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03 - Extraction

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03 - Extraction Powered By Docstoc
					ExtractionS
              Liquid




           Extraction
Super-
                        Solid
critical
                        phase
 fluid
   Solute Distribution Equilibrium
• In LLE, most common: 2 immiscible L

            Saq D Sorg                 
                                         S 
                                          org
                                KD
                                          S 
                                           aq


• Preferable condition:
  – One solute KD<1, while another KD>1

                     
          % E  1  q n  100
                                   n
                        Vaq       
          %E  1                   100
                    K DVorg  Vaq 
                                  
 So, how many time of extraction?
• One big batch of solvent, of several small
  batches?
                  D=1

  1 L of water     5g    1 L organic solvent  50% recovered
   containing
 10 g of solute    5g    1 L aqueous        50% left in raffinate
        D= 1
                                              Ratio of 1:2

 1 L of water            3.3333 g     500 mL organic solvent  recovered
  containing
10 g of solute           6.6666 g     1000 mL aqueous  raffinate




1 L of water
                         2.2222 g    500 mL organic solvent
 containing
6.6666 g of
   solute
                         4.4444 g    1000 mL aqueous

                                                        For most analysis,
                                                        recovery must at least
 Total recovery: 2.2222 g + 3.3333 g = 5.5555 g         99.9% in order to be
          Smaller batches are better!                   quantitatively reliable!
Now, calculate if extraction been done
      using 4 portion of solvent
Consider solute of ML

• If no other equilibrium exist, CML = [ML], D =
  KD
• But certain solute forms more than 1 sp. &
  involves more than 1 equilibrium within one
  or both phase
  – Eg: involving ionizing complex
  – Mn+ + Ln- D ML
• E.g.: involving ionizing complex
                   Mn+ + Ln- D ML
                  (metal) (ligand) (complex)

• So, equilibrium expression:


   K ML 
            ML               CML.aq  M aq  Laq
          M aq Laq
  K ML 
           ML                                M aq    ML
         M aq Laq                                    K ML Laq

If no equilibrium exist within organic phase,

      MLorg
D
   MLaq  M aq                                              The distribution of
                                                                complex not only
                                                                depends on KD but
         MLorg             K D K ML Laq                     also conc. of ligand
D                         
             M aq  K ML Laq  1
   MLaq              
             K ML Laq                                  Also applicable if other
                                                         types of equilibrium exist
                                                           • e.g.: pH, masking agent
                          Solvent
• Essential part of extraction especially LLE is
  the solvent itself!
• Criteria of solvent:
  – Solubility distribution coefficient, KD
  – Solubility of extractant in phase 1 solvent
     • Refer Jadual 4.1
                    Solvent Extraction
                  Liquid
                extraction

                                 Liquid                In cleaning process:
Solid sample                                            continuous, so that
                                sample
                                                       all analyte can be
                                                       extracted out
    Batch S-L          Cross-         Counter-
      ext.           current LLE     current LLE

   Continuous
                             Batch          Batch
     S-L ext.


                        Continuous        Continuous
        Solid sample extraction
• Easiest way, immerse in solvent
  that can dissolve analyte w/out
  using high T
  – Usually not
    thermolabile
  – E.g.: Soxhlet
            Liquid sample extraction
• Known as LLE
• Based on distribution of analyte between 2
  immiscible solvents

 Phase 1             Phase 2
 - Contain analyte   - Extractant
 - Usually aq        - Usually aq
Solutions?
Solid Phase Extraction
Solid Phase Microextraction
 Stir Bar Sorptive Extraction
                                    Vial
                                    Sample
                         Magnetic   solution
                         stir bar
                                    Stir bar
Coating material Glass              Magnetic
                                    stirrer
                                                           70% recovery
                       SPME               SBSE




Figure 2.7: Theoretical recovery for solutes as function of KO/W for SBSE (10 mL
       sample, 50 μL PDMS) and SPME (10 mL sample, 0.5 μL PDMS).
Supercritical Fluid Extraction

				
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posted:10/11/2011
language:English
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