A review is presented of the issues associated with the generation of large-volume, high-pressure, nonequilibrium plasmas, as well as the approaches that have been developed for generating these plasmas using electrical discharges in gases. The various instabilities that have been overcome to obtained these plasmas as well as the techniques for quenching them are also reviewed. Last, recent efforts to obtain atmospheric pressure plasmas are discussed with particular emphasis on the capillary plasma electrode discharge, which we have used to obtain high (electron) density nonequilibrium plasmas.

Generation of large-volume, atmospheric-pressure, nonequilibrium plasmas

PrefaceIntroduction1 BASIC PRINCIPLES Atomic structure Plasmas Emission and absorption of radiation Ionization Dissociation Sources for atomic spectrometry Analytical atomic spectrometry 2 SPECTROMETRIC INSTRUMENTATION Figures of merit of an analytical method Optical spectrometers Mass spectrometers Data acquisition and treatment SAMPLE INTRODUCTION DEVICES Pneumatic nebulization Ultrasonic nebulization Hydride generation Eletrothermal evaporation Direct solids sampling Cathodic sputtering 4 ATOMIC ABSORPTION SPECTROMETRY Principles Atomic absorption spectrometers Flame atomic absorption Electrothermal atomic absorption Hydride generation Background correction techniques Fields of application 5 ATOMIC EMISSION SPECTROMETRY Principles Atomic emission spectrometers Flame emission Arcs and sparks Plasma sources Glow discharges Laser sources Fields of application 6 PLASMA MASS SPECTROMETRY Principles Instrumentation Glow discharge mass spectrometry ICP mass spectrometry Fields of application 7 ATOMIC FLUORESCENCE SPECTROMETRY Principles Figures of merit 8 LASER ENHANCED IONIZATION SPECTROMETRY Principles Figues of merit Analytical Applications9 SAMPLE PREPARATION FOR ATOMIC SPECTROMETRY Sample Preparation in direct compact sample analysisGrinding, sieving and compaction of powdersSample dissolutionWet chemical methodsFusion ProceduresMicrowave-assisted methodsCombustion TechniquesFlow injection analysisLeaching sample preparation methods 10 COMPARISON WITH OTHER METHODS Power of detection Analytical accuracy Economic aspectsLiteratureIndex

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Analytical Atomic Spectrometry with Flames and Plasmas

Abstract : A miniature inductively coupled plasma source for atomic emission spectrometry is described and a preliminary evaluation of its analytical capabilities is presented. The mini-ICP is very economical to sustain and works well with less than 1 kW of RF power and 8L/min of argon coolant gas. In addition, the new source possesses some unique operating characteristics which simplify sample introduction. In this paper, detection limits, multi-element capabilities, and other analytical features of the mini-ICP are compared with those demonstrated by a conventional ICP source and shown to be comparable. In addition, the two plasmas are shown to exhibit similar excitation temperatures in the respective analyte observation regions (i.e., plasma tail flames). These results suggest that the mini-ICP possesses the same desirable atomization and excitation characteristics as conventional ICP sources. (Author)

Development and characterization of miniature inductively coupled plasma source for atomic emission spectrometry

Polyatomic anions derived from several dinitrotoluene isomers, 2,4,6-trinitrotoluene, and 1,3,5-trinitro-1,3,5-triazacyclohexane have been formed by use of negative ion chemical ionization and trapped in an ion trap mass spectrometer. Mass spectrometry/mass spectrometry daughter ion spectra were obtained for most of these ions. In most cases, the parent anions were converted very efficiently to daughter ions (>10%), but for the (M - H)/sup -/ ions the efficiencies were relatively low. Conversion efficiencies were observed to differ by as much as 2 orders of magnitude between anions. The major cause for these differences is attributable to differences in the propensity for collisional electron detachment vs. that for collision-activated dissociation.

Collision-activated dissociation of negative ions in an ion trap mass spectrometer

Development and investigation of microwave plasma techniques in analytical atomic spectrometry

A microwave-induced plasma has been sustained with the use of nitrogen as the nebulizer and plasma supporting gas A concentric tube torch was constructed so the plasma could be easily ignited and maintained This new plasma emission source has a flame-like appearance and extends 10 cm beyond the cavity, at an applied power of 250 W The nitrogen plasma readily accepts aerosol samples and is compatible with sample introduced from a conventional nebulizer system The radial (side-on) optical viewing configuration was found to have lower background emission than the more commonly employed axial (end-on) configuration Optimum operating conditions were established from the effects of applied power, flow rate, and signal-to-background noise on the intensity of both atom and ion transitions A discussion of the background spectral features and the analytical potential of this new source is presented

Development of a Microwave-Induced Nitrogen Discharge at Atmospheric Pressure (MINDAP)

A microwave-induced plasma (MIP) is sustained at atmospheric pressure with the use of nitrogen as the plasma and nebulizer gas. The plasma is operated at 2450 MHz and has been optimized at 250 W of rf power with a total nitrogen flow rate of 1.78 L/min. The analytical performance of this plasma has been evaluated and compared with other atmospheric pressure plasma systems. Detection limits were typically in the part-per-billion concentration range, and calibration curves were linear over three-to-five orders of magnitude. Interelement interferences were observed but were overcome with the use of releasing agents. Precision for an analytical measurement was generally better than 2% relative standard deviation.

Analytical Characteristics of the Microwave-Induced Nitrogen Discharge at Atmospheric Pressure (MINDAP)

The use of a microarc atomizer as a device for microsample introduction into the inductively coupled plasma (ICP) is described. The microarc, a high-voltage, low-current, pulsating dc discharge, efficiently vaporizes desolvated, discrete microvolumes of sample solution into the plasma. The microarc-ICP combination exhibits relative detection limits and working curves comparable to those of other methods of sample introduction but functions with sample volumes in the 0.5 to 1.0 μl range. Matrix and ionization interference effects are absent or trivially overcome. Computer control of the instrument adds simplicity of operation.

The Use of a Microarc Atomizer for Sample Introduction into an Inductively Coupled Plasma

The noise from the emission signal of the microwave-induced nitrogen discharge at atmospheric pressure (MINDAP) has been analyzed. Wavelength-scan flicker-ratio, precision measurements, time-trace correlation and noise amplitude spectra were used to determine the individual components of the system noise. Noise spectra are reported with the use of a nebulizer sample introduction system for desolvated and undesolvated aerosol, for varying analyte concentration, and for background emission from nitrogen and water vapor. The analytical system appears to be flicker-noise-limited below about 1 Hz for all measurements made. Only 60 and 120 Hz peaks are detected in the frequency region extending to 700 Hz, and presumably arise from the microwave power supply

R. D. Deutsch

Papers

Development of a Microwave-Induced Nitrogen Discharge at Atmospheric Pressure (MINDAP)

Analytical Characteristics of the Microwave-Induced Nitrogen Discharge at Atmospheric Pressure (MINDAP)

The Use of a Microarc Atomizer for Sample Introduction into an Inductively Coupled Plasma

Identification of limiting noise sources in the microwave-induced nitrogen discharge at atmospheric pressure