Supercritical fluids chromatoghraphy (SFC)

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  • Awesome presentation. Might be useful to dwell more on the concept that the pressure change is due to the changing in volume. Therefore the density more is a function of, feature of sharing a more confined, volume. The pressure increase is incidental, related to the decreasing volume change. I am reading through McHugh's book and he neglects this feature also. Makes the concepts rational when explained in terms of volume change. This is essentially how a piston compressors functions. Not by increasing the pressure but, decreasing the volume which, results in a pressure change. Yes?
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  • Mobile Phases - Component solvents/mobile phases to make up gradient Gradient Controller - Sets up gradient - linearity, steps, ramps, number of solvents/mobile phases (binary, ternary, quaternary). Pump - Dual piston, Pulse free, Able to deliver 4000PSI, Precision flow rates of 0.001mL/min, Flow range 0.001-10.001 mL/min. Injector - How do you inject a sample in to a flowing sream at 4000PSI? If you tried you’d have the syringe plunger go thru a wall! The sample injector utilizes a set of valves in which a sample loop switchs in-and-out the flowing stream. You introduce the sample by injecting it into the sample loop which has a fixed volume. The fixed volume injected replaces the contents of the loop so therefore for manual injection you should have enough injected to completely replace the previous loop contents. The sample is automatically introduced into the flowing stream by valve switching.
  • Supercritical fluids chromatoghraphy (SFC)

    1. 1. SUPERCRITICAL FLUIDSUPERCRITICAL FLUID EXTRACTION (SFE) SUPERCRITICAL FLUID CHROMATOGRAPHY (SFC) 19-1
    2. 2. What is a supercritical fluid? 19-2
    3. 3. Supercritical FluidA supercritical fluid is any substance at a temperature andpressure above its critical point.It can diffuse through solids like a gas, and dissolve materialslike a liquid.Additionally, close to the critical point, small changes inpressure or temperature result in large changes in density,allowing many properties to be "tuned".Supercritical fluids are suitable as a substitute for organicsolvents in a range of industrial and laboratory processes. 19-3
    4. 4. In the Supercritical region the substance is neither agas nor a liquid – it is a fluid that has properties ofboth.There are no sharp boundaries between gas andliquid.Properties of SCFs can be very different from thenormal liquid phase. 19-4
    5. 5. 19-5
    6. 6. Critical properties of various solvents Solvent Molecular Critical Critical Critical weight temperature pressure density g/mol K MPa (atm) g/cm3Carbon 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. 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. 8. Carbon dioxide is known to be the most stable andan excellent solvent compound and is normallyused in mobile phases for supercritical fluidchromatography (SFC) as well as in supercriticalfluid extraction (SFE) 19-8
    9. 9. Carbon dioxide pressure-temperature phasediagram 19-9
    10. 10. This is not …Above the critical point, the phase boundary (meniscus)between liquid and vapor phases disappears, and thesubstance is a single homogeneous fluid. 19-10
    11. 11. One homogenous phasecalled the"supercritical fluid”Carbon Dioxide 19-11
    12. 12. Comparison of Gases, Supercritical Fluids and Liquids Density (kg/ Viscosity ( Diffusivity m 3) µPa∙s) (mm²/s) Gases 1 10 1-10Supercritical 100-1000 50-100 0.01-0.1 Fluids Liquids 1000 500-1000 0.001 19-12
    13. 13. SUPERCRITICAL FLUID EXTRACTION (SFE) 19-13
    14. 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. 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. 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. 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 solventof 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. 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. 19. Supercritical Fluid ExtractionAdvantages of supercritical fluid extraction(SFE):a. SFE is generally fast. The rate of masstransfer between a sample matrix and anextraction fluid is determined by the rate ofdiffusion of a species in the fluid and the viscosityof the fluid—the greater the diffusion rate andthe lower the viscosity, the greater will be therate of mass transfer. 19-19
    20. 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. 21. SFE InstrumentationInstrument components include a fluid source,commonly a tank of carbon dioxide followed by asyringe pump having a pressure rating of at least400 atm, a valve to control the flow of the criticalfluid into a heated extraction cell having acapacity of a few ml, and lastly an exit valveleading to a flow restrictor that depressurizes thefluid and transfers it into a collection device. 19-21
    22. 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-containingsupercritical fluid decompress into an empty vial,through a solvent, or onto a solid sorbent material. 19-22
    23. 23. Supercritical Fluid Extraction 19-23
    24. 24. Extractions can be performed in dynamic,static, or combination modes.In a dynamic extraction the supercritical fluidcontinuously flows through the sample in theextraction vessel and out the restrictor to thetrapping vessel. 19-24
    25. 25. In static mode the supercritical fluid circulates in aloop containing the extraction vessel for someperiod of time before being released through therestrictor to the trapping vessel.In the combination mode, a static extraction isperformed for some period of time, followed by adynamic extraction. 19-25
    26. 26. 19-26
    27. 27. 19-27
    28. 28. 19-28
    29. 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. 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. 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. 32. SUPERCRITICAL FLUIDCHROMATOGRAPHY (SFC) 19-32
    33. 33. IntroductionSupercritical fluid chromatography (SFC) is ahybrid of gas and liquid chromatography thatcombines some of the best features of each.Supercritical fluid chromatography is ofimportance because it permits the separation anddetermination of a group of compounds that arenot conveniently handled by either gas liquid orliquid chromatography. 19-33
    34. 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. 35. Supercritical fluid chromatography (SFC)c. SFC is of importance because it permits theseparation and determination of a group ofcompounds that are not conveniently handled byeither GC or LC.These compounds (1) are either non-volatile orthermally labile so that the GC are in-applicable, and(2) contain no functional groups that make impossibleto be detected by means of spectroscopic orelectrochemical techniques employed in LC. 19-35
    36. 36. Supercritical fluid chromatography 19-36
    37. 37. Theory of SFCSince supercritical fluids have propertiesbetween those of gases and liquid, their use as amobile phase offers several advantages. 19-37
    38. 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. 39. The plate height of a SFC System is given by the vanDeemter equation. H = A + B/u + Cu 19-39
    40. 40. 19-40
    41. 41. b. SFs have higher densities than gas, so thatmobile phase has a greater chance of interactingwith the solute than that in GC (i.e., carrier gas).This makes the mobile phase important indetermining the retention of solutes on the systemand give more flexibility in optimizing theseparation. 19-41
    42. 42. For example, retention of solutes in SFC can bechanged by using a different column (i.e.different stationary phases) as in GC, or bychanging the mobile phase strength as in LC. 19-42
    43. 43. isobaric Flow-rate programming Pressure programming 19-43
    44. 44. c. One major advantage of SFC is its ability touse detector available for either GC or LC, suchas FID, UV-Vis, and Fluorescence detectors.This gives it a wide range of both universal andselective detections for use in either analyticalor preparative-scale work. 19-44
    45. 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. 46. Schematic of a gas chromatograph 19-46
    47. 47. Schematic of a liquid chromatographGradientController • Pump Column Detector InjectorMobilePhases 19-47
    48. 48. Instrumentation for SFCInstrumentation for SFC can be obtained commerciallyor 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. 49. 19-49
    50. 50. The main difference of a SFC than a LC or GC system isthe need to control both temperature and pressure ofmobile phase. This must be done to keep the mobilephase as a supercritical fluid.Control of the pressure (density) of the supercritical fluidcan also used to vary strength of mobile phase during thegradient elution in SFC .The column is usually a capillary GC column, but packedLC columns can also be used. The FID is the mostcommon detector, but other GC or LC detectors can alsobe used. 19-50
    51. 51. Supercritical fluid chromatograph 19-51
    52. 52. Depending on which supercritical fluid is used, it isalso possible to use SFC at lower T than GC. Thismakes it more useful in the separation of thermallyunstable compounds.The stationary phases used in SFC can be similar tothose in LC as well as GC. Either packed or open-tubular columns may be used.Because of these advantages, SFC is commonlyviewed as a technique which is complementary to bothLC and GC. 19-52
    53. 53. 19-53
    54. 54. Stationary Phases / ColumnsThere are two types of analytical columns used inSFC, packed and capillary.Packed columns contain small deactivated particles towhich the stationary phases adhear. The columns areconventionally stainless steel. Capillary columns areopen tubular columns of narrow internal diametermade of fused silica, with the stationary phase bondedto the wall of the column. 19-54
    55. 55. 19-55
    56. 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. 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. 58. DetectorsSFC is compatible with both HPLC and GC detectors.As a result, optical detectors, flame detectors, andspectroscopic detectors can be used. However, themobile phase composition, column type, and flow ratemust be taken into account when the detector isselected as they will determine which detector is able tobe used. Some care must also be taken such that thedetector components are capable of withstanding thehigh pressures of SFC. 19-58
    59. 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. 60. 19-60
    61. 61. 19-61
    62. 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. 63. Dimethylpolysiloxane: non-volatileand special function groups 19-63
    64. 64. 19-64
    65. 65. 19-65
    66. 66. 19-66
    67. 67. 19-67

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