Your question is not clear. What do you want to do by using AAS. We can use AAS to measure the metal concentration in food and soil also.

Hello Fahim,

I send you some lines of my basic lessons script on AAS (flame method), unfortunately without figure (can be found in standard text books on chemistry or physics) . You have to be aware of the high complexity of the subject. To approach an adequate handling it requires long standing experience and theoretical background, and this not only in AAS methods, but also in e.g. sampling, sample preparation, digestion methods, data evaluation, statistics. Very much more details to some of these issues you can find e.g. in "B. Welz, M. Sperling: Atomic Absorption Spectrometry.Wiley-VCH, 3. edition (1998). ISBN 3 527 28571 7" (or subsequent edition).

A. Flame-AAS

1. Measuring principle and equipment configuration

Supply of energy (generally in the form of heat) to atoms causes the elements to emit light. This is best known by injecting particles of sodium (e.g. NaCl) into a flame; the characteristic yellow staining is well known. The effect is due to

- the heat-triggered raising of electrons from their atom trajectories (orbitals) in the ground state to higher orbitals in the excited state

- emission of energy in the form of light due to the falling back of electrons from the higher orbitals to the ground state (cf. Grotrian diagram of, for example, sodium in standard text books on chemistry or physics).

As shown by the example of Na (Grotrian diagram Na) the electrons can jump from the ground state to a set of orbitals. Due to the defined pattern of electron orbitals for each element there exists also a characteristic pattern of emitted wavelengths of light for each element. To achieve more distant orbitals the electrons require more energy (E) and, vice versa, according to

l= h * c / E

(l- wavelength; h – Planck’s constant; c – speed of light)

dropping back from outer orbitals is connected to shorter wavelengths. In general, the transition which requires the lowest energy is the most frequent transition. Therefore, the highest light emission intensity occurs for this transition and already small amounts of Na in a flame cause high light emission intensity. In the case of Na this is the transition from the 3p- to the 3s-orbital which corresponds to a light emission of about 589 nm (Fig. 1; resonance wavelength; yellow). The other emissions are in the non visible range of light.

If the transition of electrons from an excited state to the ground state of the atom is connected to the emission of a characteristic wave length of light it must also be true, that the irradiation (immission) of the same wavelength will trigger the transition of the electron in the ground state orbital to an excited state (higher orbital). By this the energy of the immission light is transformed to the electron excitation – the light is absorbed.

This is the basic principle of AAS. It relies on the fundamental property of light waves to raise electrons from their orbitals in the ground state to (higher) orbitals in the excited state. The energy of light is limited to the transition of electrons in the outermost orbital of atoms only. Corresponding to the low input of energy which is necessary for the most frequent transition from the 3s- to the 3p-orbital at Na the adequate light immission of about 589 nm is absorbed most intensely. A noticeable absorption of this wavelength is achieved already by small amounts of Na. The absorption of an irradiation at 589 nm is a function of the Na atom concentration.

Other transitions with higher energies are not so easily excited. The transitions are more seldom and the adequate light immission wave lengths are more weakly absorbed. A noticeable absorption (weakening) of light will occur only at higher concentrations of Na.

From this follows already an important finding:

- Small amounts of Na (and other elements) can be detected by the

immission of the resonance wavelength.

- The detection of high element concentrations can be achieved by wavelengths which correspond to other orbital transitions.

- And, therefore:

the irradiation wavelength (detection wavelength) must be adapted to the concentrations of the analyte.

The most basic requirements for an AAS device are:

- a) source of adequate light,

- b) elements in the atomised ground state,

- c) detection of light absorption.

Good luck and kind regards

D. Zachmann

Atomic Absorption Spectroscopy is an Elemental analysis technique. Approximately 70 elements can be analyzed by AAS. It is a quantitative technique where in you can find out the concentrations of these elements in various samples like food products, pharmaceuticals, chemicals, metallurgical samples, etc. The list is quite long. In AAS, there are two types of methods: Flame Atomic Absorption and Flameless Atomic Absorption. Flame method is generally used for the quantification upto ppm level and Flameless method is used for much lower concentrations like ppb. It is a wonderful technique. Sample preparation is very critical in AAS.

Dear Fahim Aslam ,

In addition to all answers above, shortly, Atomic Absorption (A.A) is a sensitive and selective metod of metal analysis. The sample after its preparation for analysis by A.A, is co converted thermally, either in flame or electrical devices, into atoms. At the same time, a light produced from a lamp, called (Hollow Cathode Lamp, HCL) of the metal you want to determine. The sample in the flame, or the thermal device(such as Graphite furnace) will be atomized while the beam of of light from the HCL will pass through the atomic vapor. Tge atoms will absorb part of the HCL light, according to its concentration and registered. This readibg will be converted to concentration, usually, in ppm from a graph prepared by you, which is a calibration between ppm of a standard of the metal against C (the metal concentration). The graph will give you its concentration.

For detail of all those I said you can read any Instrumenat Analsis, or from Google, just ask Atomic Absorption. Thank You and Good Luck

AAS is a population phenomenon and you can describe the flame as a cuvette that holds the colour solution in UV-Vis spectrophotometry. While AAS is used to determine the concentration of elements, these elements typically have a valency (like cations and are also solubilized) and are able to absorb energetic photons to transit to a higher state and then emit a photon to go to a lower state. Thus, you use a Calcium lamp to determine the concentration of Calcium. But, a portion of the Calcium concentration may be emitting and a portion absorbing. Elements like Sodium, Potassium, and Cesium are ALWAYS emitting (at least the vast majority). The temperature of the flame ensures the vast majority of the population is absorbing. An ICP torch is SO hot ALL the elements are emitting.

There are special circumstances (techniques) were the above statement must be embellished, like Graphite Furnace AAS (GFAAS) for refractory elements or Hydride Generation (HGAAS) for As, Se...

Please read a textbook about basic analytical instrumentation in your library.

It is a technique used to determine the concentration of a particular metal in a sample. AAS uses the absorption of light to measure the concentration of gas phase atoms. The light that is focused into the flame is produced by a hollow cathode lamp, inside which is the sample and an anode. A high voltage is passed between the cathode and anode and the metal atoms are excited into producing light with a certain emission spectrum. As the quantity of energy put into the flame is known and the quantity emitted can be detected, it is possible to calculate the concentration of the element present. Anyway that is theory which you do not need, but interested in obtaining data for your samples. As in my study, I use it to analyze soil exchangeable cations Ca, Mg, K, Na also micro nutrients, Fe, Mn, Cu and Zn. You have to prepare standards in order to determine the concentrations of the unknown samples. This machine also measures the same metals in my sesame seed samples. As for my seed analysis (food samples), I dry ash the seeds, then dissolve in conc HCl before AAS. I prepare K, Ca standards of 0, 2, 4, 6, 8 and 10 ppm, Mg, 0, 0.1, 0.2, 0.3, 0.4 and 0.5 ppm then dilute my samples accordingly. Cheers