ASTM E355-96(2021)e1
(Practice)Standard Practice for Gas Chromatography Terms and Relationships
Standard Practice for Gas Chromatography Terms and Relationships
ABSTRACT
This practice presents the terms, parameters, symbols, units, and relationships used in gas elution chromatography. Most of the terms described herein should also apply to other kinds of gas chromatography and various liquid column chromatographic techniques. At this time, however, they are not standardized for the latter usage. These terms include names of techniques, apparatuses and reagents, parameters used in data recording and presentation of isothermal retention data, and retention parameters.
SCOPE
1.1 This practice covers primarily the terms and relationships used in gas elution chromatography. However, most of the terms should also apply to other kinds of gas chromatography and are also valid in the various liquid column chromatographic techniques, although at this time they are not standardized for the latter usage.
1.2 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
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.
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Designation: E355 − 96 (Reapproved 2021)
Standard Practice for
Gas Chromatography Terms and Relationships
This standard is issued under the fixed designation E355; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
ε NOTE—Table 1 was corrected editorially in April 2021.
1. Scope the sample is introduced as a liquid, it is vaporized in the
system prior to or during passage through the separation
1.1 This practice covers primarily the terms and relation-
column.
ships used in gas elution chromatography. However, most of
the terms should also apply to other kinds of gas chromatog- 2.5 Gas-Frontal Chromatography is a technique in which a
raphy and are also valid in the various liquid column chro- continuous stream of carrier gas mixed with sample vapor is
matographic techniques, although at this time they are not instantaneously replaced by a continuous stream of carrier gas
standardized for the latter usage. containing sample vapor at a different concentration. The
concentration profile is therefore step-shaped at the column
1.2 This international standard was developed in accor-
inlet.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
2.6 Gas-Displacement Chromatography employs a desor-
Development of International Standards, Guides and Recom- bent as the carrier gas or in the carrier gas to displace a less
mendations issued by the World Trade Organization Technical
strongly held solute from the stationary phase which in turn
Barriers to Trade (TBT) Committee. displaces the next less strongly held one etc., causing the
components to emerge in the normal order, that is, least-to-
2. Names of Techniques most strongly absorbed.
2.1 Gas Chromatography, abbreviated as GC, comprises all 2.7 Isothermal Gas Chromatography is the version of the
chromatographic methods in which the moving phase is technique in which the column temperature is held constant
gaseous. The stationary phase may be either a dry granular during the passage of the sample components through the
solid or a liquid supported by the granules or by the wall of the separation column.
column, or both. Separation is achieved by differences in the
2.8 Programmed Temperature Gas Chromatography
distribution of the components of a sample between the mobile
(PTGC), is the version of the technique in which the column
and stationary phases, causing them to move through the
temperature is changed with time during the passage of the
column at different rates and from it at different times. In this
sample components through the separation column. In linear
recommended practice gas elution chromatography is implied.
PTGC the program rate is constant during analysis. Isothermal
2.2 Gas-Liquid Chromatography, abbreviated as GLC, uti- intervals may be included in the temperature program.
lizesaliquidasthestationaryphase,whichactsasasolventfor
2.9 Programmed Flow, Pressure, or Velocity Gas Chroma-
the sample components.
tographyistheversionofthetechniqueinwhichthecarriergas
2.3 Gas-Solid Chromatography, abbreviated as GSC, uti- flow, pressure, or velocity is changed during analysis.
lizes an active solid (adsorbent) as the stationary phase.
2.10 Reaction Gas Chromatography is the version of the
technique in which the composition of the sample is changed
2.4 Gas Elution Chromatography utilizes a continuous inert
gasflowasthecarriergasandthesampleisintroducedasagas between sample introduction and the detector.The reaction can
take place upstream of the column when the chemical compo-
or a liquid with a finite volume into the carrier gas stream. If
sition of the individual components passing through the col-
umn differs from that of the original sample, or between the
column and the detector when the original sample components
This practice is under the jurisdiction of ASTM Committee E13 on Molecular
are separated in the column but their chemical composition is
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
mittee E13.19 on Separation Science.
changed prior to entering the detection device.
Current edition approved April 1, 2021. Published April 2021. Originally
2.11 Pyrolysis Gas Chromatography is the version of reac-
approved in 1968. Last previous edition approved in 2014 as E355 – 96 (2014).
DOI: 10.1520/E0355-96R21E01. tion gas chromatography in which the original sample is
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E355 − 96 (2021)
decomposed by heat to more volatile components prior to solid layer consists of the particles of a solid support which
passage through the separation column. were deposited on the inside tube wall.
3.3 Detectors, are devices that indicate the presence of
3. Apparatus
eluted components in the carrier gas emerging from the
column.
3.1 Sample Inlet Systems, represent the means for introduc-
ing samples into the separation column, including the heated 3.3.1 Differential Concentration Detectors, measure the in-
zones permitting the vaporization of the introduced liquid stantaneous proportion of eluted sample components in the
samples prior to their passage through the column. Sample carrier gas passing through the detector.
introduction can be carried out by introduction of a liquid, 3.3.2 Differential Mass Detectors, measure the instanta-
solid, or gas into the carrier-gas stream. The sample may be neous rate of arrival of sample components at the detector.
vaporized before or after introduction into the column. 3.3.3 Integral Detectors, measure the accumulated quantity
3.1.1 Direct Inlets, rapidly vaporize the sample prior to
of sample component(s) reaching the detector.
enteringthecolumn.Allofthesamplevaporentersthecolumn. 3.3.4 Spectrometric Detectors, measure and record spectra
3.1.2 On-Column Inlets, introduce a liquid sample into the
of eluting components, such as the mass spectrum of the
column. The sample vaporizes as the column section contain- infrared spectrum.
ing the liquid heats up after injection.
3.4 Traps, are devices for recovering sample components
3.1.3 Split Inlets, rapidly vaporize the sample prior to
from the mobile phase eluting from GC columns.
entering the column. A defined fraction of the sample vapor
entersthecolumn;theremainderleavestheinletthroughavent
4. Reagents
ataflowrate F .Theratioofthetotalinletflow(F + F)tothe
v v c
4.1 Carrier Gas is the Mobile Phase used to sweep or elute
column flow (F ) is called the split ratio (s):
c
the sample components through and from the column.
F 1F
v c
s 5 (1)
4.2 The Stationary Phase is composed of the active immo-
F
c
bile materials within the column that selectively delay the
3.1.4 Splitless Injection, utilizes a split inlet wherein the
passage of sample components by dissolving or adsorbing
split vent flow is blocked during the injection period such that
them, or both. Inert materials that merely provide physical
most of the sample vapor enters the column. The injection
support for the stationary phase or occupy space within the
period is typically one minute. The split vent flow is reestab-
column are not part of the stationary phase.
lished afterward usually for the remainder of the run.
4.2.1 Liquid Stationary Phase is one type of stationary
3.1.5 Programmed-Temperature Vaporizers (PTV), accept a
phase which is dispersed on the solid support or the inner
liquid sample that vaporizes as the inlet system heats up after
column wall and causes the separation of the sample compo-
injection. A PTV may operate in either a split, splitless,
nents by differences in the partitioning of the sample compo-
on-column, or direct mode.
nents between the mobile and liquid phases.
3.1.6 A Retention Gap, is a section of tubing inserted
4.2.2 An Active Solid is one that has ab- or adsorptive
between the inlet and the analytical column proper. The
properties by means of which chromatographic separations
retention gap may have an inner diameter different than the
may be achieved.
analytical column. The retention gap has significantly lower
4.3 The Solid Support is the inert material that holds the
retaining power than the analytical column; in practice the
stationary(liquid)phaseinintimatecontactwiththecarriergas
retention gap is deactivated but not coated.
flowing through it. It may consist of porous or impenetrable
3.2 Columns, consist of tubes that contain the stationary
particles or granules which hold the liquid phase and between
phase and through which the gaseous mobile phase flows.
which the carrier gas flows, or the interior wall of the column
3.2.1 Packed Columns, are filled with granular packing that
itself, or a combination of these.
is kept in place by gas-permeable plugs at both ends.
4.4 The Column Packing consists of all the material used to
3.2.2 Open-Tubular Columns, have unobstructed central
fill packed columns, including the solid support and the liquid
gasflow channels.
phase or the active solid.
3.2.2.1 Wall-Coated Open-Tubular Columns, abbreviated
4.4.1 The Liquid-Phase Loading describes the relative
WCOT columns, have the liquid phase coated directly on the
amount of liquid phase present in a packed column when the
inside, relatively smooth wall of the column tubing.
column packing consists only of the liquid phase plus the solid
3.2.2.2 Porous-Layer Open-Tubular Columns, abbreviated
support. It is usually expressed as weight percent of liquid
PLOT columns, have a solid porous layer present on the tube
phase present in the column packing:
wall but still maintain the unobstructed central gas-flow
channel. This porous solid layer can either act as an adsorbent Liquid 2 phase loading, wt% (2)
or a support which in turn is coated with a thin film of the
amount of liquid phase 3100
~ !
liquidphase,orboth.Thesolidlayercaneitherbedepositedon
~amount of liquid phase1amount of solid support!
the inside tube wall or formed by chemical means from the
wall. 4.5 Solutes are the introduced sample components that are
3.2.2.3 Support-Coated Open-Tubular Columns, abbrevi- delayed by the column as they are eluted through it by the
ated SCOT columns, refer to those PLOT Columns where the carrier gas.
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E355 − 96 (2021)
4.6 Unretained Substances are not delayed by the column 5.3 The following definitions apply to chromatograms ob-
packing. tained with integral detectors, or by integration of the records
obtained by means of differential detectors.As sample compo-
5. Gas Chromatographic Data
nents pass through the detector the baseline is displaced
cumulatively. The change in baseline position as a single
5.1 A Chromatogram is a plot of detector response against
sample component is eluted is a Step. The difference between
time or effluent volume. Idealized chromatograms obtained
straight line extensions of the baselines on both sides of the
with differential and integral detectors for an unretained
step, measured in the direction of detector response, is the Step
substance and one other component are shown in Fig. 1.
Height, NM.
5.2 The definitions in this paragraph apply to chromato-
gramsobtaineddirectlybymeansofdifferentialdetectorsorby
6. Retention Parameters
differentiating the records obtained by means of integral
6.1 Retention parameters are listed in Table 1. The interre-
detectors. The Baseline is the portion of the chromatogram
lations shown apply only to gas elution chromatography
recording the detector response in the absence of solute or
columns operated under constant conditions and for which the
solvent emerging from the column.APeak is the portion of the
partition coefficients are independent of concentration. Fig. 1
chromatogram recording the detector response while a single
can be used to illustrate some of these parameters:
component is eluted from the column. If two or more sample
Gas holdup time = OA
components emerge together, they appear as a single peak.The
Retention time = OB
Peak Base, CD in Fig. 1, is an interpolation of the baseline
Adjusted retention time = AB
betweentheextremitiesofthepeak.Theareaenclosedbetween
Partition (capacity) ratio = AB/OA
Peak width at half height = HJ
the peak and the peak base, CHFEGJD in Fig. 1,isthe Peak
Peak width at base = KL
Area. The dimension BE from the peak maximum to the peak
2 2
Number of theoretical plates = 16 (OB/KL) = v 5.54 (OB/HJ)
base measured in the direction of detector response is the Peak
Relative retention = (AB) /(AB) or (AB) /(AB)
j i i s
Height. Retention dimensions parallel to the baseline are
2fs OBd2s OBd g
j 1
Peak resolution
= =
termed as the peak widths. The retention dimension of a line
s KLd1s KLd
i j
OB 2 OB
parallel to the peak base bisecting the peak height and s d s d
j i
KL
terminating at the inflexion points FG of the tangents drawn to s d
j
Subscripts i, j, and s refer to any earlier peak, any later peak,
the inflection points (= 60.7 % of peak height) is the Peak
and a reference peak, respectively.
Width at Inflection Points, w.Theretentiondimensionofaline
i
parallel to the peak base drawn to 50 % of the peak height and
7. Presentation of Isothermal Retention Data
terminating at the sides HJ of the peak is the Peak Width at
Half Height, w .The retention dimension of the segment of the 7.1 Retention values should be reported in a form that can
h
peak base KL intercepted by the tangents drawn to the be applied for a specific stationary phase composition in
inflection points on both sides of the peak is the Peak Width at different apparatus and for different conditions of column
Base or Base Width, w . length, diameter, and inlet and outlet pressures, and for
b
FIG. 1 Typical Chromatogram
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E355 − 96 (2021)
different carrier gases and flow rate. When the solid support is 7.2 Retention in gas-liquid chromatography can be ex-
inert,itsparticle-sizerangeanddistribution,and(withinlimits) pressedonanabsolutebasisintermsofthepartitioncoefficient
the amount and mode of deposition of the liquid phase, may be
orspecificretentionvolumeofasubstance(tacitlyassumingan
varied also. While the solid support is commonly assumed to
inert solid support). Relative retentions are more conveniently
be inert, often this is not so. The p
...
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