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Microwave spectroscopy is used to map the sign of an electric dipole Rabi frequency — which depends directly on the chirality of the molecule — onto the phase of emitted microwave radiation, thereby determining the chirality of cold gas-phase molecules. Microwave spectroscopy measures chirality Chiral molecules exist as enantiomers that form non-superimposable mirror images, and chirality has a fundamental role in many aspects of chemistry and biology. It is notoriously difficult to detect and quantify chirality because conventional spectroscopic methods exploit weak effects that produce weak signals. Patterson et al . now show that microwave spectroscopy combined with a switched electric field can map the sign of an electric dipole Rabi frequency — a variable that depends directly on the chirality of the molecule — onto the phase of emitted microwave radiation. The effect is then used to determine the chirality of cold gas-phase molecules, illustrated with S and R enantiomers of 1,2-propanediol and their racemic mixture. The method produces large and definitive signatures of chirality, and is both sensitive and species-selective — making it a potentially ideal and unique tool for determining the chirality of multiple species in a mixture. Chirality plays a fundamental part in the activity of biological molecules and broad classes of chemical reactions, but detecting and quantifying it remains challenging 1 . The spectroscopic methods of choice are usually circular dichroism and vibrational circular dichroism, methods that are forbidden in the electric dipole approximation 2 . The resultant weak effects produce weak signals, and thus require high sample densities. In contrast, nonlinear techniques probing electric-dipole-allowed effects have been used for sensitive chiral analyses of liquid samples 3 , 4 , 5 , 6 , 7 . Here we extend this class of approaches by carrying out nonlinear resonant phase-sensitive microwave spectroscopy of gas phase samples in the presence of an adiabatically switched non-resonant orthogonal electric field; we use this technique to map the enantiomer-dependent sign of an electric dipole Rabi frequency onto the phase of emitted microwave radiation. We outline theoretically how this results in a sensitive and species-selective method for determining the chirality of cold gas-phase molecules, and implement it experimentally to distinguish between the S and R enantiomers of 1,2-propanediol and their racemic mixture. This technique produces a large and definitive signature of chirality, and has the potential to determine the chirality of multiple species in a mixture.

Isoprene is a substantial contributor to the global secondary organic aerosol (SOA) burden, with implications for public health and the climate system. The mechanism by which isoprene-derived SOA is formed and the influence of environmental conditions, however, remain unclear. We present evidence from controlled smog chamber experiments and field measurements that in the presence of high levels of nitrogen oxides (NO ₓ = NO + NO ₂) typical of urban atmospheres, 2-methyloxirane-2-carboxylic acid (methacrylic acid epoxide, MAE) is a precursor to known isoprene-derived SOA tracers, and ultimately to SOA. We propose that MAE arises from decomposition of the OH adduct of methacryloylperoxynitrate (MPAN). This hypothesis is supported by the similarity of SOA constituents derived from MAE to those from photooxidation of isoprene, methacrolein, and MPAN under high-NO ₓ conditions. Strong support is further derived from computational chemistry calculations and Community Multiscale Air Quality model simulations, yielding predictions consistent with field observations. Field measurements taken in Chapel Hill, North Carolina, considered along with the modeling results indicate the atmospheric significance and relevance of MAE chemistry across the United States, especially in urban areas heavily impacted by isoprene emissions. Identification of MAE implies a major role of atmospheric epoxides in forming SOA from isoprene photooxidation. Updating current atmospheric modeling frameworks with MAE chemistry could improve the way that SOA has been attributed to isoprene based on ambient tracer measurements, and lead to SOA parameterizations that better capture the dependency of yield on NO ₓ.

This article provides an overview of the state-of-the-art and future trends of the application of LC-high resolution mass spectrometry to the environmental analysis of polar micropollutants. Highly resolved and accurate hybrid tandem mass spectrometry such as quadrupole/time-of-flight and linear ion trap/orbitrap technology allows for a more reliable target analysis with reference standards, a screening for suspected analytes without reference standards, and a screening for unknowns. A reliable identification requires both high resolving power and high mass spectral accuracy to increase selectivity against the matrix background and for a correct molecular formula assignment to unknown compounds. For the identification and structure elucidation of unknown compounds within a reasonable time frame and with a reasonable soundness, advanced automated software solutions as well as improved prediction systems for theoretical fragmentation patterns, retention times, and ionization behavior are needed. [graphic removed]

Abnormal formation and organization of collagen network is commonly observed in many organ pathologies, but analytical techniques able to reveal the collagen biodistribution are still lacking. In this study, Fourier-transform infrared (FTIR) spectroscopy has been used to analyze type I, III, IV, V, and VI collagens, the most important compounds of connective tissues. A robust classification of 30 FTIR spectra per collagen type could be obtained by using a combination of four spectral intervals [ν(C=O) absorption of amide I (1,700-1,600 cm⁻¹), δ(CH₂), and δ(CH₃) absorptions (1,480-1,350 cm⁻¹), ν(C-N), and δ(N-H) absorptions of amide III (1,300-1,180 cm⁻¹), and ν(C-O) and ν(C-O-C) absorptions of carbohydrate moieties (1,100-1,005 cm⁻¹)]. Then, a submolecular justification of this classification model was sought using a curve fitting analysis of the four spectral intervals. Results demonstrated that every spectral interval used for the classification contained highly discriminant absorption bands between all collagen types (multivariate analysis of variance, p < 0.01; Dunnett's T3 post hoc test, p < 0.05). All conditions seem thus joined to make FTIR spectroscopy and imaging major tools for implementing innovative methods in the field of molecular histology, which would be very helpful for the diagnosis of a wide range of pathologies.

Mass spectrometry has recently undergone a second contemporary revolution with the introduction of a new group of desorption/ionization (DI) techniques known collectively as ambient mass spectrometry. Performed in an open atmosphere directly on samples in their natural environments or matrices, or by using auxiliary surfaces, ambient mass spectrometry (MS) has greatly simplified and increased the speed of MS analysis. Since its debut in 2004 there has been explosive growth in the applications and variants of ambient MS, and a very comprehensive set of techniques based on different desorption and ionization mechanisms is now available. Most types of molecules with a large range of masses and polarities can be ionized with great ease and simplicity with the outstanding combination of the speed, selectivity, and sensitivity of MS detection. This review describes and compares the basis of ionization and the concepts of the most promising ambient MS techniques known to date and illustrates, via typical analytical and bioanalytical applications, how ambient MS is helping to bring MS analysis deeper than ever into the “real world” open atmosphere environment—to wherever MS is needed. [graphic removed]

In the last few decades many new polymers have been synthesized that are now being used in cultural heritage conservation. The physical and chemical properties and the long-term behaviors of these new polymers are determined by the chemical composition of the starting materials used in their synthesis along with the nature of the substances added to facilitate their production. The practical applications of these polymers depend on their composition and form (foam, film, sheets, pressure-sensitive adhesives, heat-seal adhesives, etc.). Some materials are used in restoration works and others for the exhibition, storage and transport of works of art. In all cases, it is absolutely necessary to know their compositions. Furthermore, many different materials that are manufactured for other objectives are also used for conservation and restoration. The technical information about the materials provided by the manufacturer is usually incomplete, so it is necessary to analytically characterize such materials. FTIR spectrometry is widely used for polymer identification, and, more recently, ATR-FTIR has been shown to give excellent results. This paper reports the ATR-FTIR analysis of samples of polymeric materials used in the conservation of artworks. These samples were examined directly in the solid material without sample preparation. [graphic removed]

Latent fingerprints (LFPs) potentially contain more forensic information than the simple identification of the subject; they may contain evidence of contacts with explosives or substances of abuse. Chemical information can also be useful in resolving overlapping LFPs from different individuals. We used desorption electrospray ionization mass spectrometry in an imaging mode to record compound-specific chemical fingerprints.

Using a fifth-order aberration-corrected scanning transmission electron microscope, which provides a factor of 100 increase in signal over an uncorrected instrument, we demonstrated two-dimensional elemental and valence-sensitive imaging at atomic resolution by means of electron energy-loss spectroscopy, with acquisition times of well under a minute (for a 4096-pixel image). Applying this method to the study of a La₀.₇Sr₀.₃MnO₃/SrTiO₃ multilayer, we found an asymmetry between the chemical intermixing on the manganese-titanium and lanthanum-strontium sublattices. The measured changes in the titanium bonding as the local environment changed allowed us to distinguish chemical interdiffusion from imaging artifacts.

A method for the simultaneous determination of seven commonly used artificial sweeteners in water is presented. The analytes were extracted by solid phase extraction using Bakerbond SDB 1 cartridges at pH 3 and analyzed by liquid chromatography electrospray ionization tandem mass spectrometry in negative ionization mode. Ionization was enhanced by post-column addition of the alkaline modifier Tris(hydroxymethyl)amino methane. Except for aspartame and neohesperidin dihydrochalcone, recoveries were higher than 75% in potable water with comparable results for surface water. Matrix effects due to reduced extraction yields in undiluted waste water were negligible for aspartame and neotame but considerable for the other compounds. The widespread distribution of acesulfame, saccharin, cyclamate, and sucralose in the aquatic environment could be proven. Concentrations in two influents of German sewage treatment plants (STPs) were up to 190 μg/L for cyclamate, about 40 μg/L for acesulfame and saccharin, and less than 1 μg/L for sucralose. Removal in the STPs was limited for acesulfame and sucralose and >94% for saccharin and cyclamate. The persistence of some artificial sweeteners during soil aquifer treatment was demonstrated and confirmed their environmental relevance. The use of sucralose and acesulfame as tracers for anthropogenic contamination is conceivable. In German surface waters, acesulfame was the predominant artificial sweetener with concentrations exceeding 2 μg/L. Other sweeteners were detected up to several hundred nanograms per liter in the order saccharin [almost equal to] cyclamate > sucralose. [graphic removed]

We report the use of paper-based microfluidic devices fabricated from a novel polymer blend for the monitoring of urinary ketones, glucose, and salivary nitrite. Paper-based devices were fabricated via photolithography in less than 3 min and were immediately ready for use for these diagnostically relevant assays. Patterned channels on filter paper as small as 90 μm wide with barriers as narrow as 250 μm could be reliably patterned to permit and block fluid wicking, respectively. Colorimetric assays for ketones and nitrite were adapted from the dipstick format to this paper microfluidic chip for the quantification of acetoacetate in artificial urine, as well as nitrite in artificial saliva. Glucose assays were based on those previously demonstrated (Martinez et al., Angew Chem Int Ed 8:1318–1320, 1 ; Martinez et al., Anal Chem 10:3699–3707, 2 ; Martinez et al., Proc Nat Acad Sci USA 50:19606–19611, 3 ; Lu et al., Electrophoresis 9:1497–1500, 4 ; Abe et al., Anal Chem 18:6928–6934, 5 ). Reagents were spotted on the detection pad of the paper device and allowed to dry prior to spotting of samples. The ketone test was a two-step reaction requiring a derivitization step between the sample spotting pad and the detection pad, thus for the first time, confirming the ability of these paper devices to perform online multi-step chemical reactions. Following the spotting of the reagents and sample solution onto the paper device and subsequent drying, color images of the paper chips were recorded using a flatbed scanner, and images were converted to CMYK format in Adobe Photoshop CS4 where the intensity of the color change was quantified using the same software. The limit of detection (LOD) for acetoacetate in artificial urine was 0.5 mM, while the LOD for salivary nitrite was 5 μM, placing both of these analytes within the clinically relevant range for these assays. Calibration curves for urinary ketone (5 to 16 mM) and salivary nitrite (5 to 2,000 μM) were generated. The time of device fabrication to the time of test results was about 25 min. Paper-based microfluidic chip illustrating the colorimetric detection of salivary nitrite. Color intensities were quantified using a flatbed scanner and image manipulation software and plotted against concentration to produce calibration curves for the assay