Mass and Infrared Spectrometry Flashcards
What is infrared spectroscopy?
In infrared (IR) radiation, a beam of IR radiation is passed through a sample of a chemical.
The IR radiation is absorbed by the covalent bonds in the molecules, increasing their vibrational energy.
Bonds between different atoms and bonds in different places absorb different frequencies of IR radiation.
So the OH group in an alcohol and the OH in a carboxylic acid absorb different frequencies.
What does an infrared spectrometer do?
It produces a graph that shows you what frequencies of radiation the molecules are absorbing.
How can mass spectrometry be used to identify compounds?
The molecules in the sample are bombarded with electrons and a molecular ion, M+ is formed when the electrons remove an electron from the molecule.
To find the relative molecular mass of a compound you look at the molecular ion peak.
The mass/charge value of the molecular ion peak is the molecular mass.
What’s on the y axis of a mass spectrum?
The abundance of ions.
What’s on the x axis of a mass spectrum?
Mass/charge ratio
What is fragmentation?
The bombarding electrons make some of the molecular ions break up into fragments.
The fragments that are ions show up on the mass spectrum, making a fragmentation pattern.
How do you work out structural formula?
You’ve got to work out what ion could have made each peak from its m/z value. (You assume that the m/z value of a peak matches the mass of the ion that made it.)
How is mass spectrometry used to differentiate between similar molecules?
Even if two different compounds contain the same atom, you can still tell them apart with mass spectrometry, because they won’t produce the same fragments.
Every compound produces a different mass spectrum- so the spectrum’s like a finger print for the compound.
Large computer databases of mass spectra can be used to identify a compound from it spectrum.
What are some uses of mass spectrometry?
1) Probes to Mars have carried small mass spectrometers to study the composition of the surface of Mars and to look for molecules that might suggest of life.
2) Mass spectrometry can also be used to measure the levels of pollutants present in the environment e.g the amount of lead or pesticides entering the food chain via vegetables.
