Chromatography

Question 1

What is the partition coefficient?

Answer 1

The equilibrium constant for a solute that is partial between two immiscible liquids

Question 2

Columns in Chromatography?

Answer 2

Sample is flushed through the column stationary phase by mobile eluent. Movement of analyte down a column only occurs in mobile phase.

Question 3

Chromatogram?

Answer 3

A plot of detector response vs retention time.

Question 4

On a chromatogram when does the width of the band increase?

Answer 4

With time or distance

Question 5

Adsorption

Answer 5

Solute equilibrates between mobile phase and surface of stationary phase. Adsorbed on surface of stationary phase

Question 6

Ion- Exchange

Answer 6

Ions in mobile phase are attracted to counterions covalently attached to stationary phase. Anion exchange resin

Question 7

Partition

Answer 7

Solute equilibrates between mobile phase and film of liquid attached to stationary phase. Bonded to surface of column

Question 8

Size Exclusion

Answer 8

Large molecules are excluded

Question 9

Affinity

Answer 9

Solute in mobile phase is attracted to specific groups covalently attached to stationary phase. All other molecules wash through

Question 10

How is separation increased in the chromatogram?

Answer 10

Increasing band/peak separation or decreasing amount of spreading

Question 11

Theoretical plate

Answer 11

Indication of efficiency of a column. Approximately the length of column required for one equilibration of solute between mobile and stationary phase.

Question 12

Extraction vs Chromatography?

Answer 12

Extraction uses two immiscible liquids, chromatography uses stationary phase and mobile phase which are miscible

Question 13

Van deemter equation!!
KNOW

Answer 13

Used to find the optimal flow rate for the best resolution!

Question 14

H of Van deemter equation

Answer 14

Plate height

Question 15

A of Van deemter equation

Answer 15

Multiple Flow Paths
The residence time in the column for molecules of the same species is variable. Some flow paths are longer than others.

Question 16

B/Ux of Van deemter equation

Answer 16

Longitudinal Diffusion
Diffusional broadening of a band. Takes place along axis of column and while band is moving along column by flow of solvent. Species migrate from a more concentrated part of medium to a more dilute. The faster the less diffusional broadening.

Question 17

Cux of Van deemter equation

Answer 17

Mass Transfer Coefficients
The finite time required for solute to equilibrate between mobile and stationary phases. Cs Rate of mas transfer through stationary phase. Cm is “ “ mobile phase

Question 18

How can resolution be increased

Answer 18

as plate height is decreased

Question 19

Peak area is proportional to…

Answer 19

Concentration

Question 20

Chromatography applications
Qualitative and Quantitative

Answer 20

Qualitative: gives either retention time or position on the stationary phase

Quantitative: Peak height (amount of analyte present), Peak area (Shows concentration)

Question 21

How is peak area affected?

Answer 21

Changes in retention time or column efficiency

Question 22

Peak height is inversely related to…

Answer 22

Peak width

Question 23

Chromatography advantages?

Answer 23

Cheap, fast, and simple

Question 24

Gas vs Liquid chromatography
what is it
mobile phase
stationary phase
cost
analytes
Separation
Van D
Detectors

Answer 24

Look at table on desktop!

Question 25

Gas Chromatography

Answer 25

Gas flow through a glass or metal column which separates compounds based on volatility and interaction with the liquid stationary phase

Question 26

Open Tubular Column Advantages and Disadvantages

Answer 26

Common in GC. Made of fused silica and plymides or support and protection. Offers high resolution, short analysis time and greater sensitivity then packed columns. has a less sample capacity

Question 27

Three types of open tubular columns?

Answer 27

Wall Coated: Has a thick film of stationary liquid on inner walls Support coated: Has solid particles coated with stationary liquid. Can handle larger samples but performance isn't as good Porous Layer: Solid particles are the active stationary phase

Question 28

Why are narrow columns better and worse?

Answer 28

provide better resolution but require a higher pressure and have a lower sample capacity

Question 29

Making Liquid Stationary phase

Answer 29

The choice is base on "like dissolves like" non-polar columns are the best for non-polar solutes (strong for strong ect..). Surface silanol groups are exposed and strongly retain polar compounds by adsorption. To prevent stationary phase bleed silanol is bonded to silica surface. Column surface deactivated by silanization.

Question 30

Column Bleeding?

Answer 30

Occurs at high temperatures where the stationary phase decomposes and the products elevate background signal and increase interference.

Question 31

How to reduce column bleeding?

Answer 31

To reduce this use the thinnest stationary phase on the narrowest and shortest column

Question 32

Temperature programming?

Answer 32

Temperature of column is raised during separation to increase analyte vapour pressure and decrease retention time.

Question 33

Flame ionization detector Advantages and Disadvantages

Answer 33

Effluent from column is directed into small flame which produces ions. The current produced by collecting charged carriers is measured. highly sensitive and can measure a wide range of analytes. slow and can be affected by interference

Question 34

Electron capture detector Advantages and Disadvantages

Answer 34

Selectively responds to halogen-containing compounds. The sample eluate from column is passed over a radioactive beta emitter. An electron causes ionization of carrier gas and the production of an electron burst. The eluent passes through and electron capture detector. highly sensitive and doesnt alter the sample requires a special license to operate and several carrier gasses are needed

Question 35

Olfactometry

Answer 35

Allows for identification of odour active compounds

Question 36

Derivatization

Answer 36

Manipulating analyte to make its properties more optimal for separation and detection