Chromatographic separations Separation of species prior to detection Description Migration rates Efficiency Applications

Description Different components of chromatography column support stationary phase Different degree of reaction Chemicals separate into bands Characteristics of phase exploited to maximize separation mobile phase Gas, liquid, supercritical fluid

Description Different methods available column chromatography paper chromatography gas-liquid chromatography thin layer chromatography (TLC) high-pressure liquid chromatography HPLC Also called high-performance liquid chromatography

Column Chromatography chromatogram concentration versus elution time strongly retained species elutes last elution order analyte is diluted during elution dispersion zone broadening proportional to elution time

Column Chromatography Separations enhanced by varying experimental conditions adjust migration rates for A and B increase band separation adjust zone broadening decrease band spread

Retention Time Time for analyte to reach detector Retention time (tR) Ideal tracer Dead time (tM) Migration rate v=L/ tR L=column length For mobile phase u=L/ tM

Retention time Relationship between retention time and distribution constant V (volume) c (concentration) M (mobile phase) S (stationary phase)

Capacity Factor Retention rates on column k'A can be used to evaluate separation Optimal from 2-10 Poor at 1 Slow >20 Selectivity factor (a) Larger a means better separations

Broadening Individual molecule undergoes "random walk" Many thousands of adsorption/desorption processes Average time for each step with some variations Gaussian peak like random errors Breadth of band increases down column because more time Efficient separations have minimal broadening

Theoretical plates Column efficiency increases with number of plates N=L/H N= number of plates, L = column length, H= plate height Assume equilibrium occurs at each plate Movement down column modeled

Theoretical Plates Plate number can be found experimentally Other factors that impact efficiency Mobile Phase Velocity Higher mobile phase velocity less time on column less zone broadening H = A + B/ u + Cu = A + B/ u + (CS + CM)u A multipath term B longitudinal diffusion term C mass transfer term

Efficiency Multipath Molecules move through different paths Larger difference in path lengths for larger particles diffusion allows particles to switch between paths quickly and reduces variation in transit time Diffusion term Diffusion from zone (front and tail) Proportional to mobile phase diffusion coefficient Inversely proportional to flow rate high flow, less time for diffusion

Efficiency

Ion Exchange Resins General resin information Functional Groups Synthesis Types Structure Resin Data Kinetics Thermodynamics Distribution Radiation effects Ion Specific Resins

Ion Exchange Resins Resins Organic or inorganic polymer used to exchange cations or anions from a solution phase General Structure Polymer backbone not involved in bonding Functional group for complexing anion or cation

Resins Properties Capacity Amount of exchangeable ions per unit quantity of material Proton exchange capacity (PEC) Selectivity Cation or anion exchange Cations are positive ions Anions are negative ions Some selectivities within group Distribution of metal ion can vary with solution

Resins Exchange proceeds on an equivalent basis Charge of the exchange ion must be neutralized Z=3 must bind with 3 proton exchanging groups Organic Exchange Resins Backbone Cross linked polymer chain Divinylbenzene, polystyrene Cross linking limits swelling, restricts cavity size

Organic Resins Functional group Functionalize benzene Sulfonated to produce cation exchanger Chlorinated to produce anion exchanger

Resin Synthesis HO OH HO OH NaOH, H O HCOH resorcinol n OH OH OH OH 2 HCOH resorcinol n OH OH OH OH NaOH, H O 2 HCOH catechol n a a a

Resins Structure Randomness in crosslinking produces disordered structure Range of distances between sites Environments Near organic backbone or mainly interacting with solution Sorption based resins Organic with long carbon chains (XAD resins) Sorbs organics from aqueous solutions Can be used to make functionalized exchangers

Organic Resin groups Linkage group Cation exchange Anion exchange Chloride

Resin Structure

Inorganic Resins More formalized structures Silicates (SiO4) Alumina (AlO4) Both tetrahedral Can be combined (Ca,Na)(Si4Al2O12).6H2O Aluminosilicates zeolite, montmorillonites Cation exchangers Can be synthesized Zirconium, Tin- phosphate

Zeolite

Inorganic Ion Exchanger Easy to synthesis Metal salt with phosphate Precipitate forms Grind and sieve Zr can be replaced by other tetravalent metals Sn, Th, U

Kinetics Diffusion controlled Film diffusion On surface of resin Particle diffusion Movement into resin Rate is generally fast Increase in crosslinking decrease rate Theoretical plates used to estimate reactions Swelling Solvation increases exchange Greater swelling decreases selectivity

Selectivity Distribution Coefficient D=Ion per mass dry resin/Ion per volume The stability constants for metal ions can be found Based on molality (equivalents/kg solute) Ratio (neutralized equivalents) Equilibrium constants related to selectivity constants Thermodynamic concentration based upon amount of sites available Constants can be evaluated for resins Need to determine site concentration

Ion Selective Resins Selected extraction of radionuclides Cs for waste reduction Am and Cm from lanthanides Reprocessing Transmutation Separation based on differences in radii and ligand interaction size and ligand Prefer solid-liquid extraction Metal ion used as template

Characteristics of Resins Ability to construct specific metal ion selectivity Use metal ion as template Ease of Synthesis High degree of metal ion complexation Flexibility of applications Different functional groups Phenol Catechol Resorcinol 8-Hydroxyquinoline

Resorcinol Formaldehyde Resin Catechol Formaldehyde Resin OH Resorcinol Formaldehyde Resin Catechol Formaldehyde Resin N m x x = 0, Phenol-8-Hydroxyquinoline Formaldehyde Resin x = 1, Catechol-8-Hydroxyquinoline Formaldehyde Resin x = 1, Resorcinol-8-Hydroxyquinoline Formaldehyde Resin

Experimental Distribution studies With H+ and Na+ forms 0.05 g resin 10 mL of 0.005-.1 M metal ion Metal concentration determined by ICP-AES or radiochemically Distribution coefficient Ci = initial concentration Cf = final solution concentration V= solution volume (mL) m = resin mass (g)

Distribution Coefficients for Group 1 elements. All metal ions as hydroxides at 0.02 M, 5 mL solution, 25 mg resin, mixing time 5 hours D (mL/g (dry) Selectivity Resin Li Na K Rb Cs Cs/Na Cs/K PF 10.5 0.01 8.0 13.0 79.8 7980 10 RF 93.9 59.4 71.9 85.2 229.5 3.9 3.2 CF 128.2 66.7 68.5 77.5 112.8 1.7 1.6

Cesium Column Studies with RF pH 14, Na, Cs, K, Al, V, As

Eu-La Separation

Solvent Extraction Based on separating aqueous phase from organic phase Used in many separations U, Zr, Hf, Th, Lanthanides, Ta, Nb, Co, Ni Can be a multistage separation Can vary aqueous phase, organic phase, ligands Uncomplexed metal ions are not soluble in organic phase Metals complexed by organics can be extracted into organic phase Considered as liquid ion exchangers

Extraction Reaction Phases are mixed Ligand in organic phase complexes metal ion in aqueous phase Conditions can select specific metal ions oxidation state ionic radius stability with extracting ligands Phase are separated Metal ion removed from organic phase Evaporation Back Extraction

(CH3CH2)2O Diethyl ether

Reactions Tributyl Phosphate (TBP) (C4H9O)3P=O Resonance of double bond between P and O UO22+(aq) + 2NO3-(aq) + 2TBP(org) <-->UO2(NO3)2.2TBP(org) Consider Pu4+ Thenoyltrifluoroacetone (TTA) Keto Enol Hydrate

Problems with solvent extraction TTA General Reaction Mz+(aq) + zHTTA(org) <-->M(TTA)z(org) + H+(aq) What is the equilibrium constant? Problems with solvent extraction Waste Degradation of ligands Ternary phase formation Solubility