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Chem 311 Exam > Chromatography > Flashcards

Chromatography Flashcards

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1
Q

What is the partition coefficient?

A

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

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2
Q

Columns in Chromatography?

A

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

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3
Q

Chromatogram?

A

A plot of detector response vs retention time.

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4
Q

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

A

With time or distance

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5
Q

Adsorption

A

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

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6
Q

Ion- Exchange

A

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

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7
Q

Partition

A

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

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8
Q

Size Exclusion

A

Large molecules are excluded

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9
Q

Affinity

A

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

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10
Q

How is separation increased in the chromatogram?

A

Increasing band/peak separation or decreasing amount of spreading

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11
Q

Theoretical plate

A

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

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12
Q

Extraction vs Chromatography?

A

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

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13
Q

Van deemter equation!!
KNOW

A

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

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14
Q

H of Van deemter equation

A

Plate height

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15
Q

A of Van deemter equation

A

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

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16
Q

B/Ux of Van deemter equation

A

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.

17
Q

Cux of Van deemter equation

A

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

18
Q

How can resolution be increased

A

as plate height is decreased

19
Q

Peak area is proportional to…

A

Concentration

20
Q

Chromatography applications
Qualitative and Quantitative

A

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

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

21
Q

How is peak area affected?

A

Changes in retention time or column efficiency

22
Q

Peak height is inversely related to…

A

Peak width

23
Q

Chromatography advantages?

A

Cheap, fast, and simple

24
Q

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

A

Look at table on desktop!

25
Q

Gas Chromatography

A

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

26
Q

Open Tubular Column
Advantages and Disadvantages

A

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

27
Q

Three types of open tubular columns?

A

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

28
Q

Why are narrow columns better and worse?

A

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

29
Q

Making Liquid Stationary phase

A

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.

30
Q

Column Bleeding?

A

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

31
Q

How to reduce column bleeding?

A

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

32
Q

Temperature programming?

A

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

33
Q

Flame ionization detector
Advantages and Disadvantages

A

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

34
Q

Electron capture detector
Advantages and Disadvantages

A

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

35
Q

Olfactometry

A

Allows for identification of odour active compounds

36
Q

Derivatization

A

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

Chem 311 Exam (4 decks)

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