Download - Ion Chromatography Lecture
Ion Chromatography: Separation of Polar and Ionic Compounds
Tracy Benson, Ph.D.
Typical LC System Operation
! Analytes adsorb onto solid surface due to analyte/surface intermolecular forces ! “Good” chromatography occurs from proper selection of adsorbent material and mobile phase ! Changes in conc gradient of mobile phase disturbs the analyte/surface forces and analyte migrates through bed and onto the dectector
Mobile Phase Conc Gradient !
Packed Tubular Column
ADSORPTION PHENOMENON
Adsorption is " The attraction of molecules onto a
particle surface " Driven by a concentration gradient " Interacted by molecular forces
(short range and long range) between the adsorbate and adsorbent
" An exothermic process
CA,b
Porous Pellet
Internal
Diffusion
CA,s CA
IC Solid Surface Chemistry
Retention is based on the affinity of different ions for the site and on a number of other solution parameters (pH, ionic strength, counterion type, etc.).
Ion - Pair Chemistry
Ion: particle formed when a neutral atom or group of atoms gains or loses one or more electrons. An atom that loses an electron forms a positively charged ion (cation); an atom that gains an electron forms a negatively charged ion (anion).
In Solution
Aaqm+ + Baq
n- "! (nAm+ · mBn-)org
• Ion pairs are oppositely charged ions held together by coulombic attractions, non-covalently, and behave as a single unit
On a Solid Surface
Am+ + Bm
- "! Abm
Am+ + Ym
- + Ls "! SYLs
Bm- + Zm
+ + Ls " ! BZLs
Am+ + Bm
- + Ls " ! ABLs
• Ion pair formation in mobile phase
• Adsorption of solute ion onto ligand
• Adsorption of counter-ion onto ligand
• Adsorption of ion pair onto ligand
EQUILIBRIUM DRIVEN BUT KINETICALLY CONTROLLED
Eluent Bo*le (CO3/HCO3) Pump
Guard Column
Analy5cal Column
Suppressor
Regen In (H2SO4)
Conduc5vity Cell
Chromatograph So?ware Ion
Exchange Separa5on
Post-‐Suppression Conduc5vity
Data Handling and Instrument Control
Sample Injec5on
Regen Out (H2SO4)
Conventional Ion Chromatographic System Anion Analysis
Pump Module
Pump Module
Specification Highlights • Flow
– Range = 0.001 to 10 mL/min – Accuracy = 0.1% at 1 mL/min – Precision = 0.1% at 1 mL/min
• Gradient reproducibility = +/- 0.5% • Gradient accuracy = 0.5% • Delay volume < 400 µL • Pressure range = 50 to 5000 psi • Pressure ripple typically < 1.0%
DP Dual Pump
Eluent Generator Module
Eluent Generator Module
• Same device supports single or dual chemistry
– OH, MSA, CO3,
• CO3:HCO3 eluents • Supports CR-TC technology
• Supports CRD technology • Supports EPM
(Electrolytic pH Modifier)
• Slide-out tray
• Optical leak sensor • Status bar for basic operation
• Same footprint for single or dual
EG Eluent Generator
RFIC System Advantages • Provides reliable and convenient eluent sources and eliminate the conven5onal eluent prepara5on errors
• Simplifies and performs both isocra5c and gradient ion chromatographic separa5ons
• “Just add water”—prolongs pump seals, reduces maintenance
• Be*er gradient performance • Lower cost of ownership
Eluent Generator Module
Advantages of Using Eluent Generators
• Use only deionized water • On-line high purity eluent
generation • Insure reproducible eluent
concentration— minimal gradient delay
• Reduce pump maintenance • Gradient eluent
programming now practical
MSA Eluent Generation for Cation Analysis
MSA– Electrolyte Reservoir
EluGen® MSA Cartridge
Anion-‐Exchange Connector MSA
Genera5on Chamber
Vent
Pump
H2O
Pt Anode
Pt Cathode (2 H2O + 2e– 2OH– + H2)
[MSA] α Current
Flow Rate [ – ]
[ + ]
MSA + O2 MSA
O2
Degas
Unit
(H2O 2H+ + 1/2O2 + 2e–) MSA = Methanesulfonic Acid
CR-‐CTC Ca5on Trap
MSA–
Improved Performance for Trace Anion Analysis Using a KOH Eluent Generator
Column: IonPac® AG11, AS11, 2 mm Eluent: (A) NaOH
(B) KOH (EGC-KOH cartridge) 0.5 mM to 2.5 min, to 5.0 mM at 6 min, to 26 mM at 20 min
Flow Rate: 0.5 mL/min Inj. Volume: 1.0 mL Suppressor: ASRS®, external water mode Detection: Suppressed conductivity
Peaks: 1. Fluoride 0.37 µg/L (ppb) 2. Acetate 1.0 3. Formate 0.93 4. Chloride 0.44 5. Nitrite 0.27 6. Bromide 1.0 7. Nitrate 0.33 8. Carbonate – 9. Sulfate 0.64 10. Oxalate 0.39 11. Phosphate 1.1
µS
1.20
0
(A) ConvenRonal Gradient
11 10
9
8
7 6
5 4
3 2 1
Minutes 0 5 10 15 20
0
µS
1.20
(B) EG Gradient
11 10
9
8
1 2 3 4
567
Column: IonPac® AG11, AS11, 4 mm
Eluent: 0.5 to 25 mmol/L KOH
From: EG40 or 0.1 mol/L KOH
Flow Rate: 2 mL/min
Injec5on: 25 µL
Detec5on: Conduc5vity a?er ASRS®
suppression, recycle mode
Peaks: 1. Fluoride 0.2 mg/L 2. Chloride 0.3 3. Nitrate 1.0 4. Sulfate 1.5 5. Phosphate 1.5
µS
0 2 4 6 8 10 0 1 2 3 4
(A) Gradient EG40
5 4 3
2 1
Minutes
0 2 4 6 8 10 0
1
2
3
4
µS
(B) ConvenRonal Gradient
1 2 3
4
5
Detector Module
• Three dis5nct sec5ons for separa5on, detec5on and automa5on
• Separate temperature control for columns and detectors
Automa5on
Detec5on
Separa5on 10 to 70 °C
15 to 40 °C
Dual Thermal Compartments
Sec5on DC Module
Detector Module
Role of Suppression in Conductivity Detection
• Neutralize eluent and reduce background conductance to a low or negligible level
• Increase sensitivity by converting the analyte ions to highly conductive form
• Removes sample counter ions (cations or anions)
λ = λΝa+ + λCl-
⇓
λ = λΗ+ + λCl-
Equivalent Conduc5vi5es
Anions λº OH– 198
F– 54
Cl– 76
NO3– 71
Acetate– 41
Benzoate– 32
20585
Cations λº H+ 350
Li + 39
Na+ 50
K+ 74
CH3 NH3+ 58
N(CH3 CH2)4+ 33
Range of IC Autosamplers
5 mL
AS40 AS AS-HV
10 mL
250 mL