Chapter 10 Atomic Emission Spectrometry

10A EMISSION SPECTROSCOPY BASED ON PLASMA SOURCES

Inductively coupled plasma (ICP) Direct current plasma (DCP) Microwave induced plasma (MIP)

10A-1 The Inductivity Coupled Plasma Source

FIGURE 10-1 A typical ICP source. Position A shows radial viewing of the torch, and position B shows axial viewing.

Sample introduction

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.

Plasma Appearance and Spectra Analyte Atomization and Ionization

FIGURE 10-3 Device for electrothermal vaporization.

FIGURE 10-4 Temperatures in a typical ICP course.

10A-2 The Direct Current Plasma Source

FIGURE 10-5 A three-electrode DC plasma jet.

10A-3 Plasma Source Spectrometers

Instruments for emission spectroscopy are of three basic types: sequential, simultaneous multichannel, and Fourier transform.

TABLE 10-1 Desirable Properties of an Emission Spectrometer

Sequential Instruments Slew-Scan Spectrometers Scanning Echelle Spectrometers

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 by the 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.

FIGURE 10-7 Schematic of an echelle spectrograph system.

Multichannel Spectrometers Polychromators.

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.

ICP-AES

A Charge-Injection Device Instrument

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

FIGURE 10-10

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.

FIGURE 10-10(b) Intensity profile for an iron line. All of the radiation from the line falls on the 3 × 3 examination window.

A Charge-Coupled Device Instrument A Combination Instrument

FIGURE 10-11 An echelle spectrometer with segmented array of CCDs.

FIGURE 10-12 Schematic of an array segment showing phototransducers, storage and output registers, and readout circuitry.

Fourier Transform Spectrometers Fourier, Joseph

10A-4 Applications of Plasma Sources

Sample Preparation Elements Determined

Line Selection Calibration Curves

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.

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

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.

Interferences Detection Limits

10B EMISSION SPECTROSCOPY BASED ON ARC AND SPARK SOURCES

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,

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

10B-1 Sample Types and Sample Handling

Metals Nonmetallic Solids

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

FIGURE 10-16 Some typical graphite electrode shapes. Narrow necks are to reduce thermal conductivity.

10B-2 Instruments for Arc and Spark Source Spectroscopy

Spectrographs

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

Multichannel Photoelectric Spectrometers Multichannel Photomultiplier Instruments. Array-Based Multichannel Instruments.

10B-3 Arc Source Emission Spectroscopy

Characteristics of Arc Sources Cyanogen Spectral Bands. Rates or Emission.

Applications of Arc Sources

10B-4 Spark Sources and Spark Spectra

Applications of Spark Source Spectroscopy

10C MISCELLANEOUS SOURCES FOR OPTICAL EMISSION SPECTROSCOPY

10C-1 Flame Emission Sources

10C-2 Glow-Discharge Sources

10C-3 Laser Microprobe Sources