ASTM E697 - 96 (2026) 气相色谱法中电子俘获检测器使用的标准实施规程

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标准小能手 2026-06-17 10 373.35KB 13 页 26星币

Designation: E697 −96 (Reapproved 2026)
Standard Practice for
Use of Electron-Capture Detectors in Gas Chromatography
1
This standard is issued under the ﬁxed designation E697; 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.
1. Scope
1.1 This practice covers the use of an electron-capture
detector (ECD) as the detection component of a gas chromato-
graphic system.
1.2 This practice is intended to describe the operation and
performance of the ECD as a guide for its use in a complete
chromatographic system.
1.3 For general gas chromatographic procedures, Practice
E260 or Practice E1510 should be followed except where
speciﬁc changes are recommended in this practice for use of an
ECD. For a deﬁnition of gas chromatography and its various
terms, see Practice E355. These standards also describe the
performance of the detector in terms which the analyst can use
to predict overall system performance when the detector is
coupled to the column and other chromatographic components.
1.4 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
standard.
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
For speciﬁc safety information, see Section 3.
1.6 This international standard was developed in accor-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
2
E260 Practice for Packed Column Gas Chromatography
E355 Practice for Gas Chromatography Terms and Relation-
ships
E1510 Practice for Installing Fused Silica Open Tubular
Capillary Columns in Gas Chromatographs
2.2 CGA Standards:
3
CGA G-5.4 Standard for Hydrogen Piping Systems at Con-
sumer Locations
CGA P-1 Standard for Safe Handling of Compressed Gases
in Containers
CGA P-9 The Inert Gases: Argon, Nitrogen and Helium
CGA P-12 Safe Handling of Cryogenic Liquids
CGA V-7 Standard Method of Determining Cylinder Valve
Outlet Connections for Industrial Gas Mixtures
HB-3 Handbook of Compressed Gases
2.3 Federal Standard:
4
Title 10 Code of Federal Regulations, Part 20
3. Hazards
3.1 Gas Handling Safety—The safe handling of compressed
gases and cryogenic liquids for use in chromatography is the
responsibility of every laboratory. The Compressed Gas Asso-
ciation (CGA), a member group of specialty and bulk gas
suppliers, publishes the following guidelines to assist the
laboratory chemist to establish a safe work environment.
Applicable CGA publications include: CGA P-1, CGA G-5.4,
CGA P-9, CGA V-7, CGA P-12, and HB-3.
3.2 The electron capture detector contains a radioactive
isotope that emits β-particles into the gas ﬂowing through the
detector. The gas effluent of the detector must be vented to a
fume hood to prevent possible radioactive contamination in the
laboratory. Venting must conform to Title 10, Part 20 and
Appendix B.
4. Principles of Electron Capture Detection
4.1 The ECD is an ionizating detector comprising a source
of thermal electrons inside a reaction/detection chamber ﬁlled
with an appropriate reagent gas. In packed column GC the
carrier gas generally fullﬁlls the requirements of the reagent
gas. In capillary column GC the make-up gas acts as the
1
This practice is under the jurisdiction of ASTM Committee E13 on Molecular
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
mittee E13.19 on Separation Science.
Current edition approved Jan. 1, 2026. Published January 2026. Originally
approved in 1979. Last previous edition approved in 2019 as E697 – 96 (2019).
DOI: 10.1520/E0697-96R26.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at www.astm.org/contact. For Annual Book of
ASTM Standards volume information, refer to the standard’s Document Summary
page on the ASTM website.
3
Available from Compressed Gas Association (CGA), 14501 George Carter
Way, Suite 103, Chantilly, VA 20151, http://www.cganet.com.
4
Available from U.S. Government Publishing Office, 732 N. Capitol St., NW,
Washington, DC 20401, http://www.gpo.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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.
1

reagent gas and also sweeps the detector volume in order to
pass column eluate efficiently through the detector. While the
carrier/reagent gas ﬂows through the chamber the device
detects those compounds entering the chamber that are capable
of reacting with the thermal electrons to form negative ions.
These electron capturing reactions cause a decrease in the
concentration of free electrons in the chamber. The detector
response is therefore a measure of the concentration and the
change in concentration of electrons (1-17).
5
4.2 A radioactive source inside the detector provides a
source of β-rays, which in turn ionize the carrier gas to produce
a source of electrons (18). A constant or intermittent negative
potential, usually less than 100 V, is applied across the reaction
chamber to collect these electrons at the anode. This ﬂow of
“secondary” electrons produces a background or “standing”
current and is measured by a suitable electrometer-ampliﬁer
and recording system.
4.3 As sample components pass through the detector, they
combine with electrons. This causes a decrease in the standing
current or an increase in frequency of potential pulses depend-
ing on the mode of ECD operation (see 5.3). The magnitude of
current reduction or frequency increase is a measure of the
concentration and electron capture rate of the compound. The
ECD is unique among ionizing detectors because it is this loss
in electron concentration that is measured rather than an
increase in signal.
4.4 The two major classiﬁcations of electron-capture reac-
tions in the ECD are the dissociative and nondissociative
mechanisms.
4.4.1 In the dissociative-capture mechanism, the sample
molecule AB reacts with the electron and dissociates into a free
radical and a negative ion: AB + e →A + B
−
. This dissociative
electron-capture reaction is favored at high detector tempera-
tures. Thus, an increase in noncoulometric ECD response with
increasing detector temperature is evidence of the dissociative
electron-capture reaction for a compound. Naturally, detect-
ability is increased at higher detector temperatures for those
compounds which undergo dissociative mechanisms.
4.4.2 In the nondissociative reaction, the sample molecule
AB reacts with the electron and forms a molecular negative
ion: AB + e →AB
−
. The cross section for electron absorption
decreases with an increase in detector temperature in the case
of the nondissociative mechanism. Consequently, the nondis-
sociative reaction is favored at lower detector temperatures and
the noncoulometric ECD response will decrease if the detector
temperature is increased.
4.4.3 Beside the two main types of electron capture
reactions, resonance electron absorption processes are also
possible in the ECD (for example, AB + e = AB
−
). These
resonance reactions are characterized when an electron absorb-
ing compound exhibits a large increase in absorption cross
section over a narrow range of electron energies. This is an
extremely temperature sensitive reaction due to the reverse
reaction which is a thermal electron deactivation reaction. For
solutes in this category a maximum detector temperature is
reached at which higher temperatures diminish the response to
the analyte (19).
4.5 The ECD is very selective for those compounds that
have a high electron-capture rate and the principal use of the
detector is for the measurement of trace quantities of these
materials, 10
−9
g or less. Often, compounds can be derivatized
by suitable reagents to provide detection of very low levels by
ECD (20,21). For applications requiring less sensitivity, other
detectors are recommended.
4.6 A compound with a high electron-capture rate often
contains an electrophoric group, that is, a highly polar moiety
that provides an electron-deﬁcient center in the molecule. This
group promotes the ability of the molecule to attach free
electrons and also may stabilize the resultant negative
molecule-ion. Examples of a few electrophores are the
halogens, sulfur, phosphorus, and nitro- and α-dicarbonyl
groups (22-26).
4.7 A compound could also have a high electron-capture
rate without containing an obvious electrophore in its structure,
or its electron-capture rate could be much greater than that due
to the known electrophore that might be present. In these cases
certain structural features, which by themselves are only
weakly electrophoric, are combined so as to give the molecule
its electrophoric character. A few examples of these are the
quinones, cyclooctatetracene, 3,17-diketosteroids, o-phthalates
and conjugated diketones (27-33).
4.8 Enhanced response toward certain compounds has been
reported after the addition of either oxygen or nitrous oxide to
the carrier gas. Oxygen doping can increase the response
toward CO
2
, certain halogenated hydrocarbons, and polycyclic
aromatic compounds (34). Small amounts of nitrous oxide can
increase the response toward methane, carbon dioxide, and
hydrogen.
4.9 While it is true that the ECD is an extremely sensitive
detector capable of picogram and even femtogram levels of
detection, its response characteristics vary tremendously from
one chemical class to another. Furthermore, the response
characteristic for a speciﬁc solute of interest can also be
enhanced or diminished depending on the detector’s operating
temperature (35)(see 4.4 and 5.5). The detector’s response
characteristic to a solute is also dependent on the choice of
reagent gas and since the ECD is a concentration dependent
detector, it is also dependent on the total gas ﬂow rate through
the detector (see 5.5). These two parameters affect both the
absolute sensitivity and the linear range an ECD has to a given
solute. It is prudent of the operator of the ECD to understand
the inﬂuence that each of the aforementioned parameters has
on the detection of a solute of interest and, to optimize the
parameters prior to ﬁnal testing.
5
The boldface numbers in parentheses refer to a list of references at the end of
this practice.
E697 − 96 (2026)
2

5. Detector Construction
5.1 Geometry of the Detector Cell:
5.1.1 Three basic types of β-ray ionization-detector geom-
etries can be considered applicable as electron-capture detector
cells: the parallel-plate design, the concentric-tube or coaxial-
tube design, and recessed electrode or asymmetric type (36-
39). The latter could be considered a variation of the
concentric-tube design. Both the plane-plate geometry and
concentric geometry are used almost exclusively for pulsed
operation. Although the asymmetric conﬁguration is primarily
employed in the d-c operation of electron-capture detectors, a
unique version of the asymmetric design (referred to as a
displaced-coaxial-cylinder geometry) has been developed for
pulse-modulated operation. The optimum mode of operation is
usually different for each detector geometry and this must be
considered, where necessary, in choosing certain operating
parameters.
5.1.2 In general, more efficient operation is achieved if the
detector is polarized such that the gas ﬂow is counter to the
ﬂow of electrons toward the anode. In this regard, the radio-
active source should be placed at the cathode or as near to it as
possible.
5.1.3 Other geometric factors that affect cell response and
operation are cell volume and electrode spacing, which may or
may not be altered concurrently depending upon the construc-
tion of the detector. Of course, both these variables can be
signiﬁcant at the extremes, and optimum values will also
depend upon other parameters of operation. In the pulsed
operational mode, the electrons within the cell must be able to
reach the anode or collector electrode during the 0.1 to 1.0 µs
voltage pulse. Generally, electrode distances of 0.5 to 1.0 cm
are acceptable and can be used optimally by the proper choice
of operating conditions. Cell volume should be small enough to
maintain effective electron capture without encountering other
types of electron reactions and also small enough so as not to
lose any resolution that may have been achieved by high-
resolution chromatographic systems. Typical ECD cell vol-
umes range from approximately 2 to 0.3 cm
3
. A detector cell
with a relatively low internal volume is particularly important
when the ECD is used with open tubular columns. In addition
to the preceding electrical and chromatographic requirements,
the electrode dimensions of the detector are also determined by
the range of the particular β-rays.
5.2 Radioactive Source:
5.2.1 Many β-ray-emitting isotopes can be used as the
primary ionization source. The two most suitable are
3
H
(tritium) (40,41). and
63
Ni (42).
5.2.1.1 Tritium—This isotope is usually coated on 302
stainless steel or Hastelloy C, which is a nickel-base alloy. The
tritium attached to the former foil material is in the form of
Ti
3
H
2
; however, there is uncertainty concerning the exact
means of tritium attachment to the scandium (Sc) substrate of
the Hastelloy C foil. The proposed methods of attachment
include Sc
3
H
3
and
3
H
2
as the occluded gas. The nominal source
activity for tritium is 250 mCi in titanium sources and 1000
mCi in scandium sources. Department of Energy regulations
permit a maximum operating temperature of 225 °C for the
Ti
3
H
2
source and 325 °C for the Sc
3
H
3
source. Naturally,
detector temperatures that are less than the maximum values
will lengthen the lifetimes of the tritiated sources by reducing
the tritium emanation rates. The newer scandium sources are
more effective at minimizing the contamination problems
associated with electron-capture detectors because of their
capability for operation at 325 °C. Furthermore, the tritiated-
scandium source displays a factor-of-three detectability in-
crease for dissociative electron-capturing species, that is,
halogenated molecules. Another advantage of scandium tritide
sources is their availability at much higher speciﬁc activities
than nickel-63 sources; therefore, Sc
3
H
3
sources are smaller
and permit the construction of detector cells with smaller
internal volumes. The maximum energy of the β-rays emitted
by tritium is 0.018 MeV.
5.2.1.2 Nickel-63 (
63
Ni)—This radioactive isotope is usu-
ally either electroplated directly on a gold foil in the detector
cell or is plated directly onto the interior of the cell block.
Since the maximum energy of the β-rays from the
63
Ni is 0.067
MeV and
63
Ni is a more effective radiation source than tritium,
the normal
63
Ni activity is typically 10 to 15 mCi. An
advantage of
63
Ni is its ability to be heated to 350 °C and the
concomitant decrease in detector contamination during chro-
matographic operation. Another advantage of the high detector
temperatures available with
63
Ni is an enhanced sensitivity for
compounds that undergo dissociative electron capture.
5.2.2 Although the energies and the practical source
strengths for these two radioactive isotopes are different, no
signiﬁcant differences in the results of operation need be
encountered. However, optimum interelectrode distance in the
detector cell is generally greater for
63
Ni than for tritium, that
is, less than 2.5 mm for tritium and 10 mm for
63
Ni. Thus,
tritium sources have the potential of greater sensitivity for
those compounds which undergo undissociative electron at-
tachment because of tritium’s higher speciﬁc activity and its
ability to be used in a smaller volume detector. Because low
levels of radioactive
3
H or
63
Ni are released to the laboratory
environment, it is a wise safety precaution to vent electron-
capture detectors by means of hood exhaust systems.
5.3 Operational Modes:
5.3.1 Three operational modes are presently available with
commercial electron-capture detectors: constant-dc-voltage
method (43), constant-frequency method, and the constant-
current method (44-49). Within each mode of operation, there
lies the ability to optimize performance by selective adjust-
ments of various ECD operational parameters. This may
include, among other things, not only the choice of reagent gas
to be used in the ECD (see 5.4) but also setting the detector’s
pulse time constant on the electrometer to correspond to the gas
used.
5.3.1.1 DC-Voltage Method—A negative d-c voltage is ap-
plied to the cathode resulting in an increasing detector current
with increasing voltage until saturation is reached. The ECD
response for the d-c mode is only linear over a narrow voltage
range of approximately 10 to 15 V. Therefore, optimum
operation is obtained when the detector current is about 80 %
of the saturation level. At higher voltages, the response
becomes nonlinear and this nonlinearity becomes extreme on
the saturation plateau. At d-c voltages below the optimum
E697 − 96 (2026)
3

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摘要：

本页面提供关于 ASTM E697 - 96 (2026) 标准实施规程的详细解读，该规程专门针对气相色谱法中电子俘获检测器（ECD）的正确使用与性能优化。作为国际公认的分析测试标准，ASTM E697 旨在指导实验室人员如何高效、稳定地操作电子俘获检测器，以准确测定卤代化合物、硝基化合物及含氧有机物等微量成分。该规程覆盖了检测器安装、系统参数设置、载气选择及老化处理等关键环节，并强调了减少污染、提高灵敏度与重现性的最佳实践。无论是环境监测、食品安全分析还是化学研究领域，遵循本规程能有效确保痕量

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