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THE SPECTRO-PAEDIA

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absorbance
adsorption
Atomization
bandwidth
Beamsplitters
bioluminescence
chemiluminescence
chromatography
electroluminescence
electromagnetic
emission
Emissivity
Fluorescence
luminescence
Michelson
monochromators
photo-multiplier
Phosphorescence
photodiodes
photoelectric
photoluminescence
Rayleigh
Raman
spectrofluorometer
spectrometer
spectrophotometer
Spectrum
Transmittance
ultraviolet
Visible
wavelength
Wavenumber
UV Light
Beer's Law
Diode Array
Deuterium Discharge Lamp
Low Pressure Zinc Discharge Lamp
High Pressure Mercury Discharge Lamp
Low Pressure Cadmium Lamp
Tungsten Halogen Lamp
Lens and Window Material in Spectrometers
Cuvettes
Luminescence
Photoluminescence
Fluorescence
Phosphorescence
Bioluminescence
Radioluminescence
Electroluminescence
Fluorescence Reagents
Spectrum
Diffraction Grating
Interferogram
Fourier Transform IR Spectrometer
FT-IR
Halide Disks
Mull Samples
Film Samples for IR Spectroscopy
Light Pipes
Attenuated Total Reflectance Spectroscopy
Multiple Internal Reflectance
External Reflectance
Specular Reflectance
Diffuse Reflectance
Photoacoustic Spectroscopy
Beam Splitter
Raman Scattering
Rayleigh Scattering
Raman Spectroscopy
Atomic Spectroscopy
Atomic Emission Spectroscopy
Atomic Absorption Spectroscopy
The Inductively Coupled Plasma Torch
The Helium Plasma Torch
Emission Spectrometer
Atomic Absorption Spectrometry
Flame Atomic Absorption Spectrometer
Flame AA
Hollow Cathode Lamp
Electrothermal Atomization
Graphite Furnace
L’vov Platform
Electron Paramagnetic Resonance
Zeeman Effect
Continuous Wave
Electron Paramagnetic Resonance
Pulsed EPR
Electron Spin Echo
Multple Resonance Spectroscopy
Magnetic Resonance Spectroscopy
NMR
Precessing
Nucleus Spin Decoupling in NMR
Superconducting Magnets
NMR Microcells
Electron Impact Ionisation
Chemical Ionization
Inductively Coupled Plasma Ionization
Secondary Ion Mass Spectrometry
Fast Atom Bombardment
Plasma Desorption Mass Spectrometry
Laser Desorption Mass Spectrometry
Matrix Assisted Desorption mass Spectrometry
Field Desorption Ionization
Thermospray Ionization
Electrospray Ionization
Atmospheric Pressure Ionization
Particle Beam Interface
Permeable Membrane Interface
Sector Mass Spectrometer
Quadrupole Mass Spectrometer
Ion Trap Mass Spectrometer
Time of Flight Mass Spectrometer
Optical RotationCircular Dichroism
Circularly Polarized Light
Verdet Constant
Faraday Effect
 

The Atomic Emission Spectrometer


The atomic emission spectrometer is versatile, highly sensitive and very selective. The procedure is to aspirate the sample, which will be a solution of the element (usually an aqueous solution) into the high temperature volume of the emission system and then monitor the light emitted with a suitable optical system that usually terminates in a Diode Array sensor. The nebulizer is normally a very simple device a diagram of which is shown in figure 2.

Figure 2. An Atomic Spectroscometer Sample Nebulizer.

The sample, often in an aqueous solution, is pumped by means of a peristaltic pump through a jet into a concentric tubular cavity through which a suitable gas is flowing at relative high velocity. The system tends to act as a miniature ‘spray drier’ the liquid breaking up into fine droplets that evaporate and leave the solid sample as minute particles entrained in the moving gas. The evaporation process, however, is not completely efficient and water is carried forward with the particles and must be removed. Another type of nebulizer is the ‘cross-flow nebulizer’ a diagram of which is shown in figure 3.

 

Figure 3. The ‘Cross-Flow Nebulizer’

The advantage claimed for this type of nebulizer is more efficient spray production due to the sample liquid being fed in, normal and close to the nebulizing gas stream. However, this is also not one hundred percent efficient and a device still has to be incorporated into the sampling system that removes excess, liquid sample. The device used for this purpose is also very simple and is called the spray ‘chamber’. A diagram of a spray chamber is shown in figure 4.

Figure 4. The Nebulizer ‘Spray Chamber’

It is seen that the spray chamber consists of two concentric tubes sealed at either end. The outer tube has an exit at the top that allows the gas containing the particles to pass to the ‘torch’. At the bottom of the tube there is a ‘drain’ exit where the liquid caught on the walls of the inner and outer tubes collect and pass to waste. The gas carrying the sample particles then passes into the torch where the sample atoms are heated to a very high temperature A diagram of a ‘torch’ is shown in figure 5. The torch consists of three concentric tubes made of quartz or some other appropriate material. A copper coil, though which water circulates for cooling purposes, surrounds the top portion of the torch and is connected to a radio frequency source. The plasma gas, e.g. argon, is used as the nebulizing gas and a second flow of argon enters the torch at the base to act both as a coolant and as part of the plasma forming agent. In many torches the base of the torch is also cooled by a water jacket. A spark produced by a Tesla coil initiates the plasma formation by generating some electrons. The RF power (0.2 to 2.0 kW and 27 to 40 Mhz)) produces electric and magnetic fields that accelerates the electrons by inductive coupling (inductively coupled plasma ICP) The resulting high energy electrons cause further argon ionization by collision which continues as a chain reaction producing the plasma. The temperature of the plasma ranges from 6000 C to 10,000 C and appears as an intense brilliant white ‘tear-drop’ shaped fireball.

Figure 5. The ICP Torch

Figure 6. The Different Zones in an ICP Plasma

The distribution of the different zones in the plasma is depicted in figure 6. The lower part of the plasma is the induction zone where the effect of the RF radiation starts to become affective. Above this is the initial radiation zone where the plasma temperature may reach as high as 10,000 C. Above the initial zone is a larger plasma volume that is called the analytical zone and it is the light from this area that is used for analytical purposes. The analytical zone changes into a plasma tail before it eventually becomes extinguished. The nebulizer spray chamber, torch and other essential parts of the instrument are connected together if the manner shown in figure 7.

Figure 7. Assembly of Major Components of Spectrometer

Figure 7 shows a general layout of ICP the atomic Emission Spectrometer system. Individual instruments may differ in detail but the layout given in figure 7 will be a reliable guideline for most atomic Emission Spectrometers


 

About the Author
RAYMOND PETER WILLIAM SCOTT was born on June 20 1924 in Erith, Kent, UK. He studied at the University of London, obtaining his B.Sc. degree in 1946 and his D.Sc. degree in 1960. After spending more than a decade at Benzole Producers, Ltd. Where he became head of the Physical Chemistry Laboratory, he moved to Unilever Research Laboratories as Manager of their Physical Chemistry department. In 1969 he became Director of Physical Chemistry at Hoffmann-La Roche, Nutley, NJ, U.S.A. and subsequently accepted the position of Director of the Applied Research Department at the Perkin-Elmer Corporation, Norwalk, CT, U.S.A.
In 1986 he became an independent consultant and was appointed Visiting Professor at Georgetown
University, Washington, DC, U.S.A. and at Berkbeck College of the University of London; in 1986 he retired but continues to write technical books dealing with various aspects of physical chemistry and physical chemical techniques. Dr. Scott has authored or co-authored over 200 peer reviewed scientific papers and authored, co-authored or edited over thirty books on various aspects of physical and analytical chemistry. Dr. Scott was a founding member of the British chromatography Society and received the American Chemical society Award in chromatography (1977), the M. S. Tswett chromatography Medal (1978), the Tswett chromatography Medal U.S.S.R., (1979), the A. J. P. Martin chromatography Award (1982) and the Royal Society of Chemistry Award in Analysis and Instrumentation (1988).
Dr. Scott’s activities in gas chromatography started at the inception of the technique, inventing the Heat of Combustion Detector (the precursor of the Flame Ionization Detector), pioneered work on high sensitivity detectors, high efficiency columns and presented fundamental treatments of the relationship between the theory and practice of the technique. He established the viability of the moving bed continuous preparative gas chromatography, examined both theoretically and experimentally those factors that controlled dispersion in packed beds and helped establish the gas chromatograph as a process monitoring instrument. Dr. Scott took and active part in the renaissance of liquid chromatography, was involved in the development of high performance liquid chromatography and invented the wire transport detector. He invented the liquid chromatography mass spectrometry transport interface, introduced micro-bore liquid chromatography columns and used them to provide columns of 750,000 theoretical plates and liquid chromatography separations in less than a second. Dr. Scott has always been a “hands-on” scientist with a remarkable record of accomplishments in chromatography ranging from hardware design to the development of fundamental theory. He has never shied away from questioning “conventional wisdom” and his original approach to problems has often produced significant breakthroughs.

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