ASTM E2105-00(2016)
(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
4.1 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 E1131 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).2
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. No other units of measurement are included in this standard.
1.5 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.
General Information
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Standards Content (Sample)
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: E2105 − 00 (Reapproved 2016)
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- E131Terminology Relating to Molecular Spectroscopy
sis(TGA)coupledwithinfrared(IR)spectrometrictechniques. E168Practices for General Techniques of Infrared Quanti-
The combination of these techniques is often referred to as tative Analysis
TGA/IR. E334Practice for General Techniques of Infrared Micro-
analysis
1.2 A sample heated in a TGA furnace using a predeter-
E473Terminology Relating to Thermal Analysis and Rhe-
mined temperature profile typically undergoes one or more
ology
weightlosses.Materialsevolvedduringtheseweightlossesare
E1131Test Method for CompositionalAnalysis byThermo-
thenanalyzedusinginfraredspectroscopytodeterminechemi-
gravimetry
cal identity. The analysis may involve collecting discrete
E1252Practice for General Techniques for Obtaining Infra-
evolved gas samples or, more commonly, may involve passing
red Spectra for Qualitative Analysis
the evolved gas through a heated flowcell during the TGA
E1421Practice for Describing and Measuring Performance
experiment. The general techniques of TGA/IR and other
of Fourier Transform Mid-Infrared (FT-MIR) Spectrom-
corresponding techniques, such as TGA coupled with mass
eters: Level Zero and Level One Tests
spectroscopy(TGA/MS),aswellas,TGA,usedinconjunction
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
perform both thermogravimetric analysis and differential scan-
symbols, refer to Terminologies E131 and E473.
ning calorimetry simultaneously. This type of instrument is
3.2 Definitions of Terms Specific to This Standard:
sometimes called a simultaneous thermal analyzer (STA). The
3.2.1 evolved gas, n—any material (or mixture) evolved
evolved gas analysis performed with an STAinstrument (5) is
from a sample during a thermogravimetric or simultaneous
similar to that with a TGA, and so, would be covered by this
thermal analysis experiment. Materials evolved from the
practice. With use of a simultaneous thermal analyzer, the
sample may be in the form of a gas, a vapor, an aerosol or as
coupled method typically is labeled STA/IR.
particulate matter. For brevity, the term “evolved gas” will be
1.4 The values stated in SI units are to be regarded as
used throughout this practice to indicate any material form or
standard. No other units of measurement are included in this
mixture evolved from a sample.
standard.
3.2.2 evolved gas analysis (EGA), n—a technique in which
1.5 This statement does not purport to address all of the
the nature and amount of gas evolved from a sample is
safety concerns, if any, associated with its use. It is the
monitored against time or temperature during a programmed
responsibility of the user of this standard to establish appro-
change in temperature of the sample.
priate safety and health practices and determine the applica-
3.2.3 evolved gas profile (EGP), n—an indication of the
bility of regulatory limitations prior to use.
total amount of gases evolved, as a function of time or
temperature, during the thermogravimetric experiment. In
1 TGA/IR, this profile is calculated from the infrared spectro-
This practice is under the jurisdiction ofASTM Committee E13 on Molecular
Spectroscopy and Separation Science and is the direct responsibility of Subcom-
scopic data recorded by application of the Gram-Schmidt
mittee E13.03 on Infrared and Near Infrared Spectroscopy.
Current edition approved April 1, 2016. Published June 2016. Originally
approved in 2000. Last previous edition approved in 2010 as E2105–00(2010). For referenced ASTM standards, visit the ASTM website, www.astm.org, or
DOI: 10.1520/E2105-00R16. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to a list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2105 − 00 (2016)
reconstruction (GSR) algorithm (6,7). Because the GSR was condensed phase material for subsequent analysis (8). Infrared
designed for use in gas chromatography coupled with infrared spectrometry is performed with either a monochromator, a
(GC/IR) analysis, the evolved gas profile has sometimes been filter spectrometer or a Fourier transform spectrometer. See
erroneously called the evolved gas chromatogram. also Practices E334 and E1252 for general techniques on
microanalysis and qualitative practices.
3.2.4 functional group profile (FGP), n—an indication of
5.2.1 Since the analyte of interest is static when employing
the amount of gas evolved during the thermogravimetric
an evolved gas trapping technique, the spectrum can be
experiment that contains a particular chemical functionality
recorded using a long integration time or increasing scan
measured as a function of time or temperature. This profile is
co-addition to improve the signal-to-noise ratio (SNR).
calculated from the infrared spectroscopic data recorded by
However, in vapor phase evolved gas trapping, the sample
integrationoftheabsorbancesoverselectedspectralregionsas
integrity can be compromised by slow decomposition or by
theexperimentprogresses.Typically,anumberofsuchprofiles
deposition on the cell walls. A spectrum should be obtained
are calculated in real-time.Additional profiles (using different
initially within a short co-addition time to create a reference
spectral regions) can often be calculated after the experiment
spectrum to ensure the integrity of the spectrum obtained after
from the stored spectroscopic data. Because the software used
long co-addition.
has similarities with that used for GC/IR analysis, the func-
tional group profile has sometimes been erroneously called the
5.3 Evolved Gas Analysis Using a Flowcell—Another way
functional group chromatogram.
to examine the gases evolved during a TGA/IR experiment is
3.2.5 hit quality index (HQI), n—the numerical ranking of touseaspeciallydesignedflowcell.Thisflowcellissituatedin
infrared reference spectra against that of an analyte spectrum the IR beam of the infrared spectrometer. IR monochromators
through the use of search algorithms that measure a compara- andfilterspectrometersaretypicallyusedtomonitoraspecific
tive fit spectral data. frequencyrangeduringtheTGAexperiment.Ifafullspectrum
is to be obtained with these IR devices, the evolved gas is
3.2.6 specific gas profile (SGP), n—a special type of func-
trapped via a stopped flow routine and the spectrometers are
tional group profile arises when the selected region of the
permittedtoscantheinfraredspectrum.Incontrast,theFourier
spectrum contains absorbances due to a specific gas such as
transform IR spectrometer permits the acquisition of the
ammonia or carbon monoxide.
completeIRspectruminbrieftimeframeswithoutimpactupon
the typical TGA experiment, that is, continuous spectral
4. Significance and Use
collection without interruption of evolved gas flow or sample
4.1 This practice provides general guidelines for the prac-
heating.
tice of thermogravimetry coupled with infrared spectrometric
5.3.1 In the typical TGA/IR experiment, the evolved gas is
detection and analysis (TGA/IR). This practice assumes that
monitored in real-time by the IR spectrometer. The temporal
the thermogravimetry involved in the practice is proper. It is
resolutionrequiredduringaTGA/IRexperimentisontheorder
not the intention of this practice to instruct the user on proper
of 5–60 s/spectral data acquisition event. If the full IR
thermogravimetric techniques. Please refer to Test Method
spectrumistobeacquired,therapidityoftheTGAexperiment
E1131 for more information.
requires a Fourier-transform infrared (FT-IR) spectrometer to
maintain sufficient temporal resolution. Such instruments in-
5. General TGA/IR Techniques
clude a computer that is capable of storing large amounts of
5.1 Two different types of TGA/IR techniques are used to
spectroscopic data for subsequent evaluation.
analyze samples. These consist of discrete evolved gas trap-
5.3.2 Some spectrometer data systems may have limited
ping and use of a heated flowcell interface. It should be noted
software, or data storage capabilities. Such instrument systems
that only the latter technique allows for the calculation of the
are capable of recording suitable spectra during the TGA/IR
evolved gas and functional group profiles.
experiment, but may not be able to calculate the evolved gas
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
TGA, analyzed, then flushed out by the TGA effluent. When 5.3.4 It should be noted that any metal surface inside the
thenextaliquotofinterestisinthegascell,theflowisstopped TGA furnace, transfer line or flowcell assembly may react
again for analysis. This process can be made more convenient with,andsometimesdestroy,specificclassesofevolvedgases,
by designing the TGA temperature profile such that the forexample,amines.Thiscanresultinchangestothechemical
temperature is held constant while a trapped sample is being natureoftheevolvedgas.Consequently,itispossibletofailto
analyzed (ramp-and-hold method).Alternatively, fractions can identify the presence of such compound in the mixture. This
betrappedinthecondensedphasebypassingtheTGAeffluent situation can sometimes be identified by comparison of the
through a solvent, a powdered solid, or a cold trap to yield TGA weight loss profile with the evolved gas profile.
E2105 − 00 (2016)
5.3.5 The infrared energy throughput of the flowcell should 6. Component Design Considerations for TGA/IR Using
be periodically monitored since this indicates the overall a Flowcell
condition of this assembly. It is important that all tests be
6.1 Transfer Line—A transfer line from the TGA to the
conducted at a constant flowcell temperature because of the
flowcell must present an inert, nonporous surface to the
effect of the emitted energy on the detector (see 6.3.1). It is
evolved gas. Evolved gas transfer lines must be heated to
recommended that records be kept of the interferogram signal
temperatures sufficient to prevent condensation of the evolved
strength, single-beam energy response and the ratio of two
gas species. Typically, the transfer line is constructed of a
successive single-beam curves (as appropriate to the instru-
narrow-bore steel tube that has either a removable liner or is
ment used). For more information on such tests, refer to
coated internally with silica. The temperature of the transfer
Practice E1421. If a mercury-cadmium-telluride (MCT) detec-
line is normally held constant during an experiment at a level
tor is being employed, these tests will also reveal degradation chosen to avoid both condensation and degradation of the
of performance due to loss of the Dewar vacuum and conse-
evolved gases. Typical working temperatures have a range of
quent buildup of ice on the detector face. In general, when a 150 to 300°C. The flowcell usually is held at a slightly greater
lossoftransmittedenergygreaterthan10%ofthetotalenergy temperature, ca. 10°C higher, to avoid condensation of the
evolved gas.
is found, cleaning of the flowcell is recommended.
6.1.1 The use of a TGA/IR system to analyze complex
5.3.6 Care must be taken to stabilize or, preferably, remove
materials, such as polymers or natural products, will result in
interfering spectral features that result from atmospheric ab-
carbonaceous material, high-molecular weight polymers and
sorptions in the IR beam path of the spectrometer. Best results
other high boiling materials accumulating in the transfer line
will be obtained by purging the entire optical path of the
and the flowcell.Aperiodic removal of these materials can be
spectrometer with dry nitrogen gas. Alternatively, dry air can
accomplished by passing air (or oxygen) through the hot line:
be used as the spectrometer purge gas; however, this will lead
however, the condensation of material will eventually yield a
to interferences in the regions of carbon dioxide absorption
reduction in gas flow.At this point, it is necessary to clean out
−1 −1
(2500 go 2200 cm and 720 to 620 cm ) due to the presence
the line before it clogs completely. Flushing the transfer line
of carbon dioxide in air. Further, commercially-available air
with one or more solvents, such as acetone, pentane or
scrubbers, that remove both water vapor and carbon dioxide,
chloroform may remove condensed materials. Alternatively,
provide adequate purging of the spectrometer. In some
some commercial systems use a transfer line with a disposable
instruments, the beam path is sealed in the presence of a
liner that can be replaced.
desiccant, but interferences from both carbon dioxide and
−1
6.2 Design of the Infrared Flowcell—The flowcell is opti-
water vapor (1900 to 1400 cm ) may be found. Similarly, the
mized to give maximum optical throughput, to minimize
TGA furnace, the transfer line and the gas cell interface are
decomposition and mixing of analyte gas
...
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