1、Designation: E2937 13Standard 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 revision.
2、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 form of s
3、mall 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 contained wi
4、thin a single paint layer. This information can be used toclassify both binders and pigments in coating materials. The classification information may then beutilized to identify probable types of paint such as architectural, automotive, or maintenance.Additionally, the use of automotive paint databa
5、ses may allow the determination of information suchas potential vehicle year, make and model. Databases may 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 to the forensic IR ana
6、lysis of paintsand coatings and is intended to supplement information pre-sented in the Forensic Paint Analysis and Comparison Guide-lines (1)2written by Scientific Working Group on MaterialsAnalysis (SWGMAT). This guideline is limited to the discus-sion of Fourier Transform Infrared (FTIR) instrume
7、nts andprovides information on FTIR instrument setup, performanceassessment, sample preparation, analysis and data interpreta-tion. It is intended to provide an understanding of therequirements, benefits, limitations and proper use of IR acces-sories and sampling methods available for use by forensi
8、c paintexaminers. The following accessory techniques will be dis-cussed: FTIR microspectroscopy (transmission andreflectance), diamond cell and attenuated total reflectance. Theparticular methods employed by each examiner or laboratory,or both, are dependent upon available equipment, examinertrainin
9、g, specimen size or suitability, and purpose of examina-tion. This guideline does not cover the theoretical aspects ofmany of the topics presented. These can be found in texts suchas An Infrared Spectroscopy Atlas for the Coatings Industry(Federation of Societies for Coatings, 1991) (2) and FourierT
10、ransform Infrared Spectrometry (Griffiths and de Haseth,1986) (3).1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It i
11、s 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:3D16 Terminology for Paint, Related Coatings, Materials, andApplicationsE131 Termin
12、ology Relating to Molecular SpectroscopyE1421 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 Laboratory1This gui
13、de is under the jurisdiction of ASTM Committee E30 on ForensicSciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved Sept. 1, 2013. Published October 2013. DOI: 10.1520/E2937-13.2The boldface numbers in parentheses refer to the list of references
14、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 website.Copyright ASTM International, 100
15、Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1E1610 Guide for Forensic Paint Analysis and Comparison3. Terminology3.1 DefinitionsFor definitions of terms used in this guideother than those listed here, see Terminologies D16 and E131.3.2 Definitions of Terms Specific
16、 to This Standard:3.2.1 100 % linecalculated by ratioing two backgroundspectra taken under identical conditions; the slope and noise of100 % lines are used to measure the performance of theinstrument.3.2.2 absorbance (A)the logarithm to the base 10 of thereciprocal of transmittance T, written as A =
17、 log 10 (1/T) =log10T.3.2.3 absorbance spectruma representation of the infraredspectrum in which the ordinate is defined in absorbance units(A); absorbance is linearly proportional to concentration and istherefore used in quantitative analysis.3.2.4 additive (modifier)any substance added in a smallq
18、uantity to improve properties; additives may include sub-stances such as driers, corrosion inhibitors, catalysts, ultravio-let absorbers, and plasticizers.3.2.5 attenuated total reflectance (ATR)a method of spec-trophotometric analysis based on the reflection of energy at theinterface of two media t
19、hat have different refractive indices andare in intimate contact with each other.3.2.6 aperturean opening in an optical system that con-trols the amount of light passing through a system.3.2.7 backgroundthe signal produced by the entire ana-lytical system apart from the material of interest.3.2.8 be
20、am condensera series of mirrors that focus theinfrared beam in the sample compartment to permit theexamination of smaller specimens.3.2.9 beam splitteran optical component that partiallyreflects and partially transmits radiation from the source insuch a manner as to direct part to a fixed mirror and
21、 the otherpart to a moving mirror.3.2.10 bindera nonvolatile portion of the liquid vehicle ofa coating, which serves to bind or cement the pigment particlestogether.3.2.11 coatinga generic term for paint, lacquer, enamel, orother liquid or liquefiable material that is converted to a solid,protective
22、, or decorative film or a combination of these types offilms after application.3.2.12 deuterated triglycine sulfate (DTGS) detectorathermal detector that operates at room temperature but lacksthe sensitivity for use with microscope accessories.3.2.13 extraneous material (contaminant, foreignmaterial
23、)material originating from a source other than thespecimen.3.2.14 interferograma plot of the detector output as afunction of retardation.3.2.15 microtomya sample preparation method that se-quentially passes a blade at a shallow depth through aspecimen, resulting in sections of selected thickness.3.2
24、.16 mercury cadmium telluride (MCT) detectora quan-tum detector that utilizes a semi-conducting material andrequires cooling with liquid nitrogen to be operated; this typeof detector is commonly used in microscope accessories due toits sensitivity.3.2.17 painta pigmented coating.3.2.18 pigmenta fine
25、ly ground, inorganic or organic,insoluble, and dispersed particle; besides color, a pigment mayprovide many of the essential properties of paint such asopacity, hardness, durability, and corrosion resistance; the termpigment includes extenders.3.2.19 representative samplea portion of the specimensel
26、ected and prepared for analysis that exhibits all of thecharacteristics of the parent specimen.3.2.20 significant differencea difference between twosamples that indicates that they do not share a common origin.3.2.21 smeara transfer of paint resulting from contactbetween two objects; these transfers
27、 may consist of co-mingledparticles from two or more sources, fragments, or contributionsfrom a single source.3.2.22 specimena material submitted for examination;samples are removed from a specimen for analysis.3.2.23 transmittance (T)the ratio of the energy of theradiation transmitted by the sample
28、 to the background, usuallyexpressed as a percentage.3.2.24 transmittance spectruma representation of the in-frared spectrum in which the ordinate is defined in %T;transmittance is not linearly proportional to concentration.3.2.25 wavelengththe distance, measured along the line ofpropagation, betwee
29、n two points that are in phase on adjacentwaves.3.2.26 wavenumberthe inverse of the wavelength; or, thenumber of waves per unit length, usually conveyed in recip-rocal centimeters (cm-1).4. Summary of Practice4.1 The film forming portion of a paint or coating is theorganic binder, also referred to a
30、s the resin. The binder formsa film that protects as well as displays the organic andinorganic pigments that make a coating both decorative andfunctional. Infrared spectroscopy is commonly employed forthe analysis of paint binders, pigments and other additives thatare present in detectable concentra
31、tions.4.2 Paints and coatings absorb infrared radiation at charac-teristic frequencies that are a function of the coatings compo-sition. These absorption frequencies are determined by vibra-tions of chemical bonds present in the various components.4.3 The analysis of coatings using infrared spectros
32、copy canbe carried out using either transmission or reflectance tech-niques. These measurements can be taken with a variety ofequipment configurations and sampling accessories, the mostcommon being the use of an infrared microscope. A variety ofaccessories can also be utilized in the systems main be
33、nch.E2937 132However, the use of a nonmicroscope accessory typicallyrequires a larger sample size than those that can be analyzedusing 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 handwith a sharp blade or using a
34、 microtome. It is then analyzedusing either a microscope attachment or other suitableaccessory, such as a diamond anvil cell. When thin samplessuitable for transmission FTIR are not obtainable, reflectancetechniques (ATR, reflection) may be employed using micro-scope objectives or bench accessories.
35、4.5 Basic Principles:4.5.1 Infrared spectroscopy (mid-range) is capable of utiliz-ing a spectral range between 4000 and approximately 400 cm-1.Extended range instruments are needed to take measurementsdown to approximately 200 cm-1. The actual spectral cutoffdepends upon the type of detector and opt
36、ics used.4.5.2 An FTIR spectrometer measures the intensity ofreflected or transmitted radiation over a designated range ofwavelengths. The spectrum of a sample is produced by ratioingthe transmitted or reflected infrared spectrum to a backgroundspectrum.4.5.3 Transmission spectra may be plotted eith
37、er in percenttransmittance (%T) or in absorbance (A). Reflectance spectramay be plotted either in percent reflectance (%R) or inabsorbance (A).4.6 Instrumentation:4.6.1 An FTIR instrument consists of a source to produceinfrared radiation, an interferometer, a detector and a dataprocessing device. A
38、micro-FTIR instrument also has a micro-scope equipped with a detector and infrared compatible optics.4.6.2 Most FTIR systems are equipped to collect data usingthe main bench in the range of 4000 to 400 cm-1. Extendedrange systems are equipped with a beamsplitter and optics thatallow transmission dow
39、n to approximately 200 cm-1. Systemsequipped with an FTIR microscope utilize a more sensitivedetector type. Depending on the specific detector type, micro-scopic samples can be analyzed in the range of approximately4000 to 450 cm-1.5. Significance and Use5.1 FTIR spectroscopy may be employed for the
40、 classifica-tion of paint binder types and pigments as well as for thecomparison of spectra from known and questioned coatings.When utilized for comparison purposes, the goal of theforensic examiner is to determine whether any significantdifferences exist between the known and questioned samples.5.2
41、 This guide is designed to assist an examiner in theselection of appropriate sample preparation methods and in-strumental parameters for the analysis, comparison or identi-fication of paint binders and pigments.5.3 It is not the intent of this guide to present comprehensivetheories and methods of FT
42、IR spectroscopy. It is necessary thatthe examiner have an understanding of FTIR and generalconcepts of specimen preparation prior to using this guide.This information is available from manufacturers referencematerials, training courses, and references such as: ForensicApplications of Infrared Spectr
43、oscopy (Suzuki, 1993) (4),Infrared Microspectroscopy of Forensic Paint Evidence(Ryland, 1995) (5), Use of Infrared Spectroscopy for theCharacterization of Paint Fragments (Beveridge, 2001) (6),and An Infrared Spectroscopy Atlas for the Coatings Indus-try(2).6. Sample Handling6.1 The general collecti
44、on, handling, and tracking ofsamples shall meet or exceed the requirements of PracticeE1492 as well as the relevant portions of the SWGMATsTrace Evidence Quality Assurance Guidelines (7).6.2 The work area and tools used for the preparation ofsamples shall be free of all extraneous materials that cou
45、ldtransfer to the sample.6.3 As stated in Guide E1610, a paint specimen should firstbe examined with a stereomicroscope, noting its size,appearance, layer sequence, heterogeneity within any givenlayer, and presence of any material that could interfere with theanalysis (for example, traces of adhesiv
46、e, surface abrasiontransfers, or zinc phosphate conversion coating residue on theunderside of the base primer on electro-coated parts). Somesurface materials may be of interest and therefore may beworthy of analysis before removal.6.4 Each layer of a multi-layered paint should be analyzedindividuall
47、y.6.5 When analyzing difficult items (for example, smears,dirty or heterogeneous specimens) care shall be taken whensampling the paint and in choosing appropriate analyticalconditions. An attempt should be made to remove any extra-neous material from the exhibit before sampling. It may benecessary t
48、o analyze a number of samples to ensure reproduc-ibility and understand inter/intrasample variation.6.6 Extraneous material should be removed either by scrap-ing with a suitable tool such as a scalpel or washing with water.If needed, alcohols or light aliphatic hydrocarbons can beuseful for cleaning
49、. However, it should be noted that the use oforganic solvents for cleaning paint can alter the composition byextracting soluble components such as plasticizers or dissolvethe paint binder. If solvents are used, known and unknownsamples should be treated the same, making sure no residualsolvent remains.6.7 For the accurate comparison of paint evidence, samplesshould be prepared and analyzed in the same manner.7. Analytical Techniques and Operating Conditions7.1 Paints may be analyzed by transmission or reflectanceutilizing the microscope accessory or the
