1、Designation: E 2105 00 (Reapproved 2005)Standard Practice forGeneral Techniques of Thermogravimetric Analysis (TGA)Coupled With Infrared Analysis (TGA/IR)1This standard is issued under the fixed designation E 2105; the number immediately following the designation indicates the year oforiginal adopti
2、on or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers techniques that are of general use inthe qualitative
3、 analysis of samples by thermogravimetric analy-sis (TGA) coupled with infrared (IR) spectrometric techniques.The combination of these techniques is often referred to asTGA/IR.1.2 A sample heated in a TGA furnace using a predeter-mined temperature profile typically undergoes one or moreweight losses
4、. Materials evolved during these weight losses arethen analyzed using infrared spectroscopy to determine chemi-cal identity. The analysis may involve collecting discreteevolved gas samples or, more commonly, may involve passingthe evolved gas through a heated flowcell during the TGAexperiment. The g
5、eneral techniques of TGA/IR and othercorresponding techniques, such as TGA coupled with massspectroscopy (TGA/MS), as well as, TGA, used in conjunctionwith GC/IR, are described in the referenced literature (1-4).21.3 Some thermal analysis instruments are designed toperform both thermogravimetric ana
6、lysis and differential scan-ning calorimetry simultaneously. This type of instrument issometimes called a simultaneous thermal analyzer (STA). Theevolved gas analysis performed with an STA instrument (5) issimilar to that with a TGA, and so, would be covered by thispractice. With use of a simultaneo
7、us thermal analyzer, thecoupled method typically is labeled STA/IR.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This statement does not purport to address all of thesafety concerns, if any, associated with its use. It
8、 is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E 131 Terminology Relating to Molecular SpectroscopyE 168 Practices for General
9、Techniques of Infrared Quanti-tative AnalysisE 334 Practices for General Techniques of Infrared Mi-croanalysisE 473 Terminology Relating to Thermal Analysis and Rhe-ologyE 1131 Test Method for Compositional Thermal Analysisby ThermogravimetryE 1252 Practice for General Techniques for QualitativeInfr
10、ared AnalysisE 1421 Practice for Describing and Measuring Performanceof Fourier Transform Infrared (FT-IR) Spectrometers:Level Zero and Level One Tests3. Terminology3.1 DefinitionsFor general definitions of terms and sym-bols, refer to Terminologies E 131 and E 473.3.2 Definitions of Terms Specific
11、to This Standard:3.2.1 evolved gas, nany material (or mixture) evolvedfrom a sample during a thermogravimetric or simultaneousthermal analysis experiment. Materials evolved from thesample may be in the form of a gas, a vapor, an aerosol or asparticulate matter. For brevity, the term “evolved gas” wi
12、ll beused throughout this practice to indicate any material form ormixture evolved from a sample.3.2.2 evolved gas analysis (EGA), na technique in whichthe nature and amount of gas evolved from a sample ismonitored against time or temperature during a programmedchange in temperature of the sample.3.
13、2.3 evolved gas profile (EGP), nan indication of thetotal amount of gases evolved, as a function of time ortemperature, during the thermogravimetric experiment. In1This practice is under the jurisdiction of ASTM Committee E13 on MolecularSpectroscopy and is the direct responsibility of Subcommittee
14、E13.03 on InfraredSpectroscopy.Current edition approved Sept. 1, 2005. Published September 2005. Originallyapproved in 2000. Last previous edition approved in 2000 as E 2105 002The boldface numbers in parentheses refers to the list of references at the endof this standard.3For referenced ASTM standa
15、rds, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA
16、 19428-2959, United States.TGA/IR, this profile is calculated from the infrared spectro-scopic data recorded by application of the Gram-Schmidtreconstruction (GSR) algorithm (6,7). Because the GSR wasdesigned for use in gas chromatography coupled with infrared(GC/IR) analysis, the evolved gas profil
17、e has sometimes beenerroneously called the evolved gas chromatogram.3.2.4 functional group profile (FGP), nan indication ofthe amount of gas evolved during the thermogravimetricexperiment that contains a particular chemical functionalitymeasured as a function of time or temperature. This profile isc
18、alculated from the infrared spectroscopic data recorded byintegration of the absorbances over selected spectral regions asthe experiment progresses. Typically, a number of such profilesare calculated in real-time. Additional profiles (using differentspectral regions) can often be calculated after th
19、e experimentfrom the stored spectroscopic data. Because the software usedhas similarities with that used for GC/IR analysis, the func-tional group profile has sometimes been erroneously called thefunctional group chromatogram.3.2.5 hit quality index (HQI), nthe numerical ranking ofinfrared reference
20、 spectra against that of an analyte spectrumthrough the use of search algorithms that measure a compara-tive fit spectral data.3.2.6 specific gas profile (SGP), na special type of func-tional group profile arises when the selected region of thespectrum contains absorbances due to a specific gas such
21、 asammonia or carbon monoxide.4. Significance and Use4.1 This practice provides general guidelines for the prac-tice of thermogravimetry coupled with infrared spectrometricdetection and analysis (TGA/IR). This practice assumes thatthe thermogravimetry involved in the practice is proper. It isnot the
22、 intention of this practice to instruct the user on properthermogravimetric techniques. Please refer to Test MethodE 1131 for more information.5. General TGA/IR Techniques5.1 Two different types of TGA/IR techniques are used toanalyze samples. These consist of discrete evolved gas trap-ping and use
23、of a heated flowcell interface. It should be notedthat only the latter technique allows for the calculation of theevolved gas and functional group profiles.5.2 Evolved Gas Trapping TechniquesEvolved gas trap-ping techniques are the least elaborate means for obtainingTGA/IR data. In these techniques,
24、 the evolved gas is collectedfrom the TGA furnace in discrete aliquots that are thenanalyzed. In use of such techniques, it is essential to monitorthe TGA weight loss curve to determine the time or tempera-ture at which the effluent was captured. Vapor phase samplescan be trapped in a heated low-vol
25、ume gas cell at the exit of theTGA, analyzed, then flushed out by the TGA effluent. Whenthe next aliquot of interest is in the gas cell, the flow is stoppedagain for analysis. This process can be made more convenientby designing the TGA temperature profile such that thetemperature is held constant w
26、hile a trapped sample is beinganalyzed (ramp-and-hold method). Alternatively, fractions canbe trapped in the condensed phase by passing the TGAeffluentthrough a solvent, a powdered solid, or a cold trap to yieldcondensed phase material for subsequent analysis (8). Infraredspectrometry is performed w
27、ith either a monochromator, afilter spectrometer or a Fourier transform spectrometer. Seealso Practices E 334 and E 1252 for general techniques onmicroanalysis and qualitative practices.5.2.1 Since the analyte of interest is static when employingan evolved gas trapping technique, the spectrum can be
28、recorded using a long integration time or increasing scanco-addition to improve the signal-to-noise ratio (SNR). How-ever, in vapor phase evolved gas trapping, the sample integritycan be compromised by slow decomposition or by depositionon the cell walls. A spectrum should be obtained initiallywithi
29、n a short co-addition time to create a reference spectrumto ensure the integrity of the spectrum obtained after longco-addition.5.3 Evolved Gas Analysis Using a FlowcellAnother wayto examine the gases evolved during a TGA/IR experiment isto use a specially designed flowcell. This flowcell is situate
30、d inthe IR beam of the infrared spectrometer. IR monochromatorsand filter spectrometers are typically used to monitor a specificfrequency range during the TGAexperiment. If a full spectrumis to be obtained with these IR devices, the evolved gas istrapped via a stopped flow routine and the spectromet
31、ers arepermitted to scan the infrared spectrum. In contrast, the Fouriertransform IR spectrometer permits the acquisition of thecomplete IR spectrum in brief timeframes without impact uponthe typical TGA experiment, that is, continuous spectralcollection without interruption of evolved gas flow or s
32、ampleheating.5.3.1 In the typical TGA/IR experiment, the evolved gas ismonitored in real-time by the IR spectrometer. The temporalresolution required during aTGA/IR experiment is on the orderof 560 s/spectral data acquisition event. If the full IRspectrum is to be acquired, the rapidity of the TGAex
33、perimentrequires a Fourier-transform infrared (FT-IR) spectrometer tomaintain sufficient temporal resolution. Such instruments in-clude a computer that is capable of storing large amounts ofspectroscopic data for subsequent evaluation.5.3.2 Some spectrometer data systems may have limitedsoftware, or
34、 data storage capabilities. Such instrument systemsare capable of recording suitable spectra during the TGA/IRexperiment, but may not be able to calculate the evolved gasand functional group profiles.5.3.3 The flowcell is coupled directly to the TGA via aheated transfer line. Evolved gas components
35、are analyzed asthey emerge from the transfer line. This technique typicallyyields low microgram detection limits for most analytes (1).Instruments that include the IR spectrometer, data system, thethermogravimetric analyzer, heated transfer-line, and heatedflowcell are commercially available.5.3.4 I
36、t should be noted that any metal surface inside theTGA furnace, transfer line or flowcell assembly may reactwith, and sometimes destroy, specific classes of evolved gases,for example, amines. This can result in changes to the chemicalnature of the evolved gas. Consequently, it is possible to fail to
37、identify the presence of such compound in the mixture. Thissituation can sometimes be identified by comparison of theTGA weight loss profile with the evolved gas profile.E 2105 00 (2005)25.3.5 The infrared energy throughput of the flowcell shouldbe periodically monitored since this indicates the ove
38、rallcondition of this assembly. It is important that all tests beconducted at a constant flowcell temperature because of theeffect of the emitted energy on the detector (see 6.3.1). It isrecommended that records be kept of the interferogram signalstrength, single-beam energy response and the ratio o
39、f twosuccessive single-beam curves (as appropriate to the instru-ment used). For more information on such tests, refer toPractice E 1421. If a mercury-cadmium-telluride (MCT) detec-tor is being employed, these tests will also reveal degradationof performance due to loss of the Dewar vacuum and conse
40、-quent buildup of ice on the detector face. In general, when aloss of transmitted energy greater than 10 % of the total energyis found, cleaning of the flowcell is recommended.5.3.6 Care must be taken to stabilize or, preferably, removeinterfering spectral features that result from atmospheric ab-so
41、rptions in the IR beam path of the spectrometer. Best resultswill be obtained by purging the entire optical path of thespectrometer with dry nitrogen gas. Alternatively, dry air canbe used as the spectrometer purge gas; however, this will leadto interferences in the regions of carbon dioxide absorpt
42、ion(2500 go 2200 cm1and 720 to 620 cm1) due to the presenceof carbon dioxide in air. Further, commercially-available airscrubbers, that remove both water vapor and carbon dioxide,provide adequate purging of the spectrometer. In some instru-ments, the beam path is sealed in the presence of a desiccan
43、t,but interferences from both carbon dioxide and water vapor(1900 to 1400 cm1) may be found. Similarly, the TGAfurnace, the transfer line and the gas cell interface are purgedwith a gas that does not absorb infrared energy. Typically, thisTGApurge gas is inert (nitrogen or helium) and has a flow rat
44、efrom 10 to 200 mL/min. Occasionally, oxidizing or reducingatmospheres, that is, oxygen or hydrogen respectively, are usedwith the TGA to promote specific chemical reactions. Whenpreparing for a TGA/IR experiment, the atmospheres withinthe spectrometer and within the furnace and gas cell combina-tio
45、n must be allowed to stabilize before spectral data collectionand the thermal experiment commence to minimize spectralinterferences. Atmospheric stability for the experiment can bejudged by recording the single-beam energy response and theratio of two successive single-beam spectra over a discrete t
46、imeinterval.5.3.6.1 The spectral features of both carbon dioxide and,more importantly, water vapor depend upon the temperature atwhich they were measured. This can become an awkwardproblem in TGA/IR analysis, as many samples evolve thesegases as they are heated. It may be necessary to identify these
47、molecules in the heated flowcell when there is a possiblebackground absorbance from molecules close to room tem-perature in the spectrometer and interface. It is particularlydifficult to use spectral subtraction techniques (see PracticeE 1252) to compensate for the presence of water vapor in thespec
48、trum under these conditions. The significance of thisproblem is demonstrated by the attempt to identify the presenceof a trace amount of a carbonyl compound when spectralfeatures due to water vapor also are observed.6. Component Design Considerations for TGA/IR Usinga Flowcell6.1 Transfer LineA tran
49、sfer line from the TGA to theflowcell must present an inert, nonporous surface to theevolved gas. Evolved gas transfer lines must be heated totemperatures sufficient to prevent condensation of the evolvedgas species. Typically, the transfer line is constructed of anarrow-bore steel tube that has either a removable liner or iscoated internally with silica. The temperature of the transferline is normally held constant during an experiment at a levelchosen to avoid both condensation and degradation of theevolved gases. Typical working temperatures have a range of150300C.
