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Instrumental Chemistry > Exam 3 > Flashcards

Exam 3 Flashcards

1
Q

Separation

A

Dividing a group into smaller groups that share the same type of similar trait

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2
Q

2 Common Separation Techniques

A

A. Chromatography

B. Electrophoresis

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3
Q

Chromatography

Define and give three examples

A

An interaction between two phases; the mobile phase and the stationary phase.
Ex. Gas Chromatography (GC), Liquid Chromatography, Supercritical Fluid Chromatography

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4
Q

Supercritical Fluid

A

Something that moves like a gas, but dissolves like a liquid

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5
Q

Elution

A

Describes the separation of analyses on a packed column

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6
Q

Dilution occurs in a column due to…..

A

The addition of solvents to push the analyte thru

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7
Q

Eluent

A

Portion of the sample in the mobile phase

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8
Q

Mobile Phase vs. Stationary Phase

A

The phases that interact in chromatography

  • mobile: phase that moves
  • stationary: phase that does not move
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9
Q

Partitions

A

Formed as analytes move down the column

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10
Q

Column Chromatography:

The rate that a zone migrates down a column is dependent on…..

A

How long the analyte spends in the stationary phase.

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11
Q

Chromatogram

A

Readout that shows the detector response over time

  • x-axis = time
  • y-axis can vary
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12
Q

Formula:

Distribution Constants

A

K = cs/cm

(cs=ns/vs)
(cm=nm/vm)

  • v=volume, s=stationary phase, m=mobile phase
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13
Q

Parts of the HPLC inlets (3)

A
  • injection system
  • pump
  • solvent
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14
Q

Calculating Resolution:

A

Rs = 2( (tr)B - (tr)A) ) / (WA + WB)

  • trA = retention time of A
  • trB = retention time of B
  • WA = width of peak A
  • WB = width of peak B
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15
Q

Calculating Plate Count:

A

N = L/H

N = plate count (# of plates)
L = column length
H = plate height
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16
Q

Calculating Plate Height:

A

H = sigma^2 / L

H = plate height
sigma = distance from peak, one distribution out
L = column length
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17
Q

Diffusion

A

process in which species migrate from a more concentration part of a medium to a more dilute region
*no direction

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18
Q

The _____ the analytes are on the column, the _____ the longitudinal diffusion.

A

longer; greater

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19
Q

Gas Chromatography:

  • mobile phase
  • stationary phase
A
  • mobile phase: inert gas

- stationary phase: varies (solid, gel)

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20
Q

Gas Chromatography:

Information about Inlets

A
  • sample injection is complex due to gas rapidly flowing into the column
  • injection of either liquid or gas sample
  • sample must be volatilized, temperature must be high enough
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21
Q

Gas Chromatography:

Important parts of the Inlet

A
  • septum: keeps gases separate from atmosphere
  • syringe: used to puncture septum and inject sample
  • vaporization chamber: vaporizes sample, pushes the injection mix into mobile phase
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22
Q

Gas Chromatography:

Information about the Column

A
  • piece of instrument that causes separation to occur

- 2 types of columns: Open Tubular & Packed

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23
Q

Gas Chromatography:

Open Tubular Columns

A

WCOT and SCOT

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24
Q

Gas Chromatography:

WCOT

A

“Wall Coated Open Tubular” column

- capillary tube is coated with stationary phase

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25
Q

Gas Chromatography:

SCOT

A

“Support Coated Open Tubular” column

- stuff inside the tube is coated with stationary phase

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26
Q

Gas Chromatography:

What is more efficient WCOT or SCOT?

A

WCOT is more efficient than SCOT.

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27
Q

Gas Chromatography:
Most widely used column
Advantage and Disadvantage

A

FSWC (fused silica wall coated, open tubular column)

    • thinner, flexible
    • can not add a large amount of sample
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28
Q

Gas Chromatography:

Packed Columns

A

tube packed with fine material coated with thin layer of stationary phase

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29
Q

Generic setup of GC

A

inlet –> column –> detector

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30
Q

Examples of common stationary phases

A
  • PEG
  • dimethylpolysiloxane
  • wax
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31
Q

2 Methods of Temperature Ramp

A

A. Isothermal - keep same temperature throughout analysis

B. Gradient - increase temperature at some rate

32
Q

Gas Chromatography:

As temperature _______, analytes will spend _____ time in mobile phase, _______ing the total time on the column

A

Increases; more; decreasing

33
Q

Advantage and Disadvantage of Isothermal Temperature Ramp

A

+ easier to develop method

- longer runtimes and worse separations

34
Q

Advantage and Disadvantage of Gradient Temperature Ramp

A

+ give better resolution and shorter runtime

- tricky to correct

35
Q

Gas Chromatography:

Ideal Detector Characteristics

A
  • sensitivity
  • good stability/reproducibility
  • linear response to solutes over many magnitudes
  • short response time
  • high reliability + ease of use
  • non-destructive
36
Q

Gas Chromatography:

Common Detectors

A 
A. FID
B. ECD
C. Thermionic Detectors
D. Conductivity Detectors
E. Photoionization
F. Atomic Emission
G. Flame Photometric
H. Mass Spec.
37
Q

Gas Chromatography:

FID

A

Flame Ionization Detector

  • detector in GC
  • very common
  • burns whatever comes out of column
  • mass sensitive
  • does not discriminate between hydrocarbons
38
Q

Gas Chromatography:

ECD

A

Electron Capture Detector

  • detector in GC
  • useful in detection of halogenated compounds
39
Q

Gas Chromatography:

Thermionic Detectors

A
  • detector in GC
  • specific for phosphorus and nitrogen
  • hot gas flows, forms plasma, current is generated and detected
40
Q

Gas Chromatography:

Conductivity Detector

A
  • detector in GC
  • gas dissolved in liquid to produce conductive solution
  • detected in conductivity cell
41
Q

Gas Chromatography:

Photoionization

A
  • detector in GC

- uses light to ionize

42
Q

Gas Chromatography:

Atomic Emission

A
  • detector in GC

- converts sample to plasma and observes emissions

43
Q

Gas Chromatography:

Flame Photometric

A
  • detector in GC

- used for pollution studies

44
Q

Liquid Chromatography:

Common Types

A
  • HPLC
  • UPLC
  • Column Chromatography
  • TLC
  • Paper Chromatography
45
Q

HPLC

A

High Pressure Liquid Chromatography

46
Q

UPLC

A

Ultra high Pressure Liquid Chromatography

47
Q

TLC

A

Thin Layer Chromatography (Liquid)

48
Q

Liquid Chromatography:
Mobile Phase:
Stationary Phase:

A

Mobile Phase: liquid

Stationary Phase: varies

49
Q

Liquid Chromatography:

Information about Columns

A
  • columns generally packed with small particles

- smaller the particles, the better the efficiency of the column

50
Q

Isocratic

A

same solvent at all times during run

51
Q

Gradient

A

mixture of 2 solvents with different polarities; mixture changes during run

52
Q

Liquid Chromatography:

Parts of the Inlet

A
  • injection system
  • pump
  • solvent
53
Q

Liquid Chromatography:

Function of Injection System

A
  • allows ability to inject sample; would not be able to inject sample into just the inlet due to high pressure area
54
Q

Liquid Chromatography:

Function of Pumps

A

forces solvent thru the inlet; irregular flow can cause issues that alter data

55
Q

Liquid Chromatography:

Function of Column

A

where separation occurs; polarity based separations

56
Q

Liquid Chromatography:

Separations are based on

57
Q

Polarity of long CH chains…..

A

long CH chains are NON-POLAR

58
Q

The larger the chain……

A

the more non-polar the molecule

59
Q

Liquid Chromatography:

Common Columns in HPLC

A

A. Normal Phase

B. Reversed Phase

60
Q

Liquid Chromatography:

Normal Phase

A

Column in HPLC

*polar stationary phase

61
Q

Liquid Chromatography:

Reversed Phase

A

Column in HPLC

*non-polar stationary phase

62
Q

Liquid Chromatography:

Rules for Columns in HPLC

A

like dissolves like
molecules with corresponding polarity to stationary phase will remain on column.
If column is polar, polar molecules will remain on column.

63
Q

Column Types

A

A. Guard Column - short, filled with packing material; purpose is to catch anything that will damage analytical column
B. Analytical Column - where separation occurs

64
Q

What can affect column performance?

A

TEMPERATURE; temperature should be kept constant throughout analysis

65
Q

Liquid Chromatography:

Selection of Detector is based on

A

SAMPLE CONCENTRATION

66
Q

Liquid Chromatography:

Types of Detectors

A

A. Bulk Detectors - measures some property of mobile phase

B. Solute-Property Detectors - measures some property of solutes (analytes)

67
Q

Liquid Chromatography:

Advantage and Disadvantage of IR and Diode Array Detectors

A

+ gives structural info about analyte

- 3D graphs can be resource problematic

68
Q

Liquid Chromatography:

Advatgage and Disadvantage of Electrochemical Detectors

A

+ cheap to install, high sensitivity, quick and easy

- pH dependent which impacts redox potentials

69
Q

Electrophoresis

A

Is NOT Chromatography

70
Q

Is electrophoresis Chromatography?

71
Q

Electrophoresis is NOT Chromatography

72
Q

Types of electrophoresis

A
  1. Capillary electrophoresis
  2. Slab gel electrophoresis
  3. Combinations
73
Q

Slab gel electrophoresis

A

Uses thin flat layer/slab of porous gel containing aqueous buffer solution in its pores; analytes form bands as electricity is applied

74
Q

What field is slab gel electrophoresis used in?

A

BIOLOGY; separation of DNA/proteins

75
Q

Why does pH matter in electrophoresis?

A

Due to supply of ions; lower pH gives larger supply of H+ ions

Instrumental Chemistry (5 decks)

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