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What Is a Flame Spectrophotometer?

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  • Written By: Ray Hawk
  • Edited By: E. E. Hubbard
  • Last Modified Date: 12 November 2016
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A flame spectrophotometer, also known as an atomic emission spectrophotometer, is a device for measuring light as it interacts with or is emitted by atoms to determine the chemical makeup of substances. Light waves are measured either as they are absorbed by an atom as it adds energy to it and pushes electrons to a higher energy shell, or light is measured that is emitted as these excited electrons return to a lower energy shell. Spectroscopy can be used to determine the quantity of elements present in essentially any substance, but it works best for metals such as sodium, potassium, and copper. This is because metals are easily excited to higher energy states with a low temperature in flame spectrophotometer analysis.

An atomic absorption spectrometer works only with visible light. A flame spectrophotometer can bombard an atom with ultraviolet light, however, if fluorescence spectroscopy is used to also examine atomic compositions. These wavelengths of light can be directly correlated to changes in energy states of the outer shell electrons in atoms. Other types of spectroscopy, such as the study of x-ray emissions, are used to examine changes in energy states for electrons in the inner energy shells of atomic structures. Molecular compounds also have unique rotational states among the atoms involved, which lead to spectroscopy emissions in the microwave bands for their study.

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The light intensity in a flame spectrophotometer is related directly to how much of an element exists in a sample. Emission colors, or spectral lines, are distinct enough that elements can be easily distinguished from one another. The process that a flame spectrophotometer uses for elemental samples is considered so precise that it can measure quantities of an element down to parts per million in a sample.

Equipment designed to do flame spectrophotometer analysis is considered to be built upon fairly simple instruments. The temperature required to provide atomic excitation, however, is high, and is usually done by burning acetylene or propane to 3,632° to 5,432° Fahrenheit (2,000° to 3,000° Celsius). The light emitted by the sample is passed through optical filters for analysis. It is also channeled so that it impacts with a photomultiplier detector that converts it to an electrical signal to record light intensity for elemental concentration measurements.

Spectrophotometers are widespread laboratory machines used in clinical research or to determine the presence of metals in environmental samples. Their main drawback is that they require precise calibration against established samples to produce reliable readings, especially with complicated sample mixtures. The history of the process of spectroscopy can be traced all the way back to Aristophanes' study of the lens in 423 BC. It wasn't until the 1800s that the basic law of atomic absorption was quantified and made it possible to build machines based on the flame spectrophotometer effect, which states that matter absorbs light at the same wavelength that it emits light.

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