analytical techniques Flashcards
What do the peaks on an infrared spectrum represent?
Absorbance of energy from the infrared radiation
What are the 2 peaks that must be present to identify a substance as a carboxylic acid
- Very broad peak at 2500-3300 cm-1 for an OH group
- Sharp peak at 1680-1750 for C=O group
What happens inside a mass spectrometer?
- Ionisation
- Acceleration
- Deflection
- Detection
Describe ionisation in mass spectrometry
Ions are vaporised, the atoms/molecule is ionised by knocking 2 or more electrons off to give a positive ion, this is done by bombarding it with electrons.
The positive ions are brought together to form a narrow beam.
Describe acceleration in mass spectrometry
Ions are accelerated so they have the same kinetic energy, it’s done by using a negatively charged accelerating plate
Describe deflection in mass spectrometry
Ions are deflected by the magnetic field by their mass/charge ratio.
The amount of deflection depends on the positive charge on the ion (how many electrons are knocked off
Describe detection mass spectrometry
The beam of ions passing through the machine is detected electrically, a signal is amplified and recorded
What is the symbol of molecular ion?
M+
Is fragmentation predictable? Why?
No, because it can happen anywhere in the molecule
In a mass spectrometry graph, how is a molecular ion represented?
It is the peak with the highest mass/charge ratio
The molecular mass of the molecular ion is equal to what?
Relative molecular mass of the compound
Will the molecular ion breaks of 2 isomers of the same compound be same or different?
Same
What is the m/z value of CH3+
15
What is the m/z value of OH- from a alcohol
17
What is the m/z value of C2H5+?
29
