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What Is Flame Emission Spectroscopy?

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  • Written By: Mary McMahon
  • Edited By: Shereen Skola
  • Last Modified Date: 21 October 2014
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Flame emission spectroscopy is a chemical analysis technique that relies on looking at the energy emitted when excited atoms return to a ground state. Atoms associated with different elements have their own distinct spectral signatures which can be identified with a highly sensitive detector. This method of material analysis is destructive in nature, but can provide important information about the components of an unknown sample of a compound or solution.

The first step is aerosolization of the sample. To accomplish this, a fine spray of the sample material can be pumped through a flame, where the heat excites the atoms, causing them to fall back to a ground state. This causes energy loss and a characteristic emission of energy. A detector notes the wavelengths of light emitted, and records it for the benefit of the operator. This information can be printed and retained digitally in a file.

Some compounds have very characteristic signatures that may be visible with the naked eye in flame emission spectroscopy, especially if the sample is large. In lieu of aerosolization, some test methods require the technician to place a small sample in a holder that can be placed in the flame, which will create a very noticeable emission. Copper, for example, burns bright green to blue, depending on which impurities are present. Chemistry professors may use such recognizable compounds in classroom demonstrations to show students how the process works and to illustrate the varied spectral emissions of different elements.

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Differences between other compounds can be more subtle, especially when multiple elements are present in a sample. The flame emission spectroscopy process magnifies the emission and allows the operator to review it at leisure to match it up with known samples. People can look for specific bands of light that can be tell-tale signs of the presence of particular elements. Automated computer systems can also perform this match on their own and return a list of likely candidates to the user.

Charts of flame emission spectroscopy results are available to compare with samples under analysis. These can also be used for equipment calibration. To calibrate, the technician takes a known sample and subjects it to the process, comparing the end result with the chart. If the emissions do not match, there may be something wrong with the equipment. The gear may need servicing, cleaning, or other work to function correctly and return valid results for the user.

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kentuckycat
Post 4

I have never heard of turning a compound into an aerosol and putting it through a flame, but when I took a chemistry course in college, we did a couple of experiments using a spectroscope to determine chemical compositions. One of the things we did was look at different elements that had been put into a vacuum tube and then had electricity passed through it to excite the electrons. Basically, where a normal fluorescent light bulb would have mostly argon in it, these tubes had things like hydrogen and helium. They were much smaller than a light bulb, too.

After they had the electricity going through them, they would glow a certain color. Then you could look through the spectroscope, and it would break apart the spectrum into the specific wavelengths, and you could record them and compare them to the charts mentioned from the article.

We had a couple things like salts that were two elements in the same tube. The different spectra overlap, but you can start to figure out the elements eventually. Of course, in a real scientific setting, you can make computers do most of it.

jmc88
Post 3

@JimmyT - From what I know, flame spectroscopy is widely used in astronomy to test the elemental composition of stars and other things out in space. As you can imagine, the heat from stars is pretty good at burning up the various elements and emitting their spectrums into space. Astronomers can use special telescopes outfitted with spectrometers to look at the star emissions and tell what elements are present in them. This is important, since stars of different ages and sizes are made of different elements and burn at different temperatures.

I'm not positive on this, but I think astronomers are able to use emissions spectroscopy to determine the composition of planets, too. Nothing from Earth has ever visited Pluto, but we still know what its atmosphere and surface are made of. I'm sure there are some other uses I am not familiar with, as well.

jcraig
Post 2

@JimmyT - Those are some good questions. I don't think I had thought about all those things. I can tell you what I know, though, since we were doing this in my chemistry class the other day.

We just looked at a few things and the different colors they made. We tried copper, and it did turn green. When we did lithium it was pink, and sodium was kind of an orange color the same as the flame. The experiment we did, though, was basically just to help us understand how the electrons can change levels. We didn't really get too in depth about how real chemists would use those results in a lab setting.

The one thing that my teacher told us, though, is that burning the different elements is how they produce a lot of fireworks. They just pack the shells with different solid elements, and then when the firework explodes, it burns them and produces the different colors. I thought that was pretty interesting.

JimmyT
Post 1

When would someone even use something like this. I mean, I don't really remember a lot about when I took chemistry, but I understand how electrons can change energy levels within an atom. If I remember correctly, that is how a light bulb works.

I suppose there would be some instances like the article mentions where you could burn a piece of material and check the resulting spectrum, but it seems like there would usually be a lot more precise and less destructive ways you could go about the process. I would assume it takes a pretty large sample of something to get the right response.

Also, what happens when you have a molecule that is made up of more than one element? I would assume that each element emits its own specific wavelengths of light, but how would the chemist go about deciding which of the wavelengths belonged to each specific element. There has to be a certain amount of overlap, right? In other words, some elements would produce some of the same colors.

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