Nitrite poses a serious health risk because it is often present in drinking water, foods, biological systems, and agricultural products, and also acts as an environmental reagent for the production of highly carcinogenic N-nitrosamines upon interaction with proteins. Under mild conditions, tannic acid-protected fluorescence copper nanoclusters (TA-CuNCs) were found to be exclusively quenched in the presence of nitrite ions, and exhibited a good linear relationship with fluorescence intensity with a nitrite concentration within a 20–100 μM concentration window and a limit of detection of 40 nM. In addition, the mechanism associated with the sensitive fluorescence quenching response of nitrite with TA-CuNCs is discussed. The nanoprobe was used to detect nitrite in sausage, and the results were consistent with those obtained using UV-vis spectroscopy, which confirmed that the proposed method can be a rapid and reliable technique for detecting nitrite residues in real samples.

Nitrite represents a serious health-risk factor that often appears in biological, food, and environmental samples (1,2). Nitrite, in the form of sodium nitrite, is often added to meat products to maintain the red color and flavor of fresh meat while providing protection against microorganisms (3,4). The U.S. Environmental Protection Agency (EPA) defines the maximum levels of nitrite in drinking water and meat products to be 1 and 200 ppm, respectively (5). Nitrite is also one of the stable metabolites of nitric oxide, which is a messenger molecule involved in the regulation of numerous physiological and biological processes (6). Therefore, the illegal addition of nitrite to meat products and its potential harm to human health prompt the need for its sensitive detection, especially in commercial meat products. Therefore, a facile, effective, cost-effective, and sensitive method for nitrite detection needs to be developed urgently.

Various analytical methods, including chromatography (7,8), differential pulse voltammetry (9), capillary electrophoresis (10), electrochemical methods (11), and chemiluminescence methods (12), have been reported for nitrite detection. However, most of these methods are time-consuming or use toxic and environmentally unfriendly organic agents. Some of these analytical methods also require an elaborate detection process. To overcome these disadvantages, many organic molecules have been synthesized for use as fluorescent probes for sensitive nitrite detection (13,14). For example, noble metal (silver and gold) nanoclusters have been developed for trace determining of nitrite (15,16). Among the aforementioned techniques, fluorescence is well-suited, because of its sensitivity and simplicity. The fluorescence technique also satisfies the requirements of rapid nitrite screening.

Copper nanoclusters not only share similar characteristics with noble metal nanoclusters, such as fluorescence properties, particle size, and biocompatibility, but they are also inexpensive and stable (17–19). As a result, copper nanoclusters offer great potential as a nitrite-detection method that can potentially be superior to the current method of using noble metal nanoclusters (20–22). In particular, tannic acid-coated copper nanoclusters (TA-CuNCs) have attracted extensive scientific and technological interest because of their molecule-like properties, such as luminescence and unique charging properties (23,24). In this study, TA-CuNCs have been evaluated as fluorescent probes for nitrite detection and shown to possess novel and sensitive detection characteristics over a broad range of pH levels. The sensor, based on TA-CuNCs, was used to detect nitrite in commercially available sausage, illustrating potential practical applications.

Tannic acid was obtained from Sigma Aldrich. Sodium nitrite (NaNO

) was acquired from Beijing Chemical Co. All other chemicals agents were used directly. The water was purified through a Millipore purification system.

Fluorescence spectra were collected using a Shimadzu RF-5301PC fluorescence spectrophotometer. The excitation wavelengths were 360 nm for CuNCs.

UV-vis measurements were made on a Shimadzu UV-3600 spectrophotometer with 1 cm × 1 cm quartz cuvettes (4 mL volume) to determine nitrite content at a 520 nm wavelength. A simulated gastric fluid was mixed with NaCl and HCl. Then, 2 mL of 5 μg/mL sodium nitrite solution was added to 25 mL of simulated gastric fluid, and the mixture was incubated at 37 °C for 30 min. Afterwards, 2 mL of 0.4% sulfanilic acid and 1 mL of 0.2% naphthylamine were added to the mixture, which was then incubated at room temperature. The final volume of each mixture was adjusted to 50 mL.

Aqueous CuSO4 (0.2 mL, 0.1 M) and tannic acid solution (0.1 mL, 1 mM) with 20 mL water was stirred at room temperature. After 5 min, ascorbic acid solution (0.2 mL, 1 M) was added, and the mixture was incubated at 50 °C for 6 h. To remove all unreacted impurity, the product was extensively dialyzed against ultra-pure water for more than 24 h using a 3500 Da dialysis membrane, and the TA-CuNCs were freeze-dried to powder.

The extraction and clean-up procedure for nitrite in sausage was slightly modified from the previously reported investigation (25). For this procedure, a sausage sample (~25 to 50 g) was minced with a grinder and homogenized in a laboratory mixer for 3–5 min. Then, a 5 g portion was removed and extracted with saturated borax solution. Potassium ferrocyanide solution and zinc acetate solution were added to precipitate the protein, followed by 10 min of heating in a boiling water bath. The supernatant was then decanted and placed in another container.

CuNCs were stabilized with TA according to a previously described method (26). The optical properties of the TA-CuNCs were characterized by fluorescence and transmission electron microscopy (TEM). Figure 1a shows that at 360 nm excitation, the fluorescence spectrum of TA-CuNCs shows a strong band at 430 nm. As indicated from the inset of Figure 1a, the fluorescence lifetime of TA-CuNCs was 2.77 ns. The copper nanoclusters were highly dispersible and nearly spherical in shape with an average size of 2.3 nm (Figure 1b). The inset of Figure 1b suggests that the lattice fringes of the products are consistent with metallic copper and have a discerned lattice spacing of approximately 0.2989 nm. All these results suggest that the successful preparation of TA-CuNCs were consistent with the previous reports (27).

Optimization of Conditions for Detecting Sodium Nitrite Using TA-CuNCs

We attempted to modify the conditions of the detection system with the aim of accurately detecting nitrite. The fluorescence intensities of TA-CuNC solutions in the presence of nitrite over the pH range of 3.0–10.0 are shown in Figure 2a. The visible fluorescence quenching occurred in the range of 4.0–8.0, but the fluorescence quenching caused by nitrite can be lower under the extreme pH conditions (strong alkali and strong acid). Thus, TA-CuNCs are able to detect nitrite under mild pH conditions. As shown in Figure 2b, no evident difference in the fluorescence quenching was observed at different reaction temperatures. At room temperature, nitrite was immediately detected after the nitrite was added. Therefore, it can be concluded that the content of nitrite can be detected under mild conditions.

Figure 3 shows that TA-CuNCs had a maximum emission peak at 430 nm. After adding nitrite to the TA-CuNC solution, the fluorescence intensity was quenched completely. A slight red shift of the emission peak was also observed, suggesting that the size or micro-environmental changes surrounding the copper core of TA-CuNCs are associated with the nitrite interaction.

Figure 4 shows that the degree of fluorescence quenching could be gradually intensified with the increased addition of the nitrite ion. The calibration plot revealed a good linear relation between the (

) of the system and nitrite concentration (Figure 4b). The regression equation was (

) = 15.6665C – 197.4892, with a typical detectable nitrite concentration range of 20–100 μM. The limit of detection was calculated to be 40 nM for nitrite when TA-CuNCs were diluted to 0.02 mg/mL. The relative standard deviation was 2.4% obtained from five replicate detections of 50 μM nitrite, indicating good reproducibility of the method.

To test the selectivity of the developed method, we examined the influences of various metal ions and anions (the content of each substance was 50 μM) that may exist in sausage samples, including nitrate, magnesium, sodium, calcium, and potassium ions, as well as ascorbic and glutamic acids (Figure 5). The results indicate that all potentially interfering substances except nitrite had no obvious effect on the fluorescence changes of TA-CuNCs. Therefore, this fluorescence sensor exhibits good selectivity for nitrite and can be used to detect nitrite in real food and environmental samples.

To evaluate the practical application of TA-CuNCs as a fluorescence method for nitrite, the proposed technique was used to detect real samples. Sausage samples were analyzed after extraction and deproteinization. The Griess reagent method (UV-vis) for nitrite detection (28) was used to check the accuracy of the proposed method. The results of the two methods are listed in Table I. The fluorescence probe was found to have high accuracy, sensitivity, and precision, demonstrating the convenient and practical application of the proposed method for sensing nitrite analysis in real samples.

The fluorescence quenching process is actually a process by which the luminescence processes compete with each other to reduce the lifetime of the excited states of the luminescent molecules. Fluorescence quenching can be divided into static quenching and dynamic quenching, according to different quenching mechanisms. Dynamic quenching is produced by diffusion collision between the chromophore and quencher, during the fluorescence lifetime of the excited state. The quenching is caused by energy transfer or charge transfer. Static quenching is caused by a coordination reaction between the fluorescent molecules and fluorescent quencher molecules in the ground state, which results in a finite degree of binding. Structural complexes, which themselves cannot emit light, lead to fluorescence quenching of fluorescent molecules (29). To elucidate the mechanism of fluorescence quenching, the fluorescence temperature data were analyzed by the Stern-Volmer equation:

where the fluorescence intensity of TA-CuNCs with or without nitrite is 

 is quenching rate constant, and the fluorescent lifetime of TA-CuNCs is about 2.77 × 10

 s (see Figure 1). The concentration of the quenching agent is marked as [Q], and 

 at different temperatures (Figure 6 and Table II). There was a good linear relationship exhibited between 

/F and [Q]. Table II shows that the KSV value of TA-CuNCs and nitrite decreases with the increase of temperature, and the KSV is much smaller than the maximum diffusion collision quenching constant of biological macromolecules, which is 2.0 × 1010 L/mol x s. As a result, the possibility of dynamic quenching is increased, and the dissociation of the complexes formed often happens. Thus, the possibility of static quenching is reduced. It is more likely that the quenching of TA-CuNCs by nitrite ions involves a dynamic quenching process (30).

Figure 7 shows that there was a good linear relationship between 

) and 1/[Q] as a function of temperature. The effective quenching constant 

 can be calculated from the modified Stern-Volmer equation, which is displayed in equation 2:

It can be seen from Table III that a good linear relationship exists, and that the 

 value decreases gradually with an increase in temperature. This trend is consistent with 

, which is further consistent with a quenching process that belongs to dynamic quenching. The thermodynamic parameters are listed in Table III. Δ

 < 0 indicate that nitrite and TA-CuNCs are Van der Waals forces or hydrogen bonding forces (31,32).

A quantitative and confirmatory method for the determination of trace levels of nitrite ion in sausage over a broad pH range was developed based on tannic acid-stabilized CuNCs (Scheme 1). In addition to the detailed exploration of the fluorescence quenching mechanism, the most efficient quenching of TA-CuNCs induced by nitrite was ascribed to a Van der Waals force or hydrogen bonding process. The methodology described was successfully utilized as a probe to detect nitrite ion in sausage, which was further confirmed using the Griess reagent method (UV-vis). The as-synthesized CuNCs are also suitable for future application in other foods because of their good sensitivity and low toxicity.

The present work was supported by the projects of NSFC (Nos. 21902058).

(1) M.J. Moorcroft, J. Davis, and R.G. Compton, 

(4) H.J. Ahn, J.H. Kim, C. Jo, H.S. Yook, and M.W. Byun, 

(5) United States Environmental Protection Agency, 

National Primary Drinking Water Regulations: Contaminant Specific Fact Sheets, Inorganic Chemicals 

(Consumer Version, Washington, DC, 2009).

(6) S. Moncada, R.M.J. Palmer, and EA. Higgs, 

(7) Y.T. Li, J.S. Whitaker, and C.L. McCarty, 

(8) L.J. He, K.G. Zhang, C.J. Wang, X.L. Luo, and S.S. Zhang, 

(9) H. Moshage, B. Kok, J.R. Huizenga, and P.L. Jansen, 

(10) F.D. Betta, L. Vitali, R. Fett, and A.C.O. Costa, 

(11) P. Wang, M.Y. Wang, F. Y. Zhou, G.H. Yang, L.L. Qu, and X.M. Miao, 

(12) J. Wu, X. Wang, Y. T. Lin, Y. Z. Zheng, and J. M. Lin, 

(13) B. Gu, L. Y. Huang, J.L. Hu, J.J. Liu, W. Su, X.L. Duan, H.T. Li, and S. Z. Yao, 

(14) Y. M. Shen, Q.J. Zhang, X.H. Qian, and Y.J. Yang, 

(15) C. Chen, Z.Q. Yuan, H.T. Chang, F.N. Lu, Z.H. Li, and C. Lu, 

(16) Q.L. Yue, L.J. Sun, T.F. Shen, X.H. Gu, S.Q. Zhang, and J.F. Liu, 

(17) J. Feng, Y.L. Chen, Y.X. Han, J.J. Liu, S.D. Ma, H.G. Zhang, and X.G. Chen, 

(18) A.L. Han, L. Xiong, S.J. Hao, Y.Y. Yanga, X. Li, G.Z. Fang, J.F. Liu, Y. Pei, and S. Wang, 

(19) N.D. Tan, J.H. Yin, Y.Q. Yuan, L. Meng, and N. Xu, 

(20) H.Y. Cao, Z.H. Chen, H.Z. Zheng, and Y.M. Huang, 

(21) Q. Tang, T.T. Yang, and Y.M. Huang, 

(22) H.B. Rao, W. Liu, Z.W. Lu, Y.Y. Wang, H.W. Ge, P. Zou, X.X. Wang, H. He, X.Y. Zeng, and Y.J. Wang, 

(23) Q. Liu, Q. Lai, N. Li, and X.G. Su, 

(24) R.S. Aparna, S.S. Syamchand, and S. George, 

(26) H.Y. Cao, Z.H. Chen, H.Z. Zheng, and Y.M. Huang, 

(27) X.L. Cao, X. Li, F.X. Liu, Y.N. Luo, and L.Y. Yu, 

(30) H.S. Geethanjali, D. Nagaraja, R.M. Melavanki, and R. A. Kusanur, 

(31) C.Q. Jiang, M.X. Gao, and X.Z. Meng, 

 are with the College of Chemical and Pharmaceutical Engineering, at the Jilin Institute of Chemical Technology, in Jilin City, in the People’s Republic of China. 

 is with Jilin Petrochemical Company, in Jilin City, in the People’s Republic of China. Direct correspondence to: 

Articles

Peer-Reviewed Research

Nitrite poses health risks. This study evaluates the results of using tannic acid- protected fluorescence copper nanoclusters (TA-CuNCs) to detect nitrite in food.

A Facile Synthesis of Tannic Acid–Protected Copper Nanoclusters and the Sensitive Fluorescence Detection of Nitrite Ion Under Mild Conditions

Our annual review of products introduced during the past 12 months, along with an assessment of the overarching trends.

We are pleased to present our annual review of new products. As has been the case for many years now, this annual review includes products launched not only at the annual Pittsburgh conference (“Pittcon”), but also throughout the preceding year.

Nevertheless, Pittcon remains an important source of new product announcements. This year’s Pittcon, however, was held online—a first for the event—because of the Covid-19 pandemic. In the online format, you could attend technical presentations, keynote talks, short courses, workshops, and networking sessions, as well as see exhibitor demonstrations, attend the employment bureau, and—related to our interests and purposes here—you could visit exhibits and talk to exhibitor representatives. The main difference this year was that we couldn’t unexpectedly run into old friends while traversing the halls or aisles. We also could not participate in a “hands-on” demonstration of equipment.

Presumably because of the online format, there was a decrease in the size of the exposition this year (only 179 exhibitors, compared to 787 last year) and the absence of several large vendors. This year, again presumably because of the online format, no product awards were given out.

There was a significant change in attendance at the conference compared to previous years, but we have to acknowledge that we are comparing the “apples” of a live conference with the “oranges” of an online one. The overall attendance in 2020 was 12,841 registered participants. Although it was clear from the live attendance numbers visible in the online platform for this year’s event that the numbers were comparatively quite small this year, generally around 1000 at any given time, official attendance figures for 2021 were not available by our deadline. Because most features of the conference are available on demand through June 12, the conference organization will not have final numbers until then.

The review that follows is categorized by wavelength region or type of spectroscopy. This arrangement is designed to allow readers to compare instruments from different manufacturers, although this process sometimes compares handhelds and other portable instruments with high-end benchtop research tools. Our included categories fluctuate from year to year, depending on trends in new product launches. The categories appearing in this year’s review are:

Mid-infrared (Mid-IR) and terahertz (THz) spectroscopy

Near infrared (NIR) spectroscopy Raman spectroscopy

As we have reported in previous reviews, manufacturers have recently been producing instruments that incorporate two or more different, and sometimes disparate, technologies. Given that the number of such instruments has been increasing every year, we considered whether a new approach to this question was warranted. Ultimately, we decided to assign a primary category for each product, but also list potential alternate categories that the product might plausibly be listed under. For an ICP-MS instrument, for example, which could plausibly fit under either the “Atomic Spectroscopy” (for the ICP) or the “Mass Spectrometry” category, we have assigned it to the Atomic Spectroscopy category, but in that table, we show the secondary category in parentheses, in the left-hand column, below the company name, like this:

We also employed a similar label for accessories, indicating the primary technology that the accessory is intended for in parentheses.

As in the past, accessories are tools used in conjunction with an instrument, such as sample preparation or attenuated total reflectance (ATR) devices, whereas components, such as lasers or detectors, are used within an instrument. Yet no matter how we present them, there are always marginal cases, such as where a product is so large and integral to the operation of the analytical system that it is unclear where the concept of an “accessory” ends and an “instrument” begins.

For all of these reasons, even the manufacturer is sometimes unsure about what category a given device belongs to. Sometimes, the distinction depends on the perspective of the observer. An example of this is gas chromatography–infrared spectroscopy (GC–IR). From the point of view of the spectroscopist, the GC is “simply” a very sophisticated sample preparation accessory, although from the point of view of the chromatographer, the spectrometer is “merely” a very complicated detector!

The software category includes programs for instrument control, data collection, and data processing, as well as products for storage and transmission of data. The category also includes collections of data, such as databases (libraries) of spectra, as well as collections of calibration models used in conjunction with the still developing field of chemometric algorithms that analyze the data.

As is our custom, Table I lists the categories that the various companies offer instruments in.

Typically, our vendor surveys answer our question about trends in many different ways. The 2021 surveys, however, show a consistent observation about the importance of speed and efficiency. Although similar to comments given over many years, this theme was more noticeable in 2021. Many laboratories downsized or worked with limited staffing in the last year, requiring those who remained to be more productive. Further, as older subject matter experts (SMEs) retired, they were either not replaced or were replaced with less-experienced workers who had little time to gain the benefit of the SMEs’ experience. In addition, those on-site workers were often present in shorter shifts or limited days, as well as performing a lot of remote work, meaning they had to plan and execute their analyses carefully.

These variables resulted in instrument specifications growing more aggressive, with requirements like more automation, intense sources, higher signal-to-noise (S/N), and more-sensitive detectors, resulting in faster data collection. Also, software (particularly the offline analytical type) became even more prominent in instrument sales. Finally, virtual training (both general webinars and instrument-specific training on operations) became very important. Even vendors who did not specifically mention the “faster, more efficient” theme implied this through their product descriptions.

We do not expect this trend will change, even if more people return to the physical workplace for longer hours. The “need” to work at home experienced during the pandemic has transitioned to the “ability” to work at home (as a viable work option, irrespective of need), through various other sharing platforms. Many instruments can now be operated remotely, with autosamplers enabling unattended throughput. Laboratory staff need to be physically present only long enough to set up a batch and start the process; they can then monitor and tweak the process remotely. Even academic teaching laboratories are reaping the benefits of remote instrumentation, because students can now check the progress of a measurement from the library or their dorm rooms.

Another outgrowth of the loss of SMEs has been the emphasis placed on digital science and, more specifically, machine learning. Broadly, this tool enables a system (instrument plus computer plus software) to derive relationships between data and answers that can be reproduced in the absence of human intervention, enabling the system to make “intelligent” decisions about specific characteristics of a sample, such as its usability in a specific application, or an identification based on large datasets. We feel strongly this will be a key driver in the future workspace as the machine learning algorithms improve and become more broadly applicable (consider how online shopping proposes new things based on your past choices; the same logic can be applied to a production process).

We see fewer application-specific analyzers appearing this year, although some fields, like cannabis and microplastics, are attracting attention. In many cases, existing tools are being combined with new software to address these fields, such as the innovations from multiple vendors implementing microplastics analysis onto Raman, FT-IR, and quantum cascade laser (QCL)–based microscopy systems.

Handhelds and portables continue to appear, but not with the same ubiquity as a few years back when we noted every aisle at Pittcon seemed to have a handheld Raman or NIR tool on display. Many articles have appeared in the literature, and in this journal specifically, about the benefits of the handhelds and portables. There has been less discussion about the performance differential between handheld and laboratory instruments; however, this difference is largely driven by the different purposes and applications of the two types of instruments (“What is this pile of white powder? Is it dangerous?” versus “I need to analyze a tiny defect in a sheet of polymer or discolored flecks in an otherwise homogeneous product”).

Below, we highlight new introductions in each product category. Individual tables provide more detail for the products mentioned. Table I contains the index of companies and the categories where their products appear.

Exum Instruments, Inc. introduced Massbox, the first commercial instrument combining laser ablation and laser ionization under vacuum.

Lightigo exhibited FireFly, an instrument specializing on chemical imaging of solid samples and featuring a motorized objective turret, laser microfocus, and long depth of field. Lightigo’s FireFly could have also been placed in the “Imaging” category.

PerkinElmer, Inc. presented two instruments. The first is the Avio 560, an inductively coupled plasma–optical emission spectrometer (ICP-OES) instrument. The second is the NexION 5000 Multi-Quadrupole ICP-MS, the first ICP-MS instrument in its category to boast four quadrupoles, and engineered to meet and exceed the demanding requirements of ultratrace elemental analysis.

Thermo Fisher Scientific launched the Neoma Multicollector ICP-MS, featuring a new detector array that covers the broadest range of isotopic applications with Qtegra Intelligent Scientific Data Solution (ISDS) software.

See Table II for more information about atomic spectroscopy instruments.

Cubert GmbH demonstrated the Ultris X20, a UV–vis-NIR imaging spectrometer and hyperspectral snapshot camera capable of capturing a hyperspectral image (x, y, lambda) at very high resolution within a millisecond. Cubert GmbH’s product could also fit into the “UV-vis” and “NIR” categories.

Greateyes had two products on display: Alex, a low-noise charged-coupled device (CCD) camera series of highly sensitive, cooled cameras with vacuum flange equipped with ultralow noise 18-bit readout electronics for imaging applications in the vacuum ultraviolet (VUV), extreme ultraviolet (EUV), and X-ray range up to 20 keV; and ELSE, a low noise CCD camera that integrates cutting-edge low-noise electronics and ultra-deep cooling technology. The Greateyes products could also apply to the “X-Ray” category.

Monstr Sense Technologies, LLC showed Bigfoot, with ultrafast optics and radio-frequency electronics to extract weak ultrafast signals from strong excitation background light. Bigfoot could also be included in the “Raman spectroscopy” category.

Nanobase, Inc. introduced the XperRF, a hybrid Raman spectroscopy microscope instrument and a transmission spectrometer for >90% spectrum peak efficiency. This product could also fall into the “UV-vis” and “Raman spectroscopy” categories.

Pembroke Instruments, LLC introduced the SWIR-200, a short-wavelength infrared (SWIR) microscope featuring a flexible design supporting a wide range in the field of view, magnification, and working distance to the sample. This product could fall into the “NIR” category.

Princeton Infrared Technologies, Inc. showed a 2nd-generation 1280 SciCam, an InGaAs SWIR camera that is the only International Traffic in Arms Regulations (ITAR)-free 1.3 MegaPixel-cooled SWIR camera that exhibits high photo response uniformity and low dark current.

Surface Optics Corporation showed its SOC760 Hyperspectral Imaging System uniquely suited for laboratory and ground-based applications requiring high-resolution spectral data collection for the full visible near infrared (vis-NIR). Their product could also apply to the “UV-vis” and “NIR” categories.

See Table III for further details about Imaging instruments.

The Hiden Analytical SIMS-ToF Secondary Ion Mass Spectrometer has the high sensitivity, speed, and data density depth profiling capability of a quadrupole secondary ion mass spectrometry (SIMS) instrument and the surface specificity, mass resolution, and large-molecule detection of a time-of-flight (ToF) SIMS system.

The Thermo Fisher Scientific Orbitrap Exploris 240 Mass Spectrometer features a fast-scanning high-field Thermo Scientific Orbitrap mass analyzer, positive–negative mode switching for comprehensive sample coverage, and one-click calibration and method templates for fast instrument setup and ease of use.

Agilent Technologies, Inc., Exum Instruments, Inc., and PerkinElmer, Inc. also have instruments that could apply to this category; they were all placed in the “Atomic spectroscopy” category.

See Table IV for further details about Mass spectrometry instruments.

PerkinElmer, Inc. presents three FT-IR instruments. The Spectrum Two+ is a compact, powerful, and portable FT-IR spectrometer for routine compositional and quality analyses, providing fast and accurate results. The Spectrum 3 FT-IR Spectrometer, is a tri-range instrument with full integration. The EGA 4000 is the world’s first fully integrated thermogravimetric analysis-infrared spectrometry (TG-IR) system for evolved gas analysis (EGA). The Spectrum 3 could also apply to the “NIR” category.

See Table V for further details about Mid-IR instruments.

Galaxy Scientific Inc. introduced the QuasIR 2000 with a large area diffuse reflectance probe fiber optic FT-NIR spectrometer; this probe is designed to enable more accurate and repeatable NIR measurements of inhomogeneous samples.

Metrohm USA’s DS2500 Liquid Analyzer features smart accessory technology, integrated temperature control to 80 °C, and automatic background correction.

Sensors Unlimited has a high-speed, extended InGaAs photodiode linear array that offers extended wavelength range of 1.1–2.6 μm. This product could also apply to the “Components” category.

Surface Optics Corporation’s 410-Solar-i Portable Vis-NIR Reflectometer features a battery-operated handheld reflectometer for portable solar reflectance and absorbance measurements. This product could also apply to the “UV-vis” category.

Viavi Solutions Inc. presented three NIR instruments. The MicroNIR PAT-L is specifically designed for liquid applications as an immersion NIR spectrometer that features multiple configurations and various mounting options for diverse applications. The MicroNIR PAT-Ux features good manufacturing practice (GMP)–compliant software with an optional open platform communications (OPC) add-in and a rapid acquisition time. The MicroNIR PAT-Wx is rated for hazardous locations and certified as being compliant with ATmospheres EXplosible (ATEX), International Electrotechnical Commission System (IECEx), and National Electrical Code (NEC) requirements.

See Table VI for further details about NIR instruments.

Metrohm USA presented two Raman spectrometers. The Mira P Raman spectrometer makes it possible to build custom analytical methods that capture variations of complex natural product starting materials for biopharmaceutical production. The Misa Raman spectrometer is a portable analyzer system used for rapid, trace-level detection and identification of food additives and contaminants, and features a small footprint and long battery life.

Nanobase, Inc. showed its XperRF hybrid Raman spectrometer, which is a Raman microscope with fluorescence lifetime imaging and TCSPC features. It has a transmission spectrometer for over 90% spectrum peak efficiency. This product could also fall in the “UV-vis” and “Imaging” categories.

Ocean Insight presented the QE Pro-Raman+, which is a modular spectrometer for 785 nm Raman excitation applications. The QE Pro-Raman+ is a high-sensitivity instrument with a spectral range from 150 to 3000 cm

, plus low noise electronics and a TEC-cooled optical bench.

The Renishaw Virsa Raman Analyzer features fiber optic probes equipped with LiveTrack focus-tracking technology, enabling the analysis of microscopic areas of large objects with irregular surfaces, and enabling the measurement of large samples that will not fit under a conventional microscope.

Wasatch Photonics showed the WP 532 EXR, an extended-range Raman spectrometer that offers high signal, fast measurements, and low limits of detection. The design uses the company’s VPH transmission gratings and an f/1.3 input for maximum signal collection. The WP 532 EXR could also apply to the “UV-vis” category.”

See Table VII for further details about Raman instruments.

ACD/Labs introduced the Spectrus JS, which is cross-platform software that works on Windows, MacOS, and Linux. Spectrus JS (JavaScript) is the first commercially available browser-based 1D and 2D NMR data processing application. The Spectrus JS could have also formed an “NMR” category.

Eigenvector Research, Inc. has five new updated software packages: Solo version 8.9.1 Stand Alone Chemometrics Software; PLS_Toolbox version 8.9.1 Chemometrics Software for use with Matlab; MIA_Toolbox version 3.0.9 Advanced Hyperspectral Image Analysis for use with PLS_Toolbox and Solo; Solo_Predictor version 4.0.5, which is a standalone prediction engine for use with PLS_Toolbox and Solo models; and Model Exporter version 3.7, which is a standalone prediction engine for use with PLS_Toolbox and Solo models.

Microtrac MRB, part of Verder Scientific, provides Dimensions Software for the Camsizer series. The Dimensions program is a sleek and modern particle-characterization software for the Camsizer imaging instruments.

Operant LLC has Peak Spectroscopy Software for Optical Spectroscopy that reads and converts more than 60 spectroscopy file formats. It includes library search, spectral manipulations, and many more functions.

Thermo Fisher Scientific promoted its SolstiX X-ray diffractometer software that is a seamless integration with Windows authentication, protected folder for data storage, complete audit trail in time-stamped database, and tamper-proof e-signatures in all files.

Wiley introduced five new software products: A GC–MS library for biologically and environmentally important organic compounds; the Wiley Registry of Mass Spectral Data 12th edition; the Wiley Registry 12th Edition of the NIST 2020 Mass Spectral Library; the KnowItAll 2020, which contains spectroscopy software and spectral libraries; and AntiBase, a Natural Compound Identifier.

See Table VIII for further details about software.

Ibsen Photonics A/S showed the new Pebble Vis-NIR spectrophotometer. Pebble spectrometers combine a compact form factor of 20 x 15 x 8 mm with high sensitivity and environmental ruggedness, based on Ibsen’s proven diffraction grating technology. This product could also have been included in the “NIR” category.

McPherson’s 251MX is a compact spectrometer with a VUV detection range (50~200 nm) optimized around 120 nanometers. It has been updated to provide improved efficiency over a wider range.

Ocean Insight has a liquid transmission measurement system (LTMS) in-line transmission spectrometer. LTMS is an industrial-grade, IP67 transmission– absorption platform suitable for manufacturing environments.

See Table IX for further details about UV-vis instruments.

Featured Article

Our annual review of new products for atomic and molecular spectroscopy, including details by category and highlights of overarching trends.

2021 Review of New Spectroscopic Instrumentation

This year’s Atomic Spectroscopy Award recipient is L. Robert Baker, whose research focuses on time-resolved, ultrafast X-ray spectroscopy and nonlinear optics for understanding interfacial charge transfer and chemical reactions at surfaces.

L. Robert Baker is an associate professor at The Ohio State University in the Department of Chemistry and Biochemistry. His research focuses on ultrafast, time-resolved X-ray spectroscopy and nonlinear optics for understanding interfacial charge transfer and chemical reactions at surfaces. He is the winner of the 2021 Emerging Leader in Atomic Spectroscopy Award. The award was presented to Baker on February 24 at the Spectroscopy Virtual Symposium, “Atomic Spectroscopy in Practice,” where he gave a plenary lecture. The Spectroscopy Emerging Leader in Atomic Spectroscopy Award recognizes the achievements and aspirations of a talented young atomic spectroscopist who has made strides early in his or her career toward the advancement of atomic spectroscopy techniques and applications. The winner must be within 10 years of receiving his or her highest academic degree in the year the award is granted, and the winner is chosen by an independent committee.

Baker earned his undergraduate BS degree in chemistry and his MS in physical chemistry from Brigham Young University and received his PhD in 2012 in physical chemistry from the University of California, Berkeley, under Professor Gabor A. Somorjai. His thesis title was, “Charge Transfer and Catalysis at the Oxide–Metal Interface.” Following postdoctoral research at the University of California, Berkeley (mentored by Professor Stephen R. Leone), he then became an assistant professor at The Ohio State University in 2014. In 2019, he was appointed an associate professor of chemistry. He serves as a principal investigator of the NSF National eXtreme Ultrafast Science (NeXUS) facility. His awards include the Camille Dreyfus Teacher–Scholar Award, the Air Force Office of Scientific Research Young Investigator Award, a Department of Energy Early Career Award, and the Young Innovator Award in NanoEnergy.

-index of 18, and an i10 index of 24, and over 1200 citations in Google Scholar, Baker has published research in high-impact journals, such as Journal of 

. Baker’s research explores the physics and chemistry of transition metal oxide catalyst surfaces using ultrafast extreme ultraviolet refection-adsorption spectroscopy. He has used this technique to study the surfaces of single and mixed metal oxides. Such materials are used in electron transfer, energy conversion, electrochemistry, and catalysis.

As a PhD student at the University of California, Berkeley, Baker worked with Professor Somorjai using sum frequency generation (SFG) vibrational spectroscopy combined with nanomaterials chemistry to investigate heterogeneous catalytic reactions on metal oxide surfaces. Following his PhD studies, he undertook postdoctoral work with Professor Leone where he learned high harmonic transient absorption spectroscopy for studying ultrafast electron dynamics. This technique is based on laser-driven high harmonic generation, where near-infrared (IR) photons from an ultrafast laser pulse are upconverted to high energy photons that can reach even into the soft X-ray region of the electromagnetic spectrum. This technique provides extremely fast laser pulses in the extreme ultraviolet (XUV) and X-ray spectral regions. Such capabilities provide time-resolved and atom-specific information when performing transient adsorption experiments.

After Baker moved to The Ohio State University in 2014, he developed a new version of this spectroscopy based on higher harmonic generation that is able to specifically measure surface dynamics in metal oxides and other semiconductors. After several years, Baker refined this concept into what is now called XUV reflection–adsorption spectroscopy. When performed at grazing angles, this spectroscopic measurement technique is capable of obtaining time-resolved information on surface electron dynamics with atom- or element-specific resolution. Unlike traditional XUV transmission measurements, which are limited to ultrathin films, this technique may be performed even on bulk samples, making these measurements accessible to a broad range of real-world materials. At The Ohio State University, Baker’s research group is focused on using this technique to study electron dynamics and charge transfer in photocatalytic materials with applications for improving solar energy conversion.

Several recent papers by Baker, published in 2020, explore metal oxide chemistry and catalysis. This research continues to expand the exploration of the surface electronic behavior of metal oxides for photocatalysis using XUV reflection–absorption spectroscopy as well as plasmon-enhanced vibrational SFG spectroscopy.

Baker has used XUV reflection–absorption spectroscopy to study the surface electronic structure and carrier kinetics in photocatalytic transition metal oxides (1). Specifically, the dynamics of small polaron formation at hematite surfaces demonstrates that the rate of carrier self-trapping is slower than in the bulk because of the greater lattice reorganization energy required for surface polaron formation. Note that in condensed matter physics polarons represent the concept of quasiparticles used to understand the interactions between electrons and atoms. Although polarons exist throughout the bulk of a material, their energetics and transport properties are unique at a surface or interface, and these unique differences, although difficult to probe, govern the energy conversion efficiency of a catalytic system. Baker’s work shows that ultrafast XUV reflection–absorption spectroscopy can provide direction visualization of these important processes in real-time, leading to a better understanding of how to control charge transport properties at interfaces.

In situ, plasmon-enhanced vibrational sum frequency generation (SFG) spectroscopy was applied by Baker and colleagues to directly observe carbon dioxide electro-reduction on gold surfaces (2,3). Nonlinear interactions between IR and near-infrared (NIR) laser beams were used to observe the gold and electrolyte interface during active electrocatalysis and to show that the rate-determining step for this reaction is CO

 adsorption. It is important to note that this type of spectroscopy provides the capability for direct observation of interfacial processes that govern the surface kinetics of electrocatalysis. SFG vibrational spectroscopy is a powerful tool for observing interfaces, but applying it to in situ electrocatalysis can be a challenge. Baker showed that this can be effectively accomplished by using plasmon resonance to couple the electric fields of light through the electrode to measure low concentration intermediates at the electrode–electrolyte interface with high sensitivity (3). These findings reveal important details about how the composition and structure of the electrolyte actually controls catalytic chemistry on the electrode surface (2).

Baker and colleagues have also edited a special issue of the 

 on the topic of metal oxide chemistry and catalysis, which included both theoretical and experimental contributions from many of the leaders in this exciting area (4). Analytical methods delineated in this special issue included ambient pressure X-ray photoelectron spectroscopy (XPS), ambient pressure scanning tunneling microscopy (AP-STM), in situ X-ray diffraction (XRD), in situ vibrational spectroscopy, photoemission electron microscopy (PEEM), solid state nuclear magnetic resonance (ssNMR), Mössbauer spectroscopy, and cluster anion photoelectron spectroscopy (PES).

In assessing Baker’s impact on the field, it is useful to look at both his mostly highly cited papers as well as those considered most important by his mentors and peers.

In 2015, as an assistant professor at Ohio State, Baker and coworkers published a paper reviewing the role of hot electrons and metal–oxide interfaces in surface chemistry and catalytic reactions (5), which has 201 Google Scholar (G.S.) citations. This review presents and discusses the fundamental mechanisms of energy dissipation and conversion, which occur on the material surfaces and interfaces. Technical areas studied in this review include analytical and detection methods for hot electrons and for observation of energy dissipation mechanisms. It was noted that hot electron flux is highly correlated with catalytic reaction turnover rates. It was also noted that charge transfer and ion chemistry represent one of the fundamental mechanisms of chemical activation on surfaces.

As a postdoctoral researcher at the University of California, Berkeley, in 2012, Baker used SFG vibrational spectroscopy to investigate strong metal–support interactions (SMSI) in Pt/TiO

 catalysts (6). Baker and coauthors were the first researchers to report the use of SFG to study oxide–metal interfaces during catalytic reactions and have accumulated 173 G.S. citations to date. The results of this study demonstrated that charge transfer from the TiO

 catalyst occurs by an acid–base mechanism, and this charge transfer controls the reaction yield and selectivity of furfuraldehyde hydrogenation.

In 2014, as a continuation of other SFG vibrational spectroscopy studies carried out at Berkeley, Baker and colleagues performed studies of crotonaldehyde hydrogenation in the presence of supported platinum nanoparticles (7). This paper, with 93 G.S. citations, further demonstrated how to determine the interaction between supported platinum nanoparticles, which controls the catalytic performance of Pt/TiO

 catalysts. The study indicated that a unique reaction pathway was identified for Pt/TiO

, which selectively produces the desired product, crotyl alcohol.

 publication, Baker and coworkers used plasma fluorine insertion to generate highly 

-type titanium oxide (8). Such a true demonstration of the 

-type doping of titanium oxide, which precludes formation of midgap states, would allow expansion of the use of metal oxides for charge-based devices, such as re-programmable logic devices and reconfigurable built-in memory for computers.

Baker’s nomination for this award, made in 2018, cited several publications, five of which are highlighted below. These studies, from 2017 through 2018, focused on multiple aspects of physical chemistry, chemical physics, and engineering.

As mentioned above, one of Baker’s key achievements to date has been his development of the analytical technique of near grazing-angle XUV reflection–absorption (XUV-RA) spectroscopy, specifically for the study of electron dynamics (9). This technique is capable of measuring transient oxidation state changes in real-time, with surface sensitivity, and with element-specific resolution.

Baker and colleagues applied ultrafast XUV reflection–absorption spectroscopy to demonstrate that surface charge localization and small polaron formation in hematite (α-Fe

) occur via a highly correlated process (10). This research provides information that may enable improvements in the modification and potential utilization of earth-abundant resources for more efficient and practical solar energy panels.

Using femtosecond XUV reflection–absorption spectroscopy, Baker and coworkers directly observed the formation of photoexcited electrons and holes in the photocatalytic materials—hematite (Fe

), and nickel(II) oxide (NiO) (11). The ability to observe charge localization in these materials on an ultrafast time scale (femtoseconds) may demonstrate correlations between excited state electronic structure and photochemical energy conversion, which are essential properties for understanding and applying these metal oxides as photocatalysts.

Another potential naturally occurring photocatalytic material, delafossite, is a copper iron oxide mineral with the formula CuFeO

. Baker and colleagues investigated the potential of using this metal oxide as a solar photocathode for carbon dioxide conversion. By using XUV reflection–absorption and optical spectroscopy in combination with density functional theory (DFT) calculations (12), this research was able to track the element-specific electron and hole dynamics in CuFeO

 and compare its photocatalytic properties, as a solar photocathode, to those for Iron (III) oxide (Fe

Nickel(II) oxide (NiO) is a standard material used for solar energy devices. In solar panels, a photoactive layer performs light absorption, which is followed by a charge separation facilitated by a NiO hole collection layer. Baker prepared a model hole injection structure by depositing a thin layer of NiO on an Fe

 substrate. Then by using XUV-RA spectroscopy, the detailed dynamics of exciton dissociation and hole injection into NiO was studied (13).

Numerous collaborators and mentors have praised Baker’s academic work and scholarship—noting he achieved a cumulative grade point average of 4.0 in all of his graduate studies, and has published multiple high impact research papers.

“Robert Baker was one of my most brilliant graduate students,” said Professor Somorjai. “Baker’s specialty fields are spectroscopy, surface chemistry, and catalysis. He is an excellent spectroscopist and the combination of all these fields will assure that he will be the discoverer of many important chemical phenomena.”

Heather Allen is the Dow Professor and an Ohio State Distinguished Scholar at The Ohio State University. She was impressed with Baker when she first met him during his interview at the university in 2013.

“I feel a special appreciation for Robert in that I know what a treasure he is in so many ways in addition to his intellect, and his strong ethic,” Allen said. “For me, it is too early to say what his legacy will be; however, he is firing on all cylinders and in multiple directions such that he is already making his mark in a number of research areas.”

Louis DiMauro, a professor of physics at The Ohio State University and the co-Director of the National Science Foundation (NSF) NeXUS facility with Baker, has been working with Baker for almost 5 years. His first meeting with Baker also had an impact.

“I was immensely impressed by Robert’s maturity,” DiMauro said. “This was the beginning of an enjoyable collaboration.” DiMauro believes “Baker will become a leader in ultrafast X-ray science and will continue to develop and exploit XUV absorption–reflectivity spectroscopy for material science.”

Scott Cushing is an assistant professor at the California Institute of Technology (Caltech) and has now known Baker for three years. As a postdoctoral researcher, Cushing had worked with a transient XUV system that Robert had helped to pioneer. Now, the two work together closely in the field of transient XUV spectroscopy, particularly as it relates to polarons and solid state photodynamics. Considering Baker’s greatest contributions, Cushing noted that Baker proved that transient extreme ultraviolet (XUV) spectroscopy is a critical tool in understanding the photodynamics of transition metal containing solids.

“He has provided new insights into everything from charge transport in junctions, to surface chemistry, to polaron dynamics by the technique he helped to create,” Cushing said.

“Professor Baker is an emerging star in his field,” said Susan V. Olesik, the Dean of Natural and Mathematical Sciences at The Ohio State University. Olesik continued to describe Baker’s work toward the development of tabletop X-ray spectroscopy as an extremely challenging experimental endeavor. “He has not only succeeded at developing this novel experimental capability, but he has pioneered the application of this method for the study of electron dynamics at surfaces within the first five years of his career. Given his early success in this area, Robert is on the arc of a career that will help to define and establish the field of surface photochemical dynamics.”

Paul S. Cremer agrees. Cremer is the J. Lloyd Huck Chair in Natural Sciences at Penn State University and an associate editor for the Journal of the American Chemical Society.

“Professor Baker is a rising star in the fields of physical chemistry, surface science, catalysis and spectroscopy,” he said. “Indeed, he is a brilliant young scientist.”

The National eXtreme Ultrafast Science (NeXUS) Facility 

Baker is the lead principal investigator in a new NSF effort for a National eXtreme Ultrafast Science (NeXUS) Facility. This facility has plans to generate extreme ultraviolet (XUV) and soft X-ray pulses with durations from femtoseconds (1 × 10−15 s) to attoseconds (1 × 10−18 s). The NeXUS system is under development now. The facility will support experiments in time-resolved molecular imaging by laser-induced electron diffraction (LIED), attosecond science (ATTO), time-resolved X-ray absorption spectroscopy (XAS), time-resolved X-ray reflection spectroscopy (XRS), time-resolved X-ray magnetic circular dichroism (XMCD), time-resolved angle-resolved photoemission spectroscopy (ARPES), and time-resolved scanning tunneling microscopy (STM).

Colleagues noted the importance of this project.

“The NeXUS facility he is building at Ohio State is a complete game-changer for the field of XUV spectroscopy,” said Josh Vura-Weis, an associate professor of chemistry at the University of Illinois at Urbana-Champaign, who was a postdoctoral researcher together with Baker in the Berkeley Leone group. “I applaud his vision and skill to bring this to reality.”

“The NeXUS Facility is a huge commitment of time; it is selfless service to the chemistry and physics communities,” Allen added.

Given Baker’s accomplishments so far, colleagues only expect his excellent work to continue.

“Robert is already on the top of the game at Ohio State, including being the co-director of the NSF-NeXUS program,” said Cushing. He believes that the next- generation X-ray source Baker is working on will allow him to extend X-ray spectroscopy to many new fields.

Vura-Weis agrees, “He will continue to open up exciting new applications of advanced spectroscopic techniques.”

“Robert is already a major force in spectroscopy,” Allen said. “His trajectory is plotted to cross important thresholds in catalysis and in surface characterization.

“He doesn’t need any help being successful in my view as he has what it takes,” she concluded. “His academic trajectory is nothing but up.”

(1) S. Bandaranayake, E. Hruska, S. Londo, S. Biswas, and L.R. Baker, 

(2) S. Wallentine, S. Bandaranayake, S. Biswas, and L.R. Baker, 

(3) S. Wallentine, S. Bandaranayake, S. Biswas, and L.R. Baker, 

(4) L.R. Baker, U. Diebold, J.Y. Park, and A. Selloni, 

, 050401 (2020). doi.org/10.1063/5.0021819.

(5) J.Y. Park, L.R. Baker, and G.A. Somorjai, 

(6) L.R. Baker, G. Kennedy, M.Van Spronsen, A. Hervier, X. Cai, S. Chen, L.W. Wang, and G.A. Somorjai, 

(7) G. Kennedy, L.R. Baker, and G.A. Somorjai, 

(8) H. Seo, L.R. Baker, A. Hervier, J. Kim, J.L. Whitten, and G.A. Somorjai, 

(9) A. Cirri, J. Husek, S. Biswas, and L.R. Baker, 

L. Robert Baker, the 2021 Emerging Leader in Atomic Spectroscopy, applies ultra- fast, time-resolved X-ray spectroscopy to explore charge transfer at surfaces, to understand electron transfer, energy conversion, electrochemistry, and catalysis.

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