1、Designation: E2937 13E2937 18Standard Guide forUsing Infrared Spectroscopy in Forensic PaintExaminations1This standard is issued under the fixed designation E2937; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re
2、vision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONInfrared (IR) spectroscopy is commonly used by forensic laboratories for the analysis of paints andcoatings received in the f
3、orm of small chips, residues, particles, or smears, and serves as a staplecomparative technique in the assessment of whether or not questioned paint could have come from aparticular source. IR spectroscopy provides molecular structure information on many of the organicand inorganic constituents cont
4、ained within a single paint layer. This information can be used toclassify both binders and pigments in coating materials. The classification information maycan thenbe utilizedused to identify probable types of paint such as architectural, automotive, or maintenance.Additionally, the use of automoti
5、ve paint databases may allow for the determination of informationsuch as potential vehicle year, make and model. Databases maycan also aid in the interpretation of thesignificance (for example, how limited is the group of potential donor sources) of a questioned paint.1. Scope1.1 This guide applies
6、to the forensic IR analysis of paints and coatings and is intended to supplement information presentedin the Forensic Paint Analysis and Comparison Guidelines (1)2 written by Scientific Working Group on Materials Analysis(SWGMAT).This guideline is limited to the discussion of FourierTransform Infrar
7、ed (FTIR) instruments and provides informationon FTIR instrument setup, performance assessment, sample preparation, analysis and data interpretation. It is intended to providean understanding of the requirements, benefits, limitations and proper use of IR accessories and sampling methods available f
8、oruse by forensic paint examiners. The following accessory techniques will be discussed: FTIR microspectroscopy (transmission andreflectance), diamond cell and attenuated total reflectance. The particular methods employed by each examiner or laboratory, orboth, are dependent upon available equipment
9、, examiner training, specimen size or suitability, and purpose of examination. Thisguideline does not cover the theoretical aspects of many of the topics presented. These can be found in texts such as An InfraredSpectroscopy Atlas for the Coatings Industry (Federation of Societies for Coatings, 1991
10、) (2) and Fourier Transform InfraredSpectrometry (Griffiths and de Haseth, 1986) (3).1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.3 This standard does not purport to address all of the safety concerns, if any, associa
11、ted with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationa
12、lly recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3D16 Terminolog
13、y for Paint, Related Coatings, Materials, and Applications1 This guide is under the jurisdiction of ASTM Committee E30 on Forensic Sciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved Sept. 1, 2013Feb. 1, 2018. Published October 2013February 201
14、8. Originally approved in 2013. Last previous edition approved in 2013 as E2937 13. DOI: 10.1520/E2937-13.10.1520/E2937-18.2 The boldface numbers in parentheses refer to the list of references at the end of this standard.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contact
15、ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been m
16、ade to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Co
17、pyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1E131 Terminology Relating to Molecular SpectroscopyE1421 Practice for Describing and Measuring Performance of Fourier Transform Mid-Infrared (FT-MIR) Spectrometers: LevelZero and Level One
18、 TestsE1492 Practice for Receiving, Documenting, Storing, and Retrieving Evidence in a Forensic Science LaboratoryE1610 Guide for Forensic Paint Analysis and Comparison3. Terminology3.1 DefinitionsFor definitions of terms used in this guide other than those listed here, see Terminologies D16 and E13
19、1.3.2 Definitions of Terms Specific to This Standard:3.2.1 100 % linecalculated by ratioing two background spectra taken under identical conditions; the slope and noise of 100% lines are used to measure the performance of the instrument.3.2.2 absorbance (A)the logarithm to the base 10 of the recipro
20、cal of transmittance T, written as A = log 10 (1/T) = log10T.3.2.3 absorbance spectruma representation of the infrared spectrum in which the ordinate is defined in absorbance units (A);absorbance is linearly proportional to concentration and is therefore used in quantitative analysis.3.2.1 additive
21、(modifier)(modifier), nany substance added in a small quantity to improve properties; additives may includesubstances such as driers, corrosion inhibitors, catalysts, ultraviolet absorbers, and plasticizers.3.2.5 attenuated total reflectance (ATR)a method of spectrophotometric analysis based on the
22、reflection of energy at theinterface of two media that have different refractive indices and are in intimate contact with each other.3.2.6 aperturean opening in an optical system that controls the amount of light passing through a system.3.2.2 backgroundbackground, nthe signal produced by the entire
23、 analytical system apart from the material of interest.3.2.8 beam condensera series of mirrors that focus the infrared beam in the sample compartment to permit the examinationof smaller specimens.3.2.9 beam splitteran optical component that partially reflects and partially transmits radiation from t
24、he source in such amanner as to direct part to a fixed mirror and the other part to a moving mirror.3.2.3 binderbinder, na nonvolatile portion of the liquid vehicle of a coating, which serves to bindbond or cement thepigment particles together.3.2.4 coatingcoating, na generic term for paint, lacquer
25、, enamel, or other liquid or liquefiable material that is converted toa solid, protective, or decorative film or a combination of these types of films after application.3.2.12 deuterated triglycine sulfate (DTGS) detectora thermal detector that operates at room temperature but lacks thesensitivity f
26、or use with microscope accessories.3.2.5 extraneous material (contaminant, foreign material)material), nmaterial originating from a source other than thespecimen.3.2.6 interferogrammeaningful difference(s), na plot of the detector output as a function of retardation.feature or propertyof a sample th
27、at does not fall within the variation exhibited by the comparison sample, considering the limitations of the sampleor technique, and therefore indicates the two samples do not share a common origin. The use of this term does not imply the formalapplication of statistics.3.2.7 microtomymicrotomy, na
28、sample preparation method that sequentially passes a blade at a shallow depth through aspecimen, resulting in sections of selected thickness.3.2.16 mercury cadmium telluride (MCT) detectora quantum detector that utilizes a semi-conducting material and requirescooling with liquid nitrogen to be opera
29、ted; this type of detector is commonly used in microscope accessories due to its sensitivity.3.2.8 paintpaint, na pigmented coating.3.2.9 pigmentpigment, na finely ground, inorganic or organic, insoluble, and dispersed particle; besides color, a pigmentmay pigments provide many of the essential prop
30、erties of paint such as opacity, hardness, durability, and corrosion resistance; theterm pigment includes extenders.3.2.19 representative samplea portion of the specimen selected and prepared for analysis that exhibits all of the characteristicsof the parent specimen.3.2.20 significant differencea d
31、ifference between two samples that indicates that they do not share a common origin.3.2.10 smearsmear, na transfer of paint resulting from contact between two objects; these transfers maycan consist ofco-mingled particles from two or more sources, fragments, or contributions from a single source.3.2
32、.22 specimena material submitted for examination; samples are removed from a specimen for analysis.E2937 1823.2.23 transmittance (T)the ratio of the energy of the radiation transmitted by the sample to the background, usually expressedas a percentage.3.2.24 transmittance spectruma representation of
33、the infrared spectrum in which the ordinate is defined in %T; transmittanceis not linearly proportional to concentration.3.2.25 wavelengththe distance, measured along the line of propagation, between two points that are in phase on adjacentwaves.3.2.26 wavenumberthe inverse of the wavelength; or, th
34、e number of waves per unit length, usually conveyed in reciprocalcentimeters (cm-1).4. Summary of PracticeGuide4.1 The film forming portion of a paint or coating is the organic binder, also referred to as the resin. The binder forms a filmthat protects as well as displays the bonds to substrates and
35、 can contain organic and inorganic pigments that make a coating bothdecorative and functional. Infrared spectroscopy is commonly employed for the analysis of paint binders, pigments and otheradditives that are present in detectable concentrations.4.2 Paints and coatings absorb infrared radiation at
36、characteristic frequencies that are a function of the coatings composition.These absorption frequencies are determined by vibrations of chemical bonds present in the various components.4.3 The analysis of coatings using infrared spectroscopy can be carried out using either transmission or reflectanc
37、ereflectiontechniques. These measurements can be taken with a variety of equipment configurations and sampling accessories, the mostcommon being the use of an infrared microscope. A variety of accessories can also be utilizedused in the systems main bench.However, the use of a nonmicroscopenon-micro
38、scope accessory typically requires a larger sample size than those that can beanalyzed using a microscope.4.4 For transmission FTIR, a thin-peel of each paint layer, or a thin cross-section of a paint sample is made either by hand witha sharp blade or using a microtome. It is then analyzed using eit
39、her a microscope attachment or other suitable accessory, such asa diamond anvil cell. When thin samples suitable for transmission FTIR are not obtainable, reflectancereflection techniques (ATR,internal total reflection) maycan be employed using microscope objectives or bench accessories.4.5 Basic Pr
40、inciples:4.5.1 Infrared spectroscopy (mid-range) is capable of utilizing a the spectral range between 4000 and approximately 400 cm-1.Extended range instruments are needed to take measurements down to approximately 200 cm-1. The actual spectral cutoff dependsupon the type of detector and optics used
41、.4.5.2 An FTIR spectrometer measures the intensity of reflected or transmitted radiation over a designated range of wavelengths.The spectrum of a sample is produced by ratioing the calculating the ratio of the transmitted or reflected infrared spectrum to abackground spectrum.4.5.3 Transmission spec
42、tra maycan be plotted either in percent transmittance (%T)(%T), or in absorbance (A). ReflectanceRe-flection spectra maycan be plotted either in percent reflectance (%R) or in absorbance (A).log10 (R) units.4.6 Instrumentation:4.6.1 An FTIR instrument consists of a source to produce infrared radiati
43、on, an interferometer, a detector and a data processingdevice. A micro-FTIR instrument also has a microscope equipped with a detector and infrared compatible optics.4.6.2 Most FTIR systems are equipped to collect data using the main bench in the range of 4000 to 400 cm-1. Extended rangesystems are e
44、quipped with a beamsplitter and optics that allow transmission down to approximately 200 cm-1. Systems equippedwith an FTIR microscope utilizeuse a more sensitive detector type. Depending on the specific detector type, microscopic samplescan be analyzed in the range of approximately 4000 to 450 cm-1
45、.5. Significance and Use5.1 FTIR spectroscopy maycan be employed for the classification of paint binder types and pigments as well as for thecomparison of spectra from known and questioned coatings. When utilizedused for comparison purposes, the goal of the forensicexaminer is to determine whether a
46、ny significantmeaningful differences exist between the known and questioned samples.5.2 This guide is designed to assist an examiner in the selection of appropriate sample preparation methods and instrumentalparameters for the analysis, comparison or identification of paint binders and pigments.5.3
47、It is not the intent of this guide to present comprehensive theories and methods of FTIR spectroscopy. It is necessary thatthe examiner have an understanding of FTIR and general concepts of specimen preparation prior to using this guide. Thisinformation is available from manufacturers reference mate
48、rials, training courses, and references such as: Forensic Applicationsof Infrared Spectroscopy (Suzuki, 1993) (4), Infrared Microspectroscopy of Forensic Paint Evidence (Ryland, 1995) (5), Use ofInfrared Spectroscopy for the Characterization of Paint Fragments (Beveridge, 2001) (6), and An Infrared
49、Spectroscopy Atlas forthe Coatings Industry (2).E2937 1836. Sample Handling6.1 The general collection, handling, and tracking of samples shall meet or exceed the requirements of Practice E1492 as wellas the relevant portions of the SWGMATs Trace Evidence Quality Assurance Guidelines (7).6.2 The work area and tools used for the preparation of samples shall be free of all extraneous materials that could transfer tothe sample.6.3 As stated in Guide E1610, a paint specimen should first be examined withusing a stereomicroscope, noting its siz
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