ASTM E1642-00(2016)

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: E1642 − 00 (Reapproved 2016)
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 E1252Practice for General Techniques for Obtaining Infra-
red Spectra for Qualitative Analysis
1.1 Thispracticecoverstechniquesthatareofgeneralusein
E1421Practice for Describing and Measuring Performance
analyzing qualitatively multicomponent samples by using a
of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
combination of gas chromatography (GC) and infrared (IR)
eters: Level Zero and Level One Tests
spectrophotometric techniques. The mixture is separated into
E1510Practice for Installing Fused Silica Open Tubular
its individual components by GC and then these individual
Capillary Columns in Gas Chromatographs
components are analyzed by IR spectroscopy. Types of GC-IR
techniques discussed include eluent trapping, flowcell, and
3. Terminology
eluite deposition.
3.1 Definitions—Fordefinitionsoftermsandsymbols,refer
1.2 The values stated in SI units are to be regarded as
to Terminology E131 and Practice E355.
standard. No other units of measurement are included in this
standard.
4. Significance and Use
1.3 This standard does not purport to address all of the
4.1 This practice provides general guidelines for the proper
safety concerns, if any, associated with its use. It is the
practice of gas chromatography coupled with infrared spectro-
responsibility of the user of this standard to establish appro-
photometric detection and analysis (GC/IR). This practice
priate safety and health practices and determine the applica-
assumes that the chromatography involved in the practice is
bility of regulatory limitations prior to use.
adequate to separate the compounds of interest. It is not the
intentionofthispracticetoinstructtheuserhowtoperformgas
2. Referenced Documents
chromatography properly.
2.1 ASTM Standards:
5. General GC/IR Techniques
E131Terminology Relating to Molecular Spectroscopy
E168Practices for General Techniques of Infrared Quanti- 5.1 Three different types of GC/IR technique have been
tative Analysis (Withdrawn 2015) used to analyze samples. These consist of analyte trapping,
E260Practice for Packed Column Gas Chromatography flowcell, or lightpipe, and direct eluite deposition and are
E334Practice for General Techniques of Infrared Micro- presented in the order that they were first used.
analysis
5.2 The GC eluent must not be routed to a destructive GC
E355PracticeforGasChromatographyTermsandRelation-
detector (such as a flame ionization detector) prior to reaching
ships
the IR detector as this will destroy or alter the individual
E932PracticeforDescribingandMeasuringPerformanceof
components. It is acceptable to split the eluent so that part of
Dispersive Infrared Spectrometers
the stream is directed to such a detector or to pass the stream
back to the detector after infrared analysis if such techniques
are feasible.
This practice is under the jurisdiction ofASTM Committee E13 on Molecular
5.3 Eluent Trapping Techniques—Analyte trapping tech-
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
mittee E13.03 on Infrared and Near Infrared Spectroscopy.
niques are the least elaborate means for obtaining GC/IR data.
Current edition approved April 1, 2016. Published May 2016. Originally
In these techniques, the sample eluting from the chromato-
approved in 1994. Last previous edition approved in 2010 as E1642–00(2010).
graph is collected in discrete aliquots to be analyzed. In
DOI: 10.1520/E1642-00R16.
utilizing such techniques, it is essential that a GC detector be
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
employed to allow definition of component elution. If a
Standards volume information, refer to the standard’s Document Summary page on
destructive detector is employed, then post-column splitting to
the ASTM website.
that detector is required. GC fractions can be trapped in the
The last approved version of this historical standard is referenced on
www.astm.org. condensed phase by passing the GC effluent through a solvent,
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1642 − 00 (2016)
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.
5.4.3.2 The ends of the light-pipe are sealed with infrared
5.4 Flowcell Detection of Vapor Phase Components—The
transmissive windows. The optimum optical transmission is
most common GC/IR technique is the flowcell or “light-pipe”
obtained by using potassium bromide windows, but this
technique. The GC eluent stream is monitored continuously in
material is very susceptible to damage by water vapor.As the
the time frame of the chromatography (real-time) by the IR
light-pipe is used, small amounts of water vapor will etch the
spectrometer with the use of a specially designed gas cell
window surfaces, and the optical throughput of the windows
called a light-pipe. In this design, the light-pipe is coupled
will drop. Eventually these windows will have to be changed.
directly to the GC by a heated transfer line. Individual
Users who expect to analyze mixtures containing water should
components are analyzed in the vapor phase as they emerge
consider using windows made of a water-resistant material
from the transfer line. This technique typically yields low
suchaszincselenide,butthiswillresultinanoticeabledropin
nanogram detection limits for most analytes (3-5). Instruments
opticaltransmissionduetoopticalreflectionpropertiesofsuch
that include the IR spectrometer, the gas chromatograph,
materials.
heatedtransfer-line,andlight-pipearecommerciallyavailable.
5.4.3.3 Usage of the light-pipe at high temperatures may
5.4.1 The rapidity with which spectra of the individual
result in the gradual buildup of organic char on both the cell
components must be recorded requires a Fourier-transform
walls and end windows. As this occurs the optical throughput
infrared (FT-IR) spectrometer. Such instruments include a
will drop correspondingly. Eventually the light-pipe assembly
computer that is capable of storing the large amount of
will have to be reconditioned (see 5.4.3.5).
spectroscopic data generated for subsequent evaluation.
5.4.3.4 As the temperature of the light-pipe is raised above
5.4.2 ThetransferlinefromtheGCtothelight-pipemustbe
ambient, the light-pipe emits an increasing amount of infrared
made of inert, non-porous material (normally fused silica
radiation.Thisradiationisnotmodulatedbytheinterferometer
tubing) and be heated to prevent condensation. The tempera-
and is picked up by the detector as DC signal. The DC
ture of the transfer line is normally held constant during a
component becomes large at the normal working temperatures
complete analysis at a level chosen to avoid both condensation
(above 200°C), and lowers the dynamic range of the detector.
and degradation of the analytes. Typical working temperatures
TheresultofthiseffectisthattheobservedinterferometricAC
are about 100 to 300°C (normally 10°C higher than the
signal is reduced in size as the temperature increases and the
maximum temperature reached during the chromatography).
observed spectral noise level increases correspondingly. By
5.4.3 The light-pipe is normally gold-coated on the interior
raising the temperature from room temperature to 250°C, the
to give maximum optical throughput and at the same time
noise level typically doubles; it is recommended that the user
minimize decomposition of analytes. The light-pipe dimen-
create a plot of signal intensity versus light-pipe temperature
sionsaretypicallyoptimizedsothatthevolumeaccommodates
for reference purposes. As a consequence of this behavior, it
the corresponding eluent volume of a sharp chromatographic
may be advantageous to record data using relatively low
peak at the peak’s full width at half height (FWHH). The
temperatures for both temperature and transfer line for those
light-pipe is heated to a constant temperature at or slightly
GC experiments that only use a limited temperature ramp.
higher than the temperature of the transfer line.The maximum
Some instrument designs include a cold aperture between the
temperature recommended by the manufacturer should not be
light-pipeandthedetectortominimizetheamountofradiation
exceeded. In general, sustained light-pipe temperatures above
reaching the detector (see Note 1) (6,7).
300°Cmaydegradethegoldcoatingandthelifeofthecoating
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
shield.The cold shield has a circular hole (aperture) of the same diameter
necessary to temporarily raise both the temperature of the
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 (2016)
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-
mended that records be kept of the interferogram signal trapping method, the sample is deposited directly onto an
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
interferencesintheregionsofcarbondioxideabsorption(2500
6. Significant Parameters for GC/IR
−1 −1
to 2200 cm and 720 to 620 cm ). Commercially available
6.1 Where the instrumentation used is commercially
air scrubbers that remove water vapor and carbon dioxide also
available, the manufacturer’s name and model numbers for the
provide adequate purging of the spectrometer and GC inter-
total GC/IR system, or the individual components, should be
face. In some instruments, the beam path is sealed in the
given. The various instrumental and software parameters
presence of a desiccant, but invariably interferences from both
−1
which need to be recorded are listed and discussed in this
carbon dioxide and water vapor (1900 to 1400 cm ) will be
section. In addition, any modifications made to a commercial
found. If the purge is supplied to the interface when preparing
instrument that affect the instrument’s performance must be
to carry out a GC/IR experiment, the atmosphere must be
clearly noted.
allowed to stabilize before data collection commences. Atmo-
spheric stability inside the instrument can be judged by
6.2 Instrumental Parameters (IR):
recordingthesingle-beamenergyresponseandtheratiooftwo
6.2.1 Detector—The detectors typically used for GC/IR are
successive single-beam spectra.
the mercury-cadmium-telluride (MCT) narrow band photode-
tectors of high sensitivity, that have a lower frequency limit of
5.5 Direct Deposition GC/IR—The direct deposition GC/IR
−1
approximately 700 cm . It is possible to measure spectra to
technique can follow either of two methods, that of matrix
−1
frequencies lower than 700 cm by using an MCT detector
isolation (8) or continuous subambient temperature analyte
thathasabroaderbandspectralresponse,butthesensitivityof
trapping (9).Inbothofthesemethods,thegaschromatographic
suchdetectorsissignificantlylower.TheMCTdetectorshould
effluentispassedthroughaheatedtransferlineandisdeposited
notbeoperatedinalightsaturatingconditionsoastomaintain
ontoacoldsubstrate.Thesemethodspermitdetectionaslowas
linearity of signal response. Nonlinear response is found as a
subnanogram amounts of material. The subambient tempera-
nonzerosignalintensitybelowthedetectorcut-offpointinthe
ture of the substrate necessitates the use of an evacuated
single beam spectrum.
chamber to avoid condensation of atmospheric gases. By
6.2.1.1 Flowcell Temperature—For flowcell GC/IR, the gas
freezing the eluite onto the cold substrate, the components of
cell or light-pipe is usually maintained at a constant tempera-
thesampleareeffectivelystoredthere.Itispossible,therefore,
ture between 200 and 300°C (ca. 10 degrees above maximum
toanalyzethesampleaftertheGC/IRexperimenthasfinished,
temperature of the chromatographic separation) such that
as well as perform real-time analyses.
condensation of analytes does not occur. See 5.4.3 for more
5.5.1 In the matrix isolation method, a small amount of
details. The actual temperature of the cell should always be
argonisaddedtotheheliumcarriergas.Thecolumneffluentis
noted with the spectrum.
directed onto a substrate maintained at a temperature of about
6.2.1.2 Deposition Conditions—For direct deposition GC/
13K. Argon is condensed to form a solid matrix while the
IR, the temperature of the deposition surface and the speed of
helium carrier gas is pumped away. It is important that any
its motion should be noted. In the case of matrix-isolation
component eluting from the chromatograph is entrained in this
GC/IR, the ratio of argon gas to helium carrier gas should be
argon matrix at a concentration (<0.2%) sufficiently low such
given, or preferably, for a particular sample spot the ratio of
thateachanalytemoleculeissurroundedbyargonatomsandis
sample to argon matrix should be given (if known). Spot size
isolated from other analyte molecules.An instrument has been
of the deposit is directly determined by the diameter of the
devisedinwhichthebeamfromtheFT-IRspectrometerpasses capillaryrestrictionendandthedistanceseparatingtherestric-
throughthetrackofargon,isreflectedfromthegoldsurface,is
tion end from the deposition surface. If these distances are
transmitted a second time through the argon, and is finally known, they should be noted appropriately.
E1642 − 00 (2016)
NOTE 2—Most conventional light-pipe GC/IR instruments are opti-
6.2.2 Transfer Line Temperature—The temperature of the
−1
mizedtorecordaspectrumat8-cm resolutioninapproximately1s.This
transfer line should be noted. This should always be higher
allows for adequate sampling of the spectral data as a chromatographic
than the highest temperature achieved by the GC oven during
peak flows through the light-pipe. Thus, the optimal SNR is obtained for
the experiment (see 5.4.2), but at or slightly below that of the
spectral data with minimal loss of chromatographic resolution.
light-pipe.
When examining samples by cryogenic deposition GC/IR, real-time
−1
data are again optimally collected at 8-cm resolution for the above
6.3 Instrumental Parameters (GC)—The success of the
reason. When employing post-run signal averaging, however, data are
−1
GC/IR experiment is dependent on good chromatographic
normally collected at a better resolution (such as 4 cm ) to increase the
information content of the spectra, and also to match the resolution of
practices. It is not the purpose of this practice to discuss those
available spectral libraries suitable for solid-phase samples.
practices in detail, but for convenience, a list of the important
GC parameters to be noted is also given. Refer to Practices 6.4.3 Spectral Co-addition—During real-time data acquisi-
E260, E355, and E1510 for proper measurement and reporting tion it is normally advantageous to co-add several scans per
of these parameters. time increment (generally, a 1-s time frame) to improve the
SNR of the result. The actual number of co-additions depends
6.3.1 Chromatographic Column—The length and internal
on the selected scanning speed and spectral resolution.Typical
diameter of the column, along with the type and thickness of
instrumental operation would permit co-addition of four to ten
columncoating(stationaryphase)employed,mustallbenoted.
scans during each time increment, that is, a discrete infrared
6.3.2 Temperature Profile—The temperature profile should
spectrum is stored approximately every second. Spectral aver-
be specified in detail, including any initial delay or final hold
agingmaybeperformedduringpost-rundataprocessing.Here,
time.
the SNR improvement is limited to the total elution time of an
6.3.3 Carrier Gas—The type of carrier gas used (normally
analyte.
helium)shouldbenoted.Moreimportantly,theflowrateofthe
6.4.4 Data Storage Thresholding—This function must be
carrier gas must be recorded with its measurement at a
recorded if used (see 7.2).
specified oven temperature (normally room temperature) and
6.4.5 Additional Processing—If any smoothing functions,
the light-pipe and transfer line at working temperature. The
baseline correction algorithms, or spectral subtractions are
linear velocity of the carrier gas through the column is also a
applied to the spectral data either during acquisition or with
useful parameter to note. In addition, some GC ovens are
post-run data manipulation, these must be reported. It should
equipped with pressure programming, in order to maintain a
be pointed out that most commercial GC/IR instruments
specified flow rate as the oven temperature increases. This
providetheoperatoronlyalimitedcontroloverthesefunctions
feature maintains the resolution of the chromatographic peaks
and that these functions may be operating automatically. The
as the GC oven temperature is varied, and its presence (or
operator should investigate as to whether an instrument’s
absence) should be noted.
operational software includes such functions and is configured
6.3.3.1 Proper care should be taken to be certain that the
properly for data acquisition.
carriergasisclean,thatis,freeofmoisture,carbondioxideand
other molecular contaminants.This is particularly important in
7. Software Treatment of Infrared Data
the use of the direct deposition GC/IR method as carrier gas
7.1 Gram-Schmidt Reconstruction—As each interferogram
contaminants will co-deposit with the eluite and lead to
is recorded during the chromatographic separation, a method
contamination of spectral information.
called the Gram-Schmidt Reconstruction (10,11) quickly de-
6.3.4 Injection—The sample size; solvent matrix; solvent
termines the information content of the interferogram. In this
dilution factor (if appropriate); injection temperature; and type
method,asetofscansisrecordedbeforethesampleisinjected
of injection employed, that is, split (with split ratio), splitless,
intotheGC.Theseinterferogramsareusedtocreateaseriesof
oron-column,areallcriticalparametersthatmustberecorded.
basis vectors that represent the instrument background profile.
6.3.5 Chromatographic Detector Employed—Ifachromato-
During the experiment, each stored interferogram is used to
graphic detector is employed, in addition to the IR analysis,
generate a similar set of vectors, and a comparison of these
then the following information should be listed: type of
newvectorsagainstthereferencesetisperformed(generallyin
detector, scale expansion on the integrator, and whether the
real-time) to give a measure of the presence, or absence, of
detector is serial (after) the light-pipe, or parallel to it by
material eluting from the GC, and its relative concentration.
side-splitting(inwhichcasethesplitratioshouldbespecified).
Theresultingplotofvectorintensityversustimeindicateshow
the total infrared absorbance (across the spectral range being
6.4 Software Parameters:
measured) changes during the experiment. This is called the
6.4.1 Apodization Function—ForFouriertransforminfrared
Gram-Schmidt reconstructed chromatogram and, is similar in
spectrometers, it is recommended that an apodization function
appearance to the response from a flame-ionization or thermal
beappliedtotheinterferogramsbeforecomputationofspectral
conductivity detector. This chromatogram is normally dis-
data. Suitable apodization functions include triangular, Beer-
played on the computer screen or the plotter.
Norton medium, Happ Genzel, and cosine.
6.4.2 Spectral Resolution—AcompromisebetweentheSNR 7.2 Data Storage Thresholding—Witholderinstrumentsthe
of a spectrum and its information content leads to an optimum very large amounts of spectra recorded during a typical GC/IR
−1
resolutionforGC/IRspectraof8cm ifrecordedinrealtime, experiment are more than can be stored with the available
−1
and4cm if recorded subsequently on a trapped sample (see computer. Because of this, some software sets monitor the
Note 2). signalstrengthoftheinfrareddata(byusingtheGram-Schmidt
E1642 − 00 (2016)
reconstructed chromatogram), and will only store spectral data how each one operates upon the spectral data and library
whenapeakfromtheGCexceedsapresetthresholdvalue,that databases to obtain effective use of spectral searching.
is, discontinuous spectral storage. It is possible that, if a minor 7.4.3 It is common practice for users to generate their own
component is not detected during elution, no spectral data are libraries containing spectra of samples that they expect to
analyze on a routine basis. These spectra can then be obtained
stored for it. With current computer data storage capabilities,
data storage thresholding is largely ignored, as the typical under identical conditions to those used for the GC/IR experi-
ment.Recommendationsforthegenerationofreferencedatain
GC/IR files sizes (up to 30MB) are easily accommodated.
spectral libraries are available (see Note 3) (12).
7.3 Functional Group Chromatograms—As each interfero-
NOTE 3—Libraries of spectral data are available from commercial
gram is recorded, it may be converted to a spectrum in
sources. For light-pipe GC/IR the most suitable libraries are those which
real-time.Inthiscase,ausefuloperationistointegrateselected
contain spectra recorded using gaseous samples. Condensed phase GC/IR
regions of the spectrum immediately, and to present these to
data are generally matched against spectra recorded for solid phase
the screen display or plotter, along with the GramSchmidt samples.Similarlyformatrix-isolationGC/IR,alibraryofmatrixisolation
reference spectra should be used. For subambient temperature analyte
reconstructed chromatogram. Commonly selected regions of
trapping,itisoftenpossibletousethemuchlargerlibrariesofcondensed-
theinfraredspectrum,andsomeselectedfunctionalgroupsthat
phase reference spectra where the samples have been prepared either as
can be monitored in this way are as follows:
KBr disks or mineral-oil mulls. If the library available was recorded for a
−1
Saturated Hydrocarbon: 3000 to 2850 cm different phase, then problems can be minimized by setting the computer
−1 −1
Carbonyls: 1800 to 1650 cm
search to ignore data above 2000 cm .
−1
Ethers and Esters: 1300 to 1000 cm
−1 7.5 Spectral Subtraction—With the advent of Fourier-
Unsaturated and Aromatic Hydrocarbons: 3150 to 3000 cm
−1
Unsaturated Hydrocarbons: 850 to 700 cm
transformspectrometers,thismathematicaltoolmaybeusedto
improve the quality of match before performing a spectral
7.4 Spectral Searching—The normal purpose of the GC/IR
searchandhasprovenveryusefulinresolvinganalyteseluting
experiment is to identify the individual species that are
as overlapping chromatographic peaks.Additionally, the spec-
separated by the GC expe
...