Vibrational Spectroscopy I:
Infrared Spectroscopy
Spectroscopy is the study of matter and its properties by investigating light, sound, or particles that are emitted, absorbed or scattered by the matter under investigation. Spectroscopy may also be defined as the study of the interaction between light and matter. Historically, spectroscopy referred to a branch of science in which visible light was used for theoretical studies on the structure of matter and for qualitative and quantitative analyses. The definition has broadened, however, as new techniques have been developed that utilize not only visible light, but many other forms of electromagnetic and non-electromagnetic radiation, including microwaves, radiowaves, x-rays, electrons, phonons (sound waves) and others.
Impedance spectroscopy is a study of frequency response in alternating current. Spectroscopy is often used for the identification of substances through the frequency spectrum emitted or absorbed by them. A device for recording a spectrum is a spectrometer. Spectroscopy can be classified according to the physical quantity which is measured or calculated or the measurement process.
Infrared (IR) Spectroscopy
Of all the properties of an organic compound, the one that gives the most information about the compound's structure is its infrared spectrum. Thus, infrared spectroscopy is used to determine the presence of certain functional groups. Infrared frequencies of light are used to study fundamental vibrations and associated rotational-vibrational structure via vibrational resonance and selective absorption (1).
Infrared spectroscopy works because chemical bonds have specific frequencies at which they vibrate corresponding to energy levels. In order for a vibrational mode in a molecule to be IR active, it must be associated with changes in the permanent dipole. The resonant frequencies are determined by the normal modes of vibration. (Normal modes are also known as natural frequencies or resonant frequencies. There is a set of these frequencies that are unique to each molecular structure). These natural frequencies can be related to the strength of the bond, and the mass of the atoms (or harmonic oscillators) at either end of it. Thus, the frequency of the vibrations can be associated with a particular bond type.
Changes in the vibrational frequencies of a molecule are caused by the absorption of infrared light. A particular portion of the infrared spectrum is referred to either by its wavelength (in microns or Angstroms) or frequency (not Hz, but rather in wavenumbers, or reciprocal centimeters). The wavenumber is simply the number of wave periods per centimeter, and is equal to the reciprocal of the wavelength in centimeters.
Infrared portion of the electromagnetic spectrum is divided into three regions:
1) The far-IR (~ 400-10 cm-1). Adjacent to the microwave region, the longer wavelength far-IR has lower energy and may be used for rotational spectroscopy.
2) The mid-IR (~ 4000-400 cm-1) may be used to study the fundamental vibrations and associated rotational-vibrational structure.
3) The near-IR (14000-4000 cm-1) with its higher energy level and higher frequencies can excite overtone or harmonic vibrations.
A particular group of atoms gives rise to characteristic absorption bands.
E.G. The OH group absorbs strongly at 3200-3600 per cm; the double bonded C=O group of ketones absorbs strongly at 1710 per cm; the triple bonded C-N group absorbs strongly at 2250 per cm; and the CH3 group absorbs at both at 1450 and 1375 per cm (2 different modes of vibration). In a similar manner, amino groups, nitriles, aromatic rings, primary, secondary or tertiary alcohols can all be distinguished using identification methods of characteristic vibrational absorption bands.
Inorganic atomic groups also show characteristic absorption spectra.
Characteristic IR Absorption Frequencies
Interpretation of an IR spectrum is not a simple matter. Bands may be obscured by the overlapping of other bands. Overtones (or harmonics) may appear at exactly twice the frequency of the fundamental band. The absorption band of a particular group may be shifted by various structural features, such as conjugation, electron withdrawal by a neighboring substituent, angle strain or van der Waals strain, or hydrogen bonding.
Simple diatomic molecules have only one single bond, which may stretch. More complex molecules may have many bonds, and vibrations can be conjugated, leading to infrared absorptions at characteristic frequencies that may be related to specific chemical groups. E.G. The atoms in a CH2 group, commonly found in organic compounds can vibrate in six different ways, symmetrical and asymmetrical stretching, scissoring, rocking, wagging and twisting.
Sample Measurement: In order to measure a sample, a beam of infrared light is passed through the sample, and the amount of energy absorbed at each wavelength is recorded. This may be done by scanning through the spectrum with a monochromatic beam, which changes in wavelength over time. This technique works almost exclusively on covalent bonds, which are those found predominantly in organic compounds. Clear spectra are obtained from samples with few IR active bonds and high levels of purity. More complex molecular structures lead to more absorption bands and more complex spectra. The technique has been used for the characterization of very complex mixtures.
Fourier Transform Infrared (FTIR) Spectroscopy differs from traditional Infrared (IR) spectroscopy in that specially designed instrumentation is utilized to measure all wavelengths simultaneously (2-6). From this data, a transmittance or absorbance spectrum may be plotted, which shows at which wavelengths the sample absorbs the IR, and allows an interpretation of which bonds are present.
Reflectance Spectroscopy (DRIFTS):
Diffuse reflectance has been used for several decades in the UV, visible, and near-IR regions as a special purpose sampling technique (7–19). Before 1976, only limited work had been done on diffuse reflectance sampling in the mid-IR region with dispersive instrumentation. Following the introduction of the commercial rapid-scanning FTIR spectrophotometer, the possibility of performing routine diffuse reflectance measurements in the IR region became apparent. In 1976, Willey (11) demonstrated that special purpose FTIR apparatus could be used for certain types of diffuse reflectance measurements at low resolution with relatively long collection times.
Most of the early pioneering work in the IR was performed by Fuller and Griffiths (12–16) who coined the acronym DRIFTS (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) to describe this new technique. They showed that by using a commercial FTIR and a specially constructed, high-efficiency diffuse reflectance sampling accessory, good quality IR spectra for a wide variety of solid samples could be obtained at medium resolution and relatively short collection times. They investigated the effects of variations in a number of sampling parameters and conditions on the resulting spectral data (choice of reference materials, particle size, sample thickness, penetration depth of the beam, dilution factors, etc) and found optimum ranges of values for some of these experimental variables.
The art and science of reflectance FTIR spectroscopy has now been expanded to include Diffuse Reflection FTIR, Microreflection FTIR, and Internal Reflection FTIR. All of these methods have the common advantage of being non-destructive testing techniques, thus preserving the sample for additional testing.
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Applications in Forensics
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II. Controlled Substances
Infrared spectroscopy has been used suscessfully by forensic scientists for the identification of controlled substances (in tablet, capsule or powder form) as diverse as barbiturates (20-22), morphine (23), cocaine (24-25) and heroin (26). Fuller and Griffiths (15) were the first to demonstrate the feasibility of obtaining an IR spectrum directly on a whole, intact Empirin tablet using DRIFTS. The Empirin tablet examined had an APC chemical formulation which included acetylsalicylic acid (aspirin), phenacetin and a caffeine compound. These authors also presented a few examples of forensic applications of DRIFTS, including the analysis of Empirin and Valium tablets (16). Fuller and Griffiths also obtained DRIFTS spectra of this tablet after it had been ground to a fine powder, with the powder sampled ‘neat’ (or undiluted). The spectra obtained for these tow sampling methods were similar, with minor differences attributed to particle size effects.
Suzuki (24) used DRIFTS technology to conduct an extensive study on the identification of controlled substances, painkillers and tranquilizers in tablet, capsule and powder form. The list includes: methocarbamol, dl-glutethimide, apirin, d-methamphetamine hydrochloride, potassium bromide, methyprylon, methaqualone base, l-cocaine hydrochloride, ethinamate, meprobamate, mebutamate, phencyclidine base, magnesium carbonate, Doriden, Robaxin, Bufferin, Bayers, Quagesic, Noludar, Quaalude 300, Equanil, Miltown, Soma, and Valmid.
A subsequent study by Suzuki focused on the infrared properties of some particulate drug mixtures. Samples included: l-cocaine hydrochloride, sodium amobarbital, sodium secobarbital, sodium pentobarbital, allylisobutylbarbituric acid (butalbital), l-ephedrine hydrochloride and l-ephedrine sulfate, meperidine (pethidine) hydrochloride, diacetylmorphine (heroin) hydrochloride and diphenoxylate hydrochloride, Cholorodiazepoxide hydrochloride, Librax, Librum, Amytal, Seconal, Nembutal, Fiorinal / Codeine, Mepergan, and Tuinal.
Ravreby (54) used FTIR spectrophotometry in order to make conclusions regarding the quantitative aspects of compounds of interest in powder mixtures of controlled substances. In this work, cocaine hydrochloride salt (HCL) and heroin HCL were determined quantitatively by choosing a carbonyl absorption peak as the analytical peak and measuring absorbance vs. concentration. The effect of various additives and diluents such as starch, sugars, mannitol, caffeine, and procaine was also studied.
I. Polymer Textile Fibers
Analytical approaches for the analysis of textile fibers have been reviewed by Fong (27). Of the many techniques discussed for the identification and comparison of fiber evidence, visual (optical) microscopy is the most frequently used in the forensic science laboratory. The identification of generic classes of fibers can usually be made by examination of the optical properties alone. In the FBI laboratory, microscopic examination and determination of optical properties are supplemented by solubility testing and examination of fluorescent properties when appropriate.
Among the remaining analytical techniques reviewed, IR spectroscopy is the most well-established technique for analysis of synthetic polymer textile fibers. Infrared analysis can provide more specific and definitive chemical information about polymer composition. In fact, the American Society for Testing Materials (ASTM) now lists IR spectroscopy as the preferred method of analysis for identifying man-made (synthetic) fibers, stating that: "Where the data are consistent and the spectra obtained and interpreted by an experienced spectroscopist, the IR procedure has no known bias."
Many papers have addressed IR spectroscopy as a technique for the forensic characterization of synthetic textile fibers (28-43). Only the fairly recent availability of Fourier transform techniques and instrumentation have made IR analysis of single fibers feasible on a routine basis in the high volume environment of the forensic science laboratory. Moreover, a number of researchers have described the development of an IR spectral library of single polymer fibers (21). In addition to natural fibers such as silk, wool and cotton, examples of synthetic fibers include:
Acetate, Acrylic, Acrilan, Acrylonitrile (AN), Aramid, Arnel, Azlon, Cellulose (e.g. Rayon), Cellulose Acetate, Dacron, Ethylene Glycol, Kodel (Polycyclohexylene Dimethylene Terephthalate, PCDT), Methyl Acrylamide (MAA), Methyl Acrylate, Methyl Methacrylate (MMA), Methyl Vinyl Pyridine (MVP), Modacrylic, Nylon, Orlon, Polybutylene Terephthalate (PBT), Polyolefin, Polyester (e.g. Polyethylene Terephthalate, PET), Polyhydrobenzoic Acid (PHBA), Polypropylene, Vinyl Acetate and Vinyl Chloride.
*Note: The length of fiber used was typically about 2 millimeters.
Because of their widespread use in the manufacture of clothing, polyester fibers are one of the most commonly encountered fiber types in forensic casework, at least one example being present in nearly every fiber transfer case (13). Besides being found alone or in conjunction with other fiber types (e.g. cotton or viscose rayon) in clothing such as underwear, shirts, casual trousers and jeans, men's suits, sports jerseys, women's blouses, skirts and dresses, the yare also frequently found in nightshirts, housecoats, bed sheets and other household textile fabrics. It is therefore extremely important for the forensic scientist to be able to recognize these fibers and correctly identify them for comparison and confirmation purposes.
III. Automotive Paints & Pigments
Forensic examination for the identification of materials relating to motor vehicles and documents (44-82) has included sampling physical evidence including: automotive paints & primers, printing inks, paper, plastics, photocopy toners, and transfer letters. Also included are synthetic rubber, cosmetics, correction fluid, and adhesives.
The value of IR techniques in the identification and classification of automotive paints was originally demonstrated by Rogers, et al. (51). Cartwright and Rodgers (52) were the first to propose an IR database for the identification of automotive paints and primers. A comprehensive classification system for the identification and comparison of motor vehicle paint samples was introduced first by Audette and Percy (55-57) in 1982. Their IR-based data was collected strictly from cars manufactured by the Plymouth, Dodge and Chrysler Imperial Divisions of the Chrysler Corporation.
In the interpretation of their IR spectra, Audette and Percy noted that some difficulties arose concerning standard nomenclature. E.G. in certain systems, the U.S. paint vendors classified the resin system as an epoxy acrylic, while Canadian vendors identified it as an epoxy ester. To avoid any confusion, they adopted the convention that if the percent transmittance value of the carbonyl peak (wavenumber = 1730/cm) was less than or equal to that of the 1510/cm epoxy peak, the resin system was defined as an epoxy ester. Alternatively, where the carbonyl peak was greater than the epoxy peak, the resin system was defined as an epoxy acrylic. The exception occurred where the carbonyl ester stretching band indicated that the ester modification was an alkyd type (1270/cm).
To avoid problems arising in the positive identification of pigment constituents, they identified only those that were well resolved. In some instances, zinc oxide (ZnO) and titanium dioxide (TiO2) may be present. However, other pigment constituents such as china clay interfere in the positive identification of these components. Difficulties also arose in the interpretations where there was an indication of orthophosphate (PO4) ion or chromate (CrO2) ion. In these circumstances, only the anion was identified. [In many cases, it was concluded that elemental analysis and X-Ray Diffraction data (for positive identification of crystalline structure type) would be necessary in order to completely individualize all pigment components].
Judging form the analysis of of the IR topcoat spectra, alkyd melamine formaldehyde formulations were employed in the U.S. assembly plants until 1964 and in the Canadian plant until 1965. Afterwards, most of the U.S. plants converted to acrylic melamine formaldehyde formulations - with some preferring a styrene-modified formulation on conversion from alkyds to acrylics. All assembly plants converted to the styrene-modified formulations in 1969 and styrene-modified non-aqueous dispersion acrylic melamine formaldehyde formulations in 1973. Acrylonitrile-modified formulations were observed in all plants in 1974 and 1975.
A typical three layered application consisted of an undercoat of brown (with no metallic flakes), a second undercoat of gray (with no metallic flakes) and a topcoat of brown (with metallic flakes).
1) The topcoat consisted of an acrylic melamine formaldehyde resin (as described previously)
2) The gray undercoat consisted of an ester-modified epoxy resin containing titanium dioxide (TiO2), talc [hydrated magnesia silicate: MgO/SiO2/H20], and barium sulfate (BaSO4).
3) The brown undercoat was composed of an ester or alkyd-modified epoxy resin system containing ferric (iron) oxide (either FeO or Fe2O3), chromate (CrO2-) ion, silica (SiO2), talc, barium sulfate (BaSO4) and phosphate (PO4) ion.
It was concluded, however, that analysis of a greater number of topcoats would have to be conducted before a definite correlation between the color and the presence of acrylonitrile could be made. The absence of an acrylonitrile peak, although not definitive, should be noted, as it was a common modification in the mid-1970's.
Suzuki (60) points out that many metallic paints, which are commonly used for automotive finishes, can be sampled directly using DRIFTS. The density of metallic flakes used in a particular paint is the primary factor determining the applicability of this method, and it may not be possible to obtain usable spectra for low-density finishes on every system. Most paints could not be considered ideal materials for direct DRIFTS sampling in view of their smooth surfaces and relatively high absorption coefficients. Both of these factors tend to increase the amount of specular reflectance, which limits the usefulness of the resulting spectral data. Paint films or coatings having a low concentration of suspended particulates (as in most automotive paints) also are not strong scatterers of IR radiation.
Suzuki and Brown (67) determined that most metallic paints produce predominantly diffuse reflectance when sampled directly, making them ideal candidates for DRIFTS sampling methods. Chase, et al. (60) used similar principles in their study of paint pigment photodecomposition. These investigators actually added metallic flakes to paint vehicle containing the pigment under study in order to assure the diffuse (vs. specular) reflectance in situ in dried films of the paint or pigment of interest. In addition, unlike the IR Diamond Anvil Cell (DAC) method, direct DRIFTS sampling requires no sample preparation and is completely non-destructive.
According to the authors, the most useful application of this method may be to screen the Reference Collection of Automotive Paint panels rapidly. The seed for this may occur in some hit-and-run paint examinations where, given a recovered specimen chip, the make, model, and year (> 1974) of the automobile involved is desired. Assuming an original finish, characteristics of the specimen chip, including color, whether the finish is metallic or not, luster and texture, layer structures, paint compositions, sizes and concentrations of the metallic flakes (if metallic), etc. are compared to those of the various Reference Collection panels.
While the spectra of two medium density acrylic lacquers are similar to those found in studies using a diamond cell, the three acrylic melamine enamel spectra exhibit differences. In addition to little or no styrene component, these may be seen from the absence of aromatic absorptions between wavenumbers of 3200 and 3000 /cm, and the diminished intensities of the peaks between 700 and 800 / cm. Also of note are the weak overtone / combination bands from 200 to 1800 / cm. These bands are characteristic of mono-substituted benzene compounds.
While the observation of cardboard panel kaolinite peaks in the DRIFTS spectra of low-density finishes provides little useful information, the ability to make these observations can also be used to determine if kaolinite and talc are present in the undercoats. Talc [hydrated magnesia silicate: MgO/SiO2/H20], in particular is commonly used in automotive paint primers along with other inorganic pigments, including: titanium dioxide (TiO2), barium sulfate (Ba2SO3), calcium carbonate (Ca2CO3), silica (SiO2), ferric (iron) oxide (Fe2O3), and kaolinite [hydrated alumina silicate: Al2O3/SiO2/H20]. These pigments and extenders may appear alone or in combination, and their presence serves to distinguish between different primers (51, 54). Talc, like kaolinite, has a very characteristic hydroxyl (OH) stretching absorption at 3678 / cm.
Interestingly, relatively strong talc / kaolinite absorptions are observed for some panels in which these substances occur in a second undercoat layer, but not in the undercoat layer directly below the topcoat. It is thus clear that this type of DRIFTS sampling can occur through two diverse layers (one of which contains an appreciable concentration of suspended metallic/inorganic particulates) in certain cases.
Furthermore, most of the Reference Collection panels examined which had talc in an undercoat were found to have acrylic melamine enamel topcoats. In contrast, almost all of the finishes containing talc are acrylic lacquers. More significantly, the majority of these lacquers were identified as DuPont finishes, with the remainder produced by BASF Inmont and a few by PPG Industries. Since the acrylic lacquers produced by these manufacturers are used exclusively on General Motors vehicles, the presence of talc in a topcoat might be a useful supplemental feature in identifying the manufacturer or type of vehicle for certain U.S. automotive finishes.
Suzuki (82) continued his work in 1992 by using low pressure diamond anvil cell FTIR in order to focus strictly on single layer topcoats of vehicles manufactured between 1974-1989. This work is based on the differentiation and identification of acrylonitrile and ferrocyanide C-N (triple bond) stretching absorptions. Because their characteristic IR absorptions occur in a region (2300 - 2000 / cm) where few other fundamental transitions occur, they produce easily recognized absorption peaks. These peaks arise from the C-N stretching absorptions of acrylonitrile (2240 - 2238 / cm) and iron ferrocyanide (Iron Blue, Prussian Blue) an inorganic pigment used in some blue and green topcoats, which produces a single, medium broad peak at 2090 / cm.
IV. Documents: Inks & Toners
In 1985, the U.S. Secret Service reported a "dramatic increase in the use of office copiers to produce counterfeit currency and other documents" (44). Since that time, a revolution in the full-color copier market has increased the potential for such crimes. Color photocopiers provide an efficient and dangerous means of counterfeiting documents such as legal tender. Cases involving documents have increased exponentially since the introduction of the personal computer, graphics editor (e.g. PhotoShop), printer, and other office equipment utilizing the photocopy process. The ease with which original documents can be modified or falsified has been aided by the fact that modern plain paper photocopying machines allow copies to be made on a wide range of paper and plastic supports (45) . The increasing popularity and quality of both standard and color copiers and laser printers clearly demonstrates the need for forensic scientists to stay abreast of the changing technology in order to keep up with criminal activities involving the photocopy and printing processes.
For example, in the justification of their nondestructive optical studies of photocopy toner analysis, Shiver and Nelson (73) note that in 1989, a con man deposited $3 million in phony cashier's checks drawn on a New York branch of a European bank. The checks, which cleared the New York branch, were produced on check stock made with a full-color copier. One counterfeiter was convicted in an operation that produced $800 K in counterfeit currency using a Canon Color Laser Copier. A college dropout in Ontario wrote a check for $25,000 as half payment for a Canon Color Laser Copier. Then he ran off more than $24,000 in U.S. and Canadian bills. Another case involved a mailroom clerk who successfully negotiated two stolen U.S. Treasury checks with an altered black and white photocopy of a green military identification card. The card was recognized by the authorities, and the perpetrator of the crime appropriately punished. But the authors subsequently produced an excellent replica of a military identification card on a full-color copier, which, once laminated, could almost certainly enable the bearer of the card to cash checks on U.S. military installations anywhere in the world (as well was other privileges).
The physical characteristics of photocopies (paper type, toner type, toner application, fusion method, magnetic properties, etc.) have been proposed by a number of authors for use in classification of photocopy machines. For general information, Totty (71, 72) has written excellent reviews on the forensic analysis of photocopies. Shiver and Nelson (73), using IR luminescence (IRL), IR Reflectance (IRR or DRIFTS) and laser luminescence note that three different types of copiers in their research: the electrophotographic, photographic and cylithographic. The electrographic copiers make use of toners.
These copiers can be further subdivided into analog copiers and digital copiers. An analog copier images the original right onto the copier (I.E. What you see is what you get). In the digital process, the original is imaged onto an image sensor, where the optical image is then converted into data. Information is sent to the print head, types of which include LED (light emitting diode) array or a laser scanner. (Basically, digital copiers contain separate scanning and printing mechanisms that are connected by a digital channel). Digital copiers allow electronic manipulation of the finished product by the user -- typically as either JPEG, Bitmap or PDF electronic computer files.
As an industry standard, the Canon CLC is a digital laser photocopier which utilizes the electrographic method. It used black, yellow, magenta, and cyan toners. The color copies are made by four passes through the machine. One color toner is added on each pass. Although the copier uses black toner, the color black is made from a combination of cyan, magenta, and yellow, with black toner on top of the three. One of the most striking microscopic features of the Canon copier is the presence of "pitch lines" (the toner appears to lineup in rows) which result from minute vibrations during the copying process. These same vibrations do not allow the copy to be made in perfect registry, and the edges of black letters will tend to have a rainbow effect from the other three colors.
During the IRL examinations, the magenta toner exhibited a very strong luminescence. Alternatively, the cyan and yellow toners exhibited no luminescence. As a result of the layering of toners to create black text and/or graphics, the mis-registered lines of magenta toner causes copies from the Canon copiers to exhibit a halo of luminescence around black images. During laser examinations, the same type of luminescence effects were found, except that black took on an orange color and the cyan and yellow toners became darker. IRR examinations revealed that at 800 nm the image was still visible, while words became undecipherable at an illumination wavelength of 900 nm.
In contrast to the Canon CLC, the Xerox 1005 Color Copier is an analog electrophotographic copier. The Xerox copier uses cyan, yellow, and magenta toners. Black is made from a mixture of the three. None of the words on the sample were out of registry. None of the toners exhibited luminescence under wither IRL or laser examinations. Words are clearly legible at 900 nm.
Chemical analysis of the toner would appear to be a useful and logical additon to classification by physical characteristics. Since the toners are mainly compositions of organic resins (binders) such as synthetic polymers or copolymers, mixed with either carbon black or colored toners, the toners can easily be analyzed using established techniques. The desire to use nondestructive techniques has encouraged the use of optical techniques such as IR luminescecne (IRL), IR Reflectance (IRL) or DRIFTS, and laser luminescence for the examination of color copies (73-88).
Kemp and Totty (63) showed that toners used in plain paper photocopying machines could be distinguished form each other by IR spectroscopy, using small samples of solid toner removed form the surfaces of photocopied documents. Some differences were observed between the spectra of bulk toner and the spectra of toner removed form paper. These differences observed were attributed to the fusion process employed by the photocopier: heat and/or pressure.
Williams (64) took the results of Kemp and Toddy, and in 1983 was the first (and only, as far as this author can see) investigator to utilize IR group frequency analysis in order to clearly identify the chemical constituents of toners, including specific organic binders and polymers. The results are outlined below.
~ Chemical Analysis of Toners ~
Zimmerman (68) collected thirty-five photocopy toners and copies processed from machines using the respective toners from five different manufacturers. Through infrared spectrophotometry, a spectral match between the standard toner powder and the toner extracted from the respective copied document was achieved. Also toners were categorized into 18 different groups, of which 7 included more than 1 toner. Further specificity was achieved using pyrolysis gas chromatography, in which the toners in the seven different groups were distinguished from all others. Application was foreseen in an IR library search for peak match or functional groups or both to identify the toner of a questioned document, and thus the manufacturer and model of the photocopier.
Mazzella, et al. (82-83) set out to determine the practicality of using DRIFTS for the comprehensive classification and identification of photocopy toners. They concluded that: 1) There does not appear to be any significant differences between batches of the same brand of photocopying toner that can be detected by the DRIFTS technique. 2) Toner samples from photocopies produced over an extended period of time on the same machine give identical IR spectra. 3) The IR spectra can, in some cases, differentiate photocopies produced on different machines. 4) The spectrum of a toner extracted form a photocopy and measured by DRIFTS is identical to the spectrum of the raw toner powder. 5) The application of fingerprint development reagents to a photocopy dos not significantly affect the IR spectrum of the toner (insufficient quantities). In addition, their use of a silicon carbide sampling accessory for DRIFTS analysis of forensic samples was sufficient for the positive identification of certain paints, synthetic rubbers, cosmetics, corrector fluids and adhesives.
Moreover, it was possible to show that toners used in laser printers can be analyzed in the same manner as conventional photocopying toners. This was also found to be the case for toners designed for use in color copiers. Indeed, the IR spectrum for a color toner does not seem to depend on the actual color of the toner -- but rather on the organic resin base, which is usually the same for a particular application.
Merrill, et al., (87) utilized the technique of Attenuated Total Reflectance (ATR) IR Spectroscopy for the analysis of a variety of photocopy toners previously analyzed by DRIFTS (Diffuse Reflectance). The resulting spectra were somewhat noisy due to low absorptions. Cellulose absorptions from the paper beneath the toner layer appear in several obtained with the ATR objective. This is due to the penetration depth of the evanescent wave. In addition, the high concentrations of carbon black in the toners caused a great deal of dispersion in the spectra, displayed as sharp downward inflections just prior to large absorption bands. Significant improvements resulted from the use of a germanium Internal Reflection Element (IRE), with a greater refractive index than that of the diamond IRE. In instances where the lifting technique of sample preparation pulls cellulose fibers from the document, care must be taken not to focus on that area of the sample.
Mizrachi, et al., built a database library which can be used for the classification of color copiers according to different toners used by different manufacturers. Using both FTIR and GC/MS techniques for analysis of samples, they emphasized that the toner samples to be analyzed were either gently scraped or extracted from the photocopies. For the contribution of the paper document to the IR spectra, they used the scraped paper as a reference. The raw toner powder, the scraped photocopies of the same brand and model, and the scraped reference paper were analyzed by FTIR. The results confirmed their suspicions that the amounts of pigment in the toner and its contribution to the spectra are insignificant. Using this technique, however, it is nearly impossible to prevent the scraping of the fibers together with the toners. Thus, the spectra and their degree of similarity can be influenced by the depth of the scraping and the quantities of the cellulose fibers scraped from the paper together with the toners.
Andrasko (91-92) developed the technique of Microreflectance FTIR spectroscopy as applied to materials encountered in the forensic examination of documents. These include: black printing inks, paper, plastics, photocopy toners, and transfer letters. The analysis is nondestructive and can thus be repeated on the same specimen without limitation. Microreflectance FTIR spectra are similar to conventional FTIR spectra obtained for extracts from the same toner material, with little or no contribution from specular reflectance. This technique is not as sensitive as the internal reflection FTIR, but is normally available at laboratories having an FTIR spectroscope.
Various types of plastic materials encountered in forensic examination of documents were analyzed. These included ID cards, driver's licenses, and passport materials. FTIR reflectance spectra of plastics exhibit distortion caused by the specular reflectance component, which can be compensated for using dispersion relations. The cards typically contain several plastic layers. The base material (e.g. polycarbonate) is embedded in double-layer polymer material. The inner layer is usually polyethylene and the outer layer polyester.
Other investigations have include both high performance liquid chromatography (HPLC) and thin–layer chromatography (TLC) interfaces with DRIFTS (45, 48). Other investigators have also demonstrated more specific applications of DRIFTS, including analysis of coal and geological samples (49), paint pigment photodecomposition (50), and cross-linking and degradation of acrylic coatings (51).
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Suggested Reading / References
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1) Chalmers, J.M. and
Griffiths, P.R.
Handbook of Vibrational Spectroscopy
John Wiley & Sons, NY, NY (2002)
2) James, J.F.
A Student's Guide to Fourier Transforms:
Applications in Physics and Engineering
Cambridge University Press, Cambridge, UK (1995)
3) Allman, R.M. III
"Introduction to the Theory of Fourier Transforms"
Dept. of Mathematics, Pacific Lutheran University
Math 499: Senior 'Capstone' Project (May, 2005)
4) Stuart, B., George, B., McIntire, P.
Modern Infrared Spectroscopy
John Wiley & Sons, NY, NY (1996)
5) Christy, A.A., Ozaki, Y. and Gregoriou, V.G.
Modern Fourier Transform Infrared Spectroscopy
Elsevier Science (2001)
6) Stuart, B.
Infrared Spectroscopy: Fundamentals and Applications
John Wiley & Sons, NY, NY (2004)
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7) White. J.U.
"New Method for Measuring Diffuse Reflectance in the Infrared"
J. Opt. Soc. Am., Vol. 54, p.1332 (1964)
8) Wendlandt, WW. and Hecht, H.G.
Reflectance Spectroscopy, John Wiley & Sons, New York (1966)
9) Kortum, G.
Reflectance Spectroscopy, Springer-Verlag, New York (1969)
10) Wetzel, D.L.
"Near-Infrared Reflectance Analysis"
Analytical Chemistry., Vol. 55, p. 1165a (1983)
11) Willey, R.R.
"FTIR Spectrophotometer for Transmittance and Diffuse Reflectance Measurements"
Allied Spectroscopy, Vol. 30, p.593 (1976)
12) Fuller, M.P. and Griffiths, P.R.
"Diffuse Reflectance Measurements by FTIR Spectroscopy"
Analytical Chemistry, Vol. 50, p.1906 (1978)
13) Fuller, M.P. and Griffiths, P.R.
"Infrared Analysis by Diffuse Reflectance Spectroscopy"
American Laboratory, Vol. 10, p.69 (1978)
14) Fuller, M.P. and Griffiths, P.R.
"Infrared Microsampling by Diffuse Reflectance FTIR Spectroscopy"
Applied Spectroscopy, Vol. 34, p.535 (1980)
15) Griffiths, P.R., et al.
"Applications of FTIR Spectroscopy in Forensic Analysis"
Proc. Int. Symp. on Instr. Appl. in Forensic Drug Chem., p. 60, U.S. Gov't Printing, Wash., D.C. (1978)
16) Griffiths, P.R. and Fuller, M.P.
"Mid-IR Spectroscopy of Powdered Samples"
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18) Krishnan, K. et al.
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19) Suzuki, E.M. and Gresham, W.R.
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~~~~~~~~~~~ Controlled Substances ~~~~~~~~~~~~~~
20) Mesley, R.J. and Clements, R.L.
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21) Mesley, R.J.
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22) Mesely, R.J.
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23) Beckstead, H.D.and Neville, G.A.
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24) Suzuki, E.M., et al.
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25) Ravreby, M.R.
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26) Levy, R. et al.
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~~~~~~~~~~ Synthetic Fibers ~~~~~~~~~~~~~
27) Fong, W.
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28) Daniels, W.W. and Kitson, R.E.
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29) Fox, R.H. and Schuetzman, H.I.
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30) Rouen, R.A. and Reeve, V.C.
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31) Smalldon, K.W.
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33) Greive, M.C. and Kotowski, T.M.
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34) Read, L.K. and Kopec, R.J.
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35) Cook, R. and Paterson, M.D.
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36) Read, L.K. and Kopec, R.J.
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37) Garger, E.F.
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38) Hartshorne, A.W. and Laing, D.K.
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39) Hartshorne, A.W. and Laing,. D.K.
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40) Curry, C.J.
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~~~~~~~~~~~ Paints, Pigments, Inks & Toners ~~~~~~~~~~~~~~
44) Piper. J.W.
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45) Roux, C., et al.
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48) Denton, S.
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49) O'Neill, L.A.
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50) Cleverly, B.
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51) Smalldon, K.W.
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52) Tweed, F.T., et al.
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53) Rodgers, P.G., et al.
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54) Cartwright, N.S. and Rodgers, P.G.
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55) Ryland, S.G. and Kopec, R.J.
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56) Audette, R.J. and Percy, R.F.E.
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57) Percy, R.F.E. and Audette, R.J.
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58) Audette, R.J. and Percy, R.F.E.
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59) Ryland, S.G., et al.
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61) Norman, E.W.W., et al.
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62) Cartwright, L.J., et al.
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63) Kemp, G.S. and Totty, R.N.
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64) Williams, R.L.
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65) English, A.D. and Spinelli, H.J.
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66) Burke, P., et al.
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67) Shearer, J.C.
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68) Zimmerman, J., Mooney, D., Kimmet, M.J.
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69) Wilkinson, J.M.
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70) Beauchaine, J.P., et al.
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71) Harris, J.S.
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72) Suzuki, E.M. and Gresham, W.R.
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IV: Sampling Considerations"
J. For. Sci., Parts I - III, Vol. 31 - 34 (1986-87)
73) Suzuki, E.M.
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74) Suzuki, E.M. and Brown, J.A.
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93) Suzuki, E.M.
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77) Totty, R.N.
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78) Shiver, F.C. and Nelson, L.K.
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79) Compton, S. and Powell, J.
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81) Lennard, C.J. and Mazzella, W.D.
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82) Mazzella, W.D., et al.
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83) Mazzella, W.D., et al.
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92) Mazzella, W.D.
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Science and Justice Vol. 35 (1995)
84) Allen, T.J.
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Vibrational Spec., Vol. 3, p.217 (1992)
85) Merrill. R.A. and Bartick, E.G.
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86) Bartick, E.G. and Tungol, M.W.
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Microchemical Spot Tests, Microspectrophotometry, Pyrolysis GC and Diamond Anvil Cell (DAC) FTIR"
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91) Andrasko, J.
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