Supercritical fluids have properties between gases and liquids. They can dissolve materials like liquids and diffuse through solids like gases. Carbon dioxide is commonly used as a supercritical fluid in supercritical fluid extraction (SFE) and supercritical fluid chromatography (SFC). In SFE, the supercritical fluid is used to extract analytes from samples, while in SFC it is used as the mobile phase to separate analytes chromatographically. Both techniques take advantage of how the density and solvent strength of the supercritical fluid can be tuned by adjusting the pressure and temperature.

1. SUPERCRITICAL FLUID
SUPERCRITICAL FLUID EXTRACTION (SFE)
SUPERCRITICAL FLUID
CHROMATOGRAPHY (SFC)
19-1

2. What is a supercritical fluid?
19-2

3. Supercritical Fluid
A supercritical fluid is any substance at a temperature and
pressure above its critical point.
It can diffuse through solids like a gas, and dissolve materials
like a liquid.
Additionally, close to the critical point, small changes in
pressure or temperature result in large changes in density,
allowing many properties to be "tuned".
Supercritical fluids are suitable as a substitute for organic
solvents in a range of industrial and laboratory processes.
19-3

4. In the Supercritical region the substance is neither a
gas nor a liquid – it is a fluid that has properties of
both.
There are no sharp boundaries between gas and
liquid.
Properties of SCFs can be very different from the
normal liquid phase.
19-4

5. 19-5

6. Critical properties of various solvents
Solvent Molecular Critical Critical Critical
weight temperature pressure density
g/mol K MPa (atm) g/cm3
Carbon dioxide (CO2) 44.01 304.1 7.38 (72.8) 0.469
Water (H2O) 18.015 647.096 22.064 0.322
(217.755)
Methane (CH4) 16.04 190.4 4.60 (45.4) 0.162
Ethane (C2H6) 30.07 305.3 4.87 (48.1) 0.203
Propane (C3H8) 44.09 369.8 4.25 (41.9) 0.217
Ethylene (C2H4) 28.05 282.4 5.04 (49.7) 0.215
Propylene (C3H6) 42.08 364.9 4.60 (45.4) 0.232
Methanol (CH3OH) 32.04 512.6 8.09 (79.8) 0.272
Ethanol (C2H5OH) 46.07 513.9 6.14 (60.6) 0.276
Acetone (C3H6O) 58.08 508.1 4.70 (46.4) 0.278
19-6

7. Some Characteristics of Supercritical fluid
• Above the critical temperature
l no phase transition regardless of the applied
pressure
• supercritical fluid has physical and thermal
properties that are between those of the pure liquid
and gas
l fluid density is a strong function of the
temperature and pressure
l diffusivity much higher a liquid
« readily penetrates porous and fibrous solids
l Low viscosity
l Recovery of analytes
« Return T and P
19-7

8. Carbon dioxide is known to be the most stable and
an excellent solvent compound and is normally
used in mobile phases for supercritical fluid
chromatography (SFC) as well as in supercritical
fluid extraction (SFE)
19-8

9. Carbon dioxide pressure-temperature phase
diagram
19-9

10. This is not …
Above the critical point, the phase boundary (meniscus)
between liquid and vapor phases disappears, and the
substance is a single homogeneous fluid.
19-10

11. One homogenous phase
called the
"supercritical fluid”
Carbon Dioxide
19-11

12. Comparison of Gases, Supercritical Fluids and
Liquids
Density (kg/ Viscosity ( Diffusivity
m 3) µPa∙s) (mm²/s)
Gases 1 10 1-10
Supercritical 100-1000 50-100 0.01-0.1
Fluids
Liquids 1000 500-1000 0.001
19-12

13. SUPERCRITICAL FLUID
EXTRACTION (SFE)
19-13

14. Extraction in analysis
Often the analysis of complex materials requires as a
preliminary step, separation of the analyte or analytes
from a sample matrix.
Ideally, an analytical separation method:
• should be rapid, simple and inexpensive,
• should give quantitative recovery of analytes
without loss or degradation,
• should yield a solution of the analyte that is
sufficiently concentrated to permit the final
measurement to be made without the need for
concentration, and
• should generate little or no laboratory wastes
that have to be disposed of. 19-14

15. Supercritical Fluid Extraction
• SF combines desirable properties of gases and liquids
l Solubility of liquids
l Penetration power of gases
• Process flexibility: Density of SF and solubility of a
solute in it can be changed in a continuous manner by
change of pressure
• Environmental perspective: Innocuous substances such
as water and carbon dioxide can be used as extracting
solvents instead of organics
19-15

16. A practical approach of SFE
• Sample is placed in thimble or extraction cell
• Supercritical fluid is pumped through the
thimble
l extraction of the soluble compounds is
allowed to take place as the supercritical
fluid passes into a collection trap through a
restricting nozzle
l fluid is vented in the collection trap
« solvent to escapes or is recompressed
• Material left behind in the collection trap is the
product of the extraction
l batch process
19-16

17. SFE principle: (1)Solute solubility
• Density of a SF increases
with pressure i.e. more
solvent molecules per unit
volume
Solubility • Pressure packs the solvent
of solute in
SF molecules closer and
(m/v) facilitates the entrapment of
more solute molecules
• Dependence of solubility on
pressure can be utilized to
fine-tune the SFE process
Pressure
19-17

18. (2) Enhanced penetration
• Diffusivity of solvent molecules in a SF approach gaseous
state diffusivity
• Solute diffusivity within a SF approaches that shown in
gaseous phase
Solvent
(SF)
Solute
19-18

19. Supercritical Fluid Extraction
Advantages of supercritical fluid extraction
(SFE):
a. SFE is generally fast. The rate of mass
transfer between a sample matrix and an
extraction fluid is determined by the rate of
diffusion of a species in the fluid and the viscosity
of the fluid—the greater the diffusion rate and
the lower the viscosity, the greater will be the
rate of mass transfer.
19-19

20. • The solvent strength of a supercritical fluid can
be varied by changes in the pressure and to a less
extent in the temperature.
• Many supercritical fluids are gases at ambient
condition.
• Some supercritical fluid are cheap, inert, and
nontoxic.
19-20

21. SFE Instrumentation
Instrument components include a fluid source,
commonly a tank of carbon dioxide followed by a
syringe pump having a pressure rating of at least
400 atm, a valve to control the flow of the critical
fluid into a heated extraction cell having a
capacity of a few ml, and lastly an exit valve
leading to a flow restrictor that depressurizes the
fluid and transfers it into a collection device.
19-21

22. Instrumentation – important components
• a tank of the mobile phase, usually CO2,
• a pump to pressurize the gas,
• an oven containing the extraction vessel,
• a restrictor to maintain a high pressure in
the extraction line,
5. a trapping vessel.
Analytes are trapped by letting the solute-containing
supercritical fluid decompress into an empty vial,
through a solvent, or onto a solid sorbent material.
19-22

23. Supercritical Fluid Extraction
19-23

24. Extractions can be performed in dynamic,
static, or combination modes.
In a dynamic extraction the supercritical fluid
continuously flows through the sample in the
extraction vessel and out the restrictor to the
trapping vessel.
19-24

25. In static mode the supercritical fluid circulates in a
loop containing the extraction vessel for some
period of time before being released through the
restrictor to the trapping vessel.
In the combination mode, a static extraction is
performed for some period of time, followed by a
dynamic extraction.
19-25

26. 19-26

27. 19-27

28. 19-28

29. Modifier
For the purpose of increasing the polarity
of the supercritical CO2 (and thus its
extracting efficiency for more polar
components), additives such as methanol
is added to the fluid. This is known as
modifier.
Other examples of modifier include
ethanol, 1-propanol and acetonitrile
19-29

30. Some applications of SFE
• Removal of grease and other fouling material
• Removal of impurities from chemical
products
• Breaking of azeotropes
• Fractionation and purification of polymers
e.g. removal of unchanged monomers from
polymers
19-30

31. In the food and pharmaceutical industries,
SFE is used in
• Decaffeinating of coffee and tea
• Extraction of essential oils (vegetable and fish oils)
• Extraction of flavors from natural resources
(nutraceuticals)
• Extraction of ingredients from spices and red peppers
• Extraction of fat from food products
• Fractionation of polymeric materials
• Extraction from natural products
• Photo–resist cleaning
• Precision part cleaning
19-31

32. SUPERCRITICAL FLUID
CHROMATOGRAPHY (SFC)
19-32

33. Introduction
Supercritical fluid chromatography (SFC) is a
hybrid of gas and liquid chromatography that
combines some of the best features of each.
Supercritical fluid chromatography is of
importance because it permits the separation and
determination of a group of compounds that are
not conveniently handled by either gas liquid or
liquid chromatography.
19-33

34. Supercritical fluid chromatography (SFC)
• SFC is a chromatographic technique in which
the mobile phase is a supercritical fluid.
• The use of a supercritical fluid mobile phase in
chromatography was first proposed in 1958 by
J. Lovelock. The first actual report use of this
in a chromatographic system was in 1962 by
Klesper et al, who used it to separate thermally-
labile porphyrins.
19-34

35. Supercritical fluid chromatography (SFC)
c. SFC is of importance because it permits the
separation and determination of a group of
compounds that are not conveniently handled by
either GC or LC.
These compounds (1) are either non-volatile or
thermally labile so that the GC are in-applicable, and
(2) contain no functional groups that make impossible
to be detected by means of spectroscopic or
electrochemical techniques employed in LC.
19-35

36. Supercritical fluid chromatography
19-36

37. Theory of SFC
Since supercritical fluids have properties
between those of gases and liquid, their use as a
mobile phase offers several advantages.
19-37

38. Advantages of SFC:
a. One advantage is that supercritical fluid
have lower densities and viscosities than
liquids. This results in larger diffusion
coefficients for solutes in SFC than LC.
This results in better efficiencies
and higher optimum linear velocities
in SFC than LC.
19-38

39. The plate height of a SFC System is given by the van
Deemter equation.
H = A + B/u + Cu
19-39

40. 19-40

41. b. SFs have higher densities than gas, so that
mobile phase has a greater chance of interacting
with the solute than that in GC (i.e., carrier gas).
This makes the mobile phase important in
determining the retention of solutes on the system
and give more flexibility in optimizing the
separation.
19-41

42. For example, retention of solutes in SFC can be
changed by using a different column (i.e.
different stationary phases) as in GC, or by
changing the mobile phase strength as in LC.
19-42

43. isobaric Flow-rate programming Pressure programming
19-43

44. c. One major advantage of SFC is its ability to
use detector available for either GC or LC, such
as FID, UV-Vis, and Fluorescence detectors.
This gives it a wide range of both universal and
selective detections for use in either analytical
or preparative-scale work.
19-44

45. GC detectors: LC detectors:
Thermal conductivity detector Refractive Index Detector
(TCD): 10-7 M (103-fold range) (10-5 to 10-6 M)
Absorption Detector (UV/Vis)
Flame Ionization detector (10-8 M)
(FID): 10-10 M (a 105-fold range)
Fluorescence Detector
(10-10 M)
Nitrogen-phosporus detector
Conductivity Detector
(NPD): 10-10 M (a 106-fold range)
(10-6 M)
Electron capture detector Electrochemical Detector
(ECD): 10-14 ~ 10-16 M (a 103- 104 fold range) (10-11 M)
Flame photometric detector
(FPD):10-14 M (P, S)
Electrochemical detector (S, halogen,nitrogen-) 19-45

46. Schematic of a gas chromatograph
19-46

47. Schematic of a liquid chromatograph
Gradient
Controller
•
Pump Column
Detector
Injector
Mobile
Phases
19-47

48. Instrumentation for SFC
Instrumentation for SFC can be obtained commercially
or adapting system used for either LC and GC.
The chromatograph is generally consists of :
• Gas supply, usually CO2,
• Pump,
• Injector
• Oven
• Column in a thermostat-controlled oven,
• Detector
• Recorder/computer
(A restrictor is also required to maintain the high pressure in
19-48
the column, placed after the detector)

49. 19-49

50. The main difference of a SFC than a LC or GC system is
the need to control both temperature and pressure of
mobile phase. This must be done to keep the mobile
phase as a supercritical fluid.
Control of the pressure (density) of the supercritical fluid
can also used to vary strength of mobile phase during the
gradient elution in SFC .
The column is usually a capillary GC column, but packed
LC columns can also be used. The FID is the most
common detector, but other GC or LC detectors can also
be used.
19-50

51. Supercritical fluid chromatograph
19-51

52. Depending on which supercritical fluid is used, it is
also possible to use SFC at lower T than GC. This
makes it more useful in the separation of thermally
unstable compounds.
The stationary phases used in SFC can be similar to
those in LC as well as GC. Either packed or open-
tubular columns may be used.
Because of these advantages, SFC is commonly
viewed as a technique which is complementary to both
LC and GC.
19-52

53. 19-53

54. Stationary Phases / Columns
There are two types of analytical columns used in
SFC, packed and capillary.
Packed columns contain small deactivated particles to
which the stationary phases adhear. The columns are
conventionally stainless steel. Capillary columns are
open tubular columns of narrow internal diameter
made of fused silica, with the stationary phase bonded
to the wall of the column.
19-54

55. 19-55

56. Mobile Phases
• The most widely used mobile phase for SFC is
carbon dioxide. It is an excellent solvent for a
variety of organic molecules. In addition, it
transmits in the ultraviolet and is odorless,
nontoxic, readily available, and remarkably
inexpensive when compared with other
chromatographic mobile phases.
19-56

57. Effects of Pressure
• Pressure changes in supercritical
chromatography have a pronounced effect on
the capacity factor k’. This effect is a
consequence of the increase in density of mobile
phase with increase in density of the mobile
phase with increases in pressure.
19-57

58. Detectors
SFC is compatible with both HPLC and GC detectors.
As a result, optical detectors, flame detectors, and
spectroscopic detectors can be used. However, the
mobile phase composition, column type, and flow rate
must be taken into account when the detector is
selected as they will determine which detector is able to
be used. Some care must also be taken such that the
detector components are capable of withstanding the
high pressures of SFC.
19-58

59. Detectors
• A major advantage of SFC over HPLC is that
the flame ionization detector of gas
chromatography can be employed. Mass
spectrometers are also more easily adapted as
detectors for SFC than HPLC.
19-59

60. 19-60

61. 19-61

62. Applications
SFC has been applied to a wide variety of
materials, including
•Natural products,
•Drugs,
•Foods,
•Pesticides and herbicides,
•Surfactants,
•Polymers and polymer additives,
•Fossil fuels, and
•Explosives and propellants.
19-62

63. Dimethylpolysiloxane: non-volatile
and special function groups
19-63

64. 19-64

65. 19-65

66. 19-66

67. 19-67