ASTM E355-96(2001)
(Practice)Standard Practice for Gas Chromatography Terms and Relationships
Standard Practice for Gas Chromatography Terms and Relationships
SCOPE
1.1 This practice deals primarily with 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.
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Standards Content (Sample)
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Designation:E355–96(Reapproved 2001)
Standard Practice for
Gas Chromatography Terms and Relationships
This standard is issued under the fixed designation E 355; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope strongly held solute from the stationary phase which in turn
displaces the next less strongly held one etc., causing the
1.1 This practice covers primarily the terms and relation-
components to emerge in the normal order, that is, least-to-
ships used in gas elution chromatography. However, most of
most strongly absorbed.
the terms should also apply to other kinds of gas chromatog-
2.7 Isothermal Gas Chromatography is the version of the
raphy and are also valid in the various liquid column chro-
technique in which the column temperature is held constant
matographic techniques, although at this time they are not
during the passage of the sample components through the
standardized for the latter usage.
separation column.
2. Names of Techniques
2.8 Programmed Temperature Gas Chromatograp-
hy (PTGC), is the version of the technique in which the
2.1 Gas Chromatography, abbreviated as GC, comprises all
column temperature is changed with time during the passage of
chromatographic methods in which the moving phase is
the sample components through the separation column. In
gaseous. The stationary phase may be either a dry granular
linear PTGC the program rate is constant during analysis.
solid or a liquid supported by the granules or by the wall of the
Isothermal intervals may be included in the temperature
column, or both. Separation is achieved by differences in the
program.
distribution of the components of a sample between the mobile
2.9 Programmed Flow, Pressure, or Velocity Gas Chroma-
and stationary phases, causing them to move through the
tography is the version of the technique in which the carrier
column at different rates and from it at different times. In this
gas flow, pressure, or velocity is changed during analysis.
recommended practice gas elution chromatography is implied.
2.10 Reaction Gas Chromatography is the version of the
2.2 Gas-Liquid Chromatography, abbreviated as GLC, uti-
technique in which the composition of the sample is changed
lizesaliquidasthestationaryphase,whichactsasasolventfor
between sample introduction and the detector.The reaction can
the sample components.
take place upstream of the column when the chemical compo-
2.3 Gas-Solid Chromatography, abbreviated as GSC, uti-
sition of the individual components passing through the col-
lizes an active solid (adsorbent) as the stationary phase.
umn differs from that of the original sample, or between the
2.4 Gas Elution Chromatography utilizes a continuous in-
column and the detector when the original sample components
ert gas flow as the carrier gas and the sample is introduced as
are separated in the column but their chemical composition is
agasoraliquidwithafinitevolumeintothecarriergasstream.
changed prior to entering the detection device.
If the sample is introduced as a liquid, it is vaporized in the
2.11 Pyrolysis Gas Chromatography is the version of reac-
system prior to or during passage through the separation
tion gas chromatography in which the original sample is
column.
decomposed by heat to more volatile components prior to
2.5 Gas-Frontal Chromatography is a technique in which a
passage through the separation column.
continuous stream of carrier gas mixed with sample vapor is
instantaneously replaced by a continuous stream of carrier gas
3. Apparatus
containing sample vapor at a different concentration. The
3.1 Sample Inlet Systems, represent the means for introduc-
concentration profile is therefore step-shaped at the column
ing samples into the separation column, including the heated
inlet.
zones permitting the vaporization of the introduced liquid
2.6 Gas-Displacement Chromatography employs a desor-
samples prior to their passage through the column. Sample
bent as the carrier gas or in the carrier gas to displace a less
introduction can be carried out by introduction of a liquid,
solid, or gas into the carrier-gas stream. The sample may be
This practice is under the jurisdiction of ASTM Committee E13 on Molecular vaporized before or after introduction into the column.
Spectroscopy and is the direct responsibility of Subcommittee E13.19 on Chroma-
3.1.1 Direct Inlets, rapidly vaporize the sample prior to
tography.
enteringthecolumn.Allofthesamplevaporentersthecolumn.
Current edition approved April 10, 1996. Published June 1996. Originally
published as E 355–68. Last previous edition E 355-77 (1989).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E355–96 (2001)
3.1.2 On-Column Inlets, introduce a liquid sample into the 3.3.4 Spectrometric Detectors, measure and record spectra
column. The sample vaporizes as the column section contain- of eluting components, such as the mass spectrum of the
ing the liquid heats up after injection. infrared spectrum.
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
at a flow rate F . The ratio of the total inlet flow (F + F)to
v v c
the column flow ( F ) is called the split ratio (s): 4.1 Carrier Gas isthe Mobile Phaseusedtosweeporelute
c
the sample components through and from the column.
F 1 F
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) phase in intimate contact with the carrier gas
retention gap is deactivated but not coated.
flowing through it. It may consist of porous or impenetrable
particles or granules which hold the liquid phase and between
3.2 Columns, consist of tubes that contain the stationary
which the carrier gas flows, or the interior wall of the column
phase and through which the gaseous mobile phase flows.
itself, or a combination of these.
3.2.1 Packed Columns, are filled with granular packing that
4.4 The Column Packing consists of all the material used to
is kept in place by gas-permeable plugs at both ends.
fill packed columns, including the solid support and the liquid
3.2.2 Open-Tubular Columns, have unobstructed central
phase or the active solid.
gasflow channels.
4.4.1 The Liquid-Phase Loading describes the relative
3.2.2.1 Wall-Coated Open-Tubular Columns, abbreviated
amount of liquid phase present in a packed column when the
WCOT columns, have the liquid phase coated directly on the
column packing consists only of the liquid phase plus the solid
inside, relatively smooth wall of the column tubing.
support. It is usually expressed as weight percent of liquid
3.2.2.2 Porous-Layer Open-Tubular Columns, abbreviated
phase present in the column packing:
PLOT columns, have a solid porous layer present on the tube
Liquid2phase loading, wt%
wall but still maintain the unobstructed central gas-flow
~amount of liquid phase!3 100
5 (2)
channel. This porous solid layer can either act as an adsorbent
~amount of liquid phase 1 amount of solid support!
or a support which in turn is coated with a thin film of the
4.5 Solutes are the introduced sample components that are
liquid phase, or both.The solid layer can either be deposited on
delayed by the column as they are eluted through it by the
the inside tube wall or formed by chemical means from the
carrier gas.
wall.
4.6 Unretained Substances are not delayed by the column
3.2.2.3 Support-Coated Open-Tubular Columns, abbrevi-
packing.
ated SCOT columns, refer to those PLOT Columns where the
solid layer consists of the particles of a solid support which
5. Gas Chromatographic Data
were deposited on the inside tube wall.
5.1 A Chromatogram is a plot of detector response against
3.3 Detectors, are devices that indicate the presence of
time or effluent volume. Idealized chromatograms obtained
eluted components in the carrier gas emerging from the
with differential and integral detectors for an unretained
column.
substance and one other component are shown in Fig. 1.
3.3.1 Differential Concentration Detectors, measure the in-
5.2 The definitions in this paragraph apply to chromato-
stantaneous proportion of eluted sample components in the
gramsobtaineddirectlybymeansofdifferentialdetectorsorby
carrier gas passing through the detector.
differentiating the records obtained by means of integral
3.3.2 Differential Mass Detectors, measure the instanta-
detectors. The Baseline is the portion of the chromatogram
neous rate of arrival of sample components at the detector.
recording the detector response in the absence of solute or
3.3.3 Integral Detectors, measure the accumulated quantity solvent emerging from the column.APeak is the portion of the
of sample component(s) reaching the detector. chromatogram recording the detector response while a single
E355–96 (2001)
FIG. 1 Typical Chromatogram.
component is eluted from the column. If two or more sample
Gas holdup time = OA
Retention time = OB
components emerge together, they appear as a single peak.The
Adjusted retention time = AB
Peak Base, CD in Fig. 1, is an interpolation of the baseline
Partition (capacity) ratio = AB/OA
betweentheextremitiesofthepeak.Theareaenclosedbetween Peak width at half height = HJ
Peak width at base = KL
the peak and the peak base, CHFEGJD in Fig. 1, is the Peak
2 2
Number of theoretical plates = 16 (OB/KL) = v 5.54 (OB/HJ)
Area. The dimension BE from the peak maximum to the peak
Relative retention = (AB) /(AB) or (AB) /(AB)
j i i s
base measured in the direction of detector response is the Peak 2@~OB! – ~OB! #
Peak resolution = j 1
=
~KL! 1 ~KL!
i j
Height. Retention dimensions parallel to the baseline are
termed as the peak widths. The retention dimension of a line ~OB! – ~OB!
j i
~KL!
j
parallel to the peak base bisecting the peak height and
terminating at the inflexion points FG of the tangents drawn to
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.The retention dimension of a line
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
be applied for a specific stationary phase composition in
peak base KL intercepted by the tangents drawn to the
different apparatus and for different conditions of column
inflection points on both sides of the peak is the Peak Width at
length, diameter, and inlet and outlet pressures, and for
Base or Base Width, w .
b
different carrier gases and flow rate. When the solid support is
5.3 The following definitions apply to chromatograms ob-
inert,itsparticle-sizerangeanddistribution,and(withinlimits)
tained with integral detectors, or by integration of the records
the amount and mode of deposition of the liquid phase, may be
obtained by means of differential detectors.As sample compo-
varied also. While the solid support is commonly assumed to
nents pass through the detector the baseline is displaced
be inert, often this is not so. The physical disposition of the
cumulatively. The change in baseline position as a single
liquid phase may also affect retention values (1). Conse-
sample component is eluted is a Step. The difference between
quently, all components of the column packing and the
straight line extensions of the baselines on both sides of the
procedureforcombiningthemmustbefullyspecifiedtoenable
step, measured in the direction of detector response, is the Step
other workers to prepare identical compositions.
Height, NM.
7.2 Retention in gas-liquid chromatography can be ex-
6. Retention Parameters
pressed on an absolute basis in terms of the partition coefficient
6.1 Retention parameters are listed in Table 1. The interre- orspecificretentionvolumeofasubstance(tacitlyassumingan
lations shown apply only to gas elution chromatography
columns operated under constant conditions and for which the
partition coefficients are independent of concentration. Fig. 1
The boldface numbers in parentheses refer to the list of references at the end of
can be used to illustrate some of these parameters: this practice.
E355–96 (2001)
inert solid support). Relative retentions are more conveniently 7.3 Retention index is another retention parameter. It is
determined, however, and they should be expressed relative to definedrelativetotheretentionof n-alkanes,andrepresentsthe
a substance which is easily available and emerges relatively number of carbon atoms, multiplied by 100, in a hypothetical
close to the substance of int
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