Atomic emision spectroscopy
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This document discusses atomic emission spectroscopy. It begins by explaining emission and emission spectra. It then defines atomic emission spectroscopy as a procedure that uses the intensity of light from an excitation source like a plasma or flame at a specific wavelength to determine the quantity of an element in a sample. It discusses various excitation sources like flames, plasmas, sparks, arcs, and lasers. It also covers instrumentation, sample atomization methods, considerations for quantitative analysis, factors affecting accuracy, precision, sensitivity and selectivity.
Atomic emision spectroscopy
- 1. BY SAJID SARWAR M006 NABEEL AHMAD E258 H. ALI USMAN M042 HARIS ALI E293
- 2. The production and discharge of something, especially gas or radiation. Emission is the process by which a higher energy quantum mechanical state of a particle becomes converted to a lower one through the emission of a photon, resulting in the production of light. The frequencies of light that an atom can emit are dependent on states the electrons can be in.
- 3. The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state. WHAT IS SPECTROSCOPY? Spectroscopy is the study of the interaction between matter and electromagnetic radiation.
- 4. Atomic emission spectroscopy or AES is a procedure of analysing chemicals that employs the intensity of light from a plasma, flame, arc or spark at a definite wavelength to calculate the quantitative presence of an element in a particular sample. The atomic spectral line wavelength identifies the element The intensity of light is proportional to the atom count of the element. Atomic emission spectroscopy (AES or OES) uses quantitative measurement of the optical emission from excited atoms to determine analyte concentration
- 5. Emission lines from hot gases were first discovered by Angstrom, and the technique was further developed by David Alter, Gustav Kirchhoff and Robert Bunsen.
- 6. Atomic emission spectroscopy is based on the principle that when a molecule is applied energy in the form of light or heat, the molecules get excited and move from lower energy level to higher energy level. At this state the molecules are unstable. Therefore, the excited molecule jumps from higher energy level to lower energy level, emitting radiation. The radiations are emitted in the form of photons. The wavelengths of photons emitted are recorded. These radiations are recorded in the emission spectrometer.
- 7. Instrumentation for atomic emission spectroscopy is similar in design to that used for atomic absorption. Many atomic emission spectrometers, however, are dedicated instruments designed to take advantage of features unique to atomic emission, including the use of plasmas, arcs, sparks, and lasers, as atomization and excitation sources and have an enhanced capability for multielemental analysis
- 8. Atomic emission requires a means for converting an analyte in solid, liquid, or solution form to a free gaseous atom. The most common methods are 1. Flames Sources 2. Plasmas Sources Both of which are useful for liquid or solution samples. Solid samples may be analysed by dissolving in solution and using a flame or plasma atomizer.
- 9. A flame provides a high- temperature source for desolvating and vaporizing a sample to obtain free atoms for spectroscopic analysis. Atomization and excitation in flame atomic emission is accomplished using nebulization and spray chamber. The burner head consists of single or multiple slots
- 10. A plasma consists of a hot, partially ionized gas, containing an abundant concentration of cations and electrons that make the plasma a conductor Plasmas operate at much higher temperatures than flames They provide better atomization and more highly populated excited states Besides neutral atoms, the higher temperatures of a plasma also produce ions of the analyte
- 11. A direct-current plasma (DCP) is created by an electrical discharge between two electrodes. Samples can be deposited on one of the electrodes, or if conducting can make up one electrode. Insulating solid samples are placed near the discharge so that ionized gas atoms sputter the sample into the gas phase where the analyte atoms are excited. This sputtering process is often referred to as glow-discharge excitation.
- 12. An inductively coupled plasma (ICP) is a very high temperature (7000-8000K) excitation source that efficiently desolvates, vaporizes, excites, and ionizes atoms. Molecular interferences are greatly reduced with this excitation source but are not eliminated completely
- 13. When a high-energy laser pulse is focused into a gas or liquid, or onto a solid surface, it can cause dielectric breakdown and create a hot plasma. For solids the laser pulse also ablates material into the gas phase. The energy of the laser-created plasma can atomize, excite, and ionize analyte species, which can then be detected and quantified by atomic-emission spectroscopy
- 14. A high-power CO2 laser that is focused into a support gas, such as Ar, can maintain a hot plasma. The energy of the plasma can atomize, excite, and ionize analyte species present in the support gas, which can then be detected and quantified by atomic-emission spectroscopy
- 15. A microwave-induced plasma consists of a quartz tube surrounded by a microwave cavity. Microwaves produced from a magnetron (a microwave generator) fill the cavity and cause the electrons in the plasma support gas to oscillate. The oscillating electrons collide with other atoms in the flowing gas to create and maintain a high- temperature plasma. Atomic emission is measured from excited analyte atoms as they exit the microwave waveguide or cavity.
- 16. Atomic emission spectroscopy is ideally suited for multi- elemental analysis because all analytes in a sample are excited simultaneously. A scanning monochromator can be programmed to move rapidly to an analyte’s desired wavelength, pausing to record its emission intensity before moving to the next analyte’s wavelength. Proceeding in this fashion, it is possible to analyse three or four analytes per minute.
- 17. Spark and arc excitation sources use a current pulse (spark) or a continuous electrical discharge (arc) between two electrodes to vaporize and excite analyte atoms. The electrodes are either metal or graphite. If the sample to be analyzed is a metal, it can be used as one electrode. Non- conducting samples are ground with graphite powder and placed into a cup-
- 19. The development of a quantitative atomic emission method requires several considerations, including CHOICE OF ATOMIZATION AND EXCITATION SOURCE Except for the alkali metals, detection limits when using an ICP are significantly better than those obtained with flame emission. Plasmas also are subject to fewer spectral and chemical interferences. For these reasons a plasma emission source is usually the better choice.
- 20. The choice of wavelength is dictated by the need for sensitivity and freedom from interference due to unresolved emission lines from other constituents in the sample. The easiest approach to selecting a wavelength is to obtain an emission spectrum for the sample and then to look for an emission line for the analyte that provides an intense signal and is resolved from other emission lines
- 21. Flame and plasma sources are best suited for the analysis of samples in solution and liquid form. Although solids can be analysed by direct insertion into the flame or plasma, they usually are first brought into solution by digestion or extraction.
- 22. The most important spectral interference is a continuous source of background emission from the flame or plasma and emission bands from molecular species. Background corrections for flame emission are made by scanning over the emission line and drawing a baseline. Because the temperature of a plasma is much higher, background interferences due to molecular emission are less problematic.
- 23. Flame emission is subject to the same types of chemical interferences as atomic absorption. These interferences are minimized by 1. Adjusting the flame composition 2. Protecting agents 3. Releasing agents 4. Ionization suppressors. An additional chemical interference results from self-absorption.
- 24. When possible, quantitative analyses are best conducted using external standards. Emission intensity, however, is affected significantly by many parameters, including 1. The temperature of the excitation source and 2. The efficiency of atomization.
- 25. Scale of Operation The scale of operations for atomic emission is ideal for the direct analysis of trace and ultra trace analytes in macro and meso samples. With appropriate dilutions, atomic emission also can be applied to major and minor analytes.
- 26. When spectral and chemical interferences are insignificant, atomic emission is capable of producing quantitative results with accuracies of 1–5%. Accuracy in flame emission frequently is limited by chemical interferences. Accuracy when using plasma emission often is limited by stray radiation from overlap- ping emission lines.
- 27. The most important factor affecting precision is the stability of the flame’s or plasma’s temperature. For example, in a 2500 K flame a temperature fluctuation of ±2.5 K gives a relative standard deviation of 1% in emission intensity. Significant improvements in precision may be realized when using internal standards.
- 28. Sensitivity in flame atomic emission is strongly influenced by The temperature of the excitation source The composition of the sample matrix. With plasma emission, sensitivity is less influenced by the sample matrix.
- 29. The selectivity of atomic emission is similar to that of atomic absorption. Atomic emission has the further advantage of rapid sequential or simultaneous analysis