4.1.5 - Analytical techniques

Question 1

what does desorption mean?

Answer 1

dissolving into the moving phase

Question 2

what does adsorption mean?

Answer 2

attraction to the stationary phase

Question 3

what is the mobile phase?

Answer 3

solvent - one that moves through the column

Question 4

what is the solute (analyte)?

Answer 4

thing you are analysing

Question 5

what does ‘like attracts like’ mean?

Answer 5

polar substances like polar solvents –> will be carried up together

Question 6

how can you tell which substance has the highest affinity for the solvent (mobile phase)?

Answer 6

it is located at the top end of the chromatography sample
- little adsorption to stationary phase

Question 7

how can you tell which substance has the highest affinity to the stationary phase?

Answer 7

located at the lower end of the chromatography sample
- little desorption into the mobile phase

Question 8

what does Rf mean?

Answer 8

• retardation factor
• the distance that travelled over the solvent font.
• can depend on the polarity, ion charge or molecule size

Question 9

how is the Rf calculated and how can the values be interpreted?

Answer 9

• for substances that are very soluble in the liquid, Rf will be close to 1 (high desorption)
• for substances that are rather insoluble in the liquid, Rf will be close to 0 (high adsorption)

Question 10

what is column chromatography?

Answer 10

mixture moves down the column
- if like solvent = move quickly down
- doesn’t like solvent = move slowly/sticks to top

Question 11

what is thin layer chromatography?

Answer 11

mixture moves up the plate
- if like solvent = moves up quickly
- if doesn’t like solvent = stay at bottom/ move up slowly
- retention factor used

Question 12

what is the stationary phase/adsorbent?

Answer 12

• substance that stays fixed inside the column

Question 13

what is the eluent?

Answer 13

fluid entering the column

Question 14

what is the eluate?

Answer 14

fluid exiting the column (that is collected in flasks)

Question 15

what is elution?

Answer 15

the process of washing out a compound through a column using a suitable solvent

Question 16

what is the analyte?

Answer 16

mixture whose individual components have to be separated and analyzed

Question 17

what is the Rt?

Answer 17

• retardation time
• the time to travel a distance
• can depend on the polarity, ion charge or molecule size

Question 18

what is the protein analysis - chromatography size exclusion

Answer 18

• big molecules cannot penetrate the small pores in the stationary phase
  
  • they are eluted by a volume between beads of the stationary phase
• small molecules penetrate the small pores.
  
  • they are eluted by a volume of solvent equal to the total volume of mobile phase
  • smaller get trapped in the pores and held by IMF. Larger ones will just pass over

Question 19

what is mass spectrometry?

Answer 19

ionization of substances, separation and detection of the resulting ions generating a spectra
- atoms are ionized so the magnet will be able to deflect them
- the detector plate determines how many of each isotope is present
- the magnet is responsible for deflecting the ions

Question 19

recall the process of obtaining a mass spectrum

Answer 19

1. sample of a neutral molecule is vaporized
2. blast with electron beam to ionize (formation of cations with no change in mass)
3. loss of an electron results in a radical cation (no change in mass)
   fragmentation occurs
4. mixture of charged and uncharged particles
5. magnetic deflection separates charged particles by mass-to-change ratio, m/z (charge is usually +1)
6. this results in a higher mass (highest molecular weight signifies the parent chain (molecular ion)

Question 20

what are the components of a mass spectrum?

Answer 20

• detector records the frequency of each mass, the taller the peak, the more abundant the fragment
• the base peak: most abundant (rest are a comparison to this) which links to stability not amount in the structure
• parent peak/molecular ion: if unstable, highest is not the molecular ion (occurs when highly branched)