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Chem. 231 – 2/4 Lecture

Chem. 231 – 2/4 Lecture. Announcements I. Homework Set 1 is due 2/6 New Set will be available 2/6 (hopefully) which will be due 2 weeks later Quiz 1 on 2/11 on homework and topics covered in class (setting up files, data transfer and processing, and simple extraction covered today)

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Chem. 231 – 2/4 Lecture

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  1. Chem. 231 – 2/4 Lecture

  2. Announcements I • Homework Set 1 is due 2/6 • New Set will be available 2/6 (hopefully) which will be due 2 weeks later • Quiz 1 on 2/11 on homework and topics covered in class (setting up files, data transfer and processing, and simple extraction covered today) • Website Update • Writing guidelines • List of Books and Journals • Example Quiz (from 2007) • I’m Working on Procedures for Set 2 Labs

  3. Announcements II • Today’s Topics: • Simple Extractions (emphasis on equipment, procedures and tests and on ones we can do) • Solids into liquids • Gases into liquids • Gases into solids • Solids from liquids or gases (filtration) • Liquids into liquids • Solvent removal

  4. Announcements III • Lab Today • Set 1 Labs are ready (but work was not planned in syllabus) • Should plan on making a multi-component standard for qualitative analysis • Today’s work should be focused on learning to use instruments

  5. Simple Extractions • Purposes (repeat from Chem 230) • Isolate compound of interest (only very simple samples) • Trap and Concentrate Analyte(s) • Remove interferences • Split sample into classes

  6. Simple Extractions • Solid into Liquid • Best to choose solvent with good solubility for analytes (e.g. similar Kow and functional groups as solvent) • Sample prep (finely ground powder will lead to better extraction) • Agitation (shakers, ultrasound bath) • Soxhlet Extractors Soxhlet Extractor – show example to condensor Extraction Thimble round bottom flask with solvent 1) Round bottom flask is heated, solvent evaporates 2) Solvent condenses and fills extraction thimble 3) Once reaching loop, solvent siphons out and back to round bottom flask

  7. Simple ExtractionsGases to Liquids • May be used for trapping carbonyls in derivatization lab • Equipment (repeat from Chem 230) • Bubblers, mist chambers, denuders • Best Conditions (larger KH constants) • lower temperatures • solvent polarity (although less volatile solvents needed) • pH (if trapping acids or bases)

  8. Simple ExtractionsGases to Solids heating wire trapping flow • Traditional method to trap gases (e.g. volatile hydrocarbons) using cartridge • Can be combined with purging to transfer volatile compounds from water to solid • Desorption flow direction is usually reversed • Most commonly used with thermal desorption/injection into GC • Best Conditions • Keep cartridge cool during trapping • Can choose trapping material for selectivity or efficiency desorbing flow

  9. Simple ExtractionsGases to Solids - SPME SPME is used most with GC analysis More on procedure later since can also be used for liquid samples and with liquid removal Will use in extraction lab (headspace for standards and samples) Advantages: simple (no solvent for gases) efficient Disadvantages not exhaustive harder to make quantitative (must maintain similar conditions)

  10. Simple ExtractionsFiltration/Centrifugation Purpose to trap precipitated analytes/solutes (solids from liquids) to trap aerosol particles (from gases) to remove solids (needed before HPLC/GC analysis) Centrifugation (only for liquids) Best if isolating solids Filtration Large quantities (use side arm flasks) Small quantities (use syringe filters)

  11. Simple ExtractionsLiquid – Liquid Extraction • Equipment (show examples) • traditional: separatory funnel (show example) • smaller scale: conical vials (cone shape needed to remove most of one phase) + syringes • Separation Basis – polarity partitioning (remember likes dissolves likes rule) • Liquid Phases • Two phases must be immiscible (form two distinct layers) • Most common with water + organic • Also possible with polar + non polar organic (methanol + hexane), but few organic solvent sets are immiscible • Lower layer is denser (water in hexane water but chloroform in water chloroform)

  12. Simple ExtractionsLiquid – Liquid Extraction • Practical Aspects • solvent choices • common to remove compounds from water to go to organic solvent (faster evaporation, better for GC injection) • organic solvent (non-polar solvent for least polar analytes, moderately polar for somewhat polar analytes) • emulsions make some liquid – liquid extractions problematic • selectivity also is important (e.g. use of toluene to selectively retain aromatics over alkanes) • modifiers • can modify water by adjusting pH (ionized compounds stay in water) • salts can also be added to help in transferring organics to organic phase

  13. Simple ExtractionsSolvent Reduction/Removal • Purposes • Switch solvents (e.g. methanol to CDCl3 for NMR) • Concentrate sample • Remove volatiles • Nitrogen drying • used with volatile solvents/volatile solutes • often for solvent reduction (not complete removal) • Rotory Evaporators • Typically used with solvents more volatile than water • Has both pressure and temperature controls (usually manual) • Bumping can occur to vacuum bleed (control), traps and vacuum pump condensor rotation round bottom flask water bath

  14. Simple Extractions Solvent Reduction/Removal • Freeze Drying • More commonly used with water • Better for many biological samples (susceptible to thermal decomposition) • Procedure • Sample is frozen • Sample in container is connected to a vacuum (with low T water trap between sample and vacuum) • Low pressure causes water to stay in ice form • Difficult with small samples (can melt before connection is complete)

  15. Some Questions A chemist is interested in extracting furanyl compounds from charred wood. Chunks of charred wood are placed in methanol and shaken for 30 minutes. Repeated extractions show the efficiency is not great. List two ways to improve extraction. Small quantities of particulates are expected in mL samples to be analyzed by HPLC. Suggest a way to remove them. Describe how a chromatogram produced by Chemstation (Agilent 1100 system) can be transferred to an Excel file. In this method, will how it was integrated be retained?

  16. Simple ExtractionGas to Solid: SPME Procedure Will be used in SPME lab The needle pierces the septum to a sample (sample can be gas, liquid, or headspace) The sheath is removed allowing trapping of analytes on fiber Stirring helps the transfer The sheath goes back and the needle is withdrawn The needle pierces the septum to a GC, the sheath is withdrawn and the analyte is desorbed by the heated GC injector Fiber For lab work, it is critical to have the sheath on when piercing septum GC Inlet

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