ASTM E2105-00(2005)
(Practice)Standard Practice for General Techniques of Thermogravimetric Analysis (TGA) Coupled With Infrared Analysis (TGA/IR)
Standard Practice for General Techniques of Thermogravimetric Analysis (TGA) Coupled With Infrared Analysis (TGA/IR)
SIGNIFICANCE AND USE
This practice provides general guidelines for the practice of thermogravimetry coupled with infrared spectrometric detection and analysis (TGA/IR). This practice assumes that the thermogravimetry involved in the practice is proper. It is not the intention of this practice to instruct the user on proper thermogravimetric techniques. Please refer to Test Method E 1131 for more information.
SCOPE
1.1 This practice covers techniques that are of general use in the qualitative analysis of samples by thermogravimetric analysis (TGA) coupled with infrared (IR) spectrometric techniques. The combination of these techniques is often referred to as TGA/IR.
1.2 A sample heated in a TGA furnace using a predetermined temperature profile typically undergoes one or more weight losses. Materials evolved during these weight losses are then analyzed using infrared spectroscopy to determine chemical identity. The analysis may involve collecting discrete evolved gas samples or, more commonly, may involve passing the evolved gas through a heated flowcell during the TGA experiment. The general techniques of TGA/IR and other corresponding techniques, such as TGA coupled with mass spectroscopy (TGA/MS), as well as, TGA, used in conjunction with GC/IR, are described in the referenced literature (1-4).
1.3 Some thermal analysis instruments are designed to perform both thermogravimetric analysis and differential scanning calorimetry simultaneously. This type of instrument is sometimes called a simultaneous thermal analyzer (STA). The evolved gas analysis performed with an STA instrument (5) is similar to that with a TGA, and so, would be covered by this practice. With use of a simultaneous thermal analyzer, the coupled method typically is labeled STA/IR.
1.4 The values stated in SI units are to be regarded as standard.
This statement 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.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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:E2105–00(Reapproved2005)
Standard Practice for
General Techniques of Thermogravimetric Analysis (TGA)
Coupled With Infrared Analysis (TGA/IR)
This standard is issued under the fixed designation E2105; 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 2. Referenced Documents
1.1 Thispracticecoverstechniquesthatareofgeneralusein 2.1 ASTM Standards:
thequalitativeanalysisofsamplesbythermogravimetricanaly- E131 Terminology Relating to Molecular Spectroscopy
sis(TGA)coupledwithinfrared(IR)spectrometrictechniques. E168 Practices for General Techniques of Infrared Quanti-
The combination of these techniques is often referred to as tative Analysis
TGA/IR. E334 Practice for General Techniques of Infrared Mi-
1.2 A sample heated in a TGA furnace using a predeter- croanalysis
mined temperature profile typically undergoes one or more E473 Terminology Relating to Thermal Analysis and Rhe-
weightlosses.Materialsevolvedduringtheseweightlossesare ology
thenanalyzedusinginfraredspectroscopytodeterminechemi- E1131 TestMethodforCompositionalAnalysisbyThermo-
cal identity. The analysis may involve collecting discrete gravimetry
evolved gas samples or, more commonly, may involve passing E1252 PracticeforGeneralTechniquesforObtainingInfra-
the evolved gas through a heated flowcell during the TGA red Spectra for Qualitative Analysis
experiment. The general techniques of TGA/IR and other E1421 Practice for Describing and Measuring Performance
corresponding techniques, such as TGA coupled with mass of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
spectroscopy(TGA/MS),aswellas,TGA,usedinconjunction eters: Level Zero and Level One Tests
with GC/IR, are described in the referenced literature (1-4).
3. Terminology
1.3 Some thermal analysis instruments are designed to
3.1 Definitions—For general definitions of terms and sym-
perform both thermogravimetric analysis and differential scan-
bols, refer to Terminologies E131 and E473.
ning calorimetry simultaneously. This type of instrument is
sometimes called a simultaneous thermal analyzer (STA). The 3.2 Definitions of Terms Specific to This Standard:
3.2.1 evolved gas, n—any material (or mixture) evolved
evolved gas analysis performed with an STAinstrument (5) is
similar to that with a TGA, and so, would be covered by this from a sample during a thermogravimetric or simultaneous
thermal analysis experiment. Materials evolved from the
practice. With use of a simultaneous thermal analyzer, the
coupled method typically is labeled STA/IR. sample may be in the form of a gas, a vapor, an aerosol or as
particulate matter. For brevity, the term “evolved gas” will be
1.4 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this used throughout this practice to indicate any material form or
mixture evolved from a sample.
standard.
1.5 This statement does not purport to address all of the 3.2.2 evolved gas analysis (EGA), n—a technique in which
the nature and amount of gas evolved from a sample is
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- monitored against time or temperature during a programmed
change in temperature of the sample.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. 3.2.3 evolved gas profile (EGP), n—an indication of the
total amount of gases evolved, as a function of time or
temperature, during the thermogravimetric experiment. In
TGA/IR, this profile is calculated from the infrared spectro-
This practice is under the jurisdiction ofASTM Committee E13 on Molecular
scopic data recorded by application of the Gram-Schmidt
Spectroscopy and is the direct responsibility of Subcommittee E13.03 on Infrared
Spectroscopy.
Current edition approved Sept. 1, 2005. Published September 2005. Originally
approved in 2000. Last previous edition approved in 2000 as E2105–00 DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/E2105-00R05. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refers to the list of references at the end Standards volume information, refer to the standard’s Document Summary page on
of this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2105–00 (2005)
reconstruction (GSR) algorithm (6,7). Because the GSR was filter spectrometer or a Fourier transform spectrometer. See
designed for use in gas chromatography coupled with infrared also Practices E334 and E1252 for general techniques on
(GC/IR) analysis, the evolved gas profile has sometimes been microanalysis and qualitative practices.
erroneously called the evolved gas chromatogram.
5.2.1 Since the analyte of interest is static when employing
3.2.4 functional group profile (FGP), n—an indication of
an evolved gas trapping technique, the spectrum can be
the amount of gas evolved during the thermogravimetric
recorded using a long integration time or increasing scan
experiment that contains a particular chemical functionality
co-addition to improve the signal-to-noise ratio (SNR). How-
measured as a function of time or temperature. This profile is
ever, in vapor phase evolved gas trapping, the sample integrity
calculated from the infrared spectroscopic data recorded by
can be compromised by slow decomposition or by deposition
integrationoftheabsorbancesoverselectedspectralregionsas
on the cell walls. A spectrum should be obtained initially
theexperimentprogresses.Typically,anumberofsuchprofiles
within a short co-addition time to create a reference spectrum
are calculated in real-time.Additional profiles (using different
to ensure the integrity of the spectrum obtained after long
spectral regions) can often be calculated after the experiment
co-addition.
from the stored spectroscopic data. Because the software used
5.3 Evolved Gas Analysis Using a Flowcell—Another way
has similarities with that used for GC/IR analysis, the func-
to examine the gases evolved during a TGA/IR experiment is
tional group profile has sometimes been erroneously called the
touseaspeciallydesignedflowcell.Thisflowcellissituatedin
functional group chromatogram.
the IR beam of the infrared spectrometer. IR monochromators
3.2.5 hit quality index (HQI), n—the numerical ranking of
andfilterspectrometersaretypicallyusedtomonitoraspecific
infrared reference spectra against that of an analyte spectrum
frequencyrangeduringtheTGAexperiment.Ifafullspectrum
through the use of search algorithms that measure a compara-
is to be obtained with these IR devices, the evolved gas is
tive fit spectral data.
trapped via a stopped flow routine and the spectrometers are
3.2.6 specific gas profile (SGP), n—a special type of func-
permittedtoscantheinfraredspectrum.Incontrast,theFourier
tional group profile arises when the selected region of the
transform IR spectrometer permits the acquisition of the
spectrum contains absorbances due to a specific gas such as
completeIRspectruminbrieftimeframeswithoutimpactupon
ammonia or carbon monoxide.
the typical TGA experiment, that is, continuous spectral
collection without interruption of evolved gas flow or sample
4. Significance and Use
heating.
4.1 This practice provides general guidelines for the prac-
5.3.1 In the typical TGA/IR experiment, the evolved gas is
tice of thermogravimetry coupled with infrared spectrometric
monitored in real-time by the IR spectrometer. The temporal
detection and analysis (TGA/IR). This practice assumes that
resolutionrequiredduringaTGA/IRexperimentisontheorder
the thermogravimetry involved in the practice is proper. It is
of 5–60 s/spectral data acquisition event. If the full IR
not the intention of this practice to instruct the user on proper
spectrumistobeacquired,therapidityoftheTGAexperiment
thermogravimetric techniques. Please refer to Test Method
requires a Fourier-transform infrared (FT-IR) spectrometer to
E1131 for more information.
maintain sufficient temporal resolution. Such instruments in-
clude a computer that is capable of storing large amounts of
5. General TGA/IR Techniques
spectroscopic data for subsequent evaluation.
5.1 Two different types of TGA/IR techniques are used to
5.3.2 Some spectrometer data systems may have limited
analyze samples. These consist of discrete evolved gas trap-
software, or data storage capabilities. Such instrument systems
ping and use of a heated flowcell interface. It should be noted
are capable of recording suitable spectra during the TGA/IR
that only the latter technique allows for the calculation of the
experiment, but may not be able to calculate the evolved gas
evolved gas and functional group profiles.
and functional group profiles.
5.2 Evolved Gas Trapping Techniques—Evolved gas trap-
5.3.3 The flowcell is coupled directly to the TGA via a
ping techniques are the least elaborate means for obtaining
heated transfer line. Evolved gas components are analyzed as
TGA/IR data. In these techniques, the evolved gas is collected
they emerge from the transfer line. This technique typically
from the TGA furnace in discrete aliquots that are then
yields low microgram detection limits for most analytes (1).
analyzed. In use of such techniques, it is essential to monitor
Instruments that include the IR spectrometer, data system, the
the TGA weight loss curve to determine the time or tempera-
thermogravimetric analyzer, heated transfer-line, and heated
ture at which the effluent was captured. Vapor phase samples
flowcell are commercially available.
canbetrappedinaheatedlow-volumegascellattheexitofthe
5.3.4 It should be noted that any metal surface inside the
TGA, analyzed, then flushed out by the TGA effluent. When
TGA furnace, transfer line or flowcell assembly may react
thenextaliquotofinterestisinthegascell,theflowisstopped
with,andsometimesdestroy,specificclassesofevolvedgases,
again for analysis. This process can be made more convenient
forexample,amines.Thiscanresultinchangestothechemical
by designing the TGA temperature profile such that the
natureoftheevolvedgas.Consequently,itispossibletofailto
temperature is held constant while a trapped sample is being
identify the presence of such compound in the mixture. This
analyzed (ramp-and-hold method).Alternatively, fractions can
situation can sometimes be identified by comparison of the
betrappedinthecondensedphasebypassingtheTGAeffluent
TGA weight loss profile with the evolved gas profile.
through a solvent, a powdered solid, or a cold trap to yield
condensed phase material for subsequent analysis (8). Infrared 5.3.5 The infrared energy throughput of the flowcell should
spectrometry is performed with either a monochromator, a be periodically monitored since this indicates the overall
E2105–00 (2005)
condition of this assembly. It is important that all tests be 6. Component Design Considerations for TGA/IR Using
conducted at a constant flowcell temperature because of the a Flowcell
effect of the emitted energy on the detector (see 6.3.1). It is
6.1 Transfer Line—A transfer line from the TGA to the
recommended that records be kept of the interferogram signal
flowcell must present an inert, nonporous surface to the
strength, single-beam energy response and the ratio of two
evolved gas. Evolved gas transfer lines must be heated to
successive single-beam curves (as appropriate to the instru-
temperatures sufficient to prevent condensation of the evolved
ment used). For more information on such tests, refer to
gas species. Typically, the transfer line is constructed of a
Practice E1421. If a mercury-cadmium-telluride (MCT) detec-
narrow-bore steel tube that has either a removable liner or is
tor is being employed, these tests will also reveal degradation
coated internally with silica. The temperature of the transfer
of performance due to loss of the Dewar vacuum and conse-
line is normally held constant during an experiment at a level
quent buildup of ice on the detector face. In general, when a
chosen to avoid both condensation and degradation of the
lossoftransmittedenergygreaterthan10%ofthetotalenergy
evolved gases. Typical working temperatures have a range of
is found, cleaning of the flowcell is recommended.
150–300°C. The flowcell usually is held at a slightly greater
5.3.6 Care must be taken to stabilize or, preferably, remove
temperature, ca. 10°C higher, to avoid condensation of the
interfering spectral features that result from atmospheric ab-
evolved gas.
sorptions in the IR beam path of the spectrometer. Best results
6.1.1 The use of a TGA/IR system to analyze complex
will be obtained by purging the entire optical path of the
materials, such as polymers or natural products, will result in
spectrometer with dry nitrogen gas. Alternatively, dry air can
carbonaceous material, high-molecular weight polymers and
be used as the spectrometer purge gas; however, this will lead
other high boiling materials accumulating in the transfer line
to interferences in the regions of carbon dioxide absorption
and the flowcell.Aperiodic removal of these materials can be
−1 −1
(2500 go 2200 cm and 720 to 620 cm ) due to the presence
accomplished by passing air (or oxygen) through the hot line:
of carbon dioxide in air. Further, commercially-available air
however, the condensation of material will eventually yield a
scrubbers, that remove both water vapor and carbon dioxide,
reduction in gas flow.At this point, it is necessary to clean out
provide adequate purging of the spectrometer. In some instru-
the line before it clogs completely. Flushing the transfer line
ments, the beam path is sealed in the presence of a desiccant,
with one or more solvents, such as acetone, pentane or
but interferences from both carbon dioxide and water vapor
−1 chloroform may remove condensed materials. Alternatively,
(1900 to 1400 cm ) may be found. Similarly, the TGA
some commercial systems use a transfer line with a disposable
furnace, the transfer line and the gas cell interface are purged
liner that can be replaced.
with a gas that does not absorb infrared energy. Typically, this
6.2 Design of the Infrared Flowcell—The flowcell is opti-
TGApurgegasisinert(nitrogenorhelium)andhasaflowrate
mized to give maximum optical throughput, to minimize
from 10 to 200 mL/min. Occasionally, oxidizing or reducing
decomposition and mixing of analyte gas stream, and to yield
at
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