Chemical Separations

3 0 3 4 5 1 Chemical Separations Somsak Sirichai Lecturer Semester 1/2002

Code: 303451 Subject: Chemical Separations Credits: 2(2-0-4) Lecture: Chemistry building, room c310 Lecturer: Somsak Sirichai Office: Chemistry building, room c307 Phone: 038 745900 ext.3114 E-mail: sirichai@bucc4.buu.ac.th Office Hours: Tuesday 8-10 am

Course Description: Study chemical separations. Topics: Volatilization, Distillation, Extraction, Ion Exchange, Chromatography and Electroseparation Grading: Midterm exam 40% Final exam 40% Assignments 10% Quizzes 10%

Text: None • Primary References: • Karger, Snyder & Horvath; • An Introduction to Separation Science • Meloan; Chemical Separations Principles, • Techniques, and Experiments • Jönsson; Chromatographic • Theory and Basic Principles • Ahuja; Trace and Ultratrace Analysis • by HPLC • Khaledi; High Performance Capillary • Electrophoresis

What is separation? ‘a process whereby the compounds of interest are removed from the other compounds in the sample that may react similarly and interfere with a quantitative determination’ • important in the preparation of pure • compounds • often complex and may require several • different methods and much time • before the final determinative step

Terms common to chemical separations • cleanup a practical term used to describe the handling of a sample before the measuring step • spiking the addition of a known amount of a standard to a sample so that recoveries can be determined and to calibrate the signal for quantitation

Percent recovery: The amount of a spike that can be recovered when processed through the entire analysis procedure values of 95-105% are desired. if <80%, modify the method.

Separation Methods: separations involving • phase changes • extraction • ion exchange resins • chromatography • electric field • flotation • membranes • miscellaneous techniques

Phase changes sample no vacuum applied vacuum applied solid to gas or vapor solid to liquid liquid to vapor liquid to vapor solid to vapor Lyophilization zone melting volatilization (vacuum, molecular, sublimation) distillation (batch, azeotropic, extractive, steam, immiscible solvents) distillation

Extraction sample liquid solid liquid to liquid Liquid to liquid countercurrent liquid to solid solid to liquid solid to vapor Supercritical fluid (SFE) Batch, Continuous solvent heavier, Continuous solvent lighter SPE Continuous (soxhlet) countercurrent

Ion exchange resins sample Neutral molecules Ionic molecules Ionic or polar molecules Ion exchange Ion chromatography Ligand Exchange Ion retardation Ion exclusion

Chromatography column flat sample Liquid mobile phase gas mobile phase Liquid mobile phase • gas-liquid gravity flow pressure applied • paper • thin layer • displacement • multicolumn • affinity • size exclusion • flash • high performance

Electric fields sample Ions deposited as metal yes no electrodeposition Gel type matrix required yes electrophoresis no • horizontal • immunoelectrophoresis • disc • ion focusing • Capillary zone • electrophoresis • Field flow • fractionation

Volatilization ‘the conversion of all or part of solid or a liquid to a gas’ The gas may be produced by: 1. direct heating 2. applying the principle that strong acids displace weaker acids and strong bases displace weaker bases

Example: • the evolution of CO2(g), weak acid, • from solid CaCO3 by adding HCl, • a strong acid • the removal of NH3(g), a weak base, • from solid (NH4)2SO4 by adding • NaOH

3. by oxidation • burning a sulfide in air to produce • SO2 4. by reduction, or converting the elements to hydrides, such as AsH3, H2Se

Techniques 1. Moisture determination Fig. Microwave oven for drying food

2. Determination of Mercury in the Environment by Volatilization Fig. Apparatus for flameless AAS

Next lecture: Distillation

Chemical Separations