Difference Between Atomic Absorption Spectroscopy and UV Visible Spectroscopy

The key difference between atomic absorption spectroscopy and UV visible spectroscopy is that atomic absorption spectroscopy is based on the absorption of light by atoms or ions, whereas UV visible spectroscopy involves the absorption or reflectance of a part of the UV range and complete adjacent visible regions of the electromagnetic spectrum by atoms or ions.

Spectroscopy is an analytical technique in which we can study the interaction between matter and electromagnetic radiation as a function of the wavelength or frequency of the radiation.

1. Overview and Key Difference
2. What is Atomic Absorption Spectroscopy
3. What is UV Visible Spectroscopy
4. Atomic Absorption Spectroscopy vs UV Visible Spectroscopy in Tabular Form
5. Summary

What is Atomic Absorption Spectroscopy?

Atomic absorption spectroscopy is an analytical technique that is useful to determine the chemical elements in a sample quantitatively. The process inside this spectroscopy depends on the absorption of light by free metallic ions.

When considering the electrons in atoms, they are in certain energy levels of an atom. We call these energy levels atomic orbitals. These energy levels are quantized rather than being continuous. The electrons in the atomic orbitals can move from one energy level to another by either absorbing or releasing the energy they have. However, the energy the electron absorbs or emits should be equal to the energy difference between the two energy levels (between which the electron is going to move).

Figure 01: Atomic Absorption Spectrophotometer

Since each and every chemical element has a unique number of electrons at its ground state, an atom will absorb or release energy in a pattern unique to its elemental identity. Therefore, they will absorb/emit photons in a correspondingly unique pattern. Then we can determine the elemental composition of a sample by measuring the changes in light wavelength and light intensity.

After light passes through an atomic sample, if we record it, we can call it an atomic spectrum. It shows the characteristic of a type of atom. Therefore, we can use it in identifying or confirming the identity of a particular species. This kind of spectrum will have a number of very narrow absorption lines.

What is UV Visible Spectroscopy?

UV visible spectroscopy is an analytical technique that uses the absorption or reflectance of a part of the UV range and complete adjacent visible regions of the electromagnetic spectrum. This technique comes in two types as absorption spectroscopy and reflectance spectroscopy. It uses light in the visible and adjacent ranges.

Figure 02: UV Visible Spectrophotometer

Generally, the absorption or reflectance of the visible range of light can directly affect the perceived colour of the chemicals that are involved in the process. At this range of the spectrum, we can observe the atoms and molecules can undergo electronic transitions. Here, absorption spectroscopy is complementary to fluorescence spectroscopy, where fluorescence deals with transitions of electrons from the excited state to the ground state. In addition, absorption measures the transitions from the ground state to the excited state.

This spectroscopic technique is useful in analyzing different samples quantitatively, such as transition metals ions, highly conjugated organic compounds, and macromolecules in biological systems. Generally, spectroscopic analysis is carried out using solutions, but we can also use solids and gases.