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chm 343 separations > Exam 1 > Flashcards

Exam 1 Flashcards

1
Q

It is ______ effective to do three extractions with 100 mL each time than to to do one extraction with 300 mL.

A

More

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2
Q

when the pH is changed of a solute that is an acid/base the ______ also changes.

A

charge

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3
Q

(neutral/charged) species is more soluble in an organic solvent

A

neutral

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4
Q

(neutral/charged) species is more soluble in an aqueous solution.

A

charged

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5
Q

What must one do in order to extract a base into water?

A

a low enough pH must be used in order to convert B to BH+

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6
Q

What must one do in order to extract an acid HA into water?

A

a high enough pH must be used to convert HA to A-

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7
Q

The _____ the pH, the more HA in aqueous solution

A

Higher

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8
Q

The _____ the pH, the more B in aqueous solution

A

lower

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9
Q

most complexes that can be extracted into organic solvents are (charged/neutral).

A

neutral

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10
Q

what is the most common organic ligand used to separate metal ions from one another (which is also a weak acid)?

A

8-hydroxyquinoline

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11
Q

What does the distribution coefficient for a metal ion extraction depend on?

A

pH and ligand concentration

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12
Q

Who is considered the father of chromatography?

A

Russian botanist: Mikhail Tswett

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13
Q

what is chromatography

A

method.

consists of a mobile phase and stationary phase.

the mobile phase (solvent) moves through the stationary phases separating the mixture into components

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14
Q

What is usually the mobile phase?

A

a liquid or a gas moving through the column

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15
Q

What is usually the stationary phase?

A

a viscous liquid or solid particles.

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16
Q

Fluid entering the column is called ________

A

eluent

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17
Q

Fluid emerging from the end of the column is called _________

A

eluate

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18
Q

Define elution.

A

the process of passing liquid or gas through a chromatography column.

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19
Q

Name the two types of columns.

A

packed column

open tubular column

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20
Q

what is a packed column?

A

column filled with particles of stationary phase

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21
Q

what is a open tubular column?

A

a narrow, hollow capillary with sationary phase coated on the inside walls

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22
Q

Name the 5 types of chromatography

A
  1. Adsorption chromatography
  2. Partition chromatography
  3. Ion-exchange chromatography
  4. Size exclusion chromatography
  5. Affinity chromatography
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23
Q

Briefly describe:

Adsorption chromatography
Partition chromatography
Ion-exchange chromatography
Size exclusion chromatography
Affinity chromatography

A

Solute is adsorbed on the surface of a solid stationary phase.

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24
Q

In adsorption chromatography, the more strongly a solute is adsorbed, the ______ it travels through the column.

A

slower

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25
Q

Briefly describe:

Absorption chromatography
Partition chromatography
Ion-exchange chromatography
Size exclusion chromatography
Affinity chromatography

A

Solute is dissolved in liquid stationary phase which is bonded to the surface of a column

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26
Q

Briefly describe:

Absorption chromatography
Partition chromatography
Ion-exchange chromatography
Size exclusion chromatography
Affinity chromatography

A

solute ions of the opposite charge are attracted to the stationary phase (resin)

27
Q

Briefly describe:

Absorption chromatography
Partition chromatography
Ion-exchange chromatography
Size exclusion chromatography
Affinity chromatography

A

separates molecules by size with larger solutes passing through the porous stationary phase faster.

28
Q

With size exclusion chromatography, the smaller the molecule, the ______ it takes to pass though the column.

A

longer

29
Q

Briefly describe:

Absorption chromatography
Partition chromatography
Ion-exchange chromatography
Size exclusion chromatography
Affinity chromatography

A

specific solute molecules in the mobile phase interract with another molecule that is attached to the stationary phase.

30
Q

What is the most selective type of chromatgraphy?

A

Affinity chromatography

31
Q

What are the main branches of chromatography?

A
  • Gas Chromatography
  • Liquid Chromatography
  • Supercritical Fluid Chromatography
32
Q

how does an analytical column differ from a preparative column

A

Analytical columns:

  • used to separate* and *identify/measure the component of a mixture
  • In the format of long and narrow column
  • used for quality control

VS.

Preparative columns:

  • used to purify a significant quantity of a component in a mixture
  • in the format short and wide column
  • For (pharmaceutical) production purposes.
33
Q

Define a chromatogram

A

a graph showing the detector response as a function of elution time

34
Q

define a chromatograph.

A

instrument used to measure components in a mixture

35
Q

Draw a representative chromatogram and label axis, as well as injection time, minimum possible time (tm), retention time (tr), & adjusted retention time (t’r)

A
36
Q

What is the equation for Adjusted retention time

A

t’r = tr - tm

adjusted retention time = retention time - minimum possible time

37
Q

what is the equation for relative retention between to components?

A

α = t’r2 / t’r1

relative retention = 2nd adjusted retention time / 1st adjusted retention time

38
Q

The greater the relative rentention time, the ________ the separation between two components.

A

greater

39
Q

What are the two factors that contribute to how well compounds are separated by chromatography?

A
  1. the width of the peak
  2. the dfference in elution times betwen peaks
40
Q

Concerning elution time between peaks, the farher apart, the ________ their separation.

A

better

41
Q

Concerning broadness of peaks, the wider the peaks, the _________ their separation.

A

poorer

42
Q

define half-width (w1/2)

A

the width at a height equal to half of the peak height

43
Q

What resolution is highly desired for practice?

A

1.50

44
Q

the narrower the bandwidth the _________ the plate height

A

smaller

45
Q

the smaller the plate height, the _________ the column separation efficiency

A

better

46
Q

the smaller the plate height, the ________ the plate number.

A

greater

47
Q

22the greater the the plate number, the _______ the separation effciency

A
48
Q

What are the advantages of an open tubular column over a packed column

A
  • higher resoluton
  • shorter analysis time
  • increased sensitivity
  • lower sample capacity
  • increased linear flow rate
  • decreased plate height (higher resolution)
49
Q

what is 8-hydroxyquinoline ?

A

an organic ligand

50
Q

In order to scale up properly what are the requirements?

A
  • Keep the column length constant but increase the cross-section area
  • Maintain a constant linear flow rate
51
Q

What is plate height (H) proportional to?

A

the variance of a chromatographic band

52
Q

The smaller the plate height indicates what about the band

A

a narrower band

53
Q

What is eddy diffusion

A

molecules entering at the same time may take different flow paths that are longer than others, therefore eluting at different times.

54
Q

How can we decrease the chance of eddy diffusion?

A

use smaller stationary particles.

55
Q

what is longitudinal diffusion?

A

takes places along the axis where molecules diffuse from high concentration within the band to lower concentration on the edges of the band.

56
Q

How can we decrease the chance of longitudinal diffusion?

A

increase the solvent flow

57
Q

Does longitudinal diffusion occur more in LC or GC?

A

GC

58
Q

What is mass transfer?

A

mobile and stationary phase have different migration times because some of the solute gets stuck in the stationary phase, therefore spreading the overall zone of solute.

59
Q

How can we decrease the occurrence of mass transfer?

A

slow down the flow of solute

60
Q

What is the adavantage of bonding (covalently attaching) the stationary phase to the column or cross-linking the stationary phase to itself?

A

it reduces bleeding of the stationary phase when the column is in use.

61
Q

Why is splitless injection used with purge and trap sample preparation?

A

to ensure that 100% of the analyte is retained and none is lost, since purge and trap is able to collect all the analyte and splitless injection is about to retainand test all the analyte, it is best when paired together to reduce error

62
Q

State the order of decisions in method development for gas chromatography.

A
  1. Goals of Analysis
  2. Sample Preparation Method
  3. Detector
  4. Column
  5. Injection Method
63
Q
A

chm 343 separations (3 decks)

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