Spectrometers: Emission vs. Absorption Instruments

For analytical spectroscopy, there are two main categories of instruments – based on either atomic absorption or atomic emission. An example of an instrument using atomic emission is an Inductively Coupled Plasma (ICP) Spectrometer, whilst an example of one using absorption energy is an Atomic Absorption Spectrometer.

Both types of instruments use technologies based on quantum mechanics, where electrons make discrete transitions from one energy state to another. If an electron moves from a lower energy state to a higher energy state, the atom absorbs this difference in energy; moving to a lower energy state requires the atom to release this energy.

The transitional energy that is either absorbed or emitted is in the form of light and so an ICP Spectrometer measures the wavelength of light emitted by an atom and an Atomic Absorption Spectrometer measures the wavelength of light absorbed by an atom, during transitional energy changes.

The wavelength of light absorbed (atomic absorption spectrum) or emitted (atomic emission spectrum) by different atoms is unique to each element – and this is how spectrometers can identify different elements.

Typically, electrons move to a higher energy state when heated and to a lower energy state when cooled. Both types of instruments generally use some form of rapid heat process, such as an air-acetylene flame or plasma.

At temperatures above 1200 Co, electrons are receptive to a transition to a higher energy state but do not have the necessary internal energy for it to occur unaided.

So the Atomic Absorption Spectrophotometer has an external source of this required wavelength energy, which is available to the electron to absorb. Whereas with the ICP Spectrometer, the plasma provides sufficient internal energy for the electron to transition to a higher state unaided.At the cooler exhaust zone, the ICP then measures the released energy wavelengths uniquely associated with each element.

Instruments that use atomic emissions include:

  1. ICP Spectrometers
  2. ICP Spectrometer – Mass Spectrometer
  3. Arc/Spark Spectrometers
  4. Flame Emission Spectrometers

Instruments that use atomic absorption include:

  1. Spectroscopic flame systems
  2. Electrothermal graphite furnaces
  3. Hydride atomization systems

For information on any of our instruments, including Inductively Coupled Plasma (ICP) Spectrometers or atomic absorption spectrometers, please contact Analytical Solutions Australia on 07 3289 3283 or complete our enquiry form.