ASTM E1449-92(2019)
(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.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1449 − 92 (Reapproved 2019)
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 performed under a broader heading–dense gas chromatogra-
phy. Related work in the field uses subcritical or near-critical
1.1 This guide deals primarily with the terms and relation-
conditions to affect separation.
ships used in supercritical fluid chromatography.
3.2 Separation is achieved by differences in the distribution
1.2 Sincemanyofthebasictermsanddefinitionsalsoapply
of the components of a sample between the mobile and
to gas chromatography and liquid chromatography, this guide
stationaryphases,causingthemtomovethroughthecolumnat
is using, whenever possible, symbols identical to Practices
different rates (differential migration).
E355 and E682.
3.3 In supercritical fluid chromatography, the pressure may
1.3 The values stated in SI units are to be regarded as
be constant or changing during a chromatographic separation.
standard. No other units of measurement are included in this
3.3.1 Isobaric is a term used when the mobile phase is kept
standard.
at constant pressure. This may be for a specified time interval
1.4 This international standard was developed in accor-
or for the entire chromatographic separation.
dance with internationally recognized principles on standard-
3.3.2 Programmed Pressure Supercritical Fluid Chroma-
ization established in the Decision on Principles for the
tography is the version of the technique in which the column
Development of International Standards, Guides and Recom-
pressureischangedwithtimeduringthepassageofthesample
mendations issued by the World Trade Organization Technical
components through the separation column. Isobaric intervals
Barriers to Trade (TBT) Committee.
may be included in the pressure program.
3.4 In supercritical fluid chromatography, the temperature
2. Referenced Documents
may be constant, or changing during a chromatographic
2.1 ASTM Standards:
separation.
E355PracticeforGasChromatographyTermsandRelation-
3.4.1 Isothermal Supercritical Fluid Chromatography is the
ships
version of the technique in which the column temperature is
E682Practice for Liquid Chromatography Terms and Rela-
held constant during the passage of the sample components
tionships
through the separation column.
3.4.2 Programmed Temperature Supercritical Fluid Chro-
3. Names of Techniques
matography is the version of the technique in which the
3.1 Supercritical Fluid Chromatography, abbreviated as
columntemperatureischangedwithtimeduringthepassageof
SFC, comprises all chromatographic methods in which both
the sample components through the separation column. Iso-
the mobile phase is supercritical under the conditions of
thermal intervals may be included in the temperature program.
analysis and where the solvating properties of the fluid have a
3.5 In supercritical fluid chromatography, the density may
measurableaffectontheseparation.Earlyworkinthefieldwas
be constant or changing during the chromatographic separa-
tion.
This guide is under the jurisdiction of ASTM Committee E13 on Molecular
3.5.1 Isoconfertic is a term used when the density of the
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
mobile phase is kept constant for a specified time or for the
mittee E13.19 on Separation Science.
entire chromatographic separation.
Current edition approved Dec. 1, 2019. Published December 2019. Originally
3.5.2 Programmed Density Supercritical Fluid Chromatog-
approved in 1992. Last previous edition approved in 2011 as E1449–92(2011).
DOI: 10.1520/E1449–92R19.
raphy is the version of the technique in which the column
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
density is changed with time during the passage of the sample
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
components through the separation column. Isoconfertic inter-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. vals may be included in the density program.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1449 − 92 (2019)
3.5.3 Flow Programming is a technique where the mobile 4.3 Columns consist of tubes that contain the stationary
phase linear velocity is changed during the chromatographic phase and through which the supercritical fluid mobile phase
procedure. However, with fixed orifice restrictors, flow pro- flows.
grammingismorecomplexrequiringanincreaseinpressureto 4.3.1 Packed Column Supercritical Fluid Chromatography
effect an increase in linear velocity. uses an active solid or a liquid that is chemically bonded to a
solid and packed into a column, generally stainless steel or
3.6 In supercritical fluid chromatography, the composition
fused silica; as the stationary phase.
of the mobile phase may be constant or changing during a
4.3.2 Wall-Coated Open-Tubular Supercritical Fluid Chro-
chromatographic separation.
matography uses a liquid that is chemically bonded to the wall
3.6.1 The term Isocratic is used when the composition of
of an open-tubular column as stationary phase. Fused silica
the mobile phase is kept constant during a chromatographic
tubing columns, internal diameter (i.d.) > 100 µm, may shatter
separation.
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.
Isocratic intervals may be included in the gradient program. 4.4 Restrictors are devices employed to maintain the pres-
sure in the chromatographic system. The pressure of the
4. Apparatus
supercritical fluid is usually reduced to ambient after passage
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 A Converging-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
4.4.6 A Porous 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
extraction effluent containing the solutes of interest are ulti-
mately transferred to the column by the action of switching or
The boldface numbers in parentheses refer to a list of references at the end of
sampling valves. This can be accomplished with or without
this standard.
solute focusing (that is, using a suitable trap such as a
Cortez,H.,Pfeiffer,C.,Richter,B.,andStevens,T.U.S.,PatentNo.4793920,
cryogenic trapping). 1988.
E1449 − 92 (2019)
concentration of solute in the mobile phase. Detectors may be 5.3 The Stationary Phase is composed of the active immo-
divided either according to the type of measurement or the bile materials within the column that selectively retard the
principle of detection. passage of sample components. Inert materials that merely
4.5.1 Differential Concentration Detectorsmeasurethepro- provide physical support or occupy space within the columns
portion of eluted sample component(s) in the mobile phase are not part of the stationary phase.
passing through the detector. The peak area is inversely
NOTE 1—Extremely porous stationary phases may exhibit exclusion
proportional to the mobile phase flow rate.
phenomenon in addition to adsorptive interactions.
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
5.1 Supercritical Fluid is a fluid state of a substance
resultsinseparation.Octadecylsilylgroupsbondedtosilicagel
intermediate between a gas and a liquid. A supercritical fluid
particles and polydimethylsiloxane (or dimethyl polysiloxane)
maybedefinedfromtheaccompanyingphasediagram(Fig.1).
bonded to deactivated fused silica column wall represent
The supercritical fluid region is defined by temperatures and
examples for packed column and open tubular column phases,
pressures, both above the critical values.Asubcritical fluid (or
respectively.
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.
5.1.3 The Reduced Pressure is the ratio of the working
5.6 Solutes are the sample components that are introduced
pressure to the critical pressure of the substance.
into the chromatographic system and are transported by the
5.1.4 The Reduced Temperature is the ratio of the working
mobile phase and elute through the column. Some solutes may
temperature to the critical temperature of the substance.
be unretained.
5.1.5 The Densityofasupercriticalfluid(theweightperunit
volume of the fluid) in chromatographic separations is calcu-
6. Readout
lated from an empirical equation of state.
6.1 A Chromatogram is a plot of detector response against
5.2 A Modifier or co-solvent is a substance added to a
time or effluent volume. Idealized chromatograms obtained
supercritical fluid to enhance its solvent strength, usually by
withadifferentialdetectorforanunretainedsubstanceandone
increasingthepolarityofthemobilephase,orbindingtoactive
other component are shown in Fig. 2.
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-
rectly by differentiating the response of integral detectors.
6.2.1 A Baselineisthatportionofachromatogramwhereno
detectable sample components emerge from the column.
6.2.2 A Peak is that portion of a chromatogram where a
single detectable component, or two or more unresolved
detectable components, elute from the column.
FIG. 1 Phase Diagram FIG. 2 Typical Chromatogram
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