Acrylate polymers are derivatives of acrylic acid, but contain a plethora of different functional groups and are best discussed by themselves. In this column, we study the spectrum of an important polymer, polymethyl methacrylate (PMMA), which is otherwise known as plexiglass, and is found in windows, car parts, and paint. We then study the spectra of PMMA mixtures and copolymers in detail.

We have studied esters (1) and polyesters (2,3) in the past. We discuss the spectroscopy of the ester functional group in this article, amongst others. Thus, I briefly reintroduce you to the structure and spectroscopy of esters.

Esters are characterized by C=O, C-C-O, and O-C-C linkages, and are divided into the families of saturated or aromatic esters depending upon the nature of the carbon attached to the carbonyl carbon. Ester infrared (IR) spectra follow the Rule of Three (1). This means they have three big peaks at approximately 1700, 1200, and 1100 cm

 (going forward all peak positions will be in cm

 units even if not so noted). These correspond to the stretching of the C=O, C-C-O, and O-C-C units. Table I summarizes the Rule of Three group wavenumbers for esters.

The family of acrylate polymers is based on the parent molecule acrylic acid, whose structure is seen in Figure 1.

Note that acrylic acid contains a vinyl C=C bond, and a carboxylic acid, functional groups whose structures and spectra we have studied in the past (4,5). The IR spectrum of acrylic acid is seen in Figure 2.

Recall (5) that any peak associated with the O-H bond in a carboxylic acid is broadened because of hydrogen bonding. Thus, the broad O-H stretching envelope seen in Figure 2 extends from approximately 3800 to 2000, and the bottom of the O-H wagging envelope is at approximately 930. Carboxylic acids also have strong C=O and C-O stretching peaks, which fall at 1702 and 1248 in Figure 2. The C=O stretch for acrylic acid falls below that for saturated acids, because the carbonyl group conjugates with the C=C bond, similar to how aromatic rings conjugate to C=O bonds (6).

The vinyl group in acrylic acid can be reacted to form a polymer, like many other vinyl containing monomers (4). Polymers made from acrylic acid derivatives are called polyacrylates. There are many different functional groups that can be attached to the acrylic acid frame, including esters, which is the focus of this column.

Perhaps the most common polyacrylate is polymethyl methacrylate, or PMMA. This polymer is economically important, and trade names for it include PlexiGlass and Lucite (7). Because PMMA is transparent, it can be used in place of traditional glass in uses such as windows, doors, and aquariums. The IR spectrum and structure of PMMA are seen in Figure 3.

Note that there is a pendant ester group and two CH

 groups in PMMA. The first methyl in the name denotes the CH

 refers to the fact that the acrylic acid monomer has a methyl group attached to the C=C bond. The major peaks in this spectrum are, not surprisingly, the Rule of Three peaks from the ester (1). Specifically, the C=O stretch is labeled A at 1730 cm

, and they are labeled together as B in Figure 3. Unfortunately, PMMA does not strictly follow the Rule of Three peaks for saturated esters listed in Table I. The C=O stretch is 5 cm

 too low, the C-C-O stretch is in the right place at 1191, but there is no O-C-C stretch between 1100 and 1030. There is an intense peak at 1149, which, for lack of a better assignment, I will call the ester O-C-C stretch. I have no idea why PMMA does not follow the rules for esters. As I have said in the past, all the peak position ranges I give you have exceptions, which is why there are few absolutes in IR spectral interpretation.

Copolymers of polystyrene and PMMA are common materials as they are also clear and rigid. Uses of these materials include as food containers, drinkware, and as additives to things like cement and concrete. A common name for these copolymers is styrene methyl methacrylate (SMMA). The structure and IR spectrum of SMMA are seen in Figure 4.

Note that the structure of SMMA is a mixed molecule containing both saturated and unsaturated carbons. Hence, there are C-H stretches above and below 3000 (8). The styrene portion of the polymer contains a monosubstituted benzene ring, and as we have seen before (9) these have an aromatic C-H wag from 770–710, and an aromatic ring bend at 690±10. The monosubstituted benzene ring in SMMA exhibits these peaks at 757 and 695, respectively. The ring modes of the benzene ring in styrene, due to the stretching of the carbon-carbon bonds in the ring, are at 1601 and 1583. Recall (8) that these peaks are always sharp, are used to distinguish between C=C and aromatic carbon-carbon bonds, but vary in number and intensity depending upon the molecule.

The methacrylate ester part of SMMA will have three peaks because it is an ester (1). In Figure 4, the C=O stretch is at 1727, the C-C-O stretch is at 1197, and the O-C-C stretch is at 1074. These Rule of Three peaks are not as big as we are used to seeing, because the PMMA units in SMMA are diluted by the presence of polystyrene.

Figure 5 shows a comparison of the spectra of pure polystyrene and a polystyrene/PMMA copolymer. Note that the monosubstituted benzene ring peaks in the two spectra line up quite nicely, with the C-H stretches at 3060 and 3025, the ring mode at 1601, C-H wag at 756, and the aromatic ring bend at 698 in both spectra. The point here is that, even though polystyrene/PMMA copolymers have two repeat units in the same backbone, their spectra look like a simple mixture of the two. This indicates there is very little chemical interaction between the different repeat units in the polymer.

A molecule similar to PMMA is polyethyl methacrylate (PEMA), where the CH

 group attached to the chain in PMMA is replaced by an ethyl (CH

) group. This material is softer than PMMA, and is used to make artificial fingernails amongst other things (10). The structure and IR spectrum of PEMA are seen in Figure 6.

Because PEMA has both methyl and methylene groups, there are three saturated C-H stretching peaks between 3000 and 2850 (11). However, this spectrum is dominated by the Rule of Three peaks for the ester present, with the C=O stretch at 1728, the C-C-O stretch at 1147, and the O-C-C stretch at 1064.

These three peaks in PMMA fall at 1730 cm

, respectively. Thus, the spectra of these two materials are similar, but not identical.

In this article, we have studied the structure and spectra of acrylate polymers. The name for the class comes from acrylic acid. We saw that the spectrum of acrylic acid has peaks from the C=C and -COOH functional groups. Polymers made from acrylic acid monomers often times contain pendant ester groups. We covered the structure and spectrum of the economically important molecule polymethyl methacrylate, its copolymer with polystyrene, and its related molecule polyethyl methacrylate. Their spectra were dominated by the Rule of Three peaks from the esters present.

(1) Smith, B.C. The C=O Bond, Part VI: Esters and the Rule of Three. 

(2) Smith, B.C. Infrared Spectroscopy of Polymers, VIII: Polyesters and the Rule of Three. 

(3) Smith, B.C. Infrared Spectroscopy of Polymers, IX: Pendant Ester Polymers and Polycarbonates. 

(4) Smith, B.C. The Infrared Spectroscopy of Alkenes. 

(5) Smith, B.C. The C=O Bond, Part III: Carboxylic Acids. 

(6) Smith, B.C. The Carbonyl Group, Part I: Introduction. 

https://en.wikipedia.org/wiki/Poly(methyl_methacrylate)

(8) Smith, B.C. Group Wavenumbers and an Introduction to the Spectroscopy of Benzene Rings. 

(9) Smith, B.C. Distinguishing Structural Isomers: Mono- and Disubstituted Benzene Rings. 

https://en.wikipedia.org/wiki/Poly(ethyl_methacrylate)

(11) Smith, B.C. More Theory and Practice: The Thorny Problem of Mixtures and More on Straight Chain Alkanes. 

Articles

Column: IR Spectral Interpretation Workshop

We study the spectrum of polymethyl methacrylate (PMMA)—otherwise known as plexiglass—and the spectra of PMMA mixtures and copolymers.

Infrared Spectroscopy of Polymers X: Polyacrylates

In the past, moving from a concept for an analytical instrument to actually producing a functioning instrument was a relatively tedious and lengthy process. The traditional approach was to draft a design and then go through a number of iterations, along with design reviews and sign-offs. Today, if one has a good designer who is well-versed in computer-aided design (CAD) engineering software, then it is possible to significantly reduce the time to develop a good-looking functional design. However, the time to go from the CAD design to a complete piece of hardware is typically the longest part of the process. It is not unusual for machine shop delays to be up to 6–8 weeks. Today, such delays can be eliminated by producing the designed parts on a desktop with a three-dimensional (3D) printer. This article shows, by example, how a 3D printer can speed up the process of making prototype hardware for a spectral measurement system, shortening the time to produce functional hardware from weeks to days—or less.

The traditional approach to the prototyping of the optics for a spectrometric measurement system is to build the prototype, starting with an optical bench and using off-the-shelf components, such as lenses or mirrors with associated mounts, slit assemblies, source and detector modules, and so on. This approach works for testing out the optical train and allows the optics to be optimized in terms of location, beam direction, and geometry. The next step of the transition to a facsimile of the intended instrument is a little more challenging because although optical components can be obtained from optics houses, such as ThorLabs, Newport, or Edmund Optics, the basic frame and shape of the instrument has to be built up from machined parts. Obtaining the right engineering resource, such as a machinist with experience of building instruments, is not so easy, and it is a skill that is disappearing. However, there is a good practical solution available today that can fill in the gaps and enable a good-looking prototype instrument to be produced, and that is three-dimensional (3D) printing. A 3D printer not only can generate good-looking and well-finished parts, but it can simplify assembly and speed up the prototyping process. This work is made possible by the use of a desktop 3D printer, where the transition from a computer-aided design (CAD) file to a finished part is as simple as a mouse button press, thus eliminating the need to wait for parts to be made at a machine shop. This article illustrates, by practical examples, the advantages gained from 3D printing of prototype parts.

Practical Examples of the Role of 3D Printing for Instrument Prototypes 

The following are actual examples of the implementation of 3D printing as used to evaluate prototype spectral measurement concepts. As an important note, these examples are now more than 10 years old, and in terms of the technology of 3D printing, they are by no means state of the art. The technology of 3D printers and printing substrates has advanced by leaps and bounds in recent years. However, the concept and rationale for its use remains the same.

The first assembly, shown in Figure 1, involved in situ measurements on a custom extraction device with a hydrophobic membrane supported on a metal mesh. The membrane was used as the extraction medium for the isolation and direct measurement of organic contaminants in water. An issue for the measurement was the need to measure everything in situ in the presence of a high degree of optical scattering from the supported membrane. The goal was to make the measurement without the need for any additional focusing optics.

Here, the most important considerations were to rigidly retain and locate the membrane sampler, shown as C2 in Figure 1, to bring the infrared (IR) source (C) into close (and reproducible) proximity to the supported membrane, and to locate the exit of the IR radiation (D2) immediately in front of the quad detector (D). This design helps to concentrate the highly attenuated IR beam, passing though the membrane on to the four-channel detector (shown as D2 and D) without any supplemental focusing optics. The detector assembly provides four electronically independent channels representing the unique analytical wavelengths as defined by narrow bandpass filters mounted in front of the detector elements.

This design was simple and effectively inexpensive for a four-channel non-dispersive IR (NDIR) instrument. Figure 1a shows the system open with all relevant components shown and the membrane sampler location unoccupied, ready to receive a sample for analysis. Once the sampler is loaded, the lid and an actuation cam (B) is closed around hinge (A). In Figure 1b, the cam pushes the IR source assembly into the sampler (C2), making it ready to be measured by the quad detector (D2). The ability to reproduce the exact mode of measurement was invaluable, and it simplified the final instrument design, saving both time and prototyping costs. Figure 1c is a close-up of the four-channel detector.

The concept being prototyped here in Figure 2 is equivalent to the electronic nose system of measurement where gases and vapors are detected by the unique responses of individual channels made up of electrically conductive polymer membranes. In such systems, there are at least eight or nine (possibly more) individual channels that each give a unique set of responses for the compounds detected in the ambient air being sampled. In the example being prototyped here, the conductive polymer membranes are replaced by IR detectors that are responsive to specific wavelengths. Like in example 1, the wavelengths are defined for each quad detector by a set of narrow bandpass IR filters. Unlike the previous example, this system features four quad detectors, providing a total of 16 unique detection channels. The wavelengths selected cover a nominal spectral range from 2.5 μm (2500 nm or 4000 cm

). Three of the wavelengths represented common IR absorptions for C-H, carbon monoxide (CO) and carbon dioxide (CO

). The rest of the wavelengths selected were spread over the full range and included the statistically most relevant absorptions. Conceptually, this prototype can may be considered to be an improvement over the conductive polymer system because a correlation to known spectral absorption wavelengths can be established. One relevant thought here is that we are dealing with molecular vibration-based IR absorptions, and the olfactory system (smells and odors) responses are also linked to molecular vibrations.

The assembly developed (Figures 2a and 2b) is designed to be a standalone ambient air monitoring system, with 16 independent channels, as described above. The key components of the system are exposed in the “semi-transparent” version designated (Figure 2a). The spectral measurements are obtained from four quad detectors (four channels each). In this particular case, each quad is equipped with its own IR source, with the electronics set up to monitor the output of the detectors providing a set of 16 signals, representing 16 different sets of wavelengths. The system monitors the air, which is drawn in by a fan assembly on the side of the measurement chamber. Then, 16 sets of absorbance data are generated and these are normalized and presented in a histogram form (Figure 2c). In this particular example, the 3D printing provides the frame of the overall assembly and the measurement chamber that is coupled to the fan used to transport the air into the chamber. The IR beams from the individual sources transverse the chamber, with a 50-mm optical path, which is sealed at both ends with IR-transmitting windows.

Again, in this case, the 3D printing provided a testing platform that enabled the overall measurement concept to be evaluated.

Ambient air monitoring is intended to measure and monitor low concentrations of gases and vapors in the air. For the nose simulation, a relatively short optical path was used for the measurement. Although this process was effectively multiplexed with the simultaneous measurement of 16 channels the sensitivity for individual species may have been limited by the optical measurement path. For the IR measurement of individual gases (vapors) at low concentrations, it is beneficial to extend optical path to a meter or more. When working with a small measurement system, a 1-m path (or greater) can be difficult to implement within a limited space. The popular “White Cell” has been used for such measurements; however, it can yield a relatively large measurement volume. The system shown in Figure 3 was devised to enable long path measurements, of one to two meters, while maintaining a small internal measurement volume. When optimized, the cell has 4x to 5x less volume than the comparable pathlength “White Cell.”

The system shown in Figure 3a (A1/A2) is a packaged design for continuous monitoring applications where the main measurement component, a ring containing 13 mirrors (Figure 3b), is housed within a cylindrical enclosure chamber. In this case, the IR beam is injected into the chamber with an IR source mounted at A1, and is collected at A2 following multiple passages, with reflections from the mirrors mounted in the walls of the ring (Figure 3b). The beam is directed in and out of the enclosure with a pair of off-axis paraboloid mirrors (one in and one out). The ring in this case is 3D printed with the mirror recesses designed to provide an exact push fit for the mirrors. The dimensions are exact to provide a 1-m path following the multiple reflections. This design is unique insofar as it provides for a quick and easy assembly with all 13 mirrors pre-aligned with no additional alignment required.

A modified version of the ring mount is shown in Figure 3c. In this version, the ring also forms the external part of the enclosure, where the IR beam enters and exits on the horizontal axis. For this variant, the beam enters directly from the source and exits at a quad detector, both equipped with their own electronic interfaces. With the exception of these electronic components, the rest of the enclosure components are 3D printed, which are shown in gray and white. Note that the gray component is actually printed from a 50:50 polyamide:aluminum blend. The blend was preferred in this case because the aluminum helped improve the thermal characteristics of the overall package. The benefit provided in this case by the 3D printed part was that it simplified assembly, and it eliminated the need for optical alignment (by design).

In 2015, I gave a webinar on new technical advances in optical spectroscopy. At the end, a participant asked if a technology could be recommended for a Hadamard Transform spectrometer. The answer back was that a technology, such as the Texas Instruments (TI) digital light processing (DLP) chip, could be a potential solution to encoding spectral data for a Hadamard transform. It turned out that not only could the DLP enable Hadamard encoding, but it could also be applied to the design of a spectrometer and eliminate the need for a detector array. This was an unanticipated benefit because it enabled a spectrometer to be developed in a wavelength range that required an expensive array, and it enabled a higher pixel count than such high-cost arrays. A good example is the elimination of the costly extended InGaAs array from a long wavelength NIR spectrometer. In this case, a high-performance single element detector would be used in place of the array. In this case, the DLP provides the array function by collecting the dispersed NIR radiation from a planar grating, and with wavelength selection being made by addressing the individual or groups of programmable reflective pixels.

This resulted in the development of an NIR spectrometer platform based on TI’s DLP technology. It should be pointed out that not all spectral ranges benefit from the use of the DLP scanning. For example, the standard charged-coupled device (CCD) array UV-vis-NIR systems use relatively low cost, high resolution arrays and, in such cases, there is no gain from the use of a DLP. However, the benefits of DLP scanning for the long-wave NIR enables a spectrometer to be designed that covers the spectral range of 1300–2600 nm. An added benefit gained for this spectral range is that extended InGaAs requires cooling to obtain the best noise performance. Changing from an array to a single element detector significantly reduces the thermal overhead, as well as cost of implementation.

It is important to note that TI does not make instruments; it produces advanced computer chips. For the DLP technology to be evaluated, TI designed a functional optical bench and this design was made available to instrument developers and researchers. The evaluation system that was made available is shown in Figure 4. This system had a conventional design, which turned out to be difficult to assemble because each optical component required adjustment and alignment; these alignment components can be seen in Figure 4a.

In a collaboration with TI, a new lens recipe was generated based on the use of seven spherical lenses (instead of six aspherical lenses), and this resulted in a significant cost reduction. The optical layout with the spherical optics is shown in Figure 4b. It was realized that an alternative approach to the assembly could be adopted if the optical bench could be fabricated as a single component without the individual optical subassemblies. Yes, this was made possible by a transition to a 3D printed part for the optical base. A 3D printed version of an assembled instrument is shown in Figure 4c, and the components that required alignment by the conventional approach (Figure 4a) can be seen on this assembly, but no alignment is required. All lenses are just inserted into slots and are pre-aligned and optimized.

Was this transition a success? The answer was yes and no. It was possible to make one-off prototypes that performed well. However, at the time, it was hoped that a product could be made directly with this simplified 3D printed baseplate. The main issues came down to limitations of the 3D printing materials in terms of making threaded parts and thermal conductivity. These issues limited the reproducibility of optical alignments, particularly for the grating. The timeframe for this work was late in 2018. We are four years further on now with significant improvements in 3D printers and 3D printing materials. With an optimistic view, it is anticipated that many of the original goals here for instrument manufacturing can be met.

The application of 3D printing has been described in context of a prototyping and concept-proving tool. The examples shown have been limited by both “age” of hardware and materials, and the ability to describe the end-application in depth because of commercial proprietary issues. Although the examples described may appear to lack style, they were all functional and proved a point. Important early limitations were the need to use special fastening aids to enable fixtures, such as screws to be used, the inability to make metal parts and the lack of materials to make optical components, such as lenses. The closest thing to metal parts were made from a 50:50 blend of polyamide and aluminum. Most of the other structural parts were made from selective laser sintering (SLA) grade polyamide.

Today, it is possible to purchase a desktop 3D printer for a couple of thousand dollars, and so conceptually concepts and applications can be tested in “real-time”. In other words, no need to wait for parts to come back from a machine shop or an external contractor. The implied ability to transition from conceived idea to functional prototypes and on to manufactured products can be realized today. Also, the material and fabrication limitations cited above, for the most part, have been addressed. For example, both metal parts and transparent small optical parts can be produced from commercial 3D printers. Examples of 3D printed micro-spectrometers operating in the visible spectrum have been published. However, as an important caveat, it is possible that spectral measurements that require optical transparency in certain wavelength regions may not be available, at least for now, who knows what might exist in a year or two.

It has been a while since I have written an article for 

. I have shared a long-term working relationship with the magazine, going back several decades. During that time, the nature and volume of my work in spectroscopy, and the science itself, have changed significantly. Normally, I write and document in the third person, but for this article, I have deviated from this and written in both the first and third person.

My background and training were in analytical chemistry, and over time became focused on spectroscopy. However, in the 1980s I started the transition to instrumentation, with some focus on optics, opto-mechanics, and spectral data handling. Coates Consulting was established in the mid-1990s, leading to a specialization on measurement technologies and small, low-cost instrumentation.

A few months back, the editorial staff contacted me to see if I could put together an article or two on technologies tied to spectral measurements, and in particular, on key technologies that are involved with new instrumentation, such as with the miniaturization or scaling down of spectrometers, and the changes in measurement platforms. The latter involves the move away from the laboratory and toward handheld or distributed measurements involving spectrometers designed as sensors. Having agreed to write the article, I was faced with the challenge of what material I could discuss and what concepts could be presented; in recent years, most of my instrumentation projects have been covered by non-disclosure agreements (NDAs) and confidentiality documents limiting what can be discussed in public.

I started writing this publication at the beginning of July. Over that first weekend, my attention was drawn to an article published in the New York Times entitled “3D Printing Grows Beyond its Novelty Roots,” by Steve Lohr. The case being made was that the technique of 3D printing had jumped from being a tool to make one-off and prototype parts to a full-blown means of making specialized manufactured mechanical parts, with a high degree of “accuracy” and reproducibility. In my opinion, 3D printing has been a game changer for evaluating spectral measurement concepts, and I have reflected on this aspect in this text.

My personal involvement with 3D printing started around 2012. At the time, it was used for making small numbers of prototypes for projects that involved unique or complex designs for spectral measurements. At issue was how to test out a concept without great expense and without risking going down blind alleys if the “guesses” were wrong. All the systems involved making IR measurements, in the near infrared (NIR) and mid-IR spectral regions. For some applications, it is possible to simulate the application on a laboratory instrument. Although that may work for some applications, the approach may not duplicate the exact sampling or data acquisition conditions and may give a false impression relative to the “success” of the application. This situation is where the benefits of 3D printing emerged. A complete measurement system could be designed (with a standard CAD package), assembled and tested, where the 3D printing included the enclosures and assembly structures as well as some of the optical components. For reference, the CAD package used for the projects outlined here was SolidWorks (published by Dassault Systemes).

The author is not writing this article as an expert in 3D printing; in fact, quite the opposite is true. The article is written from the perspective of a person experienced in the design and implementation of spectroscopic instrumentation and spectral sensing technologies. There is no doubt that many readers may well be more expert in 3D printers and the associated technologies, and so please do not write and complain! I have included several references useful for further information on this subject (1–6).

(1) Think 3D Team, 3D Printing Tutorial (PDF): Beginner’s Guide to 3D Printing, version 0.1. 

https://www.think3d.in/landing-pages/beginners-guide-to-3d-printing.pdf

(2) Workman Jr., J.; Coates, J.; Naranjo, D. Micromirror spectrophotometer assembly. U.S. Patent 10,054,483, issued August 21, 2018.

(3) Workman Jr., J.; Coates, J.; Naranjo, D. Micromirror spectrophotometer assembly. U.S. Patent 10,309,829, issued June 4, 2019.

(4) Baumgartner, B.; Freitag, S.; Lendl, B. 3D Printing for Low-Cost and Versatile Attenuated Total Reflection Infrared Spectroscopy, 

(5) Nesterenko, P.N. 3D Printing in Analytical Chemistry: Current State and Future. 

(6) Wang L.; Pumera. M. Recent Advances of 3D Printing in Analytical Chemistry: Focus on Microfluidic, Separation, and Extraction Devices. 

Lasers & Optics Interface

A 3D printer can shorten the time to make prototype hardware for spectrometers from weeks to days—or less.

Three-Dimensional Printing and the Art of Making Small Working Prototype Spectrometers

Handheld Raman spectroscopy offers a rapid and mobile technique for determining drugs nondestructively. The technique offers further advantage for analyzing drug products (DPs) thanks to its ability to measure samples through packaging, thus preserving evidence integrity and continuity. This research evaluated the use of handheld Fourier transform (FT)-Raman spectroscopy for characterization of street DPs (

 = 254) of diverse formulations. Raman spectra of DPs inside their packaging were collected and matched against the instrumental in-built library, and then exported to Matlab 2020a for offline spectral interpretation. Reference analysis was confirmed using gas chromatography–mass spectrometry (GC–MS) and infrared (IR) spectroscopy. The main drugs present were 1,3-trifluoro- methylphenylpiperazine, cocaine, ketamine, 3,4-methylenedioxymethamfetamine, mephedrone, and 1-benzylpiprerazine. The main impurities present in DPs were benzocaine, caffeine, and lactose. The impurities affected the Raman signature (enhanced or inhibited) of DPs, enabling profiling of DPs and visualizing patterns among different products. These latter patterns were featured in the similarities highlighted by the correlation coefficient values between different DPs, and by adjacent clusters of different DPs envisaged in the principal component analysis scores plot.

Crime and violent behaviors have increased because of the widespread use of illicit drugs in contemporary societies. Amsterdam (1027.7), London (701.1), and Copenhagen (780 mg/1000 p/day) had the highest weekend daily mean cocaine usage in 2020 (1). Drug addiction endangers public health, safety, and welfare, as well as the security of the nation. Researchers and authorities require quick and accurate drug detection methods that can be adapted to the ever-increasing spectrum of illicit drugs. Currently, the primary goal of drug analysis is to detect and identify drugs of abuse.

Analytical techniques such as thin layer chromatography, gas chromatography–mass spectrometry (GC–MS), gas chromatography-flame ionization detection (GC-FID), high performance liquid chromatography (HPLC), and liquid chromatography–mass spectrometry (LC– MS) have all been proposed, developed, and used to detect illicit drugs (2). These techniques provide reliable and accurate results in drug analysis, but they are costly, time consuming, and destructive, which limits their practical ability. Vibrational spectroscopic methods, such as Fourier transform infrared (FT-IR) and Raman, address the aforementioned limitations, and they have also been applied for qualitative and quantitative investigations of illicit drugs (3,4).

Raman spectroscopy measures the vibrational modes of a sample. The spectrum is a wavelength distribution of bands that correspond to molecular vibrations in the sample under investigation. The Raman band frequencies and intensities could be used to identify and quantify the measured samples (5). Raman spectroscopy generates molecular-specific spectra with minimum or no sample preparation, permitting non-destructive in situ analysis for different forms of drugs (liquids, tablets, and powders) (6), which is very useful when a substantial number of samples need to be analyzed, and it is essential for avoiding sample contamination, reducing analysis time, and protecting the evidence under investigation. Raman spectroscopy has been used in a variety of applications, including forensics (6), industrial process control (7), biomedical purposes (8), and medical diagnostics (9). When identifying drugs, Raman can distinguish between salts, stereoisomers, and homologs with a sample size of more than 5 mg (10), and it also can reveal a high level of specificity for drugs concealed in alcohol (11). Minor variations in chemical structures can be identified, thus providing a characteristic spectrum for each chemical compound and making the identification of drugs more reliable (12). Raman spectroscopy has recently been used to check drug contents within their packaging (13), evaluate the composition and homogeneity of drug tablets (14), classify street drugs (15), and determine drug authenticity (16). Raman spectra of drug blends are often highly complex because they include spectral features corresponding to all components in the sample. Consequently, chemometric methods must be used to obtain quantitative information from complex spectra (17). This study complements previous studies in evaluating the use of handheld Raman spectroscopy for on-spot identification and characterization of street drugs in their packaging.

 = 254) were measured as received, and included powders, tablets, capsules, liquids, and rocks of different colors. Samples were measured through glass vials using a handheld FT-Raman spectrometer equipped with 490 mW of laser power, a 1064 nm laser wavelength, and cooled InGaAs detector. Spectra were collected over the wavenumber range of 250–2000 cm

. The in-built spectral algorithm was used to search matches of the drug samples against the instrumental libraries. For each sample, the library algorithm gave matches for the drugs or additives that showed spectral features. For offline analysis, the spectra of the products were interpreted considering spectral quality, functional groups, and similarities among products using correlation in wavenumber space (CWS) and principal component analysis (PCA) algorithms. Spectral quality was evaluated for the measured drug products, considering the low spectral resolution in FT-Raman (18). For the CWS method, the momentum product was calculated between the spectra of different products reporting a common drug. A threshold of 0.95 or more was considered a match and vice versa (19). For PCA, drug products’ spectra were explored for patterns among their scores. A false negative was seen when a drug product score was not grouped with product scores of the same drug, whereas false positives were seen when a drug product score was clustered with scores of different drugs. Reference analysis was conducted using GC–MS and attenuated total reflectance-Fourier transform infrared (ATR-FT-IR) spectroscopy. GC–MS and ATR-FT-IR confirmed the identity of the drugs or common impurities present in DPs, respectively (Table I).

Out of the measured DPs, 153 contained drugs or drug mixtures, most of which were not pure. The main drugs found were 1,3-trifluoromethylphenylpiperazine (TFMPP) (

 = 29), 3,4-methylenedioxymethamfetamine (MDMA) (

 = 2), 3,4-methylenedioxypyrovalerone (MDPV) (

 = 2), 1-(3-chlorophenyl)piperazine (mcPP) (

 = 1), and 1-methyl-4-benzylpiperazine (mBZP) (

The main impurities detected were caffeine (

 = 35), which were both Raman active. Lidocaine and procaine were detected less than benzocaine, and they were found in seven and two products, respectively. Benzocaine and lidocaine were mainly found as impurities in cocaine drug products, alongside other impurities such as phenacetin and caffeine. Thus, the pattern of adulterants varied between DPs. For instance, caffeine was also an adulterant in MDMA and piperazine derivatives. On the other hand, lactose was a bulking agent reported in diazepam tablets, and it contributed to the low Raman activity of these products. Likewise, dextrose and sucrose were also found in DPs of tablet- and powder-formulations and contributed to the low Raman activity of these products. Hence, drugs adulterated with the aforementioned sugars were not detected in tablets or powders using Raman spectroscopy where the Raman signal of these tablets was masked by lactose fluorescence.

Spectral quality was evaluated considering these parameters: the number of peaks (

); maximum peak position and intensity; wavenumber range; and signal-to-noise ratio (S/N) (19). In this respect, synthetic piperazine, cocaine, and mephedrone products showed strong Raman activity, ketamine products showed medium Raman activity, and MDMA products showed low Raman activity.

Synthetic piperazines’ spectral quality varied depending on the purity of the DPs and the types of impurities present in them (Figure 1). TFMPP samples showed stronger Raman activity than other piperazines, and that was related to their being either pure or cut with caffeine that in turns was Raman active. The ranges of N, maximum intensity, and S/N values for piperazine derivatives were 15–25, 1500–15000 a.u., and 10–20, respectively. Cocaine products demonstrated strong Raman activity, but that depended on the adulterants present in the cocaine sample, which affected the Raman activity (Figure 2). For cocaine, Raman active samples, 

, maximum intensity, and S/N were in the range of 11–27, 1,744–51,242 a.u. and 15–39, respectively. Similarly, mephedrone showed strong Raman activity with ranges of 

, maximum intensity and S/N in the ranges of 25–29, 1500–8000 a.u., and 18–37, respectively (Figure 3). Ketamine products showed medium Raman activity with 

, maximum intensity, and S/N in the ranges of 16–30, 700–4000 a.u., and 5.75–39, respectively (Figure 4). On the other hand, MDMA products exhibited low Raman activity with low S/N < 20), despite the high 

 in most spectra (up to 25) (Figure 5). The maximum intensity seen for MDMA products was in the range of 1500–5000 a.u.

Spectral interpretation showed characteristic scattering bands for the major drugs and impurities present in the measured DPs (Table II). Most drugs showed key bands between 500–1700 cm

 (21–25). In this respect, Raman spectra indicated key differences between different drug analogues as well as base or salt forms of the same drug. For drug analogues, piperazine derivatives (TFMPP and BZP) could be differentiated over the ranges 500–1000 and 1300–1700 cm

, respectively (Figure 1). Similarly, cocaine could be discriminated from cocaine HCl mainly in the range between 850–890 cm

, where cocaine base showed three bands around 850, 870, and 890 cm

 corresponding to the C-C stretch of the tropane ring in the cocaine base (20). On the other hand, cocaine HCl only showed two C-C stretching bands corresponding to the tropane ring around 850 and 890 cm

 (20,21). Where benzocaine was present in cocaine DPs, it could be traced by the strong absorption intensity and by the characteristic bands in the range of 850–1700 cm

When CWS was applied to the spectra of the top encountered DPs, variable correlation (

 value) ranges were observed depending on the amount of drug in DPs and on the purity of the specific DP (Figure 6). For instance, TFMPP-related products (DPN213–DPN254) did not show high 

 values against each other, and that they could not be considered a false negative because of the inconsistency in constituents in TFMPP products, indicating the presence of other additives, such as caffeine, dextrose, ephedrine, lactose, phenmetrazine, and sucrose. In this respect, the Raman activity of the constituents impacted the Raman scattering in terms of number of bands and Raman activity of the DP. For instance, caffeine had strong Raman scattering, and that influenced the signature of the TFMPP products containing them (DPN234–249). Nevertheless, the latter products contained impurities such as lactose that was only detected by Raman (and not GC–MS), which in turn influenced their Raman activity. Lactose and other sugars introduced fluorescence in the Raman spectra of TFMPP products (Figure 1). It is important to mention that the physical properties of the DPs did not influence the Raman signature. Hence, TFMPP products of similar chemical makeup and different physical characteristics (formulation, color) showed high 

 values against each other. For example, DPN217 (white tablet formulation) showed an r value of 0.95 against DPN220 (white crystal formulation). Also, DPN228 (pink tablets), DPN235 (white tablets), and DPN246 (blue tablets) showed 

 values of 0.95 against each other. It is worth noting that no false positives were seen for TFMPP-DPs except against a DP containing BZP, and this mismatch could be related to the structural similarity between TFMPP and BZP.

Cocaine DPs featured less false negatives, and that could be attributed to the consistency in the types of impurities detected in the measured cocaine DPs. For instance, samples with a cocaine/benzocaine mixture (DPN48–DPN62) showed 

 values > 0.95 against each other where both constituents in the matrix were Raman active and were strong scatterers. Where more than two constituents were present in a cocaine DP, the 

 value changed, and that also depended on the Raman activity of the constituents. Overall, the constituents were unique to cocaine mixtures where no false positives were observed with cocaine mixtures against other drugs. Similar patterns in 

 values results were seen for ketamine samples that were mainly pure, and showed 

 values < 0.95 against different drugs. Only four ketamine DPs showed low 

 values against other ketamine products (one Raman active and three Raman inactive samples). The remaining DPs (containing MDMA and mephedrone) showed false positives and false negatives related to the high number of impurities present in them, and that had been reported in the literature, especially in mephedrone DPs.

Hence, CWS results were only conclusive when the exact number of impurities were present in the reference and test tablets. Considering the aforementioned challenge in identification, PCA recognized patterns in the DPs scores that corresponded to spectral features contributing to high variances (Figure 6). The first three PCs contributed 88.8% of the variance among the DPs’ spectra, with cocaine DPs’ scores recording the highest variance. This was followed by ketamine DPs’ scores and TFMPP DPs’ scores. Cocaine, ketamine, and TFMPP DPs’ scores showed three distinct clusters with slight overlap in few scores, and that could be related to the caffeine or lactose that were impurities present in DPs of the three drugs. Some MDMA DPs that contained lactose overlapped with products of the same impurity. On the other hand, mephedrone DPs were clearly distinguished from other DPs, and that showed their unique composition.

In summary, handheld FT-Raman spectroscopy complemented GC–MS and IR in characterizing street DPs. It indicated information regarding certain impurities that could not be detected by GC–MS (such as lactose and sucrose). Another advantage encountered over IR was the ability of Raman to characterize Raman active drugs nondestructively regardless of the physical differences between the matrices (tablets, powders, or liquids). However, some limitations were encountered in processing the spectra of the drug products relating to the sensitivity of Raman in detecting drugs that contained impurities, especially fluorescent ones such as lactose. Moreover, the presence of multiple impurities introduced a challenge in the identification and characterization of the drug product. Further understanding of Raman spectra, particularly in samples of multiple impurities, is needed. Therefore, future work will consider investigating drugs in mixtures using a more quantitative approach.

The authors would like to thank Bournemouth University for access to drug products and instrumentation. Special thanks for Amy Williams, Chelsea Bailey, and Angela Buffardi for their help with spectral data collection.

European Drug Report: Trends and Developments

 (European Monitoring Centre for Drugs and Drug Addiction, Libson, Portugal, September 2020).

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Recommended Methods for the Identification and Analysis of Amphetamine, Methamphetamine and Their Ring-Substituted Analogues in Seized Materials

(3) Izake, E.L. Forensic and Homeland Security Applications of Modern Portable Raman Spectroscopy. 

(4) Praisler, M.; Van Bocxlaer, J.; De Leenheer, A.; Massart, D.L. Chemometric Detection of Thermally Degraded Samples in the Analysis of Drugs of Abuse with Gas Chromatography-Fourier Transform Infrared Spectroscopy. 

(5) Yang Y.; Thomas, R. The Benefits of a High-Performance, Handheld Raman Spectrometer for the Rapid Identification of Pharmaceutical Raw Materials. 

Modern Raman Spectroscopy: A Practical Approach

 (John Wiley & Sons, Chichester, United Kingdom, 2005).

(7) Gilbert, A.S.; Lancaster, R.W. “IR and Raman Spectroscopy. Industrial Applications,” in Encyclopedia of Spectroscopy and Spectrometry, J.C. Lindon, G.E. Tranter, and D.W. Koppenaal, eds. (Academic Press, Oxford, United Kingdom, 3rd ed., 2017), pp. 394–407.

(8) Krafft C.; Popp, J. The Many Facets of Raman Spectroscopy for Biomedical Analysis, 

(9) Kong, K.; Kendall, C.; Stone, N.; Notingher, I. Raman Spectroscopy for Medical Diagnostics — From In-Vitro Biofluid Assays to In-Vivo Cancer Detection. 

(10) Lanzarotta, A.; Witowski, M.; Batson, J. Identification of Opioids and Related Substances using Handheld Raman Spectrometers. 

(11) Burnett, A.D.; Edwards, H.G.M.; Hargreaves, M.D.; Munshi, T.; Page, K. A Forensic Case Study: The Detection of Contraband Drugs in Carrier Solutions by Raman Spectroscopy, 

(12) Mazurek S.; Szostak, R. Quantitative Determination of Diclofenac Sodium and Aminophylline in Injection Solutions by FT-Raman Spectroscopy. 

(13) McCreery, R.L.; Horn, A.J.; Spencer, J.; Jefferson, E. Noninvasive Identification of Materials Inside USP Vials with Raman Spectroscopy and a Raman Spectral Library. 

(14) Matousek, P.; Parker, A.W. Bulk Raman Analysis of Pharmaceutical Tablets. Appl. Spectrosc. 2006, 60 (12), 1353–1357. DOI: 

(15) West, M.J.; Went, M.J. Detection of Drugs of Abuse by Raman Spectroscopy. 

(16) Kalyanaraman, R.: Dobler, G.; Ribick, M. Portable Spectrometers for Pharmaceutical Counterfeit Detection. 

(17) Müller, J.; Knop, K.; Wirges, M.;  Kleinebudde, P. Validation of Raman Spectroscopic Procedures in Agreement with ICH Guideline Q2 with Considering the Transfer to Real Time Monitoring of an Active Coating Process. 

(18) Vítek, P.; Ali, E.M.; Edwards, H.G.; Jehlička, J.; Cox, R.; Page, K. Evaluation of Portable Raman Spectrometer with 1064 nm Excitation for Geological and Forensic Applications. 

(19) Assi, S. Raw Material Identification Using Dual Laser Handheld Raman Spectroscopy. 

(20) Penido, C.A.F.d.O.; Silveira Jr, L.; Pacheco, M.T.T. Quantification of Binary Mixtures of Cocaine and Adulterants Using Dispersive Raman and FT-IR Spectroscopy and Principal Component Regression. 

(21) Carter, J.C.; Brewer, W.E.; Angel, S.M. Raman Spectroscopy for the in Situ Identification of Cocaine and Selected Adulterants. 

(22) Liu, C.M.; He, H.Y.; Xu, L.; Hua, Z.D. New Qualitative Analysis Strategy for Ilicit Drugs Using Raman Spectroscopy and Characteristic Peaks Method. 

(23) Hargreaves, M.D.; Page, K.; Munshi, T.; Tomsett, R., Lynch, G.; Edwards, H.G. Analysis of Seized Drugs Using Portable Raman Spectroscopy in an Airport Environment—A Proof of Principle Study. 

(24) Milhazes,  N.; Martins,P.; Uriarte, E.; Garrido, J.; Calheiros, R.; Marques, M.P.M.; Borges, F. Electrochemical and Spectroscopic Characterisation of Amphetamine-like Drugs: Application to the Screening of 3,4-methylenedioxymethamphetamine (MDMA) and its Synthetic Precursors. 

(25) Christie, R.; Horan, E.; Fox, J.; O’Donnell, C.; Byrne, J.; McDermott, S.; Power, J.; Kavanagh, P. Discrimination of Cathinone Regioisomers, Sold as ‘Legal Highs’, by Raman Spectroscopy. 

 are with the School of Pharmacy and Biomolecular Sciences at John Moores University, in Liverpool in the United Kingdom. 

 is with the Faculty of Science at Lebanese University, in Beirut, Lebanon. 

 is also with the School of Allied Health at Anglia Ruskin University, in Chelmsford in the United Kingdom. Direct correspondence to: 

Featured Article

Handheld FT-Raman spectroscopy can complement GC–MS and IR in characterizing street drugs.

Characterization of Street Drugs Using Handheld Fourier Transform Raman Spectroscopy

This year’s Atomic Spectroscopy Award recipient is Andreas Riedo. For the past decade, Riedo’s research has focused on the development of fundamental measurement methodologies using miniaturized laser ablation–desorption ionization mass spectrometry (LIMS or LMS) for the chemical (elements, isotopes, and molecules) analysis of complex mineral surfaces, including semiconductor crystalline solids and materials found in space exploration.

Andreas Riedo of the Physics Institute at the University of Bern has won the 2023 Emerging Leader in Atomic Spectroscopy Award, which is presented by 

 magazine. This annual award, begun in 2017, recognizes the achievements and aspirations of a talented young atomic spectroscopist, selected by an independent scientific committee. The award will be presented to Riedo at the 2023 European Winter Conference on Plasma Spectrochemistry (Ljubljana, Slovenia, January 29–February 3, 2023), where he will give an award lecture.

Riedo’s research has focused on the development of fundamental measurement methodologies using laser ablation (LA) and laser ablation–desorption ionization mass spectrometry (LIMS) for the chemical analysis of complex solid materials and organic molecules that are related to space research and astrobiology.

Riedo received his PhD in physics in 2014 and has been actively involved in the field of space research and planetary exploration, focusing on the design, development, and qualification of space-capable analytical instrumentation. His interest and work in the field of laser-based MS began during his PhD studies with Prof. Peter Wurz at the Physics Institute in the division of Space Research and Planetary Sciences at the University of Bern. As a graduate student, Riedo optimized an existing LIMS system intended for in situ space research. The instrument was enhanced as a result of his work to perform analysis for quantitative element composition, isotope abundances, depth profiling, and two- and three-dimensional (3D) chemical imaging and analysis.

As a postdoctoral researcher, Riedo specialized in applying LIMS for potential astrobiology applications. Specifically, this research seeks to identify chemical biosignatures that may indicate past or present occurrence of life forms in extraterrestrial environments. To further advance the techniques required for detection of current extraterrestrial life, Riedo has measured carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur (CHNOPS) biomarkers in selected terrestrial desert soil samples. He has demonstrated single-microbe detection in such soil samples for sparse life identification. In addition, he has shown that sensitive LIMS is capable of accurate isotope ratio analysis of sulfur isotopes, which are an important class of potential life biomarkers.

After his postdoctoral work, Riedo built his own laboratory as an indepen- dent scientist at the University of Bern, where he has applied laser desorption mass spectrometry to detect complex molecules potentially relevant for Earth-like lifeforms. These molecule types include polycyclic aromatic hydrocarbons (PAHs), lipids, and amino acids. Currently, Riedo is a scientist and project manager for the Neutral gas and Ion Mass spectrometer (NIM) instrument, which is part of the scientific payload of the Jupiter’s Icy Moons explorer (JUICE) space mission of the European Space Agency (ESA).

Developing and Refining Instrumentation to Advance Astrobiology: a Miniature Laser Ablation Time-of-Flight Mass Spectrometer

Riedo has gained significant recognition in the field of experimental astrobiology. He was invited to join the studies group for instrumentation that will be part of the National Aeronautics and Space Administration (NASA) Europa Lander. His instrument project for a potential future mission would look for signs of life on the surface of Europa, one of Jupiter’s moons. Europa is slightly smaller than Earth’s moon and is primarily made of silicate rock with a water-ice crust. He is also a project manager for two LIMS instruments planned for NASA’s Artemis program on the moon. The Artemis program will land the first woman and next man on the moon by 2024 and test new technologies and approaches to gather information for sending astronauts to Mars. In addition, his Organics Information Gathering Instrument (ORIGIN) has been selected for a mission to Venus (8). “The ORIGIN space instrument is a miniature laser desorption–laser ablation ionization mass spectrometry (LIMS) instrument designed to detect large, non-volatile molecules, specifically biomolecules such as amino acids and lipids; as well as to be used in ablation mode for elemental composition analysis of extraterrestrial materials. Being able to successfully achieve an innovative system to be included on a Venus Life Finder Mission is a significant contribution,” said Jorge Pisonero of the University of Oviedo in Spain.

“Dr. Andreas Riedo designed and constructed independently a novel mass spectrometric setup based on laser desorption mass spectrometry,” Pascale Ehrenfreund from George Washington University said. “Riedo’s instrument allows the direct desorption of biomolecules that are highly relevant for life detection on planetary objects other than Earth.” When addressing Riedo’s most important contributions, Frances Westall from the CNRS-Centre de Biophysique Moléculaire in Orléans, France said. “His space-developed instrumentation is capable of providing the essential context information from a rock sample potentially hosting carbonaceous traces of life, then analyzing these specific traces.”

Developing the Miniature Laser Ablation Time‐of‐Flight Mass Spectrometer

Indeed, colleagues and the community at large are impressed by Riedo’s work on instrumentation for space exploration. “Riedo has proven his abilities to develop innovative new methods to study samples from other planetary environments,” notes Charles Cockell, a collaborator from the University of Edinburgh. Riedo’s paper reporting on the analytical performance of a miniature LMS designed for in situ investigations of planetary surfaces is his most cited paper to date (1) (Table I). The high sensitivity and high spatial resolution mass spectrometer for this instrument was designed for elemental and isotopic analysis of naturally occurring materials. An UV laser, rather than infrared (IR), was used for sample ablation with an irradiance of ~1 GW/cm

. Implementing this laser achieved stable ion formation with low sample weight loss. This instrument exhibited good reproducibility because of the use of computer control of the experimental parameters, such as laser ablation characteristics, ion-optical parameters, and sample position. The dynamic range of the instrument was reported to be more than eight decades, and the detection sensitivity for both metallic and non-metallic elements was excellent. Abundance down to tens of parts per billion (ppb) was demonstrated together with detailed isotopic patterns. This instrument has demonstrated improved performance over established instruments in planetary in situ research. “This very compact instrument shows much better performance than instrumentation used so far in planetary research,” said Peter Wurz, Riedo’s doctoral supervisor and mentor at the Physics Institute at the University of Bern in Switzerland said. “None of the established instruments in planetary in situ research has such performance.”

As part of this work, Riedo and his colleagues reported the first mass spectrometric analysis of elemental and isotopic composition of several National Institute of Standards and Technology (NIST) standards using their miniature LMS (2). This research demonstrates improvements to previous LMS systems by varying laser optics, type and wavelength, as well as data acquisition and analysis procedures. The selected femtosecond (fs)-laser ablation ion source used was a 775 nm, 190 fs, 1 kHz laser, which has exhibited reduced thermal effects and negligible sample damage, as well as substantial improvements in instrument performance, as discussed above. This work, which shows the successful introduction of femtosecond lasers in his mass spectrometry instrument, stands out to Wurz. “This paper is exemplary for the continuous development by Andreas Riedo of the analytical improvements he has pursued,” Wurz said.

In 2013, Riedo and coworkers expanded the use of the miniature LMS for precise and accurate measurements of isotope abundances (3). A pulsed UV laser (266 nm, 3 ns, and 20 Hz) was applied for ablation, atomization, and ionization for measurements of several untreated NIST standards and to measure galena, a naturally occurring mineral form of lead(II) sulfide. Relative accuracy and precision for this instrument for these samples was shown to be in the parts-per-thousand level. The results for galena were surprisingly similar to those obtained using a thermal ionization MS (TIMS) system. It was determined that a lower isotope composition in the sample (for example below 100 ppm), resulted in a measured accuracy and precision in the percentage levels. The instrument is able to estimate the age of minerals using measurements of the lead isotope 

Work published from 2017 demonstrated the importance of high-speed and high dynamic range detector systems for optimum resolution and sensitivity time-of-flight MS (12). To achieve the appropriate analytical performance, a multi-anode multichannel plate detector with high-speed data acquisition was tested. This design resulted in a lightweight, low power, compact detector system that was suitable for portable or space payload instrumentation.

Analysis of rock and soil samples on extraterrestrial planets is an important part of upcoming space missions. To that end, Riedo and collaborators reported on the development and testing of a miniaturized LMS for in situ spatial and elemental profiles of a heterogeneous rock sample to a depth of several nanometers (17). This work demonstrated that highly detailed 3D composition information, including oxidation properties could be obtained for natural, heterogeneous rock samples by applying the LMS technology. When combined with Raman spectroscopy, LMS provides even more comprehensive mineralogical analysis details. These details are important for characterization and determination of probe drilling locations that will yield the greatest information on remote planet landscapes.

The most recent developments of instrumentation and applications carried out by Riedo and coworkers has been for the detection of lipids, sulfur isotopes, elemental signatures of microbes, and amino acids on extraterrestrial and planetary analogue surfaces (7,9,10–11). These most recent publications are listed in Table II. This research further addresses advanced applications of LIMS, LMS, and Raman spectroscopy for materials characterization, such as 3D chemical imaging, structural analysis of contaminants in electrodeposited metal films, chemical depth profiling of solid materials, and in situ analysis of elemental and isotopic composition of heterogeneous materials, such as meteorites, and terrestrial rocks and minerals.

Riedo and colleagues have demonstrated that chemical imaging of metallic samples is possible using fs LIMS, with results in agreement with inductively coupled plasma–collision/reaction interface–mass spectrometry (ICP–CRI-MS) and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS). Riedo’s work has been applied to probe the spatial element composition of three ternary Cu–Sn–Pb model bronze alloys (lead bronzes: CuSn10Pb10, CuSn7Pb15, and CuSn5Pb20) (13). These alloys were selected as representing excellent cathode materials used for electro-organic synthesis involving dehalogenation or deoxygenation of pharmaceutical products. The chemical imaging was performed using spotwise measurements, by ablating material from various surface locations using a 4 × 4 raster array (50 μm pitch distance, with each ablation crater diameter of ~20 μm). Major elements (Cu, Sn, and Pb), minor elements (Ni, Zn, Ag, and Sb) and trace elements (C, P, Fe, and As) were quantified and available for constructing elemental image generation of the solid samples.

Chemical Analysis Using a Miniature Laser-Ablation Mass Analyzer

Part of the work being done by Riedo and coworkers to advance instrumentation for space exploration is to ensure its capability to detect potential extraterrestrial life. The detection of the signs of life on other planets involves the analysis of rock and soil samples for chemical and isotopic composition. Riedo and colleagues have described the method and apparatus for analysis of the chemical composition of naturally occurring microfossils using their miniature LMS system approach (5). The reported chemical analysis studies were conducted with high spatial resolution of approximately 15 μm W x 20–200nm H. The purpose of this investigation was to evaluate micrometer-sized samples for isotope abundance, isotope ratios, and element composition—and to summarize the analysis data into accurate chemical compositional maps of these samples. Results for the chemical mapping were successful, noting that an improved signal to noise ratio is required for accurate isotope ratio determination.

An LMS, designed and built at the University of Bern in the Department of Space Research and Planetary Sciences, was used to measure and characterize the elemental composition, mineralogy, and petrology of an Allende meteorite sample (6). This experiment demonstrated the feasibility for applying LMS to analyze rock samples for remote extraterrestrial applications. The mineralogical and volatile element content of the Allende meteorite—the largest carbonaceous chondrite ever found on Earth, composed mainly of silicates, oxides and sulfides, graphite, carbonates and organic compounds, including amino acids—was able to be accurately determined without sample preparation.

Field studies have been conducted by NASA teams in the Atacama desert (as a Mars analogue site), as part of the Subglacial Lake Exploration: Diversity, Geochemistry, Ecology (SLEDGE) project of the European Union to determine if Earth-based microbes of sparse life in soil samples could be detected based on element analysis (10). The purpose of this study was to test and improve the measurement capabilities of the miniature LMS instrument designed by Riedo and coworkers. For the study, 14 Martian mudstone analogue samples were used—half artificially inoculated with microbes, and half used as abiotic controls. The samples were treated in four different ways—biotic samples were cultured anaerobically and aerobically; abiotic samples were incubated with water, and some remained dry. A few of the samples were irradiated with a high dose of gamma radiation, while others were not irradiated. The study demonstrated that their instrumentation is capable of detecting microbes of sparse life in terrestrial soil samples. “This demonstrated capability allowed him to become a member of NASA teams for field studies in Mars analogue sites,” Wurz said. In summary, this research showed the first results on the detection of biogenic element pat- terns of microbial life using a miniature, space-mission-capable LIMS system.

In 2016, Riedo and his colleagues determined that direct laser desorption MS (LD-MS) was capable of measuring low molecular weight biomarkers in geological samples (14). It was following this 2016 work that the miniature LMS was first designed, built, and tested for in situ elemental and isotope analysis of solids in space research.

Chemical Depth Profiling of Solid Materials

The miniature LMS system has also been developed for applications on earth, such as chemical depth profiling of solid materials. In 2015, LMS was used for high-resolution chemical depth profiling measurements of copper films as a feasibility study to determine its spatial analysis capabilities for semiconduc- tor wafer plating and surfaces of space weathered samples (4). For this work, the custom-developed LMS used an ultrashort pulsed laser system (τ ~ 190 fs, 

 = 775 nm) for ablation and ionization of the sample surface with a subnanometer ablation rate per single laser shot. The instrument demonstrated capabilities for high vertical depth resolution, excellent sensitivity (near 10 ppb), and a dynamic range greater than 108.

In early 2016, Riedo published work describing the structural analysis of plating additives in copper films using LIMS combined with secondary ion mass spectrometry (SIMS) and focused ion beam (FIB) analysis for sample depth profiling of electrodeposited copper films (15). The LIMS technique demonstrated nanometer depth-resolution. Using the combined analytical techniques allowed for a detailed assessment of the additive’s interaction and location within the copper films.

Another published paper by Riedo in 2016 was able to demonstrate high spatial resolution using LMS for direct chemical quantitation of solids (16). In recent years, the analytical methods of choice for chemical analysis of solid materials have been SIMS, LA-ICP-MS, and glow discharge MS (GD-MS). For remote space measurements and for characterization of materials used for manufacturing semiconductors, a miniaturized LMS instrument also provides high spatial resolution measurements of such solids as metal alloys, meteorite specimens, and terrestrial fossils.

In 2015, Riedo and associates published the first paper where pulsed laser ablation was used for high spatial resolution depth profiling for solid materials (18). This work was expanded to two-dimensional surface imaging, and then to 3D composition profiling of solids. These profiles have been shown to demonstrate a nanometer scale vertical spatial resolution, while providing chemical composition information. Such a technique provides detailed information for metal layering and deposition processes as well as solid materials and geological samples.

People always seem to be interested in what makes some individuals so successful. Is it personality, enthusiasm, brilliance, work ethic, organizational skills, communication skills, or the ability to network and successfully establish important collaborative relationships in one’s field? In Riedo’s case, he clearly possesses many of these qualities.

“Andreas is a super enthusiastic person with a great knowledge about his research topics,” Pisonero said. “Andreas is an incredibly friendly person, very talkative and with great communication skills.”

“Andreas is really a hands-on person, gets fully involved in all experimental aspects and data analysis,” Wurz said. “He is also good in including students in his research, from the bachelors level all the way to PhD students.” Wurz further elaborates, “Andreas has strong networking capabilities and successfully established important collaborations in Europe and the US in the research field of astrobiology.”

“I am generally impressed by Andreas’s energy, intelligence and pursuit of his objectives,” Westall said. “In this, he is a hard worker but is also companionable and enjoys social interaction.”

“Dr. Andreas Riedo has a very positive attitude and is always constructive. He is hard working, decisive, and perseverant,” Ehrenfreund said. “He is a very positive and pragmatic person and extremely good at multitasking. He is very dedicated to outreach, which is a rare and important quality for researchers today.”

Westall summed up the feelings of several collaborators: “I am happy to have to opportunity to know and work with Andreas,” he said. “I appreciate his youthful enthusiasm, dynamism and drive. I hope, one day, to see his instruments flying!”

(1) Riedo, A.; Bieler, A.; Neuland, M.; Tulej, M.; Wurz, P. Performance Evaluation of a Miniature Laser Ablation Time‐of‐Flight Mass Spectrometer Designed for In Situ Investigations in Planetary Space Research. 

(2) Riedo, A.; Neuland, M.; Meyer, S.; Tulej, M.; Wurz, P. Coupling of LMS With a FSLaser Ablation Ion Source: Elemental and Isotope Composition Measurements. 

(3) Riedo, A.; Meyer, S.; Heredia, B.; Neuland, M.B.; Bieler, A.; Tulej, M.; Leya, I.; Iakovleva, M.; Mezger, K.; Wurz, P. Highly Accurate Isotope Composition Measurements by a Miniature Laser Ablation Mass Spectrometer Designed for In Situ Investigations on Planetary Surfaces. 

(4) Grimaudo, V.; Moreno-Garc.a, P.; Riedo, A.; Neuland, M.B.; Tulej, M.; Broekmann, P.; Wurz, P. High-Resolution Chemical Depth Profiling of Solid Material Using a Miniature Laser Ablation/Ionization Mass Spectrometer. 

(5) Tulej, M.; Neubeck, A.; Ivarsson, M.; Riedo, A.; Neuland, M.B.; Meyer, S.; Wurz, P. Chemical Composition of Micrometer-Sized Filaments in an Aragonite Host by a Miniature Laser Ablation/Ionization Mass Spectrometer. 

(6) Neuland, M.B.; Meyer, S.; Mezger, K.; Riedo, A.; Tulej, M.; Wurz, P. Probing the Allende Meteorite with a Miniature Laser-Ablation Mass Analyzer for Space Application. 

(7) Boeren, N.J.; Gruchola, S.; de Koning, C.P.; Keresztes Schmidt, P.; Kipfer, K.A.; Ligterink, N.F.W.; Tulej, M.; Wurz, P.; Riedo, A. Detecting lipids on planetary surfaces with laser desorption ionization mass spectrometry. 

(8) Ligterink, N.F.; Kipfer, K.A.; Gruchola, S.; Boeren, N.J.; Keresztes Schmidt, P.; de Koning, C.P.; Tulej, M.; Wurz, P.; Riedo, A. The ORIGIN Space Instrument for Detecting Biosignatures and Habitability Indicators on a Venus Life Finder Mission. 

(9) Riedo, A.; Grimaudo, V.; Aerts, J.W.; Lukmanov, R.; Tulej, M.; Broekmann, P.; Lindner, R.; Wurz, P.; Ehrenfreund, P. Laser Ablation Ionization Mass Spectrometry: A Space Prototype System for In Situ Sulphur Isotope Fractionation Analysis on Planetary Surfaces. 

(10) Riedo, A.; de Koning, C.; Stevens, A.H.; Cockell, C.S.; McDonald, A.; Cede Lopez, A.; Grimaudo, V.; Tulej, M.; Wurz, P.; Ehrenfreund, P. The Detection of Elemental Signatures of Microbes in Martian Mudstone Analogues Using High-Spatial Resolution Laser Ablation Ionization Mass Spectrometry. 

Andreas Riedo of the Physics Institute at the University of Bern, the 2023 winner of the Emerging Leader in Atomic Spectroscopy Award, is using laser ablation–desorption ionization mass spectrometry (LIMS) to chemically analyze complex mineral surfaces found in space exploration.

January 2023

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The 2023 Emerging Leader in Atomic Spectroscopy Award

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