ASTM E2105-00(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: 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 stream, and to yield
purged with a gas that does not absorb infrared energy.
linear infrared absorption. The flowcell dimensions are opti-
Typically, thisTGApurge gas is inert (nitrogen or helium) and
mized to accommodate a discrete volume and flow rate and
hasaflowratefrom10to200mL/min.Occasionally,oxidizing
provide sufficient optical pathlength for spectral data acquisi-
or reducing atmospheres, that is, oxygen or hydrogen
tionwithreasonabletemporalresolution.Preferably,thecellis
respectively, are used with the TGA to promote specific
heated to a constant temperature at or slightly higher than the
chemical reactions.When preparing for aTGA/IR experiment,
temperature of the transfer line, ca. 10°C or higher; however,
theatmosphereswithinthespectrometerandwithinthefurnace
the maximum temperature recommended by the manufacturer
and gas cell combination must be allowed to stabilize before
should not be exceeded. It must be noted that repeated
spectral data collection and the thermal experiment commence
temperature changes to the cell and transfer line accelerate
to minimize spectral interferences. Atmospheric stability for
aging of the seals and may cause leaks.
the experiment can be judged by recording the single-beam
6.2.1 The ends of the flowcell are sealed with infrared
energy response and the ratio of two successive single-beam
transmitting windows or window and mirror combinations.
spectra over a discrete time interval.
The optimum infrared transmission is obtained by using
5.3.6.1 The spectral features of both carbon dioxide and,
potassium bromide windows, but this material is very suscep-
more importantly, water vapor depend upon the temperature at
tible to damage by water vapor.As the flowcell is used, small
which they were measured. This can become an awkward
amounts of water vapor etch the window surfaces and the
problem in TGA/IR analysis, as many samples evolve these
opticalthroughputoftheflowcelldropsuntilapointisreached
gases as they are heated. It may be necessary to identify these
when these windows need to be replaced. Users who expect to
molecules in the heated flowcell when there is a possible
analyze mixtures containing water should consider using
background absorbance from molecules close to room tem-
windows made of a water-resistant material, such as zinc
perature in the spectrometer and interface. It is particularly
selenide(ZnSe);however,highrefractiveindexwindows,such
difficult to use spectral subtraction techniques (see Practice
asZnSe,resultinanoticeabledropinopticaltransmissiondue
E1252) to compensate for the presence of water vapor in the
to the optical properties of such materials.
spectrum under these conditions. The significance of this
6.2.2 Use of the flowcell at high temperatures may result in
problemisdemonstratedbytheattempttoidentifythepresence the gradual buildup of organic char on both the cell walls and
of a trace amount of a carbonyl compound when spectral
windows. As this occurs, the infrared throughput will drop
features due to water vapor also are observed. correspondingly.Eventually,theflowcellassemblywillhaveto
E2105 − 00 (2016)
be cleaned and reconditioned. It is suggested that, when are favored for TGA/IR experiments that show fast weight
infrared energy falls to 80% of original intensity, the flowcell losses (occurring in seconds) or where exceptional sensitivity
be cleaned and windows and mirrors be reconditioned.
is required, such as when weight losses less than 1% need to
be studied in detail. An MCT detector should not be operated
6.3 Optical Interface
in a light saturating condition so as to maintain the linearity of
6.3.1 Theflowcellmaybepositionedinthestandardsample
signal response. If detector nonlinearity is present, it will
compartment of the infrared spectrometer. It is advantageous,
severely limit the application of spectral subtraction routines.
however, to place the flowcell in a separate compartment to
This restriction may mean that a narrow-band MCT is inap-
yield a dedicated optical interface. This interface can be
propriate for some TGA/IR instruments or applications. To
designed to house the temperature controllers for the heated
determine if the MCT detector is operating in a nonlinear
flowcell and transfer line, if so desired. There are several
fashion, the single beam spectrum is examined below the
reasons for doing this:
detector’s spectral range or “cutoff.” If the values below the
6.3.1.1 A customized detector assembly can be used for
cutoff are non-zero, the detector is operating in a nonlinear
TGA/IR experiments (see 6.4.3 if using a DTGS detector);
domain. It is recommended that the operational parameters of
6.3.1.2 Theheatgeneratedbyuseoftheheatedflowcellcan
thespectrometerbeadjustedtoreduceenergythroughputtothe
be isolated from the main spectrometer optics and avoids
detector to prevent saturation and nonlinearity. While this
degradation of spectrometer stability due to heat currents;
typically occurs with MCT detectors, this phenomenon may
6.3.1.3 An optical aperture can be placed between the
also occur with DTGS detectors.
heated flowcell and the detector to act as a cold aperture (see
6.4.3 DTGS detectors are less sensitive and require slower
6.3.2 and Note 1); and,
scanningspeeds;however,theDTGSdetectorisagoodchoice
6.3.1.4 The primary sample compartment then is available
for general-purpose operation as the temporal resolution for
for routine IR spectroscopy needs without removal of the
acquisitionofspectraintheTGA/IRexperimentisontheorder
heated flowcell.
of 10 s or more and the gas evolution is sufficient to yield
6.3.2 As the temperature of the flowcell is raised above
analyte concentrations to permit adequate detection of evolved
ambient, it emits an increasing amount of infrared radiation.
species.
This radiation is not modulated by the spectrometer and is
picked up by the detector as a DC signal.When the flowcell is
6.4.3.1 Because the DTGS detector is pyroelectric in
at temperatures above 200°C, the DC portion of the signal is operation, such a detector is sensitive to temperature changes
sufficienttolowerthedynamicrangeofthedetector.Theresult
in the instrument or the optical interface; hence, the
of this effect is that the observedAC signal is reduced and the
spectrometer, the optical interface, and the detector must be in
observed spectral noise level is increased. For example, by
thermal equilibrium before spectra are acquired. In addition, a
raising the flowcell temperature from room temperature to
DTGS detector loses significant sensitivity at temperatures
250°C, the noise level typically doubles. It is recommended
greater than 30°C as the DTGS element depolarizes. This
that the user create a plot of interferogram intensity versus
problem can be avoided by using a detector equipped with a
light-pipe temperature for reference purposes. Some instru-
Peltiercooleroruseofanappropriatecoldaperture(shielding)
ment designs include a cold aperture between the flowcell and
prior to the detector.
the detector to minimize the amount of unmodulated, extrane-
ous infrared radiation reaching the detector.
7. Documentation of Significant Parameters for TGA/IR
NOTE 1—A cold aperture is a metal shield with a hole in it that is
7.1 The instrumentation used to conduct the TGA/IR ex-
maintained at room temperature. The modulated infrared beam diverging
periment should be recorded properly within prescribed stan-
from the flowcell is refocused at this cold aperture. The cold aperture has
dard operating procedures (SOPs) or laboratory notebooks as
a diameter that matches the diameter of the refocused IR beam. The IR
beam passing through the cold aperture diverges and is again refocused necessary to meet requirements for laboratory practices. If the
ontothedetectorelement.Thiscoldapertureshieldsthedetectorfromthe
equipment is commercially available, the manufacturers’
unmodulated thermal energy emitted from the heated flowcell.
namesandmodelnumbersforthecompleteTGA/IRsystem,or
6.4 Choice of Infrared Detector:
the individual components, should be recorded. The various
6.4.1 Detectors typically used for TGA/IR are either instrumental and software parameters that need to be recorded
mercury-cadmium-telluride (MCT) or deuterated triglycine are listed and discussed in 7.2 – 7.4.5. In addition, any
sulfate (DTGS). Either detector is selected with regard to
modifications made to a commercial instrument must be noted
sensitivity, detectivity and speed requirements of the TGA/IR
clearlyparticularlyiftheyaffecttheinstrument’sperformance.
experiment. To achieve the highest signal-to-noise response
7.2 Instrumental Parameters (IR):
(SNR), it is important that the detector element be filled with
7.2.1 Flow Cell Temperature—Theflowcellismaintainedat
either the image of the cold aperture, the exit aperture of the
a constant temperature, such that condensation of analytes is
flowcell or the IR source image depending on the optical
minimized.Theactualtemperatureofthecellshouldalwaysbe
design of the spectrometer and interface.
recorded.
6.4.2 MCT photoconductive detectors range from narrow
band detectors of high sensitivity that have a low limit of 7.2.2 Window Material Used in the Flowcell—The type of
−1
window material used in the flowcell must be recorded as its
approximately 700 cm to broad band detectors of modest
−1
sensitivity that have a low limit of 400 cm . MCT detectors optical properties affect transmission of the infrared beam.
E2105 − 00 (2016)
performed with post-run spectral collection and data manipulation rou-
7.2.3 Transfer Line Temperature—The transfer line is typi-
tines.
cally held at a constant temperature. The actual temperature
NOTE 3—Gas evolution from the sample often occurs over extended
and the transfer line material must be recorded.
periodsoftime.Coadditionofscansthencanbeextendedtohigherlevels,
7.2.4 Detector—The type of detector should be specified. If
forexample,100scans/spectrum,tofurtherimprovethesignal-to-noiseof
an MCT detector is used, the detector cutoff frequency should the spectrum without significant loss of resolution on the time axis. This
greatly reduces the amount of data stored and speeds up post-run data
be recorded.
treatment; however, it is important to remember that the spectral acqui-
7.3 Instrumental Parameters (TGA)—The success of the
sition should be set to accommodate the fastest weight loss or gas
evolution and the minimum time increment of the complete experiment.
TGA/IR experiment is dependent on good thermogravimetric
procedures. It is not the purpose of this to discuss TGA
7.4.4 Data Storage Threshold—This function must be re-
operational procedures in detail. For convenience, a list of the
corded if used (see 8.2).
important TGA parameters to be recorded is listed below.
7.4.5 Additional Processing—If any smoothing functions,
Please refer to Test Method E1131.
baseline correction algorithms or spectral subtractions are
7.3.1 TGA Temperature Profile—The temperature profile
applied to the data, this must be documented. It should be
should be specified in detail and include any initial delay or
pointed out that some commercial TGA/IR instruments give
final hold times.
theoperatoronlyalimitedcontroloverthesefunctionsandthe
7.3.2 TGA Purge Gas—The atmosphere used during the
instrument may be operating with these functions automati-
TGAexperiment should be recorded, as well as the purge rate
cally. The operator should investigate as to whether the
in mL/min. If the gas is switched during the run, the tempera-
instrument software does include such operations.
ture and elapsed time at which this occurs should be noted.
7.3.3 Sample Weight—The sample weight at the beginning
8. Software Treatment of Infrared Data
of the experiment must be recorded.
8.1 Gram-Schmidt Reconstruction—As each interferogram
7.3.4 Description of Sample—A detailed description of the
is recorded, a method, called Gram-Schmidt reconstruction (6,
sample’s characteristics should be recorded.
7),quicklydeterminestheinformationcontentoftheinterfero-
7.4 Software Parameters:
gram is applied. In this method, sets of interferograms are
7.4.1 Apodization Function—ForFouriertransforminfrared typically recorded once the sample has been placed in the
spectrometers, it is recommended that an apodization function
TGA, the TGA purge gas has been stabilized and before the
be applied to the interferogram before computation of spectral TGArun is started.These interferogram sets are used to create
data. Suitable apodization functions include boxcar, triangular,
a series of basis vectors that represent the experiment’s
Beer-Norton medium, Happ-Genzel, and cosine function. If TGA/IR baseline profile. During the experiment, each new
acquired spectra are to be searched against spectral reference
interferogram is used to generate a similar vector. Comparison
libraries, the apodization function of the acquired spectrum ofthisnewvectorandsubsequentvectorsagainstthereference
should match that of the reference spectra to improve spectral
vector set by orthogonalization yields a measure of the change
match quality. in total infrared energy and in the amount of material evolving
7.4.2 Spectral Resolution—Acompromise between the sig- from the TGA. The resulting plot of vector magnitude (inten-
nal to noise ratio of a spectrum and its information content sity) versus time is representative of how the total infrared
energy at any given time changes during the experiment. This
leads to an optimum spectral resolution for TGA/IR spectra of
−1 −1
4cm . If a rapid weight loss is expected, then 8 cm is called the Gram-Schmidt reconstruction (GSR) profile, or
more appropriately for TGA/IR, the Evolved Gas Profile
resolution is recommended to permit faster spectral acquisi-
tion. Data for trapped samples normally are recorded at a (EGP). This profile is similar in appearance to the first
−1
deriv
...