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Instrumental Analysis > Exam One: Introduction and Chromatographic Methods > Flashcards

Exam One: Introduction and Chromatographic Methods Flashcards

1
Q

What is limit of detection or detection limit?

A

The minimum concentration or mass of an analyte that can be detected at a known confidence level

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2
Q

Figure(s) of merit for Detection Limit

A

Cm Cm=Sm-S(bar)m/m

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3
Q

What is k commonly when calculating Sm`

A

3

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4
Q

What is linearity lost at high analyte concentration

A

High analyte concentration can lead to interaction between the analyte and other molecules

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5
Q

LOD

A

Limit of Detection

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6
Q

LOQ

A

Limit of Quantification

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7
Q

LOL

A

Limit of Linear Response

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8
Q

What is selectivity?

A

Th degree at which a method is free of interference from other species int he sample matrix

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9
Q

Figure(s) of merit of selectivity

A

selectivity coefficient kAB=(slope of B)/(slope of A)

Selectivity= (Slope of A x [A])+(slope of B x [B])+ā€¦.

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10
Q

If there is less interference, selectivity is ___

A

better

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11
Q

5 Important Sā€™s of Method Selection

A 
Sensitivity
Selectivity
Speed
Skill
\$\$
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12
Q

Questions to ask when defining a problem when selecting a method

A

What accuracy is required?
How much sample is available?
What is the concentration range of the analyte?
What components of the sample may cause interference?
What are the physical and chemical properties of the sample matrix?
How many samples are to be analyzed?

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13
Q

What kind of relationship generally exists between signal and analyte concentration?

A

Linear

Based on k, which is determined from standards

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14
Q

External Standard Calibration Methods

A

Single-Standard Calibration

Multiple-Standard Calibration

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15
Q

Standard Addition Methods

A

Single Standard Addition

Multiple Standard Addition

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16
Q

Three points when completing single standard calibration

A
  1. Good accuracy is achieved by having same conditions between the unknown and standard
  2. The standard concentration should be as close to the concentration of the unknown as possible
  3. The unknown signal should be near the middle
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17
Q

What conditions should be kept constant between standard and unknown sample

A 
analysis time
pH
solvent
temperature
analyst
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18
Q

How can you get a standard concentration close to an unknown if the unknown concentration is obviously unknown?

A
  1. choose a standard concentration, do analysis
  2. Get concentration of unknown
  3. Prep new standard with concentration closer to unknown
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19
Q

What is single standard calibration method?

A

A single standard is used to determine the concentration of an unknown sample under the same conditions

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20
Q

What is multiple standard calibration method?

A

Multiple standard with difference concentrations are prepared and analyzed. Their signals are used to make a calibration graph, which is then used to determine the unknown sample concentration

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21
Q

When are standard addition methods used?

A

When the sample matrix of a sample is very complex

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22
Q

What is single standard addition?

A

Unknown solution is spiked with known standard and that is used to determine the unknown concentration
Can be done with just spiking or can be done in volumetric flasks

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23
Q

What is multiple standard addition?

A

Using spiked standards to create a calibration graph to determine the concentration of an unknown

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24
Q

Why are internal standards used?

A

To compensate for several types of errors caused by uncontrollable variablesā€¦ coupled with other methods

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25
Q

What is an internal standard

A

substance that is similar in chemical and physical properties of the analyte that is added at a constant amount to help ā€œcorrectā€ possible errors

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26
Q

Why is chromatography used

A

To separate compounds based on physio-chemical property differences

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27
Q

6 separation methods

A 
Filtration
Centrifuging 
Distillation
Precipitation
Solvent Extraction
Chromatography
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28
Q

Filtration separates compounds based on

A

particle size

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29
Q

Centrifuging separates compounds based on

A

Density

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30
Q

Distillation separates compounds based on

A

Vapor pressure (boiling point)

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31
Q

Precipitation separates compounds based on

A

Solubility

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32
Q

Solvent Extraction separates compounds based on

A

Distribution coefficient between organic and aqueous phase

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33
Q

Chromatography separates compounds based on

A

Distribution coefficient between stationary and mobile phase

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34
Q

What is LLE?

A

Liquid-Liquid Extraction- the transfer of a solute from one liquid phase to another (usually aqueous to organic)

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35
Q

What indicates greater separation/ affinity to the organic phase

A

A larger K value

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36
Q

What is K

A

The Partition Coefficient

Solubility of A in organic phase / Solubility of A in aqueous phase

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37
Q

If an analyte is present in two forms in the aqueous and or organic phase separation is based on ___

A

D- distribution coefficient

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38
Q

What is extraction

A

Aqueous to Organic

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39
Q

What is back extraction

A

organic to aqueous

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40
Q

If an analyte is a BASE

A

BELOW the pKa, itā€™s mainly BH+

ABOVE the pKa, itā€™s mainly B

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41
Q

If the analyte is a ACID

A

BELOW the pKA itā€™s mainly HA

ABOVE the pKA itā€™s mainly A-

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42
Q

Types of solvent etxraction

A

single-step solvent extraction
multiple step solvent extraction
continuous solvent extraction
counter-current solvent extraction

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43
Q

Using __ volumes of ____ solvent multiple times makes for good extaction

A

Small volumes of Organic Solvent

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44
Q

What can be analyzed in continuous solvent extraction

A

solids

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45
Q

What canā€™t be used in continuous solvent extraction

A

Volatile compounds

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46
Q

What assumptions are made in countercurrent extraction

A

DA=1
Vaq=Vor
Extraction Efficiency then equals 50%

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47
Q

in chromatography, what does a greater K value indicate

A

the analyte has high affinity for the stationary phase

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48
Q

How is chromatography classified

A

On the physical means by which the stationary and mobile phases come into contact

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49
Q

Chromatography classification

A

Planner Chromatography

Column Chromatography

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50
Q

What is planner chromatography carried out on

A

A flat medium stationary phase

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51
Q

Types of planner chromatography

A 
Paper Chromatography (PC)
Thin Layer Chromatography (TLC)
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52
Q

Figure of merit for planner chromatography

A

Retardation factor (Rf)

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53
Q

How is qualitative analysis done on planner chromatography

A

Comparing Rf values between sample and standards

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54
Q

How is quantitative analysis done by planner chromatography

A

Spot can be scraped from the plate, then analyte can be extracted and measured

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55
Q

In column chromatography what can the mobile phase be

A

liquid or gas

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56
Q

In column chromatography what can the stationary phase be

A

solid or liquid

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57
Q

What is LSC

A

Liquid- Solid Chromatography (liquid mobile phase, solid stationary phase)

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58
Q

What is LLC

A

Liquid- Liquid Chromatography (liquid mobile phase, liquid stationary phase)

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59
Q

What is GSC

A

Gas- Solid Chromatography (gas mobile phase, solid stationary phase)

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60
Q

What is GLC

A

Gas- Liquid Chromatography (Gas mobile phase, liquid stationary phase)

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61
Q

What are chromatographic methods based on

A

Separation mechanisms

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62
Q

5 separation mechanisms

A
  1. Adsorption chromatography
  2. Partition chromatography
  3. Ion-Exchange Chromatography
  4. Molecular Exclusion Chromatography
  5. Affinity Chromatography
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63
Q

What is SFC

A

Supercritical Fluid Chromatography

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64
Q

Stationary phase in adsorption chromatography

A

Solid Particles

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65
Q

Mobile phase in adsorption chromatography

A

Gas or Liquid ( LSC or GSC)

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66
Q

Separation mechanism of adsorption chromatography

A

adsorption of the solute to the stationary phaseā€¦. the more adsorped the solute the slower it will move through the column

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67
Q

Stationary phase in partition chromatography

A

Liquid

thin liquid coat on solid support

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68
Q

Mobile phase in partition chromatography

A

Liquid or Gas (LLC or GLC)

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69
Q

Separation mechanism of partition chromatography

A

partition of solute between the two phases

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70
Q

Stationary phase in Ion-Exchange Chromatography

A

Anion or cation exchnagers (resin)

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71
Q

Mobile phase in Ion- exchange chromatography

A

liquid

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72
Q

Separation mechanism of ion-exchange chromatography

A

ion exchange

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73
Q

Stationary phase in molecular exclusion chromatography

A

molecular sleeve or porous gel

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74
Q

Mobile phase in molecular exclusion chromatography

A

Liquid or Gas

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75
Q

Separation mechanism of molecular exclusion chromatography

A

exclusion of larger solute molecules but not small molecules

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76
Q

Stationary phase in affinity chromatography

A

molecule (antibody) immobilized on support

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77
Q

Mobile phase in affinity chromatography

A

Liquid or gas

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78
Q

Separation mechanism in affinity chromatography

A

specific interactions such as antibody-antigen and chiral separation

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79
Q

Theories of chromatography

A

plate theory

rate theory

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80
Q

What does plate theory say

A

The column is divided into a large number of imaginary ā€œtheoretical plateā€ segments (N)

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81
Q

What is assumed in plate theory

A

the solute equilibrates infinitely fast between mobile phase and stationary phase
There is no kinetic limitation

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82
Q

What is HETP

A

Height Equivalent to a Theoretical Plate (H)

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83
Q

What does HETP depend on

A

column length and number of plaes

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84
Q

What distribution is plate theory assumed to be similar to?

A

counter current solvent extarction

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85
Q

What does rate theory say?

A

The equlibration of the solute between mobile and phase is not infinitely fast and resulting shape depends on elution rate

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86
Q

What does rate theory describe in elution bands and in what terms?

A

In quantitative terms, rate theory describes shapes and breadth of elution bands

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87
Q

What do we focus on?

A

What factors broaden elution bands and how we can qualitatively improve the column efficieny

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88
Q

How is column efficiency estimated

A

van Deemter equation

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89
Q

What is A in the van deemter equation

A

multiple path effects coefficent

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90
Q

What is B in van deemter equation

A

longitudinal diffusion coefficeint

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91
Q

What is Cs in van deemter equation

A

mass transfer coefficient in the stationary phase

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92
Q

What is Cm in van deemter equation

A

mass transfer coefficient in the mobile phase

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93
Q

what us u (mu) in van deemter equation

A

linear velocity of mobile phase in cm/s

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94
Q

When looking at A, what leads to higher chromatographic efficeincy

A

Smaller particles and more uniform packing leads to smaller A which leads to a smaller H and a higher N which leads to high chromatographic efficiency

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95
Q

What does the multiple paths term (A) come from

A

the multiple paths of different lengths traveled by the solute

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96
Q

What does longitudinal diffusion term (B/u) come frome

A

The diffusion parallel to the direction of flowā€¦. diffusion of the solute from the center of the solute zone (high concentration) to the edges of the zone (low concentration)

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97
Q

If the flow rate is low the ( less or more) greater the solute is spead

A

the greater the solute is spread bc it spends more time on the column

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98
Q

In which chromatography is the longitudinal diffusion term (B/u) more effective and why

A

GC more than LC due to a higher DM in gas mobile phase

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99
Q

where does the mass transfer term (Cu) come from

A

The equilibration of the solute between the mobile and stationary phase requiring a finite amount of time

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100
Q

When looking at Cu, what leads to higher chromtographic efficiency

A

A thinner stationary phase film, narrow column, and smaller column packing materials leads to a smaller Cu which leads to higher chromatographic efficiency

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101
Q

In the van Deemter plot, at what point is the optimum flow rate located

A

in the lowest point of plotting H when Contribution to H is a function of flow rate

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102
Q

7 ways to reduce band broadening

A
  1. smaller particles in stationary phase
  2. Narrower column
  3. uniform packing
  4. thinner stationary phase coating
  5. optimized mobile phase flow rate
  6. Fast injection of a SMALL sample size
  7. Controlling temperature (Specific to GC)
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103
Q

How is chromatography used quantitatively

A

Peak area is related to analyte concentration

Calibration standards and addition methods

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104
Q

How is chromatography used qualitatively

A

Retention times to identify compounds between standards and unknowns
spectroscopic methods to ID compounds

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105
Q

How is preparative chromatography used?

A

Using bigger columns to separate and purify a significant quantify of a compound in a mixture

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106
Q

Which chromatography is GSC

A

Gas-Solid Chromatographyā€¦ Adsorption chromatography

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107
Q

Which chromatography is GLC

A

Gas-Liquid chromatographyā€¦ Partition chromatography

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108
Q

What is GSC application limited

A

The semi permanent retention of active or molecules

severe tailing of elution peaks

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109
Q

What are the components of a gas chromatograph?

A 
carrier gas supply
flow controller
syringe
injector port
detector
data processor
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110
Q

What is the purpose of the injector port

A

The injector port flash evaporates the sample to introduces it to the column

111
Q

What is the temperature of the injection port normally

A

normally at least 50 degrees C above the boiling point of the least volatile component of the sample

112
Q

What makes up the injection port

A

septum
carrier gas port
heat source
liner

113
Q

What should the carrier gas in GC be

A

inert
pure
detector compatable
inexpensive

114
Q

What carrier gasses are common in GC

A

Helium
Nitrogen
Hydrogen

115
Q

What pressure range does the inlet fall between

A

10-50 psi

116
Q

In liquid injection, what syringe is used

A

microsyringe

117
Q

What is an average liquid sample size fr ordinary packed column

A

0.1-20 ĀµL

118
Q

Which GC column has split injection?

A

Capillary columns

119
Q

Which GC column has split-less injection?

A

Packed column

120
Q

How hoes a split/split-less injection work?

A
  1. Initially he split/purge is off
  2. Sample travels in
  3. After a specific TIME, the column closes
  4. split is introduced
  5. remaining sample outside the column is evacuated
121
Q

What does the ā€œsplitā€ flow do in a split/split-less injection

A

it bypasses the liner to help maintain column head pressure

122
Q

How does split injection work

A

sample splitter delivers a small specific known fraction of the sample to the column while the remainder is expelled as waste

123
Q

What is split-less flow controlled by

A

time

124
Q

what is split flow controlled by

A

volume

125
Q

In gas injection, what syringe is used

A

gas-tight syringe

126
Q

How does a gas-tight syringe work?

A
  1. uptake of sample.
  2. locking
  3. insertion of syringe
  4. unlocking
  5. injection of sample
127
Q

Pro of gas- tight locking syringe

A

good for qualitative analyss

128
Q

con of gas-tight locking syringe

A

reproducible sample size cannot be obtained due to temperature

129
Q

What are used for gas sample injection

A

Gas sampling valves

130
Q

What do gas sampling valves do

A

the lead to more reproducible sample sizes- help quantitatively

131
Q

Why is head space injection prefered

A

its the fastest and cleanest method or analyzing volatile compounds in complex samples (such as biological samples)

132
Q

Steps to head space injection

A
  1. heat vial containing samples for certain time and specific temperature
  2. Insert syringe through septum and intake space above liquid sample
133
Q

Components of solid phase micro extraction (SPME) appratus

A

Needle
Stainless steel tubing
fused silica fiber
coated phase

134
Q

Steps of SPME

A
  1. inject needle
  2. push plunger (fiber then exposed to liquid or gas sample)
  3. release plunger (fiber extracted upward with analyte on fiber)
  4. Inject into system
135
Q

common modes of SPME

A

direct (liquid exposure)

headspace (gas exposure)

136
Q

Advantages of SPME

A
  1. combination of extraction, pre-concentration, and sample introduction
  2. solvent free
  3. rapid
  4. relatively inexpensive
  5. Easily coupled to GC and LC
  6. Used both in the laboratory and in the field
  7. Used in-vitro and in-vivo
  8. Automated
137
Q

Ways to analyze solid samples by GC

A 
digestion
pyrolysis
Direct Headspace
SPME Headspace
Solid sample capsules
138
Q

How is solid sample digestion compelted

A

Solid sample digested in solvent and then injected as a liquid sample

139
Q

What is pyrolysis

A

Solid sampel is heated in special sample holder at extreme temperatures, thus causing sample so decompose into gaseous state which can be introduced to GC

140
Q

How are solid sample capsules used

A

sample inside capsule, introduced to injection area, once decomposed capsule is broken
CON: glass must be cleaned out

141
Q

Tubing materials in packed column

A 
stainless steel
glass
aluminium
copper
teflon
142
Q

General tubing length and diameter of packed column

A

Length: 1-5 m
diameter: 2-4 m

143
Q

What is included in the ideal solid support material in GSC

A
  1. small, uniform, spherical particles
  2. Good mechanical strength
  3. specific surface of at least 1mg^2/g
  4. inert at elevated temperatures
  5. uniformly coated by the liquid phase
144
Q

Common solid support packing materials

A

naturally occurring diatomaceous earth

Chromosorb P, W, G

145
Q

How does particle size of support effect column efficiency

A

decreasing the diameter of the support particle increases column efficiency

146
Q

At what pressure is it inconventent for GC system to operate

A

> 50 psi

147
Q

As particle size ___, pressure ___

A

as particle size decreases, pressure increases

148
Q

What tubular (capillary) column is used is GSC

A

Stationary solid phase particles (PLOT) porous layer

149
Q

What tubular (capillary) columns are used is GLC

A
  1. Solid support coated with liquid phase (SCOT) support coated
  2. Stationary Liquid phase (WCOT) wall coated
150
Q

What tubing materials are used in tubular (capillary) columns

A 
stainless steel
aluminium
copper
plastic
fused silica
151
Q

General tubing length and diameter of tubular (caillary) column

A

length: 10-100 m
diameter: 0.15-0.32 mm

152
Q

what are the desired properties of the stationary phase in GC

A
  1. less volatility
  2. Thermal stability
  3. Chemically inert
153
Q

Two factors in separation in GC

A

distribution coefficient

volatility

154
Q

What does a greater distribution coefficient (K) mean

A

the analyte has a higher affinity for the stationary phase and moves more slwoly with the carrier gas

155
Q

What happens as compound volatility increases

A

the quicker it will move with the carrier gas.

156
Q

More Volatile= ____ K

A

small

157
Q

less volatile= ___ K

A

larger

158
Q

If compounds are polar you want a ____ column

A

more polar

159
Q

If compounds are nonpolar you want a _____ column

A

less polar

160
Q

What does isothermal mean

A

constant temperature (or temperature ratio)

161
Q

What is temperature programmng

A

inserting ramps and gradients and alteration of temperature through the run

162
Q

What are the properties of an ideal detector

A
  1. adequate sensitivity
  2. good stability and reproducible
  3. linear response to solute
  4. temp between room and 400 degree c
  5. short response time independent of flow rate
  6. high reliability and ease of use
  7. Similar response towards all solutes, and predictable
  8. nondestructive
163
Q

Common GC detectors

A

flame ionization detector (FID)
Thermal Conductivity Detector (TCD)
Electron capture detector (ECD)
Mass Spectrometer Detector (MSD)

164
Q

how does Flame Ionization Detector (FID) work

A

solutes eluted from column, burned in small flame so ions and electrons are produced and carried through the flame
current flowing between anode and cathode is measured and translated into a signal

165
Q

What carrier gasses can be used with FID

A

N2 or Helium

166
Q

What is used if capillary (tubular) is used

A

make-up gas to fill up

167
Q

Advantages of FID

A 
highly sensitive
large linear response range
low noise
rugged and easy to use
little effect on detector response from flow change
general detector to organic species
168
Q

disadvantages of FID

A

destructive

requires additional gas

169
Q

How does Thermal Conductivity detector (TCD) work

A

Thermal conductivity of the gas is measured by electrical resistance by a heated element whetstone bridge

170
Q

Which carrier gases are commonly used in TCD

A

He and H2

171
Q

True or False: Large molecules have larger conductivity

A

FALSE! Large molecules have smaller conductivity

172
Q

_____ in some elements is related to temperature

A

Electrical resistance

173
Q

Advantages of TCD

A

Simple
Larger Linear Response (10^5)
General response to inorganic and organic species
Nondestructive

174
Q

Disadvantages of TCD

A

Relatively low sensitivity
Not very compatible with capillary (tubular) column
When micro-TCD is used, the interal volume is small

175
Q

How does electron- capture detector (ECD) work?

A

Ionization of the carrier gas causes emission of electrons which leads to a constant standing current. When there is an organic analyte with electronegative functional groups present the current decreases leading to the capture of electrons

176
Q

What is ECD good at analyzing with HIGH sensitivity

A

halogens
peroxides
quinones
nitro groups

177
Q

What is ECD insensitive to

A

amines
alcohols
hydrocarbons

178
Q

Advantages of ECD

A

highly sensitive

non-destructive

179
Q

Disadvantages of ECD

A

limited linear response (10^2)

180
Q

What is one of the most powerful detectors for GC

A

Mass Spectrometry (MS)

181
Q

When GC is paired with MS what is it considered

A

hypernated method

182
Q

What does MS separate on

A

mass to charge ratio (m/z)

183
Q

Detectors for qualitative analysis

A

MS
FTIR
NMR

184
Q

Using ____ is common in GC analysis

A

one or more internal standards

185
Q

What kind of detectors can be used in preparative GC

A

destructive detectors

186
Q

What detector is commonly used in GC

A

TCD

187
Q

What is more common: preparative LC or preparative GC

A

preparative LC

188
Q

Advantages of GC analysis

A 
high resolution
High speed
high sensitivity
high accuracy
simple
relatively cheap
189
Q

Limitations of GC

A

Only can be used on volatile compounds
More sample prep is needed for samples to be clean
another instrument is usually needed for identification

190
Q

Common GC samples

A 
Almost all gasses
volatile liquids
solids (usually after digestion)
Organic compounds
some inorganic compounds
Chiral spearation
191
Q

What leads to separation in Liquid chromatography?

A

The affinity of the analyte between the mobile and stationary phase

192
Q

What used to drive separation in early LC

A

gravity flow rates

193
Q

TO increase efficiency what was introduced to LC

A

smaller packed columns with pressurized flow

194
Q

In HPLC what is the diameter range of particles

A

3-10 Āµm

195
Q

in UPLC what is the diameter range of particles

A

< 2.5 Āµm

196
Q

As column particle size ___, LC column efficiency ___

A

as particle size decreases, column efficiency increases

197
Q

In UPLC what can changed and not effect efficieny

A

The flow rate can be increased

198
Q

What causes extracolumn band broadening in LC

A

The difference in flow rates between layers of liquid adjacent to the tube wall and center of the tube when a solute is carried through open tubes in the injection system, detector region and the piping.

199
Q

What are the velocity differences in tubing

A

velocity is less by the wall

in the middle of the tube the velocity is greater

200
Q

How can broadening be minimized

A

The radius of tubing components should be reduced

the length of extra column tubing should be as small as possible

201
Q

Flow rate is LC is ___ than GC

A

less

202
Q

LC separation is ___ than GC

A

slower

203
Q

LC HETPs is ___ than GC

A

smaller

204
Q

LC columns are ____ than GC

A

shorter

205
Q

Why must dust and dissolved gasses be removed from LC solvent

A

dissolved gases can lead to irreproducible flow rates and band broadening
dust can clog the column
Both interfere with the detector performance

206
Q

How can an LC be degasses

A

purging or sparging with an inert gas

207
Q

LC pump requirements

A 
pressure generation up to 6000 psi
pulse free output
0.1 mL/min- 10 mL/min flow rates
0.5% or better relative flow reproducabilty
corrosion resistance
208
Q

Two major LC pumps

A 
displacement pumps (screw driven syringe pum)p
Reciprocating pump
209
Q

Displacement pump function

A

large, syringe like chamber equipped with a plunger activated by a screw-driven mechanism

210
Q

Advantages of displacement pumps

A

pulse free

211
Q

Disadvantages of displacement pumps

A

limited pressure
limited solvent capacity
inconvenience when solvents need to be changed
isocratic only

212
Q

Reciprocating pump function

A

Solvent pumped in a back and forth motion from motor piston with two ball check valves controlling flow of solvent in and out of cylinder

213
Q

Advantages of reciprocating pumps

A 
small internal volume
high output pressure
adaptability to gradient elution
large solvent capacities
consistent flow rates
214
Q

Disadvantages of reciprocating pumps

A

pulsing flow (noisy base line)

215
Q

How can pulsing flow be minimized in reciprocating pumps

A

pulse damper

216
Q

What does the solvent portioning valve do?

A

used to introduce solvents from two or more reservoirs at ratios that can be varied continuously

217
Q

Two types of LC elutions

A

Isocratic

Gradient

218
Q

What is isocratic elution

A

single solvent or solvent mixture at constant composition

219
Q

What is gradient elution

A

two (or more) solvent systems that differing in polarity and are varied in composition during separation

220
Q

what is the most widely used LC injection mehtod

A

Sampling loop

221
Q

What are LC columns normally made of

A

smooth-bored stainless steel tubing
heavy walled glass tubing
polymer tubing such as polyetheretherketone (PEEK)

222
Q

Types of LC columns

A

Guard columns

analytical columns

223
Q

What do guard columns do

A

short column before the analytical column to protect the analytica column from particle matter and compounds that bind irreversibly to the stationary phase

224
Q

An LC column is generally held at this temperature

A

room temperature

225
Q

Constant column temperature leads to

A

better more reproducible chromatograms

226
Q

Types of LC column packing

A

pellicular particles

porous particles

227
Q

What is a pellicular particle

A

contains a porous layer and non porous support

228
Q

Which is better pellicular or porous?

A

porous bc smaller

229
Q

Two basic LC detectors

A

Bulk-property detector

solute- property detector

230
Q

Bulk- property reads

A

mobile phase bulk property such as refractive index, dielectric constant, density

231
Q

Solute-property read

A

solute properties such as UV abs, fluorescence, diffusion current

232
Q

Florescence detector advantage

A

one of the most sensitive LC detectors

233
Q

Because fluorescence detection is so sensitive what is it usually used for?

A

trace analysis

234
Q

Fluorescence detection disadvantages

A

Not all substances naturally fluoresce so their derivatives must be synthesized
Limited concentration range

235
Q

Electrochemical detectors are based on what

A

amperometry (current)
voltammetry (current by applying voltage)
coulometry (charge)
conductometry (conductivity)

236
Q

Refractive index detectors evaluates

A

whena solvent passes from one solvent into another causing a bend in the incident beam

237
Q

Advantages of refractive index detectors

A 
general detector (basically can respond to nearly all solutes)
reliable and uneffected by flow rate
238
Q

disadvantages to refractive index detectors

A

high temperature dependent
not as sensitive as other detectors
Not compatible with gradient

239
Q

Why canā€™t LC be directly connected to MS

A

MS need sample in gaseous state

240
Q

What is usually used to get LC sample into gaseous state for MS

A

Vaporization electrospray

241
Q

A powerful analytical technique for separation, identification and determination is

A

LC-MS

242
Q

LLC is also

A

Partition Chromatography

243
Q

LSC is also

A

Adsorption chromatography

244
Q

Classification of LC

A 
partition chromatography
adsorption chromatography
ion chromatography
size-exclusion chromatography
affinity chromatograpy
chiral chromatography
245
Q

Most widely used type of HPLC is

A

partition

246
Q

How do liquid liquid columns work

A

liquid is held in place by phsyical adsoprtion

247
Q

how do liquid bonded phase columns work?

A

the liquid is attached to the support particles by chemical bonding (usually silica gel)

248
Q

What is normal phase chromatography

A

Polar stationary phase, nonpolar mobile phase

249
Q

what is reverse phase chromatography

A

nonpolar stationary phase, polar mobile phase

250
Q

Types of partion chromatography

A

normal phase

reverse phase

251
Q

In reverse phase which analytes elute first

A

more polar

252
Q

in normal phase which analytes elute first

A

more non polar

253
Q

Unreacted SiOH groups in silica column lead to

A

tailing

254
Q

how is tailing minimized when using SiOH column

A

capping unreacted SiOHā€™s with OH

255
Q

Bond phase packing is reverse when

A

bonded coat is nonpolar

256
Q

bond phase packing is normal when

A

bond coat is poalr

257
Q

nonpolar stationary phases lead to _____

A

rapid mass transfer

258
Q

In partition chromatography have ____ chains that are ____ retentive which permits the use of ____ samples

A

longer chains
more retentive
larger samples

259
Q

In column selection for partition chromatography the ______ forces between the solute mobile phase and stationary phase need to be balanced

A

intermolecular forces

260
Q

Polarity of analytes

A

hydrocarbons

261
Q

Nonpolar molecules have weak ______

A

london forces

262
Q

polar molecules have _____

A

dipole dipole forces

263
Q

The retention factor (k) in LC can be changed with

A

solvent strength

264
Q

the selectivity factor (alpha) in LC can be changed with

A

the chemical nature of the mobile phase

265
Q

What is solvent strength related to

A

Polarity of the solvent

266
Q

What is the polarity index (Pā€™) based on

A

solubility of substance in dioxane, nitromethane, and ethyl alcohol

267
Q

The larger the polarity index number (Pā€™) the ___ polar

A

more polar

268
Q

What is normally used in the solvent of reverse phase separations

A

water and polar organic solvent

269
Q

When two bands overlap ______ must be changed

A

selectivity factor (k)

270
Q

What is widely used to optimize solvent strength

A

Solvent Selectivity Triangle

271
Q

How is qualitative LC used

A

retention times or spectroscopic detectors for ID

272
Q

how is quanitative LC used

A

peak height or area and calibration standards used to determine concentration
internal standards

273
Q

How is preparitive LC used

A

to separate components of a mixture on a large scale

274
Q

Prepatarive LC application

A 
pharmaceticals
Biochemical
food products
industrial chemicals
pollutants
forensic science
clinical chemistry

Instrumental Analysis (2 decks)

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