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Ion Chromatography. Ion Exchange Separation is facilitated by formation of ionic bonds between charged samples and charged column packings.

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Presentation on theme: "Ion Chromatography. Ion Exchange Separation is facilitated by formation of ionic bonds between charged samples and charged column packings."— Presentation transcript:

1 Ion Chromatography

2 Ion Exchange Separation is facilitated by formation of ionic bonds between charged samples and charged column packings

3 Ions Ions can be characterised as: organic, inorganic, anion or cation and mono or polyvalent

4 Chemical Considerations Anion or Cation exchanger

5 Strong vs Weak Exchange Materials Strong exchangers stay ionised as pH varies between 2 and 12. Weak exchangers can lose ionisation as a function of pH.

6 Factors Affecting Ion Exchange Retention

7 Control of Ion exchange by pH Changing the pH can eliminate the charge of the column if the column is weak, or eliminate the charge on the ion if ion is weak. Either way, the retention is reduced. Strong ion - Weak Exchanger

8 Exchange Capacity of Anion Exchanges Exchange Capacity: Number of functional groups per unit weight of resin

9 Exchange Capacity of Anion Exchanges pH has no effect on capacity of strong cation exchanges. Weak cation exchanges change dramatically with pH.

10 Control of Ion exchange by Ionic Strength Sample ZoneBGE Zone A - + As the concentration of the eluent ion increases, retention tends to decrease

11 Control of Ion exchange by Eluent Ion cations anions

12 The equilibrium constant At pH=pKa 50% is ionised and 50% is neutral At pH=pKa +1 90% is ionised At pH=pKa -1 10% is ionised

13 Common Acidic Buffers

14 Common Basic Buffers

15 Anion exchange Separation development Sample: Weak or strong? Column: weak or strong? pH ?

16 Anion exchange Separation development

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21 Cation exchange method development Column: Strong Cation Exchange Sample: Weak bases pH: acidic (all compounds are ionised)

22 Effect of ionic strength

23 Effect of pH Compare this separation at pH=4.55 and 0.05 in the previous example. Increasing pH reduced retention.

24 Effect of Temperature Increasing temperature increases efficiency, decreases k’, and may affect . This is due to improved mass transfer.

25 UV Detection UV detection. Direct detectionUV transparent eluent eg, bromide, nitrate, nitrite, Indirect Detection UV absorbing electrolyte. Anions are detected via “vacancies” in background absorbance universal detection usually used when other modes of detection are unavailable. Very specific

26 Concentration Changes

27 UV Detection

28 Direct UV Detection

29 Indirect UV Detection

30 Indirect UV detection

31 Conductivity Detection Ohms law V= IR conductance, G = Non - Suppressed direct - low conducting eluent - high conducting analytes indirect- high conducting eluents - low conducting analytes

32 Ion Conductances

33 Conductivity Detection

34 Direct Conductivity Detection

35 Waters Ion Analysis Method Eluent: Borate/Gluconate Column: IC Pak HR Flow Rate: 1ml/min Injection 50 ul Detection: Direct Conductivity Background: 274 uS

36 Indirect Conductivity

37 Conductivity Detection Suppressed

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40 Membrane Suppressor

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42 Autosuppression

43 Eluent Generation KOH

44 Eluent Generation MSA

45 Why the difference?

46 Separation of Cations

47 Practical Sessions (1)Analysis of Inorganic Anions by direct conductivity.


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