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Chapter 10

Atomic Emission Spectrometry

10A EMISSION SPECTROSCOPYBASED ON PLASMA SOURCES

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Inductively coupled plasma (ICP)

Direct current plasma (DCP)

Microwave induced plasma (MIP)

10A-1 The Inductivity Coupled Plasma Source

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FIGURE 10-1

A typical

ICP source. Position A

shows radial viewing of

the torch, and position B

shows axial viewing.

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Sample introduction

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FIGURE 10-2 The Meinhard nebulizer. The nebulizing gas flows

through an opening that surrounds the capillary concentrically. This causes a reduced pressure at the tip and aspiration of the sample. The high-velocity gas at the tip breaks up the solution into a mist.

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Plasma Appearance and Spectra

Analyte Atomization and Ionization

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FIGURE 10-3 Device for electrothermal vaporization.

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FIGURE 10-4 Temperatures in a typical ICP course.

10A-2 The Direct Current Plasma Source

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FIGURE 10-5 A three-electrode DC

plasma jet.

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10A-3 Plasma Source

Spectrometers

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Instruments for emission spectroscopy are of three

basic types: sequential, simultaneous multichannel, and

Fourier transform.

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TABLE 10-1 Desirable Properties of an Emission Spectrometer

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Sequential Instruments

Slew-Scan Spectrometers

Scanning Echelle Spectrometers

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FIGURE 10-6 Optical diagram of a sequential ICP optical emission spectrometer. All

moving parts are under computer control, and their modes of motion are indicated bythe three-dimensional arrow. Moving parts include the grating, a mirror for transducer selection, a refractor plate for optimizing signal throughput, and a viewing mirror to optimize the plasma viewing position. The spectrometer contains a mercury lamp for automatic wavelength calibration. Notice the axial viewing geometry.

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FIGURE 10-7 Schematic of an echelle spectrograph system.

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Multichannel Spectrometers

Polychromators.

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FIGURE 10-8 Direct-reading ICP emission spectrometer. The polychromator is of the Paschen-Runge design. It features a concave grating and produces a spectrum around a Rowland circle. Separate exit slits isolate each spectral line,and a separate photomulitiplier tube converts the optical information from each channel into an electrical signal. Notice the radial viewing geometry. PMT= photomultiplier tube.

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ICP-AES

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A Charge-Injection Device Instrument

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FIGURE 10-9 Optical diagram of an echelle spectrometerwith a charge-injection detector.

歐亞書局FIGURE 10-10

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FIGURE 10-10(a) Schematic representing the surface of a CID. The short horizontal lines represent the read windows. A magnified image of one of the read windows is also shown. The nine central elements form the examination window, where a line is positioned.

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FIGURE 10-10(b)

Intensity profile for an iron

line. All of the radiation

from the line falls on the

3 × 3 examination window.

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A Charge-Coupled Device Instrument

A Combination Instrument

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FIGURE 10-11 An echelle spectrometer with segmentedarray of CCDs.

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FIGURE 10-12 Schematic of an array segment showing

phototransducers, storage and output registers, and readout

circuitry.

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Fourier Transform Spectrometers

Fourier, Joseph

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10A-4 Applications of

Plasma Sources

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Sample Preparation

Elements Determined

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Line Selection

Calibration Curves

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FIGURE 10-13 Periodic table characterizing the detection power and number of useful emission lines of ICP by using a pneumatic nebulizer. The color and degree of shading indicate the range of detection limits for the useful lines. The area of shading indicates the number of useful lines.

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FIGURE 10-14 Typical calibration curves in ICP emission spectrometry.

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FIGURE 10-15 Internal

standard calibration

curves with an ICP

source. Here, an yttrium

line at 242.2 nm served

as an internal standard.

Notice the lack of

interelement

interference.

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Interferences

Detection Limits

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10B EMISSION SPECTROSCOPY BASEDON ARC AND SPARK SOURCES

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These spectra permitted the qualitative and quantitative determination of metallic elements in

a variety of sample types, including metals and alloys,

soils, minerals, and rocks,

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TABLE 10-2 Effect of Standardization Frequency on Precision of ICP Data

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10B-1 Sample Types and Sample Handling

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Metals

Nonmetallic Solids

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TABLE 10-3 Comparison of Detection Limits for Several Atomic spectral Methods

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FIGURE 10-16 Some typical graphite electrode shapes.

Narrow necks are to reduce thermal conductivity.

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10B-2 Instruments for Arc and

Spark Source Spectroscopy

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Spectrographs

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FIGRUE 10-17 The Eagle mounting for a grating spectrograph.

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Multichannel Photoelectric Spectrometers

Multichannel Photomultiplier Instruments.

Array-Based Multichannel Instruments.

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10B-3 Arc Source Emission Spectroscopy

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Characteristics of Arc Sources

Cyanogen Spectral Bands.

Rates or Emission.

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Applications of Arc Sources

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10B-4 Spark Sources and Spark Spectra

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Applications of Spark Source Spectroscopy

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10C MISCELLANEOUS SOURCESFOR OPTICAL EMISSION SPECTROSCOPY

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10C-1 Flame Emission Sources

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10C-2 Glow-Discharge Sources

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10C-3 Laser Microprobe Sources

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