9. MS Techniques

Question 1

What is IR-MS?

Answer 1

Isotope Ratio Mass Spectrometry

Question 2

What is GC-MS?

Answer 2

Gas Chromatography Mass Spectrometry

Question 3

What is LC-MS?

Answer 3

Liquid Chromatography Mass Spectrometry

Question 4

What does EI mean?

Answer 4

Electron Impact Ionization.
This is where analyte molecules are directly ionized through collision with a bombarding electron stream
-> removal of an electron to form a radical cation species.

Question 5

What do we do in mass spectrometry?

Answer 5

We determine the mass-to-charge ratio of ions formed from molecules and fragments of these.

Question 6

What are the steps in MS?

Answer 6

• Formation of ions
• Separation of ions according to their mass to charge ratio, m/z
• Measuring ion current or counting ions
• Data processing

Question 7

What is MALDI?

Answer 7

Matrix Assisted Laser Desorption Ionisation

Question 8

What API?

Answer 8

Atmospheric Pressure Ionization

Question 9

What is APCI?

Answer 9

Atmospheric Pressure Chemical Ionization

Question 10

What are some LC-MS solvents?

Answer 10

Water, acetonitrile, methanol, ethanol, propanol isopropanol.

Question 11

What are some acceptable additives for LC-MS?

Answer 11

Acetic acid, formic acid, ammonium hydroxide, ammonium format, ammonium acetate

Question 12

The ratio between C-12 and C-13 (i.e. in plants) is…?

Answer 12

not constant. It depends on photosynthesis.

Question 13

What are the steps in GC-MS?

Answer 13

Typically they include:

• Sample components separation
• Ionization of sample components
• Separation and detection of gas-phase ions

Question 14

What does the mass spectrometer do?

Answer 14

It separates gas phase ions according to their mass to charge ratio (m/z) value.

Question 15

Most common ionization methods in GC-MS?

Answer 15

Electron impact ionization (EI) and chemical ionization (CI).

Question 16

What advantages are there to GC-MS (in comparison to LC-MS)?

Answer 16

• higher chromatographic resolution
• higher peak capacity
• single mobile phase
• fewer issues (solubility and separation)

Question 17

What is CI?

Answer 17

Chemical ionization.
This is where analyte molecules are charged through reaction processes with a charged reagent gas plasma producing either anion or cation species depending upon the analyte and analyzer polarity.

Question 18

What is make-up gas?

Answer 18

Make up” gas is a gas flow that is used to sweep components through a detector to minimize band broadening

Question 19

What are the disadvantages of EI?

Answer 19

It is a relatively harsh form of ionization

-> parent molecule often breaks apart.

Question 20

How can MS-MS analysis be achieved?

Answer 20

Choose one:

• By coupling multiple analyzers (of the same or different kind)
• With an ion trap and carrying out successive fragmentations of trapped ions.

Question 21

What are some applications for GC-MS?

Answer 21

• Inorganic chemistry analysis (inorg. compounds with low mol. weight)
• Environmental sciences (analysis of a wide range of contaminants of low mol. weight)
• Food analysis (analysis of molecules of importance in the food industry)
• Pharmacochemistry (drug activity)
• Bioanalysis (quantification/identification of metabolites in biological fluids)
• Polymers (structure from behaviour at elevated temperatures)