Brooke W. Kammrath

The majority of inmates in the United States are incarcerated for drug-related offenses. It is important that the technology used to test for controlled substances be accurate and reliable. For on-scene presumptive testing, color-based field tests are commonly employed. Numerous cases have been discovered where positive color-based field tests were later proven to be false positives via confirmatory laboratory testing. Portable infrared (IR) and Raman spectroscopy are capable of providing accurate and reliable identifications at the scene, but are not generally utilized for this purpose. This research evaluated important performance characteristics of these methods to determine which is best for conducting on-scene testing of cocaine HCl. This research concluded that although portable spectrometers require a large initial financial investment, their high performance characteristics (such as ease of use, rapid analysis, non-destructive capability, acceptable limit of detection, and minimal false positives and negatives) make them a superior tool to the color-based field tests for the on-scene presumptive analysis of cocaine HCl. Portable IR spectroscopy was determined to be better than portable Raman because of the lower limit of detection, less severe adulterant interferences, and Raman fluorescence of common drugs (such as heroin or additives).

	A detailed online investigation into field-based presumptive tests for illicit drugs revealed many cases where false-positive color tests at the scene resulted in the incarceration of innocent people. The case of Amy Albritton was detailed in a 

 article, and demonstrates the problem and its significance (1). A white "crumb" found in her vehicle was tested using the cobalt thiocyanate color test, and yielded a positive result for cocaine, although Albritton claimed innocence. Albritton was arrested, and pressured into taking a plea deal by her court-appointed defense lawyer, as he insisted that the test proved she was in possession of controlled substances and, thus, she would be better off taking the plea deal. She eventually complied, served her time in county jail, and went back to her life. It was not until months later that any confirmatory testing was done on the suspect crumb, and when it was conducted, it was concluded that the crumb was not a controlled substance. This, among other cases including those of Janet Lee (2), Antonia Carranza (3), and Karlos Casche (4), brings into question the reliability of color tests and indicates a need for finding superior methods for on-scene testing of controlled substances.

	There is a significant need for field drug testing to be accurate and reliable. This is because, in drug possession cases, outcomes are often decided before they even reach a trial through the use of plea bargains to obtain a conviction. Many US Courts accept guilty pleas based solely on the results of field tests, such as those in nine of the ten jurisdictions of North Carolina, and the cities of Atlanta, Dallas, Jacksonville, Las Vegas, Los Angeles, Newark, Philadelphia, Phoenix, Salt Lake City, San Diego, Seattle, and Tampa. Research indicates that at least 90 % of drug convictions are obtained through plea deals, with some even higher (94 and 97% in Tennessee and Kansas, respectively) (1). Due to the significant errors (such as false positives and interferents) associated with color tests, portable vibrational spectroscopy, including IR and Raman methods, may provide a superior alternative for field testing of illicit substances, especially since these methods offer a higher level of confirmation of the illicit substance.

	Portable IR and Raman spectrometers are both capable of identifying controlled substances, but have not seen widespread deployment by law enforcement for field testing, primarily because of the cost of the instrumentation. Another concern of the forensic science community is that nonscientist investigators would be executing scientific analyses at crime scenes, and may incorrectly conduct the test or misinterpret the results, or both. For field portable instrumentation to become a viable presumptive test for illicit drugs by law enforcement officers, the instruments need to not only be rugged, but simple to use by nonscientist personnel.

	Recently, the National Institute of Justice (NIJ)'s Forensic Technology Center of Excellence (FTCoE) published a landscape study of portable and handheld instrumentation for presumptive drug testing in order to provide background information for law enforcement who are interested in these technologies (5). This study is an excellent resource for information, but the authors did not perform any specific laboratory or field research for comparisons of the various technologies, and instead relied on literature searches, manufacturer specifications, and interviews with current users. There was no ultimate conclusion of this landscape study, as it was determined that portable technologies provide general benefits (versatility, objectivity, specificity, safety, chain of custody collaboration, technical support, and ability to be used for multiple applications), and challenges (high up-front cost, complexity, maintenance, limited mixture interpretation, and library dependence), and each jurisdiction has its own needs and circumstances.

	Performance characteristics were assessed and compared for each technique: the Narcotics Identification Kit (NIK) Test G for cocaine produced by Safariland, a Smiths Detection HazMatID Elite portable IR spectrometer with a diamond attenuated total reflection (ATR) sampling element, and a Smiths Detection ACE-ID portable Raman spectrometer. These instruments were used due to their availability, but the research could be applied to any company's comparable portable instrumentation.

	The specific performance characteristics that were evaluated for all methods included a limit-of-detection study, an investigation into specificity (potential false positives, false negatives, and adulterant interactions), and evaluation of the ease of use, speed of analysis, skill required of the operator, and destructive nature of the method.

	Two-component mixtures were created by using pure cocaine HCl (Sigma-Aldrich) as well as the following five adulterants: lidocaine, mannitol, caffeine, Sweet 'N Low artificial sweetener, and Enfragrow powdered baby formula. Samples with concentrations of 0.1, 0.5, 1, 5, 10, 25, and 50% by mass of cocaine HCl were prepared for experimentation. When portable IR and Raman analyses were conducted, samples of 35% and 15% were subsequently made to obtain more precise limits of detection.

	A positive result for cocaine HCl with the NIK test, as shown in the left side of Figure 1, was indicated by "blue or pink with blue speckles after breaking the first ampoule, a pink result after breaking the second ampoule and a pink layer over a blue layer after breaking the third ampoule (6)." If the proper color change did not occur (right side of Figure 1), this was noted as a negative result. A positive result for cocaine HCl with the portable IR and Raman instruments was indicated by a "hit" for cocaine HCl using the library search function on the instrument (Figures 2 and 4, respectively). If a "hit" was not provided, this was noted as a negative result.

	Before experimentation, pure samples of cocaine HCl, as well as each adulterant, were analyzed to establish controls, as well as ensure the adulterants were not false positives for cocaine HCl. It was found that lidocaine was a false positive for cocaine HCl with the color-based field test. Therefore, only the sample sets containing the other four adulterants were used for color testing experimentation.

	The limit of detection determined for the color-based field test was at a 10% concentration of cocaine HCl with all four adulterants tested. Sources have conflicting reports on the average purity of cocaine HCl found in street samples. In 2016, it was reported by the Colombian National Police that the purity of cocaine leaving their country was approximately 85%, but by the time the cocaine reached the UK, the purity was approximately 60% and dropped to about 30% at the retail level (7). The US Department of Justice released an article in February 2010 indicating that from 2006 to 2009, cocaine purity had decreased from 68.1% to 46.2%. Even if the lowest reported concentration of 30% were used as a reference, this would make the limit of detection for the color-based field test acceptable.

	An extensive literature review revealed numerous known substances that would provide a positive result with the cobalt thiocyanate test other than cocaine HCl (Table I), which is the basis for the color-based field test for cocaine. One article from the 

 listed 73 different compounds, indicating a large quantity of potential false positive results with the test (8).

	The color-based field test is a destructive method that prevents any further experimentation from being conducted on the sample used. It is simple to use, with directions provided in each box. The color changes are very obvious at high concentrations of cocaine HCl; however, at lower concentrations it can be difficult to discern the color of the bottom layer. The subjectivity of determining a positive result is a problem when there is ambiguity at low concentrations. This method would also not be viable for operators with a color-determination deficiency. A single analysis is fast, taking only a few minutes, and there is little adulterant interaction that affects the limit of detection. However, one sample may require several different tests to identify the illicit drug, thus taking more time than just a single analysis. Additionally, this test requires sampling of the specimen for testing, thus potentially exposing the user to an unknown substance. There is also no reproducible record of the testing, and the color results may degrade over time, although detailed documentation with photography is a possibility.

	The cost for the color-based field test for cocaine, crack, and free base is $25.50 for a box of ten tests. Other commercially available color tests cost between $2 and 5 dollars per test (5). As these tests are one-use only, whomever is employing the tests must buy a large quantity each year. The NIJ's landscape study estimated that a large metropolitan area has approximately 500 drug-related arrests per year, with two color tests being used for each arrest, resulting in a total cost of $30,000 per year. However, this does not take into account the number of cases where no arrest was made, due to a negative results with the color test. Further, the tests are only specific to a particular drug "group," so law enforcement personnel require separate color-based field tests for cocaine HCl than for marijuana, PCP, or opiates. These tests do have expiration dates, and cannot be stored indefinitely. Consequently, the $30,000 per year calculation is likely an underestimate of the actual cost. The perceived low cost of these tests is considered by law enforcement to be a significant benefit over portable instrumentation.

	Another factor is the potential litigation fees that could arise from someone who has been falsely convicted of drug possession. A person could file a civil suit, and those litigation fees could far outweigh the cost of investing in a more reliable method of presumptive testing at crime scenes. This does not include the non-monetary costs that come along with being falsely charged with drug possession due to a faulty test result, causing considerable personal distress.

	The limit of detection for portable IR using the on-board library search algorithm for mannitol, caffeine, and baby formula were at 25%. Below 25%, the instrument did not provide positive "hits" for cocaine HCl. For artificial sweetener, the instrument was able to detect cocaine HCl at 15%, and, for lidocaine, it consistently had limits of detection at 5%. When manual spectral analysis was conducted by an educated chemist in spectral interpretation, cocaine HCl was identified in all of the spectra below the established limit of detection for the instrument's search algorithm (Figure 3). This instrument provides a Reachback feature, where the user can electronically send a spectrum to a trained spectral interpreter for technical support at any time and day. This indicates that, even if the instrument does not provide a positive "hit," the user can receive technical support to assist with interpretation and troubleshooting. The spectra could also be sent to a forensic laboratory for interpretation, depending on the agency's protocols. Additionally, as previously mentioned, the lowest concentration of street cocaine HCl was reported to be 30%, which is higher than the limit of detection for the portable IR with all adulterants tested.

	There were no false positives or negatives identified with the portable IR spectrometer; however, there were a number of misidentifications found with the portable IR spectrometer. A 

 is any substance identified by the instrument that was wrongly identified in place of an authentic mixture component. There were also false identifications made in which an extra component was identified in addition to the known components that were not actually present in the mixture (called a "false hit"). Mistaken identifications are potentially a large point of concern, but only if these incorrectly identify or prevent the identification of a controlled substance. In this research, the majority of these false hits were extra identifications that were determined to be of innocuous substances. Ultimately, as long as the cocaine HCl is still being identified, an extra hit for something because of the adulterant being used does not necessarily affect the test results.

	IR spectroscopy is a nondestructive method. Portable IR instruments are simple to operate. Step-by-step prompts with icons are shown throughout an analysis. Although these instrument are easy to use and can be operated with little training, scientific knowledge is required for sample selection, evaluating the spectral quality, and trouble shooting. A large benefit over the color tests is the chain of custody corroboration in that when a sample is tested, the results are automatically stored and time-stamped in the instrument to be exported or reviewed later. Similar to the color tests, portable IR with ATR sampling requires direct testing of the specimen, thus potentially exposing the user to an unknown substance.

	Formal training would be required for the operation of a portable IR spectrometer. However, it is simple to operate, so the training could easily be incorporated into that already provided for officers. The analysis overall does not take more than a few minutes for each sample being run, which is comparable to the speed of the color-based field test.

	Though prices on portable IR spectrometers vary by company, model, and add-ons (such as libraries, attachments, and service), the price can range from $25,000 to $65,000. There are no consumables required for portable IR spectrometers, so this is a one-time, up-front cost. Additionally, these instruments are built to be rugged and used in high stress situations; this means that, though repair on the instruments may be necessary, they will not break easily and could be used for several years. Also, portable spectrometers have the capability to identify a large number of controlled substances. Instead of buying ten different color-based field tests and making sure a police department is stocked for an entire year with all of these options, one portable spectrometer could conduct the same analysis. Finally, an increased demand for these instruments would encourage companies to increase production, which could lead to a cost reduction, thus making it a more affordable technology.

	The limit of detection for the portable Raman spectrometer using the on-board library search algorithm was consistently 25% cocaine HCl for all adulterants. In most trials, the instrument could not detect cocaine HCl at lower percentages; however, it was able to detect as low as 5% with the artificial sweetener, and 10% with the baby formula. The ability to electronically send spectra to Reachback or to a forensic laboratory for manual spectral interpretation is also available for portable Raman spectrometers. However, for these samples, manual Raman spectral analysis did not enable lower detection limits.

	One of the advantages of Raman spectroscopy is the ability to analyze samples without making contact, analyzing through some containers made of clear glass and plastic bags. The ability to analyze substances contained within clear plastic bags was tested, and the limit of detection was unaffected, remaining at 25%. This limit of detection would be acceptable to detect the lowest reported concentration of cocaine HCl in street samples. Consequently, unlike color tests and portable IR spectroscopy, portable Raman does not require direct testing, thus reducing exposure to unknown substances.

	There were no false positives or negatives identified with the portable Raman spectrometer. As with the portable IR spectrometer, there were a number of "false hits" and misidentifications that occurred during analysis. The portable Raman analysis had significantly fewer misidentifications and false hits than the portable IR, with a likely explanation being the smaller onboard Raman spectral library, which limits misidentifications and false hits. Although none of the adulterants tested suffered from Raman fluorescence, it is important to recognize that other illicit substances (such as heroin) or adulterants may fluoresce, which would interfere with the ability for chemical identification of any of the mixture components. Dark-colored samples prohibit Raman analysis because they absorb the incident radiation, thus potentially destructively burning the sample. In this situation, an orbital-raster-scanning (ORS) Raman was used to minimize the transfer of incident radiation, but not all portable Raman systems use ORS Raman. These issues may prohibit Raman analysis for the identification of cocaine or other illicit drugs in the field.

	Similar to IR spectroscopy, Raman spectroscopy is nondestructive, requires only a few minutes for analysis, and creates a reviewable record of the analysis that provides chain-of-custody corroboration. Much like the portable IR spectrometer, it is a push-button method, with step-by-step instructions on the screen. However, there is a small spot size for analysis, and focusing the LASER can be challenging at times. Sometimes, a few attempts are necessary to get a viable spectrum of the sample. As with the portable IR spectrometer, formal training would be required for the operation of the portable Raman, which could be simply incorporated into general training that officers are given. The same caveat applies for both portable spectrometers: Despite their ease of use, there is a need for educated users for proper sampling and analysis.

	Portable Raman spectrometers are generally less expensive than most portable IR spectrometers, although there are some exceptions; thus prices range from $12,500 to $60,000. Similarly to IR spectrometers, these instruments are built to be rugged and do not require consumables, so this is a one-time, up-front cost.

	Portable spectrometers have excellent potential to be employed for the on-scene analysis of cocaine HCl. Performance characteristics were compared (Table II), and the advantages of portable spectroscopy over traditional color testing were demonstrated. The limit of detection for all three methods would be acceptable at the lowest reported purity of street cocaine HCl. The speed of analysis is comparable for all three methods, taking less than 3 min for each analysis. Portable IR and Raman spectroscopy methods are nondestructive, objective, and create a reviewable record for use as evidence in adjudications, which are significant advantages over color tests. Color tests are also more prone to false positives and negatives than tests using portable spectroscopy, thus the latter are more reliable for the on-scene analysis of cocaine HCl. Portable Raman also has the ability to identify cocaine HCl through some plastic bags, reducing the potential for contamination and risk of exposure to unknown chemicals by analysts. Color tests require less knowledge or skill from the operator, however, inserting training on the different spectrometers during general training for officers would be simple and feasible because the instruments are created to be user-friendly. Although color tests are generally thought to be less expensive than portable spectrometers, the total cost over several years is comparable, if not greater than, an instrument with only a one-time up-front cost.

	Of the two portable spectroscopic methods, the authors concluded that, although both technologies have similar performance characteristics, there are some features of portable IR spectroscopy that make it the preferred technique for on-scene cocaine HCl identification. The long and reputable history of IR spectroscopy means that there are more spectral libraries and the technology has had more time to be evaluated and perfected. Additionally, fluorescence and the inability to analyze dark samples lessens the utility of the portable Raman spectrometers, whereas a portable IR spectrometer is able to produce interpretable spectra for all specimens. Although these limitations were not a problem in the specific analyses tested in this research, they could prove to be prohibitive for identification by portable Raman of cocaine mixed with other adulterants and for the analysis of other drugs, like heroin. Portable Raman spectrometers have the advantages of being generally less expensive than portable IR spectrometers, as well as being able to analyze samples through some clear glass and plastics, thus providing greater safety for the analyst. Ultimately, both portable IR and Raman spectroscopy are viable alternatives for crime scene identification of cocaine HCl.

	(1) R. Gabrielson and T. Sanders, "How a $2 Roadside Drug Test Sends Innocent People to Jail" (July 7, 2016). Retrieved April 28, 2018, from 

https://www.nytimes.com/2016/07/10/magazine/how-a-2-roadside-drug-test-sends-innocent-people-to-jail.html

	(2) J. Kelly, "False Positives Equal False Justice" (2008). Retrieved April 28, 2018, from 

https://www.mpp.org/issues/criminal-justice/false-positives/

	(3) E. Peralta, "Thinking It Was Cocaine, N.C. Police Jail Man For Cheese And Tortilla Dough" (May 16, 2011). Retrieved April 28, 2018, from 

https://www.npr.org/sections/thetwo-way/2011/05/16/136359770/thinking-it-was-cocaine-n-c-police-jail-man-for-cheese-and-tortilla-dough?ft=1&f=1001&sc=tw&utm_source=twitterfeed&utm_medium=twitter

	(4) S. Jeong, "Man Spends Three Months In Jail After False Positive On Police Drug Test" (June 28, 2017). Retrieved April 28, 2018, from 

https://www.cnn.com/2017/06/28/us/drug-test-drywall-positive-arrest-trnd/index.html

	(5) Forensic Technology Center of Excellence. Landscape Study of Field Portable Devices for Chemical and Presumptive Drug Testing. U.S. Department of Justice, National Institute of Justice, Office of Investigative and Forensic Sciences (2018).

	(6) Safariland Group. NIK Test G- Cocaine, Crack, & Free Base (2018). Retrieved August 29, 2018, from 

http://www.safariland.com/products/forensics/field-drug-tests/nik-test-g---cocaine-crack-and-free-base-1006155.html#sm0000624lqmakerfrm2cnczoduu2

	(7) United Nations Office on Drugs and Crime. World Drug Report 2012. United Nations Publication, New York (2018).

 are with the Henry C. Lee College of Criminal Justice and Forensic Sciences at the University of New Haven, in West Haven, Connecticut. 

 is with the Wisconsin State Crime Laboratory, in Milwaukee, Wisconsin. 

 is with Smiths Detection, in Edgewood, Maryland. Direct correspondence to: 

Articles

On-scene analysis of cocaine is an essential tool for law enforcement. This study defines how portable infrared and Raman spectrometers are capable of providing accurate and reliable identification of cocaine and other drugs when and where needed most.

A Comparison of Portable Infrared Spectrometers, Portable Raman Spectrometers, and Color-Based Field Tests for the On-Scene Analysis of Cocaine

Morphologically directed Raman spectroscopy (MDRS) is a novel and reliable tool that would enable criminalists to obtain more discriminatory information from forensic samples than their current capabilities. MDRS combines automated particle imaging and Raman spectroscopy into one instrument. Particle imaging is performed to determine particle size and shape distributions of components in a blended sample. Particle size is an important physical property of particulate samples and can be used in conjunction with Raman spectroscopy in the analysis of a range of samples of forensic interest, including illicit and counterfeit drugs, soils, gunshot residue (GSR), and white powders. Although measurement of particle size distributions is routinely carried out across a wide range of industries and is often a critical parameter in the manufacture and analysis of many products and substances, it is not widely used in the forensic sciences. Raman spectroscopy is used in forensic science to determine the molecular chemistry of materials because it is rapid, reliable, allows for analysis without contacting the sample, is nondestructive, and enables detection at low concentrations. Combining these two analytical techniques into a single platform allows the individual components present within a blend or mixture to be independently characterized and compared.

	Morphologically directed Raman spectroscopy (MDRS) combines the power of automated particle imaging with Raman microspectroscopy into a single platform. Particle imaging is performed to determine particle size and shape distribution of components in a blended sample. These are important physical properties of particulate samples and may have a direct influence on a sample's performance. For example, the size and surface area of a particle can be related in a significant way to the physical, chemical, and pharmacologic properties of a drug. Particle size distributions (PSDs) are routinely measured across a wide range of industries because they are important, and sometimes critical, to the manufacture and performance of substances and products. In spite of this importance, they are not widely used as methods for classification, identification, or individualization in the forensic sciences, other than in forensic soil examinations. However, characterization of materials by their microscopic morphology is used to analyze a plethora of forensic science samples, including drugs, geological materials (that is, soil minerals, rocks, and so forth), glass, dust, gunshot residue (GSR), pollen and diatoms, hairs and fibers, cosmetics, other anthropogenic materials (such as various building materials), general unknowns, and white powders used in hoax powder attacks. Raman spectroscopy is useful for determining molecular and physical chemistry because it is fast, reliable, nondestructive, and a noncontact method. Methods based on Raman spectroscopy are also used in the forensic sciences (1) for the analysis of many types of physical evidence including illicit drugs (2–5), explosives (6–8), paint (9–14), fibers (15–17), ink (14,18), and general unknowns (7). There are also several research articles on the use of Raman spectroscopy for the analysis of other types of forensic evidence, with a significant focus on analysis of the organic components of GSR (17,19–25).

	Independently, both automated particle imaging and Raman microspectroscopy are valuable methods. Even when combined into a single instrument, analysis based upon each method's independent evaluation may be useful. However, the power of a combined analytical scheme is greater than the sum of the individual approaches. Together, the data from these two methods may provide insight about the sample including its manufacturing method, history, and quality. This type of information may be invaluable during analysis of evidence in forensic casework.

	When performing MDRS, the sample's morphological data is collected using a light microscope with an automated stage. This allows for the sorting of particles based on various physical parameters. Once this particle data is collected, these parameters are then used to automatically select particles for chemical analysis using Raman microspectroscopy. The ability to perform particle selection for chemical analysis using physical parameters removes subjectivity in the measurement. In addition, the automation of the stage and of the particle selection removes the need to expose the analyst to the sample for the prolonged periods of time that would be required if manual measurements were performed (26).

	The combination of morphological and PSD analysis with Raman spectroscopy has the potential to provide unexploited information about a plethora of samples of forensic interest. This research examined the use of MDRS for the forensic analysis of four evidence types: illicit and counterfeit drugs, soils, GSR, and white powders. It is shown that MDRS can be used for the comparison of questioned and known samples, material, and mixture identification or classification as well as potential provenance determination.

	The experiments were performed using a Morphologi G3-ID particle imaging and Raman spectroscopy system (Malvern Panalytical). Samples were automatically dispersed onto a quartz plate at a pressure of 4 bar using the integrated Sample Dispersion Unit (SDU) on the Morphologi G3-ID instrument. Automated imaging analysis was performed directly on the quartz sample dispersion plate to obtain particle morphology data. All image acquisition settings were defined in a standard operating procedure (SOP) and included brightfield illumination and the use of a 10-times objective.

	Particles with a circle equivalent diameter (CED) greater than 7.0 µm and solidity greater than 0.75 were tagged for chemical targeting by the image analysis software. Morphological data was collected for more than 150,000 individual particles for each sample. Of these, 3000 particles per sample were targeted for Raman spectroscopic analysis over the spectral range of the instrument (150–1850 cm

). Raman spectra were obtained with the coupled Kaiser optical systems RamanRxn1 Raman spectrometer using a 785-nm semiconductor laser with a power of <500 mW and an exposure time of 2 s. The sampling spot size of the instrument was 3 µm. Both the particle morphology data and the Raman spectra were analyzed using the Morphologi software. All experiments were performed in triplicate.

	Spectral analysis required the creation of a spectral reference library, which was made using standards purchased from Sigma-Aldrich. The individual particle spectra from each sample were then compared against the reference spectral library and identifications made based on a correlation search algorithm where a correlation value close to one indicates a close match to that reference, and a value close to zero indicates no match. Using these correlation values, the particles were chemically classified and PSDs of the individual component populations were generated.

	A five-component mixture of illicit drugs was prepared (equal parts by weight) using cocaine, phenobarbital, pentobarbital, D-methamphetamine, and amphetamine.

	Two suspected synthetic cathinones, marketed as "bath salts," were purchased over the internet: "Arctic Rush" and "Fast Forward."

	Three counterfeit Viagra samples were obtained via the internet, where two were from Singapore and one was from India. Sampling was performed by removing a small amount of white powder from the core of each tablet, and all analyses were performed in triplicate.

	Soil samples were collected from four sites along one road in Connecticut (27). The 60–120 µm mineral fraction was separated by sieving and washing. Then 7 mm

 of minerals was deposited onto the quartz plate using evaporative dispersion. The mineral data were compared to a library made by importing the Raman spectra of minerals from the RRUFF database (28), and mineral identification was made only when there was a correlation score greater than 0.85.

	GSR was collected from cotton targets onto a quartz plate from four test fires using the same ammunition. The muzzle-to-target distances varied for each test fire, and included distances of 3, 6, 12, and 24 in.

	Three commercially available artificial sweetener blends were purchased locally, all with dextrose as the bulking agent but containing different sweetening agents. Sweet'N Low (designated as sample A) has saccharin as its sweetening agent, Splenda (Sample B) contains sucralose, and Equal (sample C) contains aspartame. An additional generic sucralose-based sweetener (NutraTaste Gold) was also purchased locally for comparison with the Splenda. Samples of the pure sweetener components were purchased from Sigma-Aldrich for addition to the spectral reference library.

	All five of the drugs were identified using MDRS. Further, the different components had different particle morphologies (Figure 1) and PSDs, which could be used in the comparison of samples from different seizures to evaluate whether they come from a common source. The particle size and shape of a substance can be useful for determination of the manufacturing process and, therefore, for comparative source attribution. Different methods of preparation can result in particles with different crystal structures and habits. Usually, slow crystallization methods form larger crystals, and rapid crystallization methods form smaller crystals.


	Figure 1: Particle images showing the different morphologies of (a) amphetamine, (b) D-methamphetamine, and (c) cocaine.

	The two suspected synthetic cathinones were analyzed by MDRS. The first, "Arctic Rush," did not contain any synthetic cathinones, and instead was composed of L-DOPA, caffeine, and an unidentified chemical. The presence of caffeine is a common cutting agent because it is a stimulant. L-DOPA is commonly used for the treatment of patients with Parkinson's disease, but there have been cases of people abusing L-DOPA as a means of enhancing the dopamine rush, which explains why it would be found in a mixture that people take to induce euphoria. It has been shown to increase aggressive behavior when taken in conjunction with methamphetamine (29). Inositol and phenethylamine were detected in the second, "Fast Forward." Inositol is a sugar alcohol that is commonly used as a cutting agent for narcotics (30). Phenethylamine has a similar chemical structure to synthetic cathinones, but there is a difference in one of the functional groups (31). Phenethylamine has a similar effect to that of synthetic cathinone, often ending in a state of excited psychosis or death (32).

	MDRS was able to identify four components in the counterfeit Viagra pills, including the active pharmaceutical ingredient (API) sildenafil citrate, and three excipients: lactose, starch, and talc. In an authentic Viagra sample, one would expect to see microcrystalline cellulose, calcium phosphate dibasic, croscarmellose sodium, and magnesium stearate. These were not detected in the counterfeit samples. Of particular interest is that the sample from India only contained the API and starch, while the two from Singapore also contained the lactose and talc (Figure 2). This has the potential to serve as a useful feature for comparison that could be used for counterfeit source attribution.


	Figure 2: A graph showing the relative percentage count of each of the components (lactose, sildenafil citrate, starch, and talc) in the three counterfeit Viagra samples, with the one from India in blue and the two from Singapore in green and red.

	The mineral morphologies of for each of the four samples were compared, and it was seen that they were all very similar. This is expected since they were collected along the same road in Connecticut. Other research has shown that the morphology of quartz can be used to differentiate different mineral environments (33–38), which could be exploited with MDRS. The PSDs for each location also proved to be indistinguishable.


	Table I: The average percent particle counts for each mineral for the four soil sample locations. The four locations can be differentiated because of the presence of some minerals in some sites that are not seen in the others, such as diopside in location C and epidote in location A, or because of differences in mineral counts, such as the higher percentage of muscovite in location B than the other sites.

	However, the samples for each location were differentiated when comparing the percent particle counts for each mineral (Table I). Multivariate statistical analysis was performed using R software (The R Foundation), using code written by N.D.K. Petraco, PhD, and adapted for this research by B.W. Kammrath, PhD. Principal component analysis (PCA) was performed on the particle count data, and in three principal components, 87.7% of the variance of the data was captured (Figure 3). Further analysis of the three-dimensional (3D) scores plot shows that there is good separation between the four data sets, with good clustering among replicates, which indicates the mineral counts achieved by MDRS can be used for sample discrimination.


	Figure 3: Three-dimensional scores plot of the autoscaled PCA results from the particle counts of the four soil locations. The three replicates cluster well for each of the four locations. 

	The collected residue from each of the four targets contained particles consistent with GSR as identified by the presence of nitrocellulose. The morphologies and PSDs of the particles were also analyzed (Figure 4). The PSDs have distributions centering on approximately the same circular-equivalent (CE) diameters, although there does appear to be a relationship between the volume distribution and the muzzle-to-target distance. This visual relationship, where the greater muzzle-to-target distance had larger volume distributions, needs to be explored in more detail with additional test fires using various ammunitions before this conclusion can be validated.


	Figure 4: Raman spectra (a) and particle image (b) of one GSR particle showing a spherical morphology and the presence of nitrocellulose. (c) The PSD of nitrocellulose-identified particles for all four muzzle-to-target distances (3, 6, 12, and 24 in. shown in red, blue, green, and brown, respectively).

	The automated imaging data alone were not enough to definitively identify the components within each of the artificial sweetener samples by particle size or shape. However, with the assistance of Raman chemical identification, individual components can be classified. Furthermore, PSDs were generated and compared for each of the chemical classes identified within a sample. Figure 5 shows the overall PSDs, the PSD of the dextrose, and PSD of the sweetening agent for each of the analyzed blends. The PSD of the entire sample and their distribution of dextrose bulking agents are the same, which shows that the PSD of the entire sample is primarily caused by the bulking agent. In addition, the PSD of the active sweetener component is markedly different from the dextrose, but does not have a detectable effect on the PSD of the entire sample. In a traditional bulk Raman analysis, smaller particles present in a lower volume are masked by the larger volume of dextrose, and thus cannot be identified. However, the particle specific targeting of MDRS enables the individual sweetening agent to be identified, which would allow for classification based on sweetener presence, and its component PSD to be analyzed.


	Figure 5: The PSD of Sweet'N Low (blue), Splenda (green), and Equal (red) for (a) all particles in a sample of each of the sweetener blends, (b) the particles identified as dextrose in a sample of each of the sweetener blends, and (c) the sweetener component in a sample of each of the sweetener blends.

	When comparing the results of the Splenda with the generic sucralose-based sweetener, the PSDs of the dextrose were the same for both samples. However, the PSDs of the sweetening agent were different (Figure 6). Thus, it was shown that even though these two samples are made with the same chemicals, the individual components have different PSDs that enable their differentiation. Consequently, the PSDs of the sweetening agent could prove to be a class characteristic of the specific manufacturer, thus its analysis could be used in determining and differentiating the particular brand of artificial sweetener.


	Figure 6: The PSD of Splenda (red) and the generic sucralose-based sweetener (green) for (a) the particles identified as dextrose in a sample of each of the sweetener blends and (b) the sucralose in a sample of each of the sweetener blends.

	MDRS is a nondestructive, relatively fast, and automated way to collect chemical and particle size information about samples of forensic interest. MDRS can be used in the forensic analysis of illicit and counterfeit drug mixtures, soil minerals, and hoax white powders by comparing two or more samples, not only based on their concentrations and identities of components, but also on the morphologies and size distributions of the particles. For illicit and counterfeit drugs, this determination of an individual components' particle size or shape distributions can provide additional information for connecting individual drug seizures and suppliers, tracing drug distribution routes and networks, and potentially identifying their geographical origin. For forensic soil analysis, MDRS enables PSDs and morphological examinations of each mineral component, which provides valuable information that can be used for comparison and source determination. In the analysis of hoax powders, MDRS can identify and characterize particles of trace components within mixtures that may be "hidden" in bulk Raman analysis. In addition, two components in a mixture with similar PSDs can be differentiated with MDRS because of the ability to chemically target specific particles, and two mixtures with the same components can be differentiated with MDRS because of their different PSDs.

	MDRS is a new approach to GSR analysis that combines Raman identification with particle size and shape information, thus making it comparable to current methods, specifically analysis by scanning electron microscopy with energy dispersive X-ray spectroscopy.

	The use of MDRS for the analysis of illicit and counterfeit drugs, soil minerals, GSR, and white powders is a novel and reliable tool that would enable criminalists to obtain more information from forensic evidence than is currently used for investigations and adjudications.

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 is with the Henry C. Lee College of Criminal Justice and Forensic Sciences, Department of Forensic Science, at the University of New Haven and the University of Verona in Verona, Italy. 

 is with Smiths Detection in Edgewood, Maryland. 

 are with Malvern Panalytical in Westborough, Massachusetts. 

 is with the Malvern Panalytical in Worcestershire, UK. Direct correspondence to: 

Can morphologically directed Raman spectroscopy obtain more discriminatory information from forensic samples than current tools?

Brooke W. Kammrath

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