Chem. 231 - PowerPoint PPT Presentation

About This Presentation
Title:

Chem. 231

Description:

... Liquid Extraction Practical Aspects solvent choices common to remove compounds from water to go to organic solvent (faster evaporation, better for GC injection) ... – PowerPoint PPT presentation

Number of Views:60
Avg rating:3.0/5.0
Slides: 17
Provided by: rdi89
Learn more at: https://www.csus.edu
Category:

less

Transcript and Presenter's Notes

Title: Chem. 231


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)
  • Im Working on Procedures for Set 2 Labs

3
Announcements II
  • Todays 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
  • Todays 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
  1. 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.
  2. Small quantities of particulates are expected in
    mL samples to be analyzed by HPLC. Suggest a way
    to remove them.
  3. 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
Write a Comment
User Comments (0)
About PowerShow.com