The detector measures the intensity of the beam of light. When some of the light is absorbed by metal, the beam's intensity is reduced. The detector records that reduction as absorption. That absorption is shown on output device by the data system. We can find the concentrations of metals in a sample running a series of calibration standards through the instrument.
The instrument will record the absorption generated by a given concentration. By plotting the absorption versus the concentrations of the standards, a calibration curve can be plotted. We can then look at the absorption for a sample solution and use the calibration curves to determine the concentration in that. Atomic absorption spectrometry is a fairly universal analytical method for determination of metallic elements when present in both trace and major concentrations.
The EPA employs this technique for determining the metal concentration in samples from a variety of matrices. A Sample preparation. Depending on the information required, total recoverable metals, dissolved metals, suspended metals, and total metals could be obtained from a certain environmental matrix.
Table 1 lists the EPA method number for sample processing in terms of the environmental matrices and information required. Appropriate acid digestion is employed in these methods. Hydrochloric acid digestion is not suitable for samples, which will be analyzed by graphite furnace atomic absorption spectroscopy because it can cause interferences during furnace atomization.
B Calibration and standard curves. As with other analytical techniques, atomic absorption spectrometry requires careful calibration. The idealized calibration or standard curve is stated by Beer's law that the absorbance of an absorbing analyte is proportional to its concentration. Unfortunately, deviations from linearity usually occur, especially as the concentration of metallic analytes increases due to various reasons, such as unabsorbed radiation, stray light, or disproportionate decomposition of molecules at high concentrations.
Figure 3 shows an idealized and deviation of response curve. The curvature could be minimized, although it is impossible to be avoided completely. It is desirable to work in the linearity response range. The rule of thumb is that a minimum of five standards and a blank should be prepared in order to have sufficient information to fit the standard curve appropriately.
Manufacturers should be consulted if a manual curvature correction function is available for a specific instrument. Figure 3. If the sample concentration is too high to permit accurate analysis in linearity response range, there are three alternatives that may help bring the absorbance into the optimum working range:.
C EPA method for metal analysis. Flame atomic absorption methods are referred to as direct aspiration determinations. They are normally completed as single element analyses and are relatively free of interelement spectral interferences. For some elements, the temperature or type of flame used is critical. If flame and analytical conditions are not properly used, chemical and ionization interferences can occur. Graphite furnace atomic absorption spectrometry replaces the flame with an electrically heated graphite furnace.
The major advantage of this technique is that the detection limit can be extremely low. It is applicable for relatively clean samples, however, interferences could be a real problem.
It is important for the analyst to establish a set of analytical protocol which is appropriate for the sample to be analyzed and for the information required. D Interferences. Since the concentration of the analyte element is considered to be proportional to the ground state atom population in the flame, any factor that affects the ground state population of the analyte element can be classified as interference. Factors that may affect the ability of the instrument to read this parameter can also be classified as interference.
The following are the most common interferences:. A Spectral interferences are due to radiation overlapping that of the light source. The interference radiation may be an emission line of another element or compound, or general background radiation from the flame, solvent, or analytical sample. This usually occurs when using organic solvents, but can also happen when determining sodium with magnesium present, iron with copper or iron with nickel.
B Formation of compounds that do not dissociate in the flame. The most common example is the formation of calcium and strontium phosphates. C Ionization of the analyte reduces the signal. This is commonly happens to barium, calcium, strontium, sodium and potassium. D Matrix interferences due to differences between surface tension and viscosity of test solutions and standards. E Broadening of a spectral line, which can occur due to a number of factors.
The most common line width broadening effects are:. Doppler effect. Type II water is generally considered sufficient for FAAS, where detection limits are typically in the ppm to ppb range.
TOC ppb. Water grade. The company offers a number of water purification systems for all forms of AAS, with each having its own advantages and limitations. The high sensitivity of AAS techniques means that it is important not to introduce sources of contamination during the preparation of blanks, standards and samples. Type your search.
Home Atomic Absorption Spectroscopy. Back to Applications. Atomic Absorption Spectroscopy. Last Updated. Atomic Absorption Spectrophotometry AAS is used to determine the concentrations of individual elements in a sample by measuring the selective absorption of light by gaseous atoms produced by spraying a solution into a flame FAAS or by evaporation in a carbon tube CFAAS. Impact of Water. Particulates The presence of particulates in samples or standards used for AAS can lead to blockages in the atomization systems, prevent efficient and reproducible spraying of the sample solution into the flame,.
Metal ions The high sensitivity of AAS means that any metal ions present in the water used to prepare samples, blanks or standards are likely to interfere during analysis. Bacteria Bacteria present in the water used for sample and standard preparation can lead to blockages in the atomization systems, similar to particulate matter.
One method is to use two light sources, a cathode lamp and a deuterium lamp, which produces broad band radiation but not specific spectral lines. By alternating measurements between the two lamps, the operator can subtract the amount of background absorption from the total readings, leaving only the figures needed for analysis. The spectrometer also incorporates a monochromator. This is an optical device that selects and transmits a specified wavelength, or spectral line.
It selects the specific light appropriate to the element from the cathode lamp and directs it onto a detector. This produces an electrical signal that is proportionate to the intensity of the light. As a form of control, A double beam spectrometer will split the beam. One beam is for reference only, with the absorbance set at zero, while the other passes through the atom cell. By constantly monitoring both the light source and the reference beam, you can ensure that the spectrum is not suffering a loss of sensitivity, as the intensity of the light source may not always stay constant.
There are various essential pieces of equipment necessary to performing atomic absorption spectroscopy:. There are also various accessories to supplement the core AAS equipment, such as auto-dilutor systems for sample preparation and continuous flow vapour generation systems. Because atoms to be analysed must be in a gas phase, the application of heat is essential to the process. The Furnace used in AAS is made from graphite. It is in the form of a graphite tube.
The flame , usually a slot-type burner, is used for analysing fluids. It vapourises them to create a gas. The spray chamber introduces the sample, aspirated then applied as drops, into the flame. The mirrors direct the light beams from the cathode and D 2 lamps , and the beam selector splits the beam into component wavelengths. The photon detector counts light in photons.
Photons are elementary particles, the tiniest possible particle of light in an electromagnetic field. Along with the equipment for performing AAS, the system requires the right kind of supporting software. This software enables precise instrument control, and acquiring, manipulating and interpreting the data that the process generates.
For more information about leading edge AAS technology and instruments , and their applications, please contact us. As an analytical technique, it uses electromagnetic wavelengths, coming from a light source. When was Atomic Absorption Spectroscopy first used? Kirchhoff and Bunsen developed the spectroscope, splitting light into wavelengths.
It was not until the s that this technique became more widely used. It is fast, sensitive, specific and user-friendly. Why should I use Atomic Absorption Spectroscopy?
AAS provides a high degree of accuracy. It is a highly sensitive method of analysis. In a given material, it can measure parts per billion of a gram. Modern AAS systems are a comparatively inexpensive means to accurately detect specific elements.
When should I use Atomic Absorption Spectroscopy? These processes include: Quality control Toxicology Environmental testing As a method, AAS can analyse the content of certain metals in various materials. In environmental testing , it can measure the concentration of various elements in rivers, drinking water and seawater. In the food and drink industry , it can measure various concentrations of elements in wine, beer and fruit drinks and test for types of contamination in food.
For pharmaceutical companies, AAS can determine the minute quantities of catalyst materials used in the manufacture of drugs, and for other impurities. In industry , there are different raw materials requiring examination and analysis to check they have sufficient amounts of certain major elements, and that there are not too many impurities, some of which could be toxic. In mining , AAS can test for the concentration of valuable materials before excavation operations.
AAS is used in agriculture , to analyse plants and soils for mineral content. Metals and other substances can have a bad effect on oil and gas, which is why the petrochemical industry uses AAS.
The technique also supports critical testing in the nuclear industry , where there could be potentially hazardous elements in the output of waste and water.
Why is Atomic Absorption Spectroscopy important? For some liquid samples, it can provide direct analysis. How does Atomic Absorption Spectroscopy work? What creates these signals? Once the excited electrons start to relax again, they emit energy in the form of photons.
What does Atomic Absorption Spectroscopy measure? What elements can Atomic Absorption Spectroscopy measure?
0コメント