1. Five consideration are involved in selecting the two liquid phases for extraction
1- two phases must be immiscible
2- phases should be saturated with each other before use to prevent change in volume
3- the two phases must separate from each other quickly, forming no emulsion
4- the recovery of the analyte from the extractant (or raffinate)
5- the rate of the system to reach equilibrium

2. multi-step extraction can be done by either of two ways
a) original sample (raffinate) is extracted several times and extractant solutions are combined together for further investigation
b) extractant from the first step is put into another spearatory funnel and both funnel are reextracted
this is an example of countercurrent extraction
results in a distribution of sample in many funnels
this produce zone broadening similar to effect in chromatography

4. Conclusion
Analyte is now distributed into five funnels, whereas it begin in one funnel, broadening has been indeed occurred
The distribution of the analyte in nonsymmetrical
The largest amount of the analyte is in the second funnel
Multi-step LLE is quite similar to LLC
Each separatory funnel could be called plate
This model represents the plate theory
Plate theory has been abandoned in favor of the rate theory for chromatography

5. Plate theory adopt chromatography in terms of distillation or extraction
Rate theory as van Deemter and modified equation
Continuous LLE
Volume of extractant is held constant and recycled, stepwise process
Two types of apparatus depending on which phase is heavier

7. Liquid-Liquid Membrane Extraction (LLME)
There is a non porous membrane
Different from dialysis
Used for two miscible solvents or liquid phases
Samples are separated by diffusion through the membrane
Mechanism is independent on membrane porosity or analyte molecular size
Depend on the nature of the membrane material
Similar to Liquid-Liquid Chromatography LLC
Liquid-Solid Extraction
The classic liquid-solid extraction (LSE) method is a continuous method using soxhlet extractor
Solid sample is placed in a thimble as solvent is passed over

8. Assisted Liquid-Solid Extraction
Increasing temperature and/or pressure of the extracting liquid are the assisting factors
Enough increase of these parameters, the solvent reaches its critical point
Then method is called supercritical fluid extraction (SFE)
Or supercritical fluid chromatography (SFC)
Subcritical fluid extraction as high pressure but below supercritical point is possible
This method is called pressurized fluid extraction (PFE)

9. e.g. hot water, heated water changes its polarity, so temperature is a very important parameter
at very high temperature, water becomes very effective for extracting nonpolar organics such as polychlorinated biphenyls (PCBs)
mainly for PCBs extraction form soil
named as accelerated solvent extraction (ASE)
hplc columns can be used
hplc pumps are used in pumping hot water and pressurizing it

10. Supercritical Fluid Extraction
Previously SFE had been used ony for commercial extractions such as decaffeination of coffee
In SFE and SFC, solvent used has been exclusively carbon dioxide
Carbon dioxide is not very polar, so modifiers such as methanol, isopropanol, or acetonitrile have been added
Now, it is used in determining fats in food replacing old soxhlet
Extraction of polynuclear aromatics (PNAs)
Benign due to no use of organic solvents
Speed and ease of use

12. Supercritical Fluid Extraction or Chromatography
Mobile phase
SFC is a hybrid of GC and LC.
SFC has the best characteristics of both GC and LC
To understand that, lets check the following:

18. Applications
Supercritical fluid chromatography is best suited to separate materials that are not volatile enough or thermally stable enough for GC and are not easily handled by HPLC due to problems like suitable detectors.
Thus high molecular-weight materials that do not absorb UV and cannot be used with UV-detectors in HPLC are commonly run by SFC with FID detection.
One example is shown in Figure 6.8; oligomers in a polymeric detergent mixture are separated using pressure programming.
Coal tar is a mixture that needs high efficiency of OT columns and approaches upper temperature limit of GC.
Figure 6.9 compares separation of coal tar components by GC & SFC.
As expected, GC is performed with programmed temperature and FC with programmed density.

19. Separations of polar solutes using packed columns and has pointed out the practical advantages of packed-column SFC in supporting combinatorial chemistry.
Many chiral columns used in HPLC have been found to work well for SFC, some even better than for HPLC.
Preparative separations are also possible and most instruments can accommodate the larger columns required.
Supercritical fluid extraction is another application of the use of supercritical fluids.

23. Summary
Just as supercritical fluids have properties intermediate between gases and liquids, so SFC is intermediate between GC and HPLC.
The technique has a great potential for separation scineces, but only time will tell.

24. Dialysis
The two phases used in dialysis are liquids (as LLE) but
They are separated by semi-permeable or porous membrane
The two phases need not be immiscible
Porosity of membrane is chosen so that only some solutes can pass through it
This selective permeation is the basis of separation
Small molecules go through membrane and large ones are retained
This is similar to size-exclusion chromatography SEC
But different where molecules diffuse in and out of the pores of the stationary phase
Its main use is in concentrating, desalting, and purifying such materials as proteins, hormones, and enzymes

25. Solid-Phase Extraction
Solid-phase extraction is a clean up and preconcentration process by
Sorbing impurities on a solid phase contained in a column or a tube
Analyte is eluted from the tube Or
Analyte is sorbed on the solid
Rest of the sample matrix is eluted
Then analyte is re-eluted using a good solvent

26. In both cases
Impurities are separated from analyte
Sample is liquid or solid dissolved in a solution
Disposable cartridges are marketed
The process has similarities to liquid chromatography especially for
affinity-chromatography High-performanceliquid chromatography (AC-HPLC)
ion-exchange high-performance liquid chromatography (IE-HPLC)
reversed-phase high performance liquid chromatography (RP-HPLC)

29. Solid-Phase Microextraction (SPME)
SPME is not just a miniaturization of SPE
Involves usage of solid phase sorbing analytes as SPE
But those phases are immersed into analyte solution