Instrumental methods
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Summary
Instrumental methods
In a nutshell
Instrumental methods are used as alternatives to wet chemical methods, such as flame tests. Flame emission spectroscopy and mass spectroscopy are examples of instrumental methods used to analyse elements and compounds.
Instrumental vs wet chemical analysis
Wet chemistry refers to classical methods of analysis, such as titrations and colorimetry. The reason why these chemical tests are classed as wet is because they are usually carried out in the liquid phase. This is not the case for all wet analytical methods, flame tests for example.
Instrumental methods on the other hand use specialised machines. The advantages of instrumental methods over wet chemistry include: faster, greater accuracy and greater sensitivity.
Flame emission spectroscopy
Flame emission spectroscopy is an instrumental method of identifying metal ions in solution.
procedure
| 1. | The sample is passed through a flame. |
| 2. | Electrons of the metal ions become excited and move to up to a higher energy level. |
| 3. | As the electrons relax, they move back down to a lower energy level. |
| 4. | During this relaxation process, light energy is emitted. |
| 5. | An emission spectrum is produced based on this pattern of light emission. |
| 6. | Different metal ions emit light at different wavelengths. This gives rise to a unique emission spectrum for each metal ion. |
| 7. | Unique spectral lines can be used to identify the metal ions in solution. |
Example
A sample produces the first spectrum, below. You can then compare the spectrum to references. In this example the sample contains ion A and ion B and the wavelengths for the sample correspond to that of ions A and B.
Mass spectroscopy
Mass spectroscopy is an instrument used to analyse elements, molecules and isotopes.
Tip: Mass spectroscopy is sometimes called mass spectrometry.
Time of flight mass spectrometer
procedure
| 1. | Elements or molecules are ionised, forming positive ions. |
| 2. | The ions are accelerated by an electric field. |
| 3. | All ions have the same (constant) kinetic energy. |
| 4. | Different ions have different velocities because their masses are different. |
| 5. | Ions drift through the flight tube according to their mass : charge ratios. |
| 6. | Ions with lower values move faster through the flight tube. |
| 7. | The time taken to reach the detector (time of flight) is used to identify the species. |
| 8. | Abundance of the species is determined by the size of current generated at the detector. |
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FAQs - Frequently Asked Questions
What is flame emission spectroscopy?
Flame emission spectroscopy is an instrumental method of identifying metal ions in solution.
What are the advantages of instrumental methods?
The advantages of instrumental methods over wet chemistry include that they are: faster, more accurate and more sensitive.
What is wet chemistry?
Wet chemistry refers to classical methods of analysis, such as titrations and colorimetry.
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