Over view

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Over view

• What is ion chromatography?
• Why this techniqu is useful?

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Ion chromatography- definition of terms

• Ion exchange-
• involves exchange of one type of
  ion in a compound
• for another.
• exchange of K, Ca 2 and Fe 3
  with Na in water.
• Ion exchange chromatography-
• involves sequential exchange and
  elution of ions
• from a column. Retention is based
  on attraction
• between solute ions and charge
  boundary on the
• stationary phase.
• Ion chromatography-
• same as ion exchange
  chromatography except that
• it includes a provision for
  removing and detecting
• (electrochemically) the ions in
  the eluting agent.

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Definitions
Ion Chromatography is a liquid chromatographic
technique, with which ionic and strongly polar
species can be separated and detected.
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Type of Ion Chromatography

• Ion Exchange Chromatography
• Ion Exclusion Chromatography
• Ion Pair (ion Retardation) Chromatography
• Alternative Technique

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Advantages of Ion Chromatography
Speed - Complete anion and cation profiles in
about 10 minutes Sensitivity - Analyses in the
lowest ppb-range without pre-concentration -
Analyses in the lowest ppt-range after
pre-concentration - Limiting factor
contaminations by ubiquitous ions such as
chloride and sodium Selectivity - Huge
variety of stationary phases - Specific
detection (suppression, UV, fluorescence, MS, ICP)
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Advantages of Ion Chromatography (cont.)
Simultaneity - Simultaneous analysis of many
sample components (Contrary AAS,
Photometry, Titration, etc.) -
Limiting factor extreme concentration
differences between the sample components
(Example Semiconductor grade chemicals) Costs -
Contract laboratories offer anion and cation
profiles with IC for US 15 - Price drop with
system hardware as in all hightech
areas Robustness - pH and solvent compatible
separators allow a variety of applications -
Analysis of complex matrices such as waste water,
foods, body fluids, etc.
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History

• Aristol experiment(384-322 B.C)
• Philasopheres(1561-1626)
• Natural Zeolites in soil(1850)
• Teoritical research(1876)
• First commerical purposes(1896)
• First synthetic compound(1903)
• First truly successful use(1905)
• Synthesise of organic compound(1935)
• Use of small particles(1946)

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Advantages of organic polymer

• High capasity
• Low sensitivity to temperature and PH
• Provided a back bone for various tyoe
• of exchange groups

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Making a cation Exchange Resin
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Ion exchangers

• Three main classes
• Resins
• (polystyrene resins used for molecules
  with Mr lt500)
• Gels
• (cellulose and dextran used for large
  molecules
• like proteins and nucleic acids)
• Inorganic exchangers
• (hydrous oxides of Zr,Ti,Sn and W used
  for separations
• under harsh conditions (high temperature,
  high radiation
• levels, strongly basic solutions and
  powerful oxidizing
• agents)

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Resin beads
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Exchange functional groups

• Cation Exchangers Anion
  Exchangers
• strong -SO3H
  -N(CH3)3,Cl
• -COOH
  -N(CH3)2CH2OH,Cl
• -CH2 SO3H
• -OH
  -NR2H,Cl
• -SH
  -NRH2,Cl
• weak -HPO2 H
  -NH3,Cl

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A Lable of a Resin

• Sulfonic acid,Na
• Mesh20-50
• 8X
• 4.4 meq/g

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Lable information

• Cross-linking Porosity Moisture
  holding capasity
• 2X High
  85-95
• 4X IM.High
  58-65
• 8X Medium
  44-48
• 12X IM.Low
  40-44
• 16X Low
  37-41

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Structure of Sodalite
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Different types of ion exchange resins

• Polymeric porous particles
• (formed from co-polymerisation of
  styrene-divinylbenzene)
• Pellicular and superficially porous particles
• (formed by coating the ion exchange resin on to
  an
• impervious inert core)
• Totally microporous particles with bonded phases

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Classification of ion exchangers

• Classified
• by the charge on the stationary phase as
• anion exchangers-contains positively charged
  groups
• cation exchangers-contains negatively charged
  groups
• as strongly or weakly acidic or basic
• strongly acidic cation exchangers eg RSO3-
• weakly acidic cation exchangers e.g RCO2-
• strongly basic anion exchangers e.g RNR3
• weakly basic anion exchangers e.g RNR2H

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Example
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Selectivity and retention in ion exchange analysis

• These are affected by the size and charge of the
  solvated sample ion.
• Ion exchangers bind strongly to ions with higher
  charges, lower hydrated radii and higher
  polarizability
• Thus order of selectivity is generally
• Pu 4 ?gtgt La 3 gt Ce 3 gt Pr 3 gt Eu 3 gt Y 3
  gt Sc 3 gt Al 3 gtgt Ba 2 gt Pb 2 gt Sr 2 gt Ca
  2 gt Ni 2 gt Cd 2 gt Cu 2 gt Co 2 gt Zn 2
  gt Mg 2 gt UO2 2 gtgt Ti gt Ag gt Rb gt K gt
  NH4 gt Na gt H gt Li

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Retention Determining Parameters (II)
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Retention Determining Parameters (III)
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Selectivity and retention in ion exchange analysis

• The pH of the mobile phase
• The total concentration and type of ionic species
  in the mobile phase
• Addition of organic solvents to the eluant
• The column temperature

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PH of the mobile phase
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Concentration
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Ion Exchange Kinetics

• There are 5 main steps
• 1)agiated
• 2)passage from the outer solution to the bead
• 3)actual exchange
• 4)migration
• 5)exit to the mobile phase

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Donnan equilibrium

• Refers to the equilibrium between ions in
  solution and ions inside the resin. This is the
  basis of ion-exclusion chromatography.
• For an anion-exchange resin, R, in its Cl- form,
  immersed in a solution of KCl
• Ki Cl-i KoCl-o
  --------(1)
• where i and o denote inside and
  outside the resin respectively.
• Inside the resin,
• Ri Ki Cl-i
  -------(2)
• Since from charge balance
• Ko Cl-o
• considerations, equation (1) becomes
• Ki(Ri Ki ) Ko2
  ------------(3)
• Thus
• Ko gt Ki

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Porous particlate andMicro porous membrane
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FASTCHROM standard module and end plates
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Applications of Ion exchange

• In water purification.
• Deionised water is made by passing water through
  a anion-exchange in it OH- form and a
  cation-exchange resin in its H form.
• Thus Cu(NO3)2 can be removed from water by the
  following reactions
• Cu 2 H ion exchange 2H? H2O
• 2NO3- OH- ion exchange 2OH-
• In water softeners
• Cation exchange is used to remove Ca 2 and Mg 2
  from hard water
• In converting one salt to another.
• In pre-concentrating trace components of a
  mixture
• Cation-exchange resins are used to concentrate
  trace metals..

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Ion chromatography

• This is the high performance version of IEC.
• Common examples are
• Suppressed cation chromatography and
• Suppressed anion chromatography
• The key feature of IC is the presence of
• an anion or cation separator column
• a membrane ion suppressor
• a detector
• The separator column separates the solutes while
  the suppressor replaces unwanted ions in the
  eluent with nonionic species

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The Instrument

• COST 40,000

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Operation Principles
Eluent from the gradient pump enters the
rheodyne injection valve port inside the
enclosure From the injection valve,
eluent and sample flow through the guard
column, the analytical column, the suppressor
and finally through the detector cell.
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The IC Schematic

• Pump, Column (800), Guard (200)
• Air Pump for sample injection

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Schematic of a Loop Injector
Injection valve
Sample loop
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Ion Chrom. for analysis of rain

• If inject sample with nitrate ion, nitrate
  replaced bicarbonate, but more bicarbonate moves
  in and kicks off nitrate
• Process continues as moves through column (ions
  go on and off beads)
• Sulfate in sample as well. Harder for
  bicarbonate to knock off.
• Conclude Nitrate exits before Sulfate

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Ion Chrom.

• See Peaks (Rain has nitrate, sulfate, some
  chloride)

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IC Report
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What are Suppressors in Ion Chromatography Good
For ?

• To reduce background conductance caused by the
  eluent and, therefore, to reduce noise
• To convert analyte ions into a more strongly
  conducting form
• To improve sensitivity
• To improve the dynamic range
• To be able to use high capacity separators with
  higher ionic strength eluents
• To be able to use gradient elution techniques in
  combination with conductivity detection

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Advantages of Continuous Suppression

• Improved stability of the system
• Very little drift and low noise
• High suppression capacity
• No external regeneremts necessary
• Simple operation no extra programming
• Simplified hardware no extra valves
• Flexible method development

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Single ion chromatography

• Used when
• Exchange capacity of the separator column is low
• Dilute eluents are employed
• Ion suppression is unnecessary
• Examples of resins with low exchange capacities
  are
• Na or K salts of benzoic, p-hydroxybenzoate
  and phthalate.

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Gradient elution

• Ionic gradient elution is similar to temperature
  or solvent gradient.
• Changing the ionic strength or pH of the eluent
  improves separation considerably.
• For example, a mixture of Na, Li, Ca 2 and Fe
  3 can be separated by using elution with
  increasing concentrations of HCl.
• The order of elution being Li , Na gt Ca 2 gt
  Fe 3

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Gradiant separation of a synthetic mixture of 36
anions in 24 min.
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Gradiant Elution
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Detector in Chromatography

• Electrochemical Detector
  - Conductivity Detector
  
  - Amperometric Detector
  
  - Pulsed Amperometric Detector
• Spectroscopy Detector
  - UV/Vis
  
  - Fluorescence
  
  - PDA

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Detection

• Conductivity detectors are the most popular
• In addition, when analytes have
• Ultraviolet absorbance
• Fluorescence or
• Radioactivity other forms of detection are
  employed.
• Many ion exchange methods require the presence of
  complexing agents (EDTA, citrate) and various
  electrolytes to achieve good resolution.
  Therefore, conductivity detectors can not be used
  without modifying the process (eg by suppressing
  some of the ions).
• Indirect detection is possible when benzoate or
  phthalate eluents are used.

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The Altec model 1000 electrochemical regenerated
ion suppression systemand Sample preconcentrator
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IC conductivity Detectors

• Detectors Based on ability of water to conduct
  electricity
• Suppressor membrane destroys bicarbonate only
• Conductivity of ions can be measured to very low
  levels

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Electrochemical palsed amperometric cell assembly
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Column size PH range
capasity Particle size Type of
packing mm
µm
Vydac 250x4.6 2-6 100
20 spherical
silica with IC

bonded quaternary


groups


INtraction 50x3.2
0-14 100 10
Neutral hydrophilic Ion100


narymacroporous

resin with covalentlyi
bond

ammonium groups
Hamilton 150x4.1 1-13 200
10 Highly crosslinked
-X100

covalentlyi bond


ammonium groups Bio-GelTSX 50x4.6
1-12 30 10
Polymetacrilat gel coated


with Anion PW

quaternaryammonium


groups Waters ic 50X4.6
1-12 30 10
Same Pak A

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One chromatogram with 5 detector
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Ion-pair chromatography

• Uses reverse phase HPLC in place of an ion
  exchange column
• A hydrophobic ion pairing reagent containing a
  counter-ion, with an opposite charge to the ion
  to be determined is added to the mobile phase.
• This counter ion combines with the ions of the
  eluent to form ion pairs in the stationary phase.
• For example, Fe(phen)3 2 forms Fe(phen)3 2
  anion ion pair.
• Retention of analytes depend on
• Alkyl chain length of the counter-ion
• Concentration of the ion pairing reagent
• Solvent strength
• Combination with ion suppressor

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Example for separation with regeneration
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• THE END