1、Designation: E3085 17Standard Guide forFourier Transform Infrared Spectroscopy in Forensic TapeExaminations1This standard is issued under the fixed designation E3085; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、 revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 Infrared spectroscopy (IR) is a valuable method for theidentification and comparison of pressure sensitive tapes (1-20).2T
3、his guide provides basic recommendations and infor-mation about infrared spectrometers and accessories, with anemphasis on sampling techniques specific to pressure sensitivetape examinations. The particular method(s) employed by eachexaminer or laboratory will depend upon available equipment,examine
4、r training, sample suitability, and sample size.1.2 This guide is intended for examiners with a basicknowledge of the theory and proficiency in the use of infraredspectroscopy as well as experience in the handling and forensicexamination of pressure sensitive tapes. Further, this guide is tobe used
5、in conjunction with a broader analytical scheme(21-23).1.3 Disclaimer: This guide offers a set of instructions forperforming one or more specific operations. This standardcannot replace knowledge, skill, or the ability acquired throughappropriate education, training, and experience and should beused
6、 in conjunction with sound professional judgment.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 standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibili
7、ty 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:3E131 Terminology Relating to Molecular SpectroscopyE573 Practices for Internal Reflection Spectrosc
8、opyE1421 Practice for Describing and Measuring Performanceof Fourier Transform Mid-Infrared (FT-MIR) Spectrom-eters: Level Zero and Level One TestsE1492 Practice for Receiving, Documenting, Storing, andRetrieving Evidence in a Forensic Science LaboratoryE2224 Guide for Forensic Analysis of Fibers by
9、 InfraredSpectroscopy3. Terminology3.1 DefinitionsFor terms relevant to molecularspectroscopy, refer to Terminology E131.3.1.1 background, nthe signal produced by the entireanalytical system apart from the material of interest.3.1.2 elastomer, nthe polymeric backbone of a pressuresensitive adhesive
10、imparting elastic properties, for example,rubber.3.1.3 fiber reinforcement, nthe fabric portion of somepressure sensitive adhesive tapes; also referred to as scrim.3.1.4 filler/extender, nan inorganic material that is addedto a tape to modify a physical property or reduce cost.3.1.5 low e-glass, na
11、dichroic mirror that is coated with anIR reflective surface.3.1.5.1 DiscussionSuch glass is suitable for use as asample support when performing IR reflection techniques.3.1.6 meaningful difference, na feature or property of asample that does not fall within the variation exhibited by thecomparison s
12、ample, considering the limitations of the sampleor technique, and therefore indicates the two samples do notshare a common origin.3.1.6.1 DiscussionThe use of this term does not imply theformal application of statistics.3.1.7 pressure-sensitive adhesive, na viscoelastic materialwhich, in solvent-fre
13、e form, remains tacky and will adhereinstantaneously to most solid surfaces with the application ofvery slight pressure.3.1.8 pressure-sensitive adhesive (PSA) tape, na combi-nation of a pressure sensitive adhesive with a continuousflexible backing (for example, cloth, paper, metal, or plastic) orwi
14、th a backing and release liner.1This guide is under the jurisdiction of ASTM Committee E30 on ForensicSciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved March 1, 2017. Published March 2017. DOI: 10.1520/E3085-17.2The boldface numbers in parent
15、heses refer to a list of references at the end ofthis standard.3For referenced ASTM standards, 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 websit
16、e.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of Int
17、ernational Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.1.8.1 DiscussionUse of the word “tape” in this guiderefers to PSA tapes and their components.3.1.9 release coat, nan inert material with a low surfaceenergy, applied
18、 to a backing film on the side opposite theadhesive, that provides ease of unwind and prevents delami-nation or tearing.3.1.10 tackifier, nsolid resins added to the adhesive basepolymer to impart the necessary tack and adhesion.4. Summary of Guide4.1 This guideline covers the analysis of tape backin
19、gs andadhesives by infrared spectroscopy. It can be applied to a widerange of infrared spectrometers and accessory configurations.4.2 For the infrared analysis of the fiber reinforcement, referto Guide E2224.5. Significance and Use5.1 This guide is designed to assist an examiner in theselection of a
20、ppropriate sample preparation methods for theanalysis, comparison, and identification of pressure sensitiveadhesive (PSA) tapes. If no meaningful differences are notedbetween the known and unknown samples regarding physicalappearance or measurements, then IR spectroscopy should bethe next step in th
21、e analytical scheme.5.2 Infrared spectroscopy can provide molecular informa-tion regarding major organic and inorganic components. Forvarious reasons, components in lesser amounts are typicallymore difficult to identify unequivocally. Reasons for thisinclude interference of the absorption bands of t
22、he majorcomponents with the less intense bands of minor componentsand sensitivity issues whereby the minor components arepresent at concentrations below the detection limits of theinstrument.5.3 Infrared spectroscopy can be used to obtain spectra forelucidation of the chemical composition of a tape
23、and forcomparison of two or more tape samples. When used forspectral comparisons, the objective is to determine whether anymeaningful differences exist between the samples.6. Sample Handling6.1 The general collection, handling, and tracking ofsamples shall meet or exceed the requirements of Practice
24、E1492.6.2 The work area and tools used for the preparation ofsamples shall be free of any materials that could transfer to thesample.6.3 When analyzing difficult samples (for example, adhe-sive residue, dirty samples, limited sample size, or inhomoge-neous samples), care shall be taken in sampling e
25、ach availabletape layer (that is, film backing, adhesive, fiber reinforcementif present) as well as in selection of appropriate analyticalconditions. An attempt shall be made to remove extraneousmaterial from the specimen before analysis. In order to ensurereproducibility and evaluate intra-sample v
26、ariations, repeatanalysis of samples is recommended. The number of replicatesis dependent on factors such as sample size and condition andis evaluated on a case-by-case basis.6.4 If necessary, the tape backing can be cleaned with anappropriate solvent (for example, methanol or hexane).Alternatively,
27、 residue can be removed by gentle scraping of thesurface. An adhesive sample can be obtained by exposing andsampling the underlying portion.6.5 The infrared analysis of tapes can be carried out usingeither transmission or reflection techniques. These measure-ments can be taken with a variety of equi
28、pment configurationsand accessories, the most common being the use of AttenuatedTotal Reflection (ATR) or an infrared microscope. However,the use of an ATR requires a larger sample size.6.6 Attenuated Total Reflection (ATR), also known as In-ternal Reflection Spectroscopy (IRS), is described in Prac
29、ticesE573. For forensic tape analysis, it offers a rapid approach tosampling a tape backing and the adhesive as virtually nosample preparation is necessary. Single or multiple reflectionelements may be used depending on the amount of areaavailable for sampling. When only a small area is available, a
30、single reflection element is desirable to avoid contamination.6.7 Transmission microspectroscopy is possible by sam-pling a small portion of the tape component (backing, oradhesive) and analyzing it as a thin film.6.8 A diamond anvil cell may be used in the bench with abeam condenser or placed under
31、 the microscope accessory toanalyze both the backing and the adhesive portions of tape.6.9 Tackifiers or plasticizers can be extracted from theadhesive or backing using a mild solvent such as hexane oracetone (20), for subsequent analysis as a thin film usingtransmission mode.6.10 Samples being comp
32、ared shall be prepared and ana-lyzed in the same manner.7. Analysis7.1 A standard mid-IR range Fourier transform infrared(FTIR) spectrometer is acceptable to conduct the necessaryanalyses. Detector cutoff no higher than 750 cm-1is recom-mended. A mid-infrared FTIR spectrometer with an extendedrange
33、down to 200 cm-1is advantageous for the classificationand comparison of inorganic fillers and pigments.7.2 Instrument Parameters:7.2.1 Performance and VerificationIt is essential thatinstrument performance and verification be evaluated routinely(for example, monthly or before use if used less freque
34、ntly).7.2.2 The preferred performance evaluation method is inaccordance with Practice E1421. In brief, this includes evalu-ation of the system throughput, single-beam spectrum, 100% Tline, and polystyrene reference spectrum.7.2.3 Sample and background scans shall be run under thesame instrument cond
35、itions (for example, aperture size).7.2.4 Typically, 16 to 256 scans are collected at a resolutionof4cm-1or less.7.2.5 When comparing spectra, the data shall be displayedin the same units (for example, Absorbance units, %Transmission, % Reflectance).E3085 1727.3 Main Bench Transmission:7.3.1 Transmi
36、ssion methods generally require more exten-sive sample preparation. The sample shall be thin enough notto over-absorb. For transmission data viewed in %transmittance, spectral peaks optimally should not fall below10 % T. For spectra displayed in absorbance, the maximumabsorbance optimally should be
37、1.0 or less. This typicallyrequires a sample thickness of approximately 510 m.7.3.2 Sample preparation techniques that may be employedfor transmission analysis in the main bench include backing oradhesive pressed in a diamond cell, a thin backing samplestretched over an aperture, or adhesive deposit
38、ed onto an alkalihalide pellet (for example, KBr, NaCl, AgCl).7.4 Main Bench ATR:7.4.1 ATR methods lend themselves to conducting theexamination of the tape intact. Since ATR is a surface tech-nique it is necessary to remove any extraneous material fromthe area to be examined.7.4.2 ATR is also useful
39、 in the analysis of duct tapebackings for layer structure evaluation as a complementarytechnique to manual cross section. The adhesive is removedwith an appropriate solvent (for example, hexane), and thebacking is analyzed on both sides. Additional analysis may beconducted on middle layers as desire
40、d. The spectra are thencompared.7.5 Microscope Accessory:7.5.1 The use of a microscope accessory is preferred forvery small samples. It is important to note that there is atradeoff between sensitivity and spectral range with the MCTdetectors. The low energy cut off for most detectors is in therange
41、of 700450 cm-1. The smallest apertures particularlylimit the energy from the longer wavelengths (smaller wave-numbers) reaching the detector due to diffraction. Heterogene-ity issues are also more pronounced when using very smallapertures.7.5.2 The microscope attachment permits the analysis ofmultip
42、le samples placed on an appropriate support material.The method affords the advantage of viewing the sampleoptically and choosing the most appropriate area for analysis.7.5.3 Spectral measurements using an FTIR microscope canbe obtained in transmission, reflection, or ATR mode.7.6 Microscope Accesso
43、ry Transmission:7.6.1 Transmission measurements are commonly used be-cause they generate spectra with fewer artifacts than othersampling modes. However, transmission methods generallyentail more sample preparation than reflection techniques. Thetape sample shall be rendered thin enough not to over-a
44、bsorb.Samples can be placed directly over a small aperture foranalysis or placed on an appropriate alkali halide plate. Thistypically requires a sample thickness of approximately 35 m.7.6.2 A diamond cell can also be used as a sample supportmedium with the FTIR microscope. The adhesive can besmeared
45、 on one of the diamond faces. A thin peel of a tapebacking is placed onto one of the diamond faces, the seconddiamond is positioned on top, and pressure is applied. Onediamond is typically removed prior to analysis once the samplehas been compressed. This leaves the thin compressed filmadhering to o
46、ne of the diamond faces.7.7 Microscope Accessory Reflection:7.7.1 If samples are analyzed directly on an infrared lightreflecting surface (for example, low e-glass or gold mirror), thereflection mode can be used to produce spectra mimickingdouble-pass transmission spectra. The technique is sometimes
47、referred to as “transflection” or “reflection/absorption.”Samples need to be approximately half the thickness of anoptimum transmission sample.7.7.2 The FTIR microscope can also be used in the specularreflection mode; however, it is not useful for tape unless thesurface of the sample is highly refle
48、ctive.7.8 Microscope Accessory ATR:7.8.1 ATR objectives are available for infrared microscopes.Applying consistent pressure to each sample can mitigatespectral variations. Intra-sample variations can result fromsample heterogeneity; therefore, multiple samplings shall beconducted as feasible.8. Clas
49、sification, Comparison, and Interpretation8.1 Classification of commonly encountered tape compo-nents is based on the interpretation of characteristic infraredabsorption bands.8.1.1 Depending on the condition of the tape and theconcentration of the material, tape components can contain thefollowing:8.1.1.1 BackingPolymer film, plasticizers, fillers,extenders, flame retardants.8.1.1.2 AdhesiveElastomer, tackifiers, fillers, extenders.8.1.1.3 Release Coating.8.1.1.4 Fiber Reinforcement.8.2 Classification of a tape component may be achieved byevaluating th
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