Presentation on theme: "Chapter 26 Other Methods. Ion-Exchange Chromatography The mechanism of separation will be the exchange of ions from the column to the solution. Water."— Presentation transcript:
Ion-Exchange Chromatography The mechanism of separation will be the exchange of ions from the column to the solution. Water softening – exchange Na ions for Ca and Mg. Water deionization – exchange H ions for cations and OH ions for anions. Leaving water. Can be larger scale. The support is modified to allow for the ion exchange equilibrium. Can be natural materials or synthetic
Which ions have greater affinity Higher charge, higher polarizability and decreased hydrated radius. Pu 4+ >>La 3+ >Ce 3+ >Pr 3+ >Eu 3+> Y 3+> Sc 3+> Al 3+ >> Ba 2+> Pb 2+ > Sr 2+ > Ca 2+ > Ni 2+ > Cd 2+ > Cu 2+ > Co 2+ >Zn 2+ > Mg 2+ > UO 2+ >> Ti + > Ag + > Rb + > K + >NH 4 + > Na + > H + > Li + Reconditioning by having higher concentration of the less tightly held ion.
Donnan Equilibrium Concentration of ions outside the resin will be higher than the inside concentration. Cations will be excluded from the inside of an anion exchanger. (Has same charge as resin site) Ion Exclusion Chromatography Non charged species can migrate in but not ions.
Ion Exchange Types Resins Gels Inorganic exchangers (Zeolites) Use a gradient to remove stronger bound ions.
Applications Preconcentration Pass much water over a resin and then elute with a high concentration of acid. Cation exchange to trap cations Chelex -100 to trap transition metals. Water deionization. Cation exchange from cation removal. Anion exchange for anion removal. Water softening
Ion Chromatography HPLC ion exchange. Detection is an issue. Ions do not absorb uv/vis light. Conduction is used to detect ions but the mobile phase will have high electrolyte like KOH We use ion suppression
Ion Pair Chromatography Separate ions on a reverse phase column. (Ammonium ions) Add a surfactant to the mobile phase. Such as sodium octane sulfonate.
Molecular Exclusion Chromatography Separation Based on Size Only Gel Filtration Gel Permeation Large molecules can not get into the internal diameter so the elute more quickly.
V t = V o + V i + V g + V ec V t is the total volume of the system. If we ignore volume outside the column then we have V t ’ = V o + V i + V g Vo is the elution volume for large molecules Vo + Vi is the elution volume for small molecules
Elution V e = V o + KV i K ave assumes that V g is very small and I suggest you not use it. K will fall between 0 and 1 unless there is another mechanism in the column.
Affinity Chromatography Stationary phase is made so that it has a very specific interaction that can cause binding to a specific substrate. Elution is carried out by disrupting this interaction. (Change pH is an example)
Capillary Electrophoresis Motive force is no longer pressure but electrical migration. Cations migrate to the cathode Anions migrate to the anode High electric field place across a capillary column.
Mobility Ion of charge q will accelerate in the potential field until the frictional force counter balances it and it travels at constant speed. u ep = q/f*E = ep E ep is electrophoretic mobility Relates speed and charge Directly related to charge, indirectly related to size
Stokes Equation F = 6 r is the measure of solution viscosity
This allows ions to move, what about neutrals. Electroosmosis