Adsorption (PY4030/PY5130) PDF

Adsorption PY4030/PY5130 Dr Gianpiero Calabrese Room MB1037, [email protected] School of Pharmacy and Chemistry Learning Outcomes To discriminate between adsorption and absorption. To understand adsorption phenomena (what, why and how?). To be able to identify various medical and pharma...

Adsorption PY4030/PY5130 Dr Gianpiero Calabrese Room MB1037, [email protected] School of Pharmacy and Chemistry Learning Outcomes To discriminate between adsorption and absorption. To understand adsorption phenomena (what, why and how?). To be able to identify various medical and pharmaceutical applications of adsorption. To understand factors controlling adsorption through Langmuir adsorption isotherms. Key definitions Absorption: a fluid permeates or is dissolved by a liquid or solid. Adsorption: adhesion of molecules of gas, liquid, or dissolved solids to a surface. Adsorbate Adsorbent Absorption It is the process through which a substance, originally present in one phase or compartment, is diffused into another compartment (typically a liquid). In Pharmacy, absorption is a pharmacokinetic parameter to describes the movement of drug (rate and extent) into bloodstream. It cannot be reversed! Adsorption It describes the tendency for materials (gas, molecules, ions) to locate at a solid surface in a concentration different than that found in the surrounding (bulk) medium. It is reversible (e.g. heating or changing pH) van der Waals forces are weak: so adsorption is reversible! Watch this video for more examples www.youtube.com/watch?v=tvmV_fIa52k Enterosgel Intestinal Adsorbent 225g 1. Oral intestinal adsorbent for diahorrea. 2. 70% Polymethylsiloxane & 30% Purified water. 3. Porous molecule, which works like a trap for bugs and harmful substances, adhering them through its pores. What brings about adsorptions? Adsorption occurs through weak physical rather than chemical alteration: • Van der Waals forces (non-ionic interactions between polar molecules) • H-bonding • Hydrophobic interactions. Other common adsorbents Silica gel - hard, granular, porous material made by precipitation from sodium silicate (Na2SiO3) solutions treated with an acid. Activated alumina - aluminium oxide (Al2O3) activated at high temperature and used primarily for moisture adsorption. Zeolites – porous spherical alluminosilicates (Al2SiO5) Not for internal use Requirements Adsorbents usually are spherical pellets or rods with diameters between 0.5 - 10 mm. High thermal stability and small pore diameters increase exposed surface area for adsorption. Must also have distinct reactive functional groups (carbonyl, amide, hydroxyl, oxides) or hydrophobic (apolar) groups. Classes Oxygen-containing compounds – typically hydrophilic & polar, e.g. Silica gel. Carbon-based compounds – typically hydrophobic & non-polar, e.g. activated carbon, graphite. Polymer-based compounds - are polar or non-polar functional groups in a porous polymer matrix, e.g. polyvinyl chloride (PVC). Adsorption in Pharmacy Reactions with 2 reactants LH mechanism ER mechanism Langmuir Adsorption Isotherm Langmuir Adsorption Isotherm Langmuir Adsorption Isotherm References And Further Reading • Aulton's Pharmaceutics: The Design and Manufacture of Medicines. • Winfield A. and Richards R. Pharmaceutical practice. • Martin's physical pharmacy and pharmaceutical sciences. 6th ed., editor, Patrick J. Sinko. 2011