What Is an Atomic Absorption Spectrophotometer?

Andrew Kirmayer
Andrew Kirmayer
Woman with hand on her hip
Woman with hand on her hip

An atomic absorption spectrophotometer is an instrument that can detect an element or substance by vaporizing it and measuring at what part of the spectrum it absorbs light. Measurements are typically indicated by a black line at a particular part of the light spectrum. The instrument can operate using a flame or a heated graphite tube. It usually includes a cathode light tube, a prism or optical filter for selecting wavelengths, and a photo-detector. A digital display is sometimes used to project experiment results, or a computer can be hooked up to the system as well.

When a material such as a metal is heated, it vaporizes. A beam of light, set at a particular wavelength, shines through the vapor and the atomic absorption spectrophotometer. The intensity of the light can change when it is absorbed by atoms in the material. Such a spectroscopy instrument can be used to detect heavy metals in the environment, like in water, soil, or rocks. It can also be used in petroleum and chemical plants and in semiconductor manufacturing.

In an atomic absorption spectrophotometer, a burner consisting of a flame or a heated tube vaporizes a sample, while light is shone through a cathode tube. The light passes through the flame and then a component called a monochromator. Lenses in this part typically act as prisms to filter out a specific wavelength, and can also filter out scattered light that could interfere with the measurement. The intensity of the light can then be detected by a photomultiplier. Traditionally, this was a vacuum tube like device, but 21st century technology has often replaced it with microchips and solid state electronics.

Modern atomic absorption spectrophotometer instruments are often controlled by a computer with specialized software that can run on common operating systems. The spectrophotometers are generally extremely sensitive to minute traces of materials. Such instruments can measure the presence of metals in parts per million, while the incorporation of a graphite furnace can boost the sensitivity to parts per billion.

Using an atomic absorption spectrophotometer requires knowledge of how to read the results of an experiment. When a sample is run, absorbance values can be calculated by software based on the spectral readings. These usually need to be compared to calibration curves previously generated. Comparing the results to known values can help understand the test results more accurately. About 70 elements can be directly identified with this instrument, along with various materials that could contain any combination of them.

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