Mass Spectroscopy and IR

Question 1

What are the three ionisation methods?

Answer 1

Electron
Chemical
Electron Spray

Question 2

What is electron ionisation?

Answer 2

Vaporised sample is exposed to a beam of electrons, leading to the abstraction of electrons to give M+. or addition to give M-.
Radical ions tend to have low stability leading to a high degree of fragmentation - hard ionisation method.

Question 3

What is chemical ionisation?

Answer 3

Similar to electrons but sample is exposed to chemical ions

Question 4

What is electron spray ionisation?

Answer 4

Solution of the sample is brought into contact with a high voltage which leads to formation of an aerosol comprimising very small and highly ionic liquid droplets. These expel ions which are more stable than other methods. This is a soft technique.

Question 5

What are the analyser types in mass spec?

Answer 5

• Sector
• Time of Flight
• Qaudrupole

Question 6

How is sector carried out?

Answer 6

Based on deflection of ionic particles by a magnetic or static electric field. Smaller more highly charged particles are deflected to a greater extent than larger less charged

Question 7

How is Time of Flight carried out?

Answer 7

Applies the same principle by accelerating ions using an electrostatic field of know strength. The rate of acceleration is controlled by m/z. Smaller more highly charged accelerate greater. Therefore, m/z can be determined by time taken to reach the detector.

Question 8

How is quadrople carried out?

Answer 8

Ions are passed through an oscillating electrostatic field generated by charged rods. The path of the ions is altered by the field, with the m/z ratio determining the trajectory of an ion at a given field strength.

Question 9

What is tandem mass spectrometry (MS/MS)

Answer 9

Ions are fragmentated to a second collission in quadrople.

Question 10

What are the advantages of MS?

Answer 10

• Provides detailed information especially coupled to other techniques
• Requires very little material
• HRMS can determine molecular composition

Question 11

What are the disadvantages of MS?

Answer 11

• Sensitive to sample preparations and precise technique used
• Not generally quantitative
• Will not pick up impurities that ionise poorly

Question 12

What is IR?

Answer 12

• Detects the different vibrations of bonds

Question 13

What are the advantages of IR?

Answer 13

• Easy / cheap to run

- Some diagnostic capacity

Question 14

What are the disadvantages of IR?

Answer 14

• Provides limited data relative to other methods