Unit 5, Instrumental Methods of Analysis, B Pharmacy 7th Sem PDF

Page 1 of 21 Carewell Pharma - A Family of Learning Subscribe Us on YouTube TOPIC: ION EXCHANGE CHROMATOGRAPH1Y Syllabus Contains: ntroduction, classification, ion exchange resins, properties, mechanism...

Page 1 of 21 Carewell Pharma - A Family of Learning Subscribe Us on YouTube TOPIC: ION EXCHANGE CHROMATOGRAPH1Y Syllabus Contains: ntroduction, classification, ion exchange resins, properties, mechanism a of ion exchange process, factors affecting ion exchange, methodology and applications rm INTRODUCTION Ton exchange chromatography can be defined as a reversible process in which ions of similar charged are exchanged between solid and liquid. The solid is known as an ion exchanger. It is an adsorption chromatography, a useful and popular method for separation of a mixture of similar charged substances into pure components. t is also known as cation- ha anion exchange chromatography. 1ON EXCHANGERS These are the substances capable of exchange of ions with the electrolytic solution. These are porous solid, swelling in water without dissolving in it. The most common properties of all ion exchanger are as follows: lP a) They are almost insoluble in water and organic solvents. b) They are complex in nature (Polymerie in nature) c) They have active or counter ions that will exchange reversibly with other ions in a surrounding solution without any substantial change in the material. l TYPE OFION EXCHANGERS There are three classes of ion exchangers, these includes we 1. Resins 2. Gels 3. Inorganic exchangers 1. RESINS re Resins are amorphous particles of organic materials which are composed of polystyrene and divinely benzene. Polystyrene contains sites for exchangeable functional groups. Divinyl benzene acts as a cross linking agents and offers adequate strength i.e., mechanical stability. Ca CH2 CHz *cHa Styrene Divinyl benzene www.carewellpharma.in (free notes) This pdf is not owned by Carewell Pharma, Source - IPT Salipur  Page 2 of 21 Carewell Pharma - A Family of Learning Subscribe Us on YouTube CLASSIFICATION OF RESINS I. According to their chemical nature, they can be classified as: 4 a a) Strong cation exchange resin: These types of resins are usetul for the chromatographic separation of amino acids, rare earths and other substances that contains sulphonic acid rm groups as the ionisable groups. b) Weak cation exchange resin: These resins are based on polymers of methacrylic acid and possess carboxyl groups. c) Strong anion exchange resin: These resins with positively charged quaternary ammonium groups attached to cross linked polystyrene frame work belong to this class. Trimethyl ha ammonium groups are used for this resin. d) Weak anion exchange resin: The tertiary amine resins and polyamine resins having a mixture of primary, secondary and tertiary amine groups on the polystyrene net work are well known. tothe source,theyare classified as lP II. According 1. Natural source: These are of two types a) Cation: E.g: Zeolytes, clay etc b) Anion: E.g: Dolomite 2. Synthetic source: These are of two types l a) norganic resins b) Organic resins : Most widely used we III. Structural types of ion exchange resins 1. Pellicular type with ion exchange film: The particle size is ranging from 30 - 40 mm with 1 2 mm film thickness. These have very low ion exchange capacity to separate the ions. Their ion exchange efficiency is 0.01 -0.1 meq/g of ion exchange capacity. re 2. Porous resin coated with exchanger beads: The particle size ranges from 5 - 10 m. They are totally porous in nature and highly efficient. Their exchange capacities are from 0.5 - 2 meq/g of ion exchange resin. 3. Macro reticular resin bead: A reticular network of the resin is seen superficially on the resin Ca beads. They are not highly efficient and have very low ion exchange capacitie 4. Surface sulfonated and thermostatically bonded with anion: It is less efficient and also has less exchangeable capacity. www.carewellpharma.in (free notes) This pdf is not owned by Carewell Pharma, Source - IPT Salipur  Page 3 of 21 Carewell Pharma - A Family of Learning Subscribe Us on YouTube lon exchange filn Anion resin beads macropores a rm Actve apacity Inert core (1) (2) (3) (4) (Fig-1: Structures of structural types of ion exchange resin) ha PROPERTIES OF1ON EXCHANGE RESIN It must be chemically stable. It should be insoluble in common solvents. The resin must be sufficiently hydrophilic. should have a sufficient degree of cross linking. lP It The swollen resin must be denser than water. It must contain sufficient numbers of ion exchange groups. 2. GELS lon exchange gels are used for the separation of large molecules like proteins, nucleic acids. l These are much softer than polystyrene resins we Dextron and its relatives are called as gels Cellouse and dextran ion exchangers which are polymers of sugar glucose possess large pore sizes and lower charge densities. 3. INORGANIC EXCHANGERS The combinations of hydrous oxides of highly charged ions, with one oxide more acidic than re the other have been found to have ion exchanging properties. The amorphous precipitates have higher exchange capacities than the crystalline compounds because of the greater surface area of the former type of compounds. E.g.: Titanium Arsenite has been used to absorb alkaloids, Hydrous antimony peroxide has Ca been used to study exchange equilibrium of K and Rb 10ns with hydrogen and other 1ons |1]. MECHANISM OF ION EXCHANGE PROCESS The mechanism of separation is by reversible exchange of ions between the ions present in the solution and those present in the ion exchange resin. Ton exchange separations are mainly carried out in columns packed with an ion exchanger. A www.carewellpharma.in (free notes) This pdf is not owned by Carewell Pharma, Source - IPT Salipur  Page 4 of 21 Carewell Pharma - A Family of Learning Subscribe Us on YouTube There are two types of ion exchanger, as follows: a) Cationic exchangers: a It possesses negatively charged groups and these will attract positively charged groups. These exchangers are also called acidic ion exchange materials since their negative rm charges result from the proteolysis of acidic groups. Commonly used cation exchange resins are S-resin, sulfate derivatives; and CM resins, carboxylate derived ions (Resin -CH2-SOs Resin -0-CH2-C ha (S-Cation exchanger) (CM-Cation exchanger) Anionic exchangers: It has positively charged groups, which will attract negatively charged molecules. This exchanger is termed as basic 1on exchange materials since their positive charges lP generally result from the association of protons with basic groups. Based upon the affinity of ions towards the matrix the ions like cation and anion are separated. The ions that have less affinity towards matrices will elute first and the ions that have more affinity towards matrices it will elute later ,[4-6]. Commonly used anion exchange resins are Q-resin, a Quaternary amine; and DEAE l resin, Di Ethyl Amino Ethane. we CHs CH2-CHs Resn N-CH3 Resin CH2CH2-NH H CH2-CH3 (Q-Anion exchanger) DEAE-Anion exchanger) re The actual ion exchange mechanism is thought to be composed of five distinct steps: 1. Diffusion of the ion to the exchanger surface. This occurs very quickly in homogeneous solutions. 2. Diffusion of the ion through the matrix to the exchanger site. This is dependent upon the Ca degree of cross linkage of the exchanger and the concentration of the solution. 3. Exchange of ions at the exchange site occurs. This occur instantaneously in an equilibrium process as follows: Resin SO3H + Na" Resins SO;Na + H Resin - N(CH3)3OH +C Resin N(CH3):CI + OH www.carewellpharma.in (free notes) This pdf is not owned by Carewell Pharma, Source - IPT Salipur  Page 5 of 21 Carewell Pharma - A Family of Learning Subscribe Us on YouTube 4. Diffusion of the exchanged ion through the exchanger to the surface 5. Selective desorption by the eluent and diffusion of the molecule into the external solution a takes places [7-9] FACTORS AFFECTING 1ON EXCHANGE rm The factor affecting ion exchange are as follows: a) Nature ofion exchange resin Cross linking & swelling is important factor which depends on the proportion of cross linking agent (Divinyl benzene & polystyrene). When more cross linking agent is present they are more rigid, but swells less. When swelling is less , separation of ions of different ha sizes is difficult as they nan not pass through the pores present & it becomes selective to ions of different sizes. When less crosslinking agent is present, they are less rigid but swells more. When swelling is more separation will not be efficient as exchange of functional groups does not take place due to wide pore hence optimum quantity of cross linking agent should be lP added to the polymeric ion exchange resins for the separation to be effective. b) Nature of exchanging ions: i) Valency of ions: At low concentration & at ordinary temperature extent of exchange increase with increase in valency. Nat < Ca*< AB+ < Th$+ l ii) Size of ions: For similar charged ions, exchange increases with decrease in the size of we hydrated ion. Li < H* < Nat