielectric breakdown of a gas occurs at the laser focal point. 

The air used for product drying should be HEPA filtered. When designed with silicone gaskets, the system will withstand sterilization temperatures. The atomizing device can be either a spray nozzle or a high speed centrifugal device. 

Spray dried products are typically temperature sensitive, therefore, air temperature should be controlled and as low as possible. Design of the atomizing device should ensure that product will not adhere to vessel walls. Surface drying and depyrogenation can be done in a continuous operated tunnel or batch oven. The former method is preferred since it minimizes the potential of particulate contamination during loading. 

Figure 7.4 Evaporative light scattering detector. At the outlet of the column the mobile phase is nebulized under a stream of nitrogen, by a specially atomizing device. When a compound elutes from the column, the droplets under evaporation give a suspension of fine particles. Illuminated by a laser source they scatter the light from a lamp via the Tyndall effect (what happens is comparable to the diffusion by fog through a car headlight beam). The signal detected by a photo-diode is proportional to the concentration of the compound illuminated. Irrespective of the substance, the response factors are very close. This detector is only useful for sample components that cannot be vaporized in the heated section of this detector.

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