Ion Chromatography Lecture

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Transcript of 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+ + Baqn- "! (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 L 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 waterprolongs 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]

    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 g/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

    S

    1.20

    0

    (A) ConvenRonal Gradient

    11 10

    9

    8

    7 6

    5 4

    3 2 1

    Minutes 0 5 10 15 20

    0

    S

    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 L

    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

    S

    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

    S

    (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)

    = a+ + Cl-

    = + + Cl-

  • Equivalent Conduc5vi5es

    Anions OH 198

    F 54

    Cl 76

    NO3 71

    Acetate 41

    Benzoate 32

    20585

    Cations 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