Instrumental analysis involves the use of complex machines in order to collect detailed pieces of information about a sample. Three common types of spectroscopies are used in order to collect this data are:
- Mass spectroscopy
- Nuclear magnetic resonance (NMR) spectroscopy
- Infrared (IR) spectroscopy
Mass spectroscopy is not only useful for determining a molecule’s mass, but also for determining its structure. For example, a sample has a large peak at a mass of 92 that is determined to be the parent peak (the whole compound intact) and then two small and roughly equal peaks at 77 and 15 mass. The molecule is known to have a benzene ring in it from other analysis. Due to the potential of part of the molecule to break off due to the mass spectroscopy analysis, the peak at 15 can be determined to be a methyl group and the peak at 77 can be determined to be the benzene ring. In more complicated compounds this process will not give you the whole structure, but it may help in determining some of the molecule’s parts.
Nuclear magnetic resonance (NMR) spectroscopy is used to find the shift (polarity) of certain atoms in a molecule. The most common types of NMR spectroscopies done are standard hydrogen (1H) and carbon (13C). Other types include various isotopes and elements, such as oxygen, nitrogen, and sulfur. The peaks within the data obtained tell where each atom is in the molecule and if certain groups exist on the compound.
Infrared (IR) spectroscopy is a more broad way to obtain data from a NMR. IR spectroscopy obtains data that verifies certain functional groups exist within the compound however it does not give you enough data to determine where the group is at in the molecule. IR is a great way to support data obtained from NMR but is not as useful. Because IR data is a lot quicker and easier to obtain, this method of analytical chemistry ideal as a simple check.