Four basic types of column chromatography

1
Four basic types of column chromatography where
mobile phase is a liquid
Partition Chromatography Bonded-Phase Liquid-Liq
uid Adsorption Chromatography Liquid-Solid Ion-
Exchange Chromatography Exclusion (or Gel)
Chromatography
2
General Advantages of LC Sensitivity Quantitativ
e Separation of nonvolatile and/or thermally
fragile compounds Wide applicability
3
Applications of LC
Source Skoog, Holler, and Nieman, Principles of
Instrumental Analysis, 5th edition, Saunders
College Publishing.
4
LC Separation Mechanisms
Source Rubinson and Rubinson, Contemporary
Instrumental Analysis, Prentice Hall Publishing.
5
Effect of Particle Size of Packing Material and
Flow Rate on Plate Height in LC
Source Skoog, Holler, and Nieman, Principles of
Instrumental Analysis, 5th edition, Saunders
College Publishing.
6
Comparison of Reversed-Phase Media of Different
Chain Length
Peak ID 1 Uracil 2 Phenol 3 Acetophenone 4
Nitrobenzene 5 Methyl Benzoate 6 Toluene
Source Rubinson and Rubinson, Contemporary
Instrumental Analysis, Prentice Hall Publishing.
7
General Schematic of LC
Source Skoog, Holler, and Nieman, Principles of
Instrumental Analysis, 5th edition, Saunders
College Publishing.
8
Source Rubinson and Rubinson, Contemporary
Instrumental Analysis, Prentice Hall Publishing.
9
Effect of Gradient Elution
Source Skoog, Holler, and Nieman, Principles of
Instrumental Analysis, 5th edition, Saunders
College Publishing.
10
LC Pumping Systems General Requirements Generate
pressures up to 6000 psi Pulse-free output Flow
rates from 0.1-10 mL/min 0.5 or better flow
control reproducibility Corrosion resistant
11

• LC Pumping Systems
• Reciprocating Pumps
• Pulsed flow must be damped
• Small internal volume
• High output pressures
• Adaptable for gradient elution
• Constant flow rates independent of column
  back-pressure or solvent viscosity
• Displacement Pumps
• Flow independent of viscosity and back-pressure
• Limited solvent capacity
• Inconvenient to change solvents
• Pneumatic Pumps
• Inexpensive
• Pulse free
• Limited capacity and pressure
• Dependent on solvent viscosity and backpressure

12
LC Columns 10-30 cm long x 4-10 mm internal
diameter Packing usually 5 or 10 mm
diameter Microcolumns 1-4.6 mm internal
diameter with 3-5 mm packings
13

• LC Packing Materials
• Pellicular
• Spherical, nonporous, glass or polymer beads
• 30-40-mm diameter
• Thin porous layer of silica, alumina, or
  ion-exchange resin deposited on surface
• Porous
• Most common
• 3-10-mm diameter
• Silica (most common), alumina, or ion-exchange
  resin
• Thin organic film bonded to surface

14

• LC Detectors
• General
• Similar characteristics to GC detectors, except
  temperature range
• Minimal internal volume to avoid peak broadening
• Types
• Respond to bulk property of mobile phase,
  modulated by presence of solute
• Respond to specific property of solute
• General response to solute following
  volatilization (removal) of mobile phase

15
Source Skoog, Holler, and Nieman, Principles of
Instrumental Analysis, 5th edition, Saunders
College Publishing.
16
Source Rubinson and Rubinson, Contemporary
Instrumental Analysis, Prentice Hall Publishing.
17
Common LC Detectors UV one of most
common Fluorescence much greater sensitivity
than UV Refractive Index widely used general
detector Electrochemical based on amperometry,
polarography, coulometry, or conductometry. High
sensitivity, wide applicability range Mass
Spectrometry becoming increasingly used since
interfacing problems figured out. Expensive.
18

• LC Mobile Phase Qualities
• High purity
• Reasonable cost (and disposal)
• Boiling point 20-50 C above column temperature
• Low viscosity
• Low reactivity
• Immiscibile with stationary phase
• Compatible with detector
• Safety limited flammability and toxicity

19

• LC Mobile Phase Selection
• k of 2-5 for two or three component mixture
• k of 0.5-20 for multicomponent mixture
• Match analyte polarity to stationary phase
  polarity
• Mobile phase of different polarity
• Normal Phase
• nonpolar solvent, polar stationary phase
• least polar component elutes first
• increasing mobile phase polarity decreases
  elution time
• Reversed Phase
• polar solvent (water, MeOH, ACN), nonpolar
  stationary phase
• most polar component elutes first
• increasing mobile phase polarity increases
  elution time
• most widely used

20
Relationship between polarity and elution times
for normal-phase and reversed-phase LC.
Source Skoog, Holler, and Nieman, Principles of
Instrumental Analysis, 5th edition, Saunders
College Publishing.
21
Reversed-Phase Ion-Pair Chromatography Mobile
phase aqueous buffer containing organic solvent
and counter-ion of opposite charge of
analyte. Ion-pair forms neutral species soluble
in nonaqueous solvent.
Source Skoog, Holler, and Nieman, Principles of
Instrumental Analysis, 5th edition, Saunders
College Publishing.
22

• Ion-Exchange Processes
• Based on exchange equilibria between ions in
  solution and
• ions of like charge on surface of essentially
  insoluble, high-
• molecular weight solid.
• Most common cation exchangers
• The strong acid sulfonic acids, SO3-H
• The weak acid carboxylic acids, COOH
• Most common anion exchangers
• The strong base ternary amines, -N(CH3)3OH-
• The weak base primary amines, -NH3OH

23
Mechanism of Ion Chromatography
Source Rubinson and Rubinson, Contemporary
Instrumental Analysis, Prentice Hall Publishing.
24

• IC Detection
• Typically done with conductivity detection
• Sensitive
• Universal for charged species
• Key to column regeneration and avoid high eluent
  conductance
• are suppressor columns. Suppressor column packed
  with
• secondary ion-exchange resin to convert solvent
  ions to
• a molecular species.

25

• Size-Exclusion Chromatography
• Packing contains network of uniform pores into
  which solute
• and solvent can diffuse.
• Solute is trapped in pore until carried away by
  solvent.
• Residence time in pore related to effective
  molecular size of solute.
• Molecules larger than average pore size are
  excluded from pore, not retained.
• Molecular diameter significantly smaller than
  pore can penetrate throughout pore, so
• elute last.
• Fractionation of intermediate-sized molecules.
  Some shape dependence.

26
Calibration Curve for SEC
Exclusion limit defines MW beyond which
no retention occurs.
Beyond permeation limit all molecules elute in
one band since they can all freely
(completely) penetrate the pores.
Source Skoog, Holler, and Nieman, Principles of
Instrumental Analysis, 5th edition, Saunders
College Publishing.
27

• Types of SEC
• Gel Filtration Chromatography
• Aqueous solvent
• Hydrophilic Packings
• Gel Permeation Chromatography
• Nonpolar Organic Solvents
• Hydrophobic Packings

28

• Advantages of SEC
• Short, well-defined separation times
• Narrow bands, good sensitivity
• No sample loss since solutes do not interact with
  stationary phase
• Absence of column deactivation
• Disadvantages of SEC
• Limited number of bands accommodated since short
  time scale
• Not applicable to similar-sized molecules, like
  isomers

29
Comparison of LC and GC Both Efficient, highly
selective, widely applicable Only requires small
sample May be nondestructive of sample May have
quantitative analysis Advantages Favorable to
LC Can separate nonvolatile or thermal unstable
samples Generally applicable to inorganic
ions Advantages Favorable to GC Simple, less
expensive equipment Rapid More efficient,
higher resolution Easily interfaced with mass
spectrometry