MS

Question 1

Define nominal mass

Answer 1

The mass of an ion or molecule calculated using the mass of the most abundant isotope of each element rounded to the nearest integer value.

Question 2

Define monoisotopic mass

Answer 2

Accurate mass of an ion or molecule calculated using the mass of the most abundant isotope of each element.

Question 3

Define Average mass

Answer 3

The mass of an ion or molecule calculated using the average mass of each element weighted for its natural abundance.

Question 4

Give the names of different methods to ionise a sample

5 points, dont require all

Answer 4

• Electron Impact (EI)
• Chemical Ionisation (CI)
• Fast Atom Bombardment (FAB)
• Electrospray (ESI)
• Matrix Assisted Laser Desorption (MALDI)

Question 5

What are the 4 stages in MALDI

Answer 5

1. Sample dissolved in an UV absorber matrix
2. UV laser focused onto a sample
3. Matrix excitation — matrix absorbs UV radiation
4. Analyte ionisation by proton transfer from matrix

Question 6

MALDI

What are two important functions of the matrix?

Answer 6

1. Absorbs photon energy from laser beam and transfers the excitation energy of the solid system
2. Serves as a solvent for analyte

Question 7

MALDI

What are the desirable characteristics for the matrix?

4 points

Answer 7

• A strong light absorption property at the wavelength of the laser flux
• The ability to form micro-crystals with the sample
• A low sublimation temperature, which facilitates the formation of an instantaneous high-pressure plume of matrix-sample material during the laser pulse duration
• The participation in some kind of a photochemical reaction so that the sample molecules can be ionized with high yields