ASTM E1642-00(2005)
(Practice)Standard Practice for General Techniques of Gas Chromatography Infrared (GC/IR) Analysis
Standard Practice for General Techniques of Gas Chromatography Infrared (GC/IR) Analysis
SIGNIFICANCE AND USE
This practice provides general guidelines for the proper practice of gas chromatography coupled with infrared spectrophotometric detection and analysis (GC/IR). This practice assumes that the chromatography involved in the practice is adequate to separate the compounds of interest. It is not the intention of this practice to instruct the user how to perform gas chromatography properly.
SCOPE
1.1 This practice covers techniques that are of general use in analyzing qualitatively multicomponent samples by using a combination of gas chromatography (GC) and infrared (IR) spectrophotometric techniques. The mixture is separated into its individual components by GC and then these individual components are analyzed by IR spectroscopy. Types of GC-IR techniques discussed include eluent trapping, flowcell, and eluite deposition.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.3 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 appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information.
Designation:E1642–00(Reapproved2005)
Standard Practice for
General Techniques of Gas Chromatography Infrared (GC/
IR) Analysis
This standard is issued under the fixed designation E1642; 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 E1421 Practice for Describing and Measuring Performance
of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
1.1 Thispracticecoverstechniquesthatareofgeneralusein
eters: Level Zero and Level One Tests
analyzing qualitatively multicomponent samples by using a
E1510 Practice for Installing Fused Silica Open Tubular
combination of gas chromatography (GC) and infrared (IR)
Capillary Columns in Gas Chromatographs
spectrophotometric techniques. The mixture is separated into
its individual components by GC and then these individual
3. Terminology
components are analyzed by IR spectroscopy. Types of GC-IR
3.1 Definitions—Fordefinitionsoftermsandsymbols,refer
techniques discussed include eluent trapping, flowcell, and
to Terminology E131 and Practice E355.
eluite deposition.
1.2 The values stated in SI units are to be regarded as
4. Significance and Use
standard. No other units of measurement are included in this
4.1 This practice provides general guidelines for the proper
standard.
practice of gas chromatography coupled with infrared spectro-
1.3 This standard does not purport to address all of the
photometric detection and analysis (GC/IR). This practice
safety concerns, if any, associated with its use. It is the
assumes that the chromatography involved in the practice is
responsibility of the user of this standard to establish appro-
adequate to separate the compounds of interest. It is not the
priate safety and health practices and determine the applica-
intentionofthispracticetoinstructtheuserhowtoperformgas
bility of regulatory limitations prior to use.
chromatography properly.
2. Referenced Documents
5. General GC/IR Techniques
2.1 ASTM Standards:
5.1 Three different types of GC/IR technique have been
E131 Terminology Relating to Molecular Spectroscopy
used to analyze samples. These consist of analyte trapping,
E168 Practices for General Techniques of Infrared Quanti-
flowcell, or lightpipe, and direct eluite deposition and are
tative Analysis
presented in the order that they were first used.
E260 Practice for Packed Column Gas Chromatography
5.2 The GC eluent must not be routed to a destructive GC
E334 Practice for General Techniques of Infrared Mi-
detector (such as a flame ionization detector) prior to reaching
croanalysis
the IR detector as this will destroy or alter the individual
E355 Practice for Gas Chromatography Terms and Rela-
components. It is acceptable to split the eluent so that part of
tionships
the stream is directed to such a detector or to pass the stream
E932 Practice for Describing and Measuring Performance
back to the detector after infrared analysis if such techniques
of Dispersive Infrared Spectrometers
are feasible.
E1252 PracticeforGeneralTechniquesforObtainingInfra-
5.3 Eluent Trapping Techniques—Analyte trapping tech-
red Spectra for Qualitative Analysis
niques are the least elaborate means for obtaining GC/IR data.
In these techniques, the sample eluting from the chromato-
This practice is under the jurisdiction ofASTM Committee E13 on Molecular
graph is collected in discrete aliquots to be analyzed. In
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
utilizing such techniques, it is essential that a GC detector be
mittee E13.03 on Infrared and Near Infrared Spectroscopy.
employed to allow definition of component elution. If a
Current edition approved Sept. 1, 2005. Published September 2005. Originally
approved in 1994. Last previous edition approved in 2000 as E1642–00. DOI: destructive detector is employed, then post-column splitting to
10.1520/E1642-00R05.
that detector is required. GC fractions can be trapped in the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
condensed phase by passing the GC effluent through a solvent,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1642–00 (2005)
a powdered solid, or a cold trap for subsequent analysis (see thecase,thetemperatureofthelight-pipeshouldbereducedto
Practice E1252) (1). Vapor phase samples can be trapped in a a safe level as soon as possible. It must be noted that repeated
heated low-volume gas cell at the exit of the GC, analyzed, temperature changes to the light-pipe and transfer line will
then flushed with the continuing GC effluent until the next cause a more rapid aging of the seals and may cause leaks.
aliquot of interest is in the gas cell when the flow is stopped 5.4.3.1 It should be noted that any metal surface inside the
again for analysis (2). Since the analyte of interest is static light-pipe assembly can react with, and sometimes destroy,
when employing an analyte trapping technique, the spectrum some specific materials (for example, amines) as they elute
can be recorded using a long co-addition time to improve the from the GC. Consequently, it is possible to fail to identify the
signal-to-noise (SNR) ratio. However, in analyte trapping, presenceofsuchacompoundinthemixture.Thissituationcan
sample integrity can be compromised by slow decomposition. be identified by comparing the response of the GC detector
A spectrum should be obtained with a short co-addition time after the flowcell to that of a GC detector in the absence of a
first, to create a reference spectrum to ensure the integrity of flowcell, or by comparing the GC/IR detector output to the
the spectrum obtained after long co-addition. results of a suitable alternate analytical technique.
5.4 Flowcell Detection of Vapor Phase Components—The 5.4.3.2 The ends of the light-pipe are sealed with infrared
most common GC/IR technique is the flowcell or “light-pipe” transmissive windows. The optimum optical transmission is
technique. The GC eluent stream is monitored continuously in obtained by using potassium bromide windows, but this
the time frame of the chromatography (real-time) by the IR material is very susceptible to damage by water vapor.As the
spectrometer with the use of a specially designed gas cell light-pipe is used, small amounts of water vapor will etch the
called a light-pipe. In this design, the light-pipe is coupled window surfaces, and the optical throughput of the windows
directly to the GC by a heated transfer line. Individual will drop. Eventually these windows will have to be changed.
components are analyzed in the vapor phase as they emerge Users who expect to analyze mixtures containing water should
from the transfer line. This technique typically yields low consider using windows made of a water-resistant material
nanogram detection limits for most analytes (3-5). Instruments suchaszincselenide,butthiswillresultinanoticeabledropin
that include the IR spectrometer, the gas chromatograph, opticaltransmissionduetoopticalreflectionpropertiesofsuch
heatedtransfer-line,andlight-pipearecommerciallyavailable. materials.
5.4.1 The rapidity with which spectra of the individual 5.4.3.3 Usage of the light-pipe at high temperatures may
components must be recorded requires a Fourier-transform result in the gradual buildup of organic char on both the cell
infrared (FT-IR) spectrometer. Such instruments include a walls and end windows. As this occurs the optical throughput
computer that is capable of storing the large amount of will drop correspondingly. Eventually the light-pipe assembly
spectroscopic data generated for subsequent evaluation. will have to be reconditioned (see 5.4.3.5).
5.4.2 ThetransferlinefromtheGCtothelight-pipemustbe 5.4.3.4 As the temperature of the light-pipe is raised above
made of inert, non-porous material (normally fused silica ambient, the light-pipe emits an increasing amount of infrared
tubing) and be heated to prevent condensation. The tempera- radiation.Thisradiationisnotmodulatedbytheinterferometer
ture of the transfer line is normally held constant during a and is picked up by the detector as DC signal. The DC
complete analysis at a level chosen to avoid both condensation component becomes large at the normal working temperatures
and degradation of the analytes. Typical working temperatures (above 200°C), and lowers the dynamic range of the detector.
are about 100 to 300°C (normally 10°C higher than the TheresultofthiseffectisthattheobservedinterferometricAC
maximum temperature reached during the chromatography). signal is reduced in size as the temperature increases and the
5.4.3 The light-pipe is normally gold-coated on the interior observed spectral noise level increases correspondingly. By
to give maximum optical throughput and at the same time raising the temperature from room temperature to 250°C, the
minimize decomposition of analytes. The light-pipe dimen- noise level typically doubles; it is recommended that the user
sionsaretypicallyoptimizedsothatthevolumeaccommodates create a plot of signal intensity versus light-pipe temperature
the corresponding eluent volume of a sharp chromatographic for reference purposes. As a consequence of this behavior, it
peak at the peak’s full width at half height (FWHH). The may be advantageous to record data using relatively low
light-pipe is heated to a constant temperature at or slightly temperatures for both temperature and transfer line for those
higher than the temperature of the transfer line.The maximum GC experiments that only use a limited temperature ramp.
temperature recommended by the manufacturer should not be Some instrument designs include a cold aperture between the
exceeded. In general, sustained light-pipe temperatures above light-pipeandthedetectortominimizetheamountofradiation
300°Cmaydegradethegoldcoatingandthelifeofthecoating reaching the detector (see Note 1) (6,7).
drops quickly with successively higher temperatures. It should
NOTE 1—A cold aperture is a metal shield, maintained at room
be pointed out that, if a chromatographic separation requires
temperature, sited between the light-pipe and the detector. The infrared
that the GC temperature be raised above this level, it may be
beam diverging from the light-pipe is refocused at the plane of the cold
necessary to temporarily raise both the temperature of the
shield.The cold shield has a circular hole (aperture) of the same diameter
as the refocused beam. After passing through the aperture and moving
light-pipe and transfer line to maximum temperature of the
away from this focal point, the beam is again focused onto the detector
chromatography to avoid condensation of the eluent. If this is
element. This small aperture shields the detector from thermal energy
emitted from the vicinity of the hot light-pipe.
5.4.3.5 The optical throughput of the light-pipe should be
The boldface numbers in parentheses refer to a list of references at the end of
this standard. periodically monitored since this is a good indicator of the
E1642–00 (2005)
overall condition of the assembly. It is important that all tests focused onto the detector (8). Additionally, other matrix
beconductedataconstanttemperaturebecauseoftheeffectof isolation interface devices are available from vendors.
5.5.2 In the case of the continuous subambient temperature
the emitted energy on the detector (see 5.4.3.4). It is recom-
trapping method, the sample is deposited directly onto an
mended that records be kept of the interferogram signal
infrared transmissive plate maintained at the temperatures
strength, single-beam energy response, and the ratio of two
sufficient to condense analytes from the eluent. The tempera-
successive single-beam curves (as appropriate to the instru-
ture of this substrate is maintained by Peltier cooling or with
ment used). For more information on such tests, refer to
liquid nitrogen.The transmissions mode of infrared analysis is
Practice E1421. These tests will also reveal when the MCT
used to obtain the spectroscopic data.
detectorisperformingpoorlyduetolossoftheDewarvacuum
5.5.3 Direct deposition techniques provide the advantage of
and consequent buildup of ice on the detector face. MCT
greater sensitivity for real-time measurements. Additionally,
detectors,asdiscussedinthistextlater,arecommonlyusedfor
extended co-addition of spectra post-run permits further im-
theseexperimentsastheyprovidegreaterdetectivityandfaster
provement of the signal-to-noise ratio of spectral results.
data acquisition.
However, slow sublimation of the analyte recrystallization of
5.4.3.6 Care must be taken to stabilize or, preferably,
the sample or ice formation, or both, may occur with direct
removeinterferingspectralfeaturesresultingfromatmospheric
depositiontechniques.Itisprudenttoobtainaspectrumwitha
absorptions in the optical beam path of the spectrometer and
short co-addition time initially to create a reference spectrum.
the GC/IR interface. Best results will be obtained by purging
This will ensure the integrity of the spectrum obtained after
the complete optical path with dry nitrogen gas.Alternatively,
longer co-addition times.
dry air can be used for the purge gas which will lead to
6. Significant Parameters for GC/IR
interferencesintheregionsofcarbondioxideabsorption(2500
−1 −1
to 2200 cm and 720 to 620 cm ). Commercially available
6.1 Where the instrumentation used is commercially avail-
air scrubbers that remove water vapor and carbon dioxide also
able,themanufacturer’snameandmodelnumbersforthetotal
provide adequate purging of the spectrometer and GC inter-
GC/IR system, or the individual components, should be given.
face. In some instruments, the beam path is sealed in the
The various instrumental and software parameters which need
presence of a desiccant, but invariably interferences from both
to be recorded are listed and discussed in this section. In
−1
carbon dioxide and water vapor (1900 to 1400 cm ) will be addition, any modifications made to a commercial instrument
found. If the purge is supplied to the interface when preparing that affect the instrument’s performance must be clearly noted.
to carry out a GC/IR experiment, the atmosphere must be 6.2 Instrumental Parameters (IR):
6.2.1 Detector—The detectors typically used for GC/IR are
allowed to stabilize before data collectio
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.