ASTM E1449-92(2011)
(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, apparatuses, 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 E355 and E682.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
General Information
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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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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 2011)
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 is a term used when the mobile phase is kept
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
1.3 The values stated in SI units are to be regarded as
components through the separation column. Isobaric intervals
standard. No other units of measurement are included in this
may be included in the pressure program.
standard.
3.4 In supercritical fluid chromatography, the temperature
may be constant, or changing during a chromatographic
2. Referenced Documents
separation.
2.1 ASTM Standards:
3.4.1 Isothermal Supercritical Fluid Chromatography is the
E355PracticeforGasChromatographyTermsandRelation-
version of the technique in which the column temperature is
ships
held constant during the passage of the sample components
E682Practice for Liquid Chromatography Terms and Rela-
through the separation column.
tionships
3.4.2 Programmed Temperature Supercritical Fluid Chro-
matography is the version of the technique in which the
3. Names of Techniques
columntemperatureischangedwithtimeduringthepassageof
3.1 Supercritical Fluid Chromatography, abbreviated as
the sample components through the separation column. Iso-
SFC, comprises all chromatographic methods in which both
thermal intervals may be included in the temperature program.
the mobile phase is supercritical under the conditions of
3.5 In supercritical fluid chromatography, the density may
analysis and where the solvating properties of the fluid have a
be constant or changing during the chromatographic separa-
measurableaffectontheseparation.Earlyworkinthefieldwas
tion.
performed under a broader heading–dense gas chromatogra-
3.5.1 Isoconfertic is a term used when the density of the
phy. Related work in the field uses subcritical or near-critical
mobile phase is kept constant for a specified time or for the
conditions to affect separation.
entire chromatographic separation.
3.2 Separation is achieved by differences in the distribution
3.5.2 Programmed Density Supercritical Fluid Chromatog-
of the components of a sample between the mobile and
raphy is the version of the technique in which the column
stationaryphases,causingthemtomovethroughthecolumnat
density is changed with time during the passage of the sample
different rates (differential migration).
components through the separation column. Isoconfertic inter-
vals may be included in the density program.
3.5.3 Flow Programming is a technique where the mobile
This guide is under the jurisdiction of ASTM Committee E13 on Molecular
phase linear velocity is changed during the chromatographic
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
mittee E13.19 on Separation Science.
procedure. However, with fixed orifice restrictors, flow pro-
Current edition approved Nov. 1, 2011. Published December 2011. Originally
grammingismorecomplexrequiringanincreaseinpressureto
approved in 1992. Last previous edition approved in 2006 as E1449–92(2006).
effect an increase in linear velocity.
DOI: 10.1520/E1449-92R11.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
3.6 In supercritical fluid chromatography, the composition
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
of the mobile phase may be constant or changing during a
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. chromatographic separation.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1449 − 92 (2011)
3.6.1 The term Isocratic is used when the composition of 4.3.2 Wall-Coated Open-Tubular Supercritical Fluid Chro-
the mobile phase is kept constant during a chromatographic matography uses a liquid that is chemically bonded to the wall
separation. of an open-tubular column as stationary phase. Fused silica
tubing columns, internal diameter (i.d.) > 100 µm, may shatter
3.6.2 The term Gradient Elution is used to specify the
atpressuresemployedinSFC.Ahighdegreeofcrosslinkingis
technique when a deliberate change in the mobile phase
desirable to reduce stationary phase solubility in the mobile
composition is made during the chromatographic procedure.
phase.
Isocratic intervals may be included in the gradient program.
4.4 Restrictors are devices employed to maintain the pres-
4. Apparatus
sure in the chromatographic system. The pressure of the
supercritical fluid is usually reduced to ambient after passage
4.1 Pumps—The function of the pumps is to deliver the
throughtherestrictor.Themobilephaseflowrateisdetermined
mobile phase at a controlled flow rate to the chromatographic
by the restrictor dimensions or operation. The restrictor is
column.
placed before some types of detectors (for example, flame
4.1.1 Syringe Pumps have a piston that advances at a
ionization, mass spectrometer) and after other types of detec-
controlledratewithinasmoothcylindertodisplacethemobile
tors (for example, UV).
phase.
4.4.1 A Linear Restrictor is a length of small i.d. tubing of
4.1.2 Reciprocating Pumps have a single or dual chamber
uniform bore. Linear restrictors are made of polyimidecoated
from which mobile phase is displaced by reciprocating pis-
fused silica tubing, or stainless steel or other tubing of the
ton(s) or diaphragm(s).
appropriate diameter. The amount of restriction provided is
4.2 Sample Inlet Systems represent the means for introduc-
dependent upon both the length and i.d. of the tubing.
ing samples into the columns.
4.4.2 A Tapered Restrictor is a length of small i.d. tubing
4.2.1 Direct Injection is a sample introduction technique
where one end has been reduced by drawing in a flame in the
wherebytheentirevolumeofsampleissweptontotheheadof
case of fused silica tubing, or crimped in the case of metal
the analytical column. Its use is most prevalent in packed
tubing.
column SFC.
4.4.3 An Integral Restrictor (1) consists of a length of
4.2.2 Split-Flow Injection introduces only a portion of the
fused silica tubing with one end closed by heating with a
sample volume onto the analytical column so as to prevent
microtorch.Thisclosedendisthengrounduntilaholewiththe
overloading of the column in open tubular SFC. This is
desired initial linear velocity is obtained.
achievedbytheuseofasplitterteeorsimilarcontrivance,such
4.4.4 A Converging-Diverging Restrictor (2)hasthewallof
that the incoming slug of sample is divided between the
the tubing collapsed slightly near one end forming a constric-
analytical column and a flow restrictor vented to waste. The
tion. This constriction is similar to a venturi in profile and the
amount of sample deposited on the column is a function of the
point of smallest diameter is located about 1 to 2 mm from the
ratio of the flow to the column versus the flow through this
end of the tubing.
restrictor. This ratio can thus be adjusted for different samples
4.4.5 An Orifice is a type of restrictor which uses a metal
and column capacities.
disk or diaphragm with an appropriately sized opening. This
4.2.3 Timed-Split (Moving-Split) Injection achieves the
type normally requires an adapter or holder specifically de-
same end result as split-flow injection. The volume of sample signed to couple the device to a detector.
introducedontothecolumnisgovernedbytherapidback-and-
4.4.6 A Porous Frit Restrictor consistsofalengthoffused
forth motion of an internal-loop sample rotor in a valve. The silica tubing containing a porous plug at one end.
time interval between the two motions determines the volume
4.4.7 A Back Pressure Regulator consists of a diaphragm
of sample injected, with shorter times delivering smaller valvewhichcanbeadjustedtocontrolthepressuremaintained
volumes.
on its inlet (instrument) side. The outlet discharge pressure is
4.2.4 On-Line Supercritical Extraction is a means of di- nominally one atmosphere.
rectly introducing a sample or portion of a sample into a
4.5 Detectors are devices that respond to the presence of
supercritical fluid chromatograph. The sample is placed in an
eluted solutes in the mobile phase emerging from the column.
extraction cell and extracted with the supercritical fluid. The
Ideally, the response should be proportional to the mass or
extraction effluent containing the solutes of interest are ulti-
concentration of solute in the mobile phase. Detectors may be
mately transferred to the column by the action of switching or
divided either according to the type of measurement or the
sampling valves. This can be accomplished with or without
principle of detection.
solute focusing (that is, using a suitable trap such as a
4.5.1 Differential Concentration Detectorsmeasurethepro-
cryogenic trapping).
portion of eluted sample component(s) in the mobile phase
4.3 Columns consist of tubes that contain the stationary passing through the detector. The peak area is inversely
proportional to the mobile phase flow rate.
phase and through which the supercritical fluid mobile phase
flows.
4.3.1 Packed Column Supercritical Fluid Chromatography
The boldface numbers in parentheses refer to a list of references at the end of
uses an active solid or a liquid that is chemically bonded to a
this standard.
solid and packed into a column, generally stainless steel or
Cortez,H.,Pfeiffer,C.,Richter,B.,andStevens,T.U.S.,PatentNo.4793920,
fused silica; as the stationary phase. 1988.
E1449 − 92 (2011)
4.5.2 Differential Mass Detectorsmeasuretheinstantaneous 5.3.1 An Interactive Solidisastationaryphasematerialwith
mass of a component within the detector per unit time (g/s). bulk homogeneity where the surface effects separation by
The area under the curve is independent of the mobile phase adsorptive interactions. Examples are silica and alumina.
flow rate. 5.3.2 A Bonded Phase is a stationary phase that has been
covalentlyattachedtoasolidsupport.Thesamplecomponents
5. Reagents
partition between the stationary and mobile phases which
resultsinseparation.Octadecylsilylgroupsbondedtosilicagel
5.1 Supercritical Fluid is a fluid state of a substance
particles and polydimethylsiloxane (or dimethyl polysiloxane)
intermediate between a gas and a liquid. A supercritical fluid
bonded to deactivated fused silica column wall represent
maybedefinedfromtheaccompanyingphasediagram(Fig.1).
examples for packed column and open tubular column phases,
The supercritical fluid region is defined by temperatures and
respectively.
pressures, both above the critical values.Asubcritical fluid (or
liquid) is a compound that would usually be a gas at ambient
5.4 The Solid Support is the inert material that holds the
temperature but is held as a liquid by the application of
stationary phase in intimate contact with the mobile phase. It
pressure below its supercritical point.
may consist of porous or impenetrable particles or granules or
5.1.1 The Critical Temperature is the temperature above
theinteriorwallofthecolumnitself,oracombinationofthese.
which a substance cannot be liquefied or condensed no matter
5.5 The Column Packing consists of all the material used to
how great the applied pressure.
fillpackedcolumns,includingthesolidsupportandthebonded
5.1.2 The Critical Pressure is the pressure that would just
phase or the interactive solid.
suffice to liquefy the fluid at its critical temperature.
5.6 Solutes are the sample components that are introduced
5.1.3 The Reduced Pressure is the ratio of the working
into the chromatographic system and are transported by the
pressure to the critical pressure of the substance.
mobile phase and elute through the column. Some solutes may
5.1.4 The Reduced Temperature is the ratio of the working
be unretained.
temperature to the critical temperature of the substance.
5.1.5 The Densityofasupercriticalfluid(theweightperunit
6. Readout
volume of the fluid) in chromatographic separations is calcu-
lated from an empirical equation of state. 6.1 A Chromatogram is a plot of detector response against
time or effluent volume. Idealized chromatograms obtained
5.2 A Modifier or co-solvent is a substance added to a
withadifferentialdetectorforanunretainedsubstanceandone
supercritical fluid to enhance its solvent strength, usually by
other component are shown in Fig. 2.
increasingthepolarityofthemobilephase,orbindingtoactive
sites on a stationary phase.
6.2 The definitions in 6.2.1 – 6.2.6 apply to chromatograms
obtained directly by means of differential detectors or indi-
5.3 The Stationary Phase is composed of the active immo-
rectly by differentiating the response of integral detectors.
bile materials within the column that selectively retard the
6.2.1 A Baselineisthatportionofachromatogramwhereno
passage of sample components. Inert materials that merely
detectable sample components emerge from the column.
provide physical support or occupy space within the columns
6.2.2 A Peak is that portion of a chromatogram where a
are not part of the stationary phase.
single detectable component, or two or more unresolved
NOTE 1—Extremely porous stationary phases may exhibit exclusion
detectable components, elute from the column.
phenomenon in addition to adsorptive interactions.
6.2.3 The Peak Base,CDinFig.2,istheinterpolationofthe
baseline between the extremities of a peak.
6.2.4 The Peak Area, CHFEGJD in Fig. 2, is the area
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.
FIG. 1 Phase Diagram FIG. 2 Typical Chromatogram
E1449 − 92 (2011)
6.2.6 Peak Widthsrepresentretentiondimensionsparallelto retention dime
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