ASTM E1449-92(2006)
(Guide)Standard Guide for Supercritical Fluid Chromatography Terms and Relationships
Standard Guide for Supercritical Fluid Chromatography Terms and Relationships
ABSTRACT
This guide deals primarily with the terms and relationships used in supercritical fluid chromatography, including techniques, apparatus, and reagents.
SCOPE
1.1 This guide deals primarily with the terms and relationships used in supercritical fluid chromatography.
1.2 Since many of the basic terms and definitions also apply to gas chromatography and liquid chromatography, this guide is using, whenever possible, symbols identical to Practices E 355 and E 682.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:E1449–92 (Reapproved 2006)
Standard Guide for
Supercritical Fluid Chromatography Terms and
Relationships
This standard is issued under the fixed designation E1449; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.3 In supercritical fluid chromatography, the pressure may
be constant or changing during a chromatographic separation.
1.1 This guide deals primarily with the terms and relation-
3.3.1 Isobaric isatermusedwhenthemobilephaseiskept
ships used in supercritical fluid chromatography.
at constant pressure. This may be for a specified time interval
1.2 Sincemanyofthebasictermsanddefinitionsalsoapply
or for the entire chromatographic separation.
to gas chromatography and liquid chromatography, this guide
3.3.2 Programmed Pressure Supercritical Fluid Chroma-
is using, whenever possible, symbols identical to Practices
tography is the version of the technique in which the column
E355 and E682.
pressureischangedwithtimeduringthepassageofthesample
2. Referenced Documents
components through the separation column. Isobaric intervals
may be included in the pressure program.
2.1 ASTM Standards:
3.4 In supercritical fluid chromatography, the temperature
E355 Practice for Gas Chromatography Terms and Rela-
may be constant, or changing during a chromatographic
tionships
separation.
E682 Practice for Liquid ChromatographyTerms and Rela-
3.4.1 Isothermal Supercritical Fluid Chromatography is
tionships
the version of the technique in which the column temperature
3. Names of Techniques
is held constant during the passage of the sample components
through the separation column.
3.1 Supercritical Fluid Chromatography, abbreviated as
3.4.2 Programmed Temperature Supercritical Fluid Chro-
SFC, comprises all chromatographic methods in which both
matography is the version of the technique in which the
the mobile phase is supercritical under the conditions of
columntemperatureischangedwithtimeduringthepassageof
analysis and where the solvating properties of the fluid have a
the sample components through the separation column. Iso-
measurableaffectontheseparation.Earlyworkinthefieldwas
thermal intervals may be included in the temperature program.
performed under a broader heading–dense gas chromatogra-
3.5 In supercritical fluid chromatography, the density may
phy. Related work in the field uses subcritical or near-critical
be constant or changing during the chromatographic separa-
conditions to affect separation.
tion.
3.2 Separation is achieved by differences in the distribution
3.5.1 Isoconfertic is a term used when the density of the
of the components of a sample between the mobile and
mobile phase is kept constant for a specified time or for the
stationaryphases,causingthemtomovethroughthecolumnat
entire chromatographic separation.
different rates (differential migration).
3.5.2 Programmed Density Supercritical Fluid Chromatog-
raphy is the version of the technique in which the column
This guide is under the jurisdiction of ASTM Committee E13 on Molecular density is changed with time during the passage of the sample
Spectroscopy and is the direct responsibility of Subcommittee E13.19 on Chroma-
components through the separation column. Isoconfertic inter-
tography.
vals may be included in the density program.
Current edition approved Sept. 1, 2006. Published September 2006. Originally
3.5.3 Flow Programming is a technique where the mobile
approved in 1992. Last previous edition approved in 2000 as E1449–92(2000).
DOI: 10.1520/E1449-92R06.
phase linear velocity is changed during the chromatographic
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
procedure. However, with fixed orifice restrictors, flow pro-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
grammingismorecomplexrequiringanincreaseinpressureto
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. effect an increase in linear velocity.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1449–92 (2006)
3.6 In supercritical fluid chromatography, the composition solid and packed into a column, generally stainless steel or
of the mobile phase may be constant or changing during a fused silica; as the stationary phase.
chromatographic separation. 4.3.2 Wall-Coated Open-Tubular Supercritical Fluid Chro-
3.6.1 The term Isocratic is used when the composition of matography usesaliquidthatischemicallybondedtothewall
of an open-tubular column as stationary phase. Fused silica
the mobile phase is kept constant during a chromatographic
separation. tubing columns, internal diameter (i.d.) > 100 µm, may shatter
atpressuresemployedinSFC.Ahighdegreeofcrosslinkingis
3.6.2 The term Gradient Elution is used to specify the
desirable to reduce stationary phase solubility in the mobile
technique when a deliberate change in the mobile phase
phase.
composition is made during the chromatographic procedure.
4.4 Restrictors are devices employed to maintain the pres-
Isocratic intervals may be included in the gradient program.
sure in the chromatographic system. The pressure of the
supercritical fluid is usually reduced to ambient after passage
4. Apparatus
throughtherestrictor.Themobilephaseflowrateisdetermined
4.1 Pumps—The function of the pumps is to deliver the
by the restrictor dimensions or operation. The restrictor is
mobile phase at a controlled flow rate to the chromatographic
placed before some types of detectors (for example, flame
column.
ionization, mass spectrometer) and after other types of detec-
4.1.1 Syringe Pumps have a piston that advances at a
tors (for example, UV).
controlledratewithinasmoothcylindertodisplacethemobile
4.4.1 A Linear Restrictor is a length of small i.d. tubing of
phase.
uniform bore. Linear restrictors are made of polyimidecoated
4.1.2 Reciprocating Pumps have a single or dual chamber
fused silica tubing, or stainless steel or other tubing of the
from which mobile phase is displaced by reciprocating pis-
appropriate diameter. The amount of restriction provided is
ton(s) or diaphragm(s).
dependent upon both the length and i.d. of the tubing.
4.2 Sample Inlet Systems represent the means for introduc-
4.4.2 A Tapered Restrictor is a length of small i.d. tubing
ing samples into the columns.
where one end has been reduced by drawing in a flame in the
4.2.1 Direct Injection is a sample introduction technique
case of fused silica tubing, or crimped in the case of metal
wherebytheentirevolumeofsampleissweptontotheheadof
tubing.
the analytical column. Its use is most prevalent in packed
4.4.3 An Integral Restrictor (1) consists of a length of
column SFC.
fused silica tubing with one end closed by heating with a
4.2.2 Split-Flow Injection introduces only a portion of the
microtorch.Thisclosedendisthengrounduntilaholewiththe
sample volume onto the analytical column so as to prevent
desired initial linear velocity is obtained.
overloading of the column in open tubular SFC. This is
4.4.4 AConverging-Diverging Restrictor(2)hasthewallof
achievedbytheuseofasplitterteeorsimilarcontrivance,such
the tubing collapsed slightly near one end forming a constric-
that the incoming slug of sample is divided between the
tion. This constriction is similar to a venturi in profile and the
analytical column and a flow restrictor vented to waste. The
point of smallest diameter is located about 1 to 2 mm from the
amount of sample deposited on the column is a function of the
end of the tubing.
ratio of the flow to the column versus the flow through this
4.4.5 An Orifice is a type of restrictor which uses a metal
restrictor. This ratio can thus be adjusted for different samples
disk or diaphragm with an appropriately sized opening. This
and column capacities.
type normally requires an adapter or holder specifically de-
4.2.3 Timed-Split (Moving-Split) Injection achieves the
signed to couple the device to a detector.
same end result as split-flow injection. The volume of sample 4
4.4.6 APorous Frit Restrictor consistsofalengthoffused
introducedontothecolumnisgovernedbytherapidback-and-
silica tubing containing a porous plug at one end.
forth motion of an internal-loop sample rotor in a valve. The
4.4.7 A Back Pressure Regulator consists of a diaphragm
time interval between the two motions determines the volume
valvewhichcanbeadjustedtocontrolthepressuremaintained
of sample injected, with shorter times delivering smaller
on its inlet (instrument) side. The outlet discharge pressure is
volumes.
nominally one atmosphere.
4.2.4 On-Line Supercritical Extraction is a means of di-
4.5 Detectors are devices that respond to the presence of
rectly introducing a sample or portion of a sample into a
eluted solutes in the mobile phase emerging from the column.
supercritical fluid chromatograph. The sample is placed in an
Ideally, the response should be proportional to the mass or
extraction cell and extracted with the supercritical fluid. The
concentration of solute in the mobile phase. Detectors may be
extraction effluent containing the solutes of interest are ulti-
divided either according to the type of measurement or the
mately transferred to the column by the action of switching or
principle of detection.
sampling valves. This can be accomplished with or without
4.5.1 Differential Concentration Detectors measure the
solute focusing (that is, using a suitable trap such as a
proportion of eluted sample component(s) in the mobile phase
cryogenic trapping).
4.3 Columns consist of tubes that contain the stationary
phase and through which the supercritical fluid mobile phase
The boldface numbers in parentheses refer to the list of references at the end
flows.
of this guide.
4.3.1 Packed Column Supercritical Fluid Chromatography-
Cortez,H.,Pfeiffer,C.,Richter,B.,andStevens,T.U.S.,PatentNo.4793920,
uses an active solid or a liquid that is chemically bonded to a 1988.
E1449–92 (2006)
passing through the detector. The peak area is inversely 5.3.1 AnInteractiveSolidisastationaryphasematerialwith
proportional to the mobile phase flow rate. bulk homogeneity where the surface effects separation by
4.5.2 Differential Mass Detectors measure the instanta- adsorptive interactions. Examples are silica and alumina.
neous mass of a component within the detector per unit time 5.3.2 A Bonded Phase is a stationary phase that has been
(g/s). The area under the curve is independent of the mobile covalentlyattachedtoasolidsupport.Thesamplecomponents
phase flow rate. partition between the stationary and mobile phases which
resultsinseparation.Octadecylsilylgroupsbondedtosilicagel
5. Reagents
particles and polydimethylsiloxane (or dimethyl polysiloxane)
bonded to deactivated fused silica column wall represent
5.1 Supercritical Fluid is a fluid state of a substance inter-
examples for packed column and open tubular column phases,
mediate between a gas and a liquid. A supercritical fluid may
respectively.
bedefinedfromtheaccompanyingphasediagram(Fig.1).The
5.4 The Solid Support is the inert material that holds the
supercritical fluid region is defined by temperatures and
stationary phase in intimate contact with the mobile phase. It
pressures, both above the critical values.Asubcritical fluid (or
may consist of porous or impenetrable particles or granules or
liquid) is a compound that would usually be a gas at ambient
theinteriorwallofthecolumnitself,oracombinationofthese.
temperature but is held as a liquid by the application of
5.5 The Column Packing consists of all the material used to
pressure below its supercritical point.
fillpackedcolumns,includingthesolidsupportandthebonded
5.1.1 The Critical Temperature is the temperature above
phase or the interactive solid.
which a substance cannot be liquefied or condensed no matter
5.6 Solutes are the sample components that are introduced
how great the applied pressure.
into the chromatographic system and are transported by the
5.1.2 The Critical Pressure is the pressure that would just
mobile phase and elute through the column. Some solutes may
suffice to liquefy the fluid at its critical temperature.
be unretained.
5.1.3 The Reduced Pressure is the ratio of the working
pressure to the critical pressure of the substance.
6. Readout
5.1.4 The Reduced Temperature is the ratio of the working
6.1 A Chromatogram is a plot of detector response against
temperature to the critical temperature of the substance.
time or effluent volume. Idealized chromatograms obtained
5.1.5 TheDensityofasupercriticalfluid(theweightperunit
volume of the fluid) in chromatographic separations is calcu- withadifferentialdetectorforanunretainedsubstanceandone
other component are shown in Fig. 2.
lated from an empirical equation of state.
5.2 A Modifier or co-solvent is a substance added to a 6.2 The definitions in 6.2.1-6.2.6 apply to chromatograms
obtained directly by means of differential detectors or indi-
supercritical fluid to enhance its solvent strength, usually by
increasingthepolarityofthemobilephase,orbindingtoactive rectly by differentiating the response of integral detectors.
6.2.1 ABaselineisthatportionofachromatogramwhereno
sites on a stationary phase.
5.3 The Stationary Phase is composed of the active immo- detectable sample components emerge from the column.
6.2.2 A Peak is that portion of a chromatogram where a
bile materials within the column that selectively retard the
passage of sample components. Inert materials that merely single detectable component, or two or more unresolved
detectable components, elute from the column.
provide physical support or occupy space within the columns
are not part of the stationary phase. 6.2.3 ThePeakBase,CDinFig.2,istheinterpolationofthe
baseline between the extremities of a peak.
NOTE 1—Extremely porous stationary phases may exhibit exclusion
6.2.4 The Peak Area, CHFEGJD in Fig. 2, is the area
phenomenon in addition to adsorptive interactions.
enclosed between the peak and the peak base.
6.2.5 Peak Height,EBin Fig. 2, is the perpendicular
distance measured in the direction of detector response, from
the peak base to peak maximum.
6.2.6 Peak Widths represent retention dimensions parallel
tothebaseline.Peakwidthatbaseorbasewidth,KLinFig.2,
is the retention dimension of the peak base intercepted by the
FIG. 1 Phase Diagram FIG. 2 Typical Chromatogram
E1449–92 (2006)
tangents drawn to the inflection points on both sides of the 7. Retentio
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