Atomic Absorption Spectrometry (AAS)

Introduction to Atomic Absorption Spectrometry

Atomic absorption spectrometry (AAS) detects elements in liquid or solid samples using distinctive wavelengths of electromagnetic radiation from a light source. Individual elements absorb wavelengths differently, and their absorbances are compared to standards. In effect, AAS makes use of the various radiation wavelengths absorbed by different atoms.  In AAS, analytes are first atomized, and their distinctive wavelengths are released and recorded.

Principle and Methodology of Atomic Absorption Spectrometry

AAS is a method used to measure light absorption by atoms or ions at specific wavelengths. AAS works based on light absorption by ground-state atoms in a sample. For example, when exposed to light at the characteristic wavelength of Cu, only Cu atoms or ions absorb the light. The amount of light absorbed is directly proportional to the concentration of the absorbing ions or atoms. Electrons within an atom exist at various energy levels, and when exposed to their unique wavelength, they absorb energy (photons) and move from a ground state to an excited state. The radiant energy absorbed by electrons is directly proportional to the transition. An atomic absorption spectrometer uses these principles in practical quantitative analysis, consisting of four main components: the light source, atomization system, monochromator, and detection system.

AAS Spectrometer

A typical AAS spectrometer has several key components, including a light source (hollow cathode lamp or electrodeless discharge lamp), a monochromator to isolate the desired wavelength, a sample introduction system, an atomizer (flame or graphite furnace), and a detector (photomultiplier tube). Modern devices also have computerized data processing and automation elements to improve accuracy and efficiency.

Application of Atomic Absorption Spectrometry

Atomic absorption spectroscopy is used in a variety of industries and plays an important role in detecting metals in samples. As a result, this procedure is widely used in pharmacology, archaeology, manufacturing, mining, and forensics. It is used to analyze metals and metalloids in environmental samples, determine trace elements in biological fluids, check quality in the pharmaceutical and food industries, analyze metals in geological materials, and discover dangerous elements in forensic investigations.

Strengths and Limitations of Atomic Absorption Spectrometry

The benefits of AAS far outweigh the restrictions stated below.

Strengths: 

• Low cost per analysis
• Mostly devoid of inter-element interference.
• Easy to operate.
• Wide applications throughout multiple industries.
• High sensitivity and selectivity for specific components. 
• A wide dynamic range enables the study of both trace and main components. 
• The sample preparation process is rather easy. 
• The procedure is well-established and follows standardized protocols.

Limitations:

• Cannot detect nonmetals.
• New equipment is costly.
• More targeted towards liquid analysis.
• The sample is destroyed.
• Multiplexing capabilities are limited when compared to other techniques, such as ICP-MS. 
• Interference from matrix components can degrade accuracy.
• To ensure accurate quantification, calibration standards are required. 
• It is limited to elements that can be atomized in the instrument’s atomizer. 
• It is relatively sluggish when compared to other analytical methods.