Transcript Supercritical fluid extraction (SFE) / Supercritical fluid chromatography (SFC)

Supercritical fluid extraction (SFE) /
Supercritical fluid chromatography
(SFC)
Supercritical Fluid (SCF)
At temperatures above Tc
and pressures beyond Pc,
substance exists as
supercritical fluid , and
not as gas or liquid. The
SCF expands and
contracts like gas and has
solvent properties like
liquid.
Phase diagram for supercritical fluid
Comparison of the properties of gas,
Supercritical fluid and liquid
Mobile phase
Density
(g／ml)
Viscosity
(m2／s)
Diffusion
coefficient
(cm2／s)
Gas
0.6～2.0×10-3
( 0.01)
0.5～3.5×10-4
( 0.01)
0.01～1.0
( 10,000)
Supercritical
fluid
0.2～0.9 (~ 0.5)
2.0～9.9×10-4
(0.01)
0.5～3.3×10-4
( 10-100)
Liquid
0.8～1.0 (1)
0.3～2.4×10-2( 1) 0.5～2.0×10-5 ( 1)
SCFs are used as extraction solvents (e.g. extracting
caffeine from coffee beans, fats from potato chips),
carrier medium for chromatography, and solvents for
disposal of organic hazardous wastes
Advantages of Supercritical Fluids
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lower operating temperatures
improved yield
improved product properties
favorable combination of process steps
easier regeneration of the SC solvent
lower production cost
solvent power comparable to liquid solvents
very high volatility compared to the dissolved substances
complete separation of solvent from extract and raffinate
Disadvantages of Supercritical Fluids
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elevated pressures required
relative high costs of investment
unusual operating conditions
complicated phase behavior
Physical Parameters of Selected Supercritical
Fluids
a
Data taken from Refs. 62 and 63.
B The density at 400 atm (p,,,,) end T, = 1.03 was calculated from compressibility data.”
C measurements were made under saturated conditions if no pressure is specified or were
performed at 25°C if no temperature is specified.
Benefits of supercritical carbon dioxide
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Moderate critical pressure (73.8 bar)
Low critical temperature (31.1℃)
Low toxicity and reactivity
High purity at low cost
Useful for extractions at temperature < 150℃
Benefits of supercritical carbon dioxide Ctd.
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Ideal for extraction of thermally labile compounds
Ideal extractant for non-polar species, e. g. alkanes
Reasonably good for moderately polar species, e. g. PAHs
Can directly vent to atmosphere
Little opportunity for chemical change in absence of light and
oxygen
Gas at room temperature, allows for coupling to gas
chromatography and SFC
Phase diagrams for CO2 and H2O
Supercritical Fluid extraction (SFE) /
chromatography (SFC) Components
pump
( extraction cell)
Supercritical Fluid extraction
Supercritical Fluid chromatography
Commercial instruments
Jasco SFC/SFE system (packed column)
Oven
Mixer
Pre-heating coil
Injector
CO2 pump
Liquid CO2 Cylinder
Stop valve
Extraction vessel
or column
Stop valve (optional)
Cooling circulator
Line switching valve
Modifier pump
Modifier
Detector
Back pressure regulator
Pumps
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Reciprocating pump
Syringe pump
Other pump modules
Types of extraction cell
Flow-through cell
Headspace-sampling cell
Columns
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Open tubular capillary columns
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Packed columns
Restrictors
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Fixed restrictors
linear restrictor (fused-silica)
tapered desire
Integral restrictor
ceramic frit restrictor
metal restrictor (platinum, platinum-iridium or steel)
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Variable restrictors
variable nozzle (HP)
backpressure regulator (BPR) (Jasco)
Fixed restrictors
linear restrictor
tapered desire
Integral restrictor
ceramic frit restrictor
Backpressure regulator
Gap-adjustment screw
Needle-driven solenoid
Return spring
Needle seal
Valve needle
Valve seat
heater
Detectors
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UV detection
Fluorescence detection
Flame ionization detection
Electron capture detection
Mass spectrometric detection
Characteristics of supercritical fluid
extraction
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Potential for reduced extraction times
Controllable extraction conditions
Potential for fractionation
Reduced risk of contamination
Compatibility with on-line methods of analysis (e.g.
chromatography)
Flexibility with off-line analysis (e. g.
spectrophotometry)
Possibility of class-selective extraction by appropriate
choice of conditions
Supercritical fluid extraction
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Static extraction mode (steady state extraction)
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Dynamic extraction mode (non-steady state extraction)
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Recirculating mode
Supercritical fluid extraction
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Off-line
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On-line
SFE-GC
SFE-LC
SFE-MS
SFE-SFC
Off-line SFE
Device for the preparation of modified
supercritical fluid
pump
heated tube
four port valve
extraction cell
modifier chamber
solvent vial
on-line SFE
Cryotrapheater
Schematic diagram of on-line SFE-SFC system a) CO2 cylinder b) pump c)
extraction vessel d) cryotrapheater e) injection port f) chromatography column g)
column oven h) detector i) transfer lines.
Advantages of on-line SFE
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Direct coupling of the analyte-containing supercritical fluid to
a chromatographic separation system with appropriate
detection
Eliminating sample handling after loading in the extraction
cell
Disadvantages of on-line SFE
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Long periods of time
Understand the nature of analytes
Directly coupled SFE-SFC
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Dynamic focusing
Cryogenic focusing
Thermal modulator
Collection on a solid support
Static extraction
SFE/SFC
The direct connection of
supercritical fluid extraction and
supercritical fluid chromatography
(SFE/SFC) has found many
applications recently. SFE/SFC has
the advantages of not requiring a
concentrating procedure or a cleanup
procedure before analysis. SFE/SFC
is applied for various compounds
from different matrixes, including
caffeine extraction, tocopherol
enrichment, flavors extraction and
analysis of pesticide residues. The
direct coupling of SFE with GC,
GPC, etc. in an on-line approach is
conceptually straightforward,
assuming quantitative deposition of
the extracted analyte into the
chromatographic inlet. SFC-MS has
found several useful applications in
recent years.
Three-dimensional chromatogram of the extract
from the petroleum residue with supercritical
carbon dioxide obtained by direct introduction
into SFC [JASCO Corp].
Recovery & solubility
(a) Percentage recovery of atrazine from soil
by SFE with carbon dioxide at different
pressures after 15 min at 80℃ and constant
flow rate
(b) Calculated solubility at the same temperature
Percentage extraction versus time of
extraction
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Modifiers for SFE/SFC
The role of Modifier on SFE
MeCN
MeOH
1-propanol
EtOH
• Plots of modifier effects on efficiency for nonpolar solutes on C18 column at 80 oC and 210 bar, 2.0
mL/min. Solute: (A) naphthalene; (B) anthracene; Modifier: solid line with = methanol; broken line
with = ethanol; dotted line with = 1-propanol; dashed line with = acetonitrile [Zou & Dorsey, 2000] ◆
The parameters effect on solubility
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The vapor pressure of the component
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Interaction with the supercritical fluid
( Temperature, pressure, density and additives)
Reduced solubility parameter
Δ= δ1/δ2
δ1= 1.25 Pc1/2 [ρ/ρliq ]
δ2＝(Δε/ Δν)1/2
δ1 : solubility parameter of the fluid
Pc : the critical pressure
ρ : the density of the supercritical fluid
ρliq: the density of the liquid gas
δ2 : solubility parameter of solute
Δε: the energy of vaporization at a
given temperature
Δν: the corresponding molar
volume
Calculation of the solubility parameters, δ2
Group
Megastrol acetate
5*CH3
6*CH2
3*CH
2*HC=
3*C
2*C=
2*C=O
OCO
4 ring closure 5-6 atoms
2 conjugated double bonds
Δε (cal/mol)
Δν (cm3/mol)
5(1125)
6(1180)
3(820)
2(1030)
3(350)
2(1030)
2(4150)
4300
4(250)
2(400)
5(33.5)
6(16.1)
3(-1.0)
2(13.5)
3(-19.0)
2(-5.5)
2(10.8)
18.0
4(16.0)
2(2.2)
34735
328.1
δ2＝(Δε/ Δν)1/2= 10.29 cal1/2 cm-3/2
Solubility in carbon dioxide at different
temperature and pressures
Anthracene
Measured by
the online FID
method
J . Chromatogr .A 785 (1997) 57–64
Method development for SFE
SFC characteristics:
Faster linear velocity than LC
Greater separation efficiency per unit time than LC
Greater solute solubility than GC
Greater mobile phase selectivity than GC
Advantages compared to LC or GC:
Compared to GC: Can separate thermally unstable compounds
Can separate compounds beyond the
volatility range of GC
Compared to LC: Reduced analysis time
Comparison of MW
elution ranges for
different types of
column chromatography
Source: Skoog, Holler, and Nieman, Principles of Instrumental Analysis, 5th edition, Saunders College Publishing.
Advantages of supercritical fluid
chromatography (SFC)
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Applications in quality control and sample
Minimizes use of organic solvents
Detection down to ppb or μg (depending on choice of
detector)
Non-destructive method for isolation or purification
of compounds
Preparative separations
Disadvantages of supercritical fluid
chromatography
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Limited chemical information (depending on detection system)
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Complex samples can have low resolution
Supercritical Fluid extraction (SFE) /
chromatography (SFC) Components
pump
( extraction cell)
Supercritical Fluid extraction
Supercritical Fluid chromatography
The role of Modifier on SFC
Different i.d. restrictors
6mm
6mm
160 atm
9mm
160 atm
12 m m
160 atm
15 m m
Chromatograms of enantiomers of -phenylethanol using different i.d. restrictors.(A) 6 m m, (B) 9 m m, (C )12 m m, (D) 15 m m.
Effect of restrictor internal diameter on
separation parameters
SFC vs. HPLC: Resolution
SFC: Speed and Resolution
液體
ＳＦ
氣體
密度
1
~1/4
0.001
黏滯性
1
0.01
0.01
擴散係數
1
10-100 10,000
SFC vs.
比LC 快
Peak比LC寬
比GC窄
SFC vs. HPLC: Speed
SFC: effect of Pressure
P↗ → n↗ → 溶解度↗ →tR↘
Effects of temperature and pressure on
retention factors
J . Chromatogr .A 785 (1997) 57–64
Effect of temperature
in SFC
140°C
160°C
170°C
Figure 1.10. Selected segments of SFC
chromatograms from a complicated
sample, showing the effect of
temperature on selectivity at (A)
14O”C, (B) 16OT,and (C) 170°C. Two
families of unknown peaks (l-3 and 47) overlap with some coelution at
140%, but are resolved at 170°C.
Conditions: 10-m x 50-pm i.d. open
tubular column, poly(308
biphenyl)methylsiloxane stationary
phase; CO,; 5 atm min-‘, FID.
Applications of SFC Separations
Qualitative and Quantitative
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Fractionation of complex mixtures
Nondestructive, separation of closely related compounds
Samples
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Environmental sensing
Monitoring pesticides and insecticides
Purification of complex mixtures
Surfactants and hydrocarbons
Active drugs, synthetic byproducts, and degradation products
Separation of polymers and polymer additives
Determination of molecular weight distribution
Limitations
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Sensitivity and detection limits dependent on the type of
detector used
Resolution is difficult for complex mixtures
Sample types
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Solid samples
Liquid samples
Aqueous samples ◆
High viscosity liquids