Atomic Absorption
Atomic Absorption
Atomic Absorption Spectrometry (AAS)
This device is one of the modern laboratory equipment belonging to the Geological Survey, its central laboratory department, and works on the analysis of many important elements, whether in minerals, water or food.
It is a quantitative analytical method that means the absorption of light at a specific wavelength ג and fixed for one element by its free atoms, and the amount of absorbed radiation increases at this wavelength by increasing the number of atoms of the element present in the path of the rays, where the spectrum is related to the focus. It is very high, up to 1 in a million, and therefore it is possible to know the components of the sample, even if it is a very small percentage.
Explanation of the device’s work and pictures, along with the device’s brochure from the producing company, at the end of the article
Scientific basis Atomic Absorption
This method depends on converting the metallic substance into free atoms, i.e. converting the substance to the atomic state and estimating the radioactive energy absorbed by these atoms “where the degree of absorption is proportional to the number of atoms present in the sample of the element to be determined is directly proportional to the concentration of this element.” This atoms absorb in their normal state the light rays At a given wavelength, the atom moves to the exited atom, and the amount of absorbed rays increases at this wavelength by increasing the number of atoms of the wave element in the rays path.
That is, this method depends on the fragmentation of the material particles into their atoms and the study of the radioactive energy absorbed by these atoms, where electronic transitions occur between energy levels as a result of energy absorption.
The substance to be designated must be in the liquid state. The process of converting elements from linked molecules to free atoms is done by exposing compounds to heat energy sufficient to break chemical bonds by spraying the compound solution in a flame of an appropriate temperature.
It is also possible to make an electrical excitation through the electric furnace of the graphite element, so that the atoms in this case are able to absorb the light rays.
device components Atomic Absorption
1- The radiation source (cathode tube)
This is the source that emits the spectrum of the element to be specified, as each element needs rays of a specific wavelength to excite it.
Installing the cathode bulb:
It is a cylindrical tube with a thin wall of thin glass containing neon or argon gas under low pressure, and the cathode is the “negative electrode” of the element to be estimated and identified, while the anode is a tungsten wire facing the black and the cathode is connected to the anode by tungsten wires This and each bulb has special operating conditions that must be taken into account according to each element, such as the beam aperture, the wavelength of the rays, and others. The device contains bulbs for the elements to be specified, and each bulb has a specific voltage.
2 – power source by atomizer
Or the unit of converting related elements into the atomic image, and it works to excite the element to be specified in the sample and this source by producing free atoms, and if they are found in compounds in the sample, each element is obtained individually. The source of energy is of two types:
A thermography way
Heat is produced in this case from different gases, and it works to transform the material from a partial state to a free state, and these raids are such as acetylene with compressed air, acetylene with nitrous oxide, or propane with compressed air.
This method is carried out by spraying the sample in the form of a fine atomizer in the flame resulting from the combustion of acetylene and air as an oxidizing substance.
B electric source
The graphite furnace is a cylindrical graphite rod 50 mm long and 10 mm in diameter. A sample of 1: 1000 μm can be placed through an opening with a diameter of 2 mm in the upper part by means of a special syringe. The tube is cleaned by inert gas.
Features of this method:
1- Allergies
2- Use a small amount of the sample
3- Temperature control where the element is heated to the appropriate degree for it.
* The method of work:
First: evaporation
Second: burning
Third: Reaching the temperature needed for glow and converting elements into atoms.
Where the rays pass through the tube and pass through the free atoms inside the tube, absorption occurs, and then the rays fall on the detector, then the amplifier, and then the recorder.
C atomic vapor:
The sample is chemically treated by the pour generation system to convert it into volatile products and then submit it to the absorber in the form of steam.
3- The unit for separation of waves “monechramater”: –
It is used to separate the wavelength rays used to estimate the element from the rest of the source rays in order to improve the selection ability of the spectroscopy method, as the process of separation of rays to get rid of unwanted rays and even can interfere in the measurement process if they are separated causing diffraction.
4- A unit for measuring the energy of the rays or the detector:
It is a composite photovoltaic cell to convert radiant energy into electrical signals that can be recorded on the measurement board in the form of absorption or light transmission.
The spectral beam is directed from the chromatograph to the detector, and the detector is a highly sensitive photoelectric cell. When the rays fall on it, an electric current is generated whose intensity is proportional to the intensity of the spectral beam. The current is proportional to the absorbance and even proportional to the concentration.
The conditions that must be met in the detector are:
1- His response should be stable and sensitive to the rays falling on him.
2- That his response to other stimuli is low.
3- That its response time is short because the time required for the process of absorbing rays is short.
5- The unit of x-ray magnification “the Magnifier”:
6- The recorder or measurement unit:
And using the ammeter or recording unit draw curves.
7- A computer to process the resulting measurements and output them in the form of data.
How to useAtomic Absorption
1- Prepare the sample:
A specific weight of the sample is weighed, let it be 1 g:
B – The mixture used in dissolving the sample is placed “the sample is poured into one of the acids”, then the degree of absorption of the mixture is calculated, then the degree of absorption of the sample, then the difference is calculated.
C- The sample, after dissolving it in one of the acids, is transferred to a vial of known volume, 250 or 500, and the rest is completed with water.
D – The element to be estimated is placed as a negative electrode.
2- Turn on the device:
A – The device is connected to the electrical current
B – The lamp of the element to be set is placed and turned on for the warm-up period.
C – The oven or the flame is cleaned by raising the oven temperature to the maximum possible degree to expel any element previously appointed.
D – The device is set to the appropriate temperature for the three stages:
1 evaporation stage 2 stage 3 agitation stage.
After that, the percentage of the element is calculated. In this method, the very few percentages in the sample are calculated, and the percentage of concentration of the elements is calculated through the law.
Features of atomic absorption technology
Selectivity, which is the possibility of assigning an element to a complex background without the need for separation operations, because each element has its own light source.
Disadvantages of atomic absorption technology:
1 It is used in the analysis of inorganic substances only, as organic substances are the main component of carbon, which is impossible to use as a cathode because it is not a conductor of electricity.
2- It is used in the analysis of materials, which are in the liquid state only, where the archaeological sample is first dissolved in one of the acids.
3- It takes a lot of time to prepare the sample, which requires high accuracy, and changing the ray bulbs for each element takes time.
4 This method is very stressful and very expensive, as it is necessary to have all the bulbs of the elements, and it also needs a background on the nature of the materials in it.
5- Dispersion of the atoms may occur in the flame.
6- The large size of the device and subject to accurate calculations and measurements.
7- It is considered one of the destructive methods where the sample is lost when it is thawed and therefore it should be the last method used.
ATOMIC ABSORPTION SPECTROSCOPY APPLICATIONS
In the field of archeology
porcelain
Analysis of the elements in ceramics using the atomic absorption device allows to identify the origin of these ceramic products. In one of the Chinese studies, the atomic absorption device was used to determine the chemical composition that could be related to production in different parts of China in different periods.
the glass
The atomic absorption device can be used to distinguish archaeological glass. The formation of the glass can be determined using this method. The button absorption device has also proven its efficiency in distinguishing modern glass compared to stained glass in the Middle Ages.
the stones
The atomic absorption device can be used to distinguish and identify historical building materials, and this approach can be used to study the decomposition products and help us understand the deterioration processes, for example, in a study on sandstone and limestone at Trinity College, Dublin used the button absorber to measure the calcium ion concentration (Ca2+). The enrichment of the calcium ion in the stone and its depletion from the surface mortar indicates that the calcium ion is washed from the mortar into the solution and deposited on the surface. It was observed in the calcium ion precipitation of calcite in a vertical form that works to block the pores of the stones and is believed to be the main reason for impeding the movement of water.
Writing materials
The analysis of paper and ink elements is better with an atomic absorption device. Both the flame and graphite furnaces of the atomic absorption device can be used to determine the mineral composition of ancient manuscripts. Iron and copper elements can indicate the presence of species responsible for the degradation of paper, so their concentrations can be measured to aid in the preservation process, and samples of paper as much as milligrams are suitable and sufficient for analysis.
art paintings
Heat absorption device is used to determine the pigments. His sample was gently pricked from the surface of his plate with a cotton swab. Only 1-2 μg of pigment was removed during the procedure. The cotton was cleaned with nitric acid to identify the minerals in the samples. It can also be associated with certain pigments, for example, atomic absorption device furnaces determine the presence of copper. By using Raman spectra, the presence of green was determined, and by mixing the two methods, zinc white could be determined in the dyes.
Metal:
The composition of metallic bodies can be easily determined using atomic absorption methods. Information about the methods of producing these bodies can be obtained from these analyzes. One of the studies used zero absorption methods to study a beveled alloy of pre-Hispanic gold and copper from Colombia.
A small fragment of the artifact was removed for analysis. The results of the analysis were for gold (48.34%), copper (38.79%), silver (10.71%) and iron (0.04%). The current silver is the result of the use of native Colombian gold which is known to contain some silver.
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