Atomic Absorption Spectroscopy

“Verily, all things have We created by measure” [Quran 54:49]

Atomic Absorption Spectroscopy

Introduction

Atomic Absorption Spectroscopy (AAS) in analytical chemistry is a technique for determining the concentration of a particular metal element within a sample.

It measure the amount of energy (in the form of photons of light, and thus a change in the wavelength) absorbed by the sample.

Principle

The principle used in atomic absorption spectroscopy was discovered in 1802 by Wollaston when he observed the "Fraunhofer lines" or absorption lines in the spectrum of the sun, yet this principle was only applied in 1955 by an Australian physicist, Alan Walsh. The principle states that "Matter absorbs light at the same wavelength at which it emits light".

Basically this means that atoms in the ground state absorb the same radiation as they emit in the excited state. An atom in the ground state will absorb an amount of energy equal to the energy difference between the energy level of the electron in the excited state and the energy level that the electron occupies in the excited state.

Schematic of an atomic-absorption experiment

Process

The element is detected by an atomic absorption spectrum, by the light intensity emitted by the sample. This is a series of coloured lines on a dark background, depending on the element, at differing wavelengths. Each element has a unique spectrum :

Continuous spectrum, emission spectrum and atomic absorption spectrum (lines should be black)

“And We have produced therein everything in balance.” [Quran 55:7]


Applications

This process is employed in both qualitative and quantitative use. AAS is a rapid method for the former, if only a few elements are being tested. However if many elements are of interest the process can be too time consuming and uneconomical. The usual quantitative method brackets the sample's absorption spectrum with that of standard concentrations to produce a linear calibration curve.

Absorption spectroscopy is used in chemistry and physics to identify the characteristic and unchanging absorption spectrum for specific elements and compounds. The absorption of quanta of light by substances is determined by the promotion and demotion of electrons to and from atomic and molecular orbitals, and the measured wavelengths are individual and unique to each substance.

Examples of the applications of AAS include:

• Analysis of water for metals like lead, mercury and cadmium
• Analysis of rocks on space missions
  
• Drug testing
• Identification of unknown compositions
• Measures the concentrations of metals in the samples

Source :

1. Galbraith
2. gmu
3. The Chemistry Hypermedia Project
4. The International Society for Complexity, Information, and Design (ISCID)
5. Wesleylearning

“And He has made the ships to be of service unto you, that they may sail the sea by His command, and the rivers He has made of service unto you. And He has made the sun and the moon, constant in their courses, to be of service unto you, and He has made of service unto you the night and day. And He gives you all you seek of Him: If you would count the bounty of God, you could never reckon it.”
[Quran 14:32-34]