Advanced Analytical Chemistry

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• Chapter 10
• Supercritical fluid chromatography and
  Extraction (SFC SFE)
• References
• Roger M. Smith, Supercritical Fluid
  Chromatography, 1988.
• Skoog book, p768
• S.A. Westwood, Supercritical Fluid Extraction and
  its use in chromatographic sample preparation,

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• 1. Principles
• 1.1 Brief history
• To be able to use supercritical fluid (SF) as a
  chromatographic mobile phase, the SF has to have
  ability to dissolve substances. The dissolving
  ability of SE was discovered probably first by
  Hannay and Hogarth in 1879, when they studied the
  solubility of cobalt and iron chlorides in
  supercritical ethanol.
• Lovelock in 1958 suggested that a SF might be
  used as a mobile phase in chromatography.

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• E. Klesper was first demonstrated in 1962 SFC by
  separation of nickel porphyrins using
  supercritical chlorofluoromethanes as mobile
  phases.
• In the following years (1960s), further
  developments were carried out both practically
  and theoretically by number of groups, among
  many, Sie, Rijnders, and Giddings.

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• Another important development is the
  demonstration of SFC with capillary columns by
  Novotny and M. Lee in 1981. One of the most
  interesting patents in the history of SFC was
  filed for in early 1982 by Novotny, Lee, Peaden
  et al. for the fundamental use of open-tubular
  capillary columns for SFC. This patent had
  aroused some controversy in the SFC industry, and
  consequently it was subjected to a review in late
  1985 and 1986. On December 31, 1986 the claims of
  the patent were preliminary rejected. However,
  after amendments were made, the fundamental
  patent for capillary SFC patent was validated in
  March 1987. It is held by Brighham Young
  University and licensed exclusively to Lee
  Scientific and these groups have done much to
  promote the subsequent interest in SFC.

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
1.2 Supercritical fluid
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• The critical temperature of a substance is the
  temperature above which a distinct liquid phase
  cannot exist, regardless of pressure.
• The vapor pressure of a substance at its critical
  temperature is its critical pressure.
• At temperature and pressures above its critical
  temperature and pressure (its critical point), a
  substance is called a supercritical fluid.

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• Several important properties of SF
• High density remarkable ability to dissolve
  large, nonvolatile molecules (e.g extraction
  caffeine from coffee bean to give decaffeinated
  coffee and extracting nicotine from cigarette
  tobacco).
• Viscosity reduced pressure drop across the
  column. Liquid viscosity is greater by a factor
  of ca. 100, the pressure drop in HPLC is between
  10 to 100 times greater than in SFC and GC.

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• Solute diffusion coefficient the mass transfer
  properties resulting from the solute diffusion
  coefficients in SF lead to the analysis speeds
  which increase in the sequence HPLC, SFC, and GC.
• Analyte recovery in most cases analyte dissolved
  in the SF can be recovered easily by simply
  allowing the solution to equilibrate with the
  atmosphere at relatively low temperature.

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
11
Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• 1.3 Supercritical Fluid Chromatography
• 1.3.1 Mobile Phase in SFC
• The most common used mobile phase for
  supercritical fluid chromatography is carbon
  dioxide.
• Major advantages
• Nontoxic, odorless
• Inexpensive
• Suitable critical temperature and pressure (31 ?C
  and 72.9 atm)
• Readily available

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• Modify the solubility or the partition
  coefficient of the analyte
• Change pressure, hence the density of the SF.
• Add polar organic modifiers such as methanol
• It is important to be aware of the
  modifier-fluid phase diagram to ensure that the
  solvent is in one phase.

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• 2. Instrumental considerations
• Capillary SFC was developed on principles based
  on capillary GC
• Nearly all previous SFC instruments employed
  components normally used in conventional HPLC
  system, including high pressure pumps, stainless
  steel tubing, injection valves, and columns, with
  few modifications, or not at all.

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• 2.1 Stationary phase
• Both open-tubular and packed columns are used
  for SFC, although currently the former is
  favored. Both columns are similar to those used
  in GC and HPLC.
• 2.2 Detectors
• A major advantage of SFC over HPLC that the
  universal detector flame ionization detector of
  gas chromatography can be employed.
• Conventional detectors from both GLC and HPLC
  have been successfully adapted to SFC, such as
  UV, FID, FPD et al.
• SFC/MS

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• Challenges in SFC
• SFC faces a strong competition from the
  high-temperature Gas-liquid chromatography (GLC)
  and HPLC. By using high-temperature Gas-liquid
  chromatography (GLC), many high molecular weigh
  compounds can be separated. It is also facing
  competition from HPLC and CE. The future needs
  for SFC would be the development of
  instrumentation, particularly in sample
  introduction system, column and restrictor
  techniques, and the use of polar mobile phases.

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
3. Supercritical Fluid Extraction (SFE) An
offline separation technique, or a sample
preparation technique. 3.1 Principles of
SFE Three interrelated factors influence
recovery of the target compounds as shown in the
SFE triangle
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
25
Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• Solubility
• The solute must, firstly, be sufficiently
  soluble in the supercritical fluid.
• Solubility
• Change pressure
• Add modifier

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• Diffusion
• The solute must be transported sufficiently
  rapidly by diffusion from the interior of the
  matrix in which it is contained.

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• Matrix
• The third factor is that of the matrix (other
  than its effects on diffusion). Matrix effects
  mean that, although in many cases SFE will
  extract all of a particular compound in a sample,
  in some cases not all of a compound is
  extractable the rest being locked into the
  structure of matrix, or too strongly bound to its
  surface.

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• Of these three factors, that of the matrix is the
  least well understood at present and a detailed
  scientific discussion cannot be given.
• Of the two remaining factors, solubility and
  diffusion, the latter is of more concerned in
  analytical extractions. This firstly because in
  most applications, the analyte is present in
  small quantities in the matrix and secondly a
  fluid and conditions will have to chosen in which
  the analyte is soluble at least to some extent.

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
Solubility is only important at the beginning of
an extraction in a typical flow system.
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• 3.2 Instrumentation
• Offline method
• Dynamic
• The sample is continuously supplied with fresh
  supercritical fluid and the extracted analytes
  are constantly swept into the collection device.
• Static
• The out let of the extraction cell is shut off
  and the cell is pressed under static
  (non-flowing) conditions. Following an
  appropriate extraction time, the analytes are
  recovered from the static extraction, generally
  by opening a value at the outlet of the cell and
  performing a short dynamic extraction.

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• Dynamic mode is preferred for solubility
  controlled extraction
• Static mode is preferred for diffusion controlled
  extraction

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
33
Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE

• on-line SFE extraction

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
35
Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE
36
Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
11/6/2006 Chapter 10 SFC-SFE