Using Raman spectroscopy as a tool for the detection of iron in glass

Raman spectroscopy has been used to identify iron‐containing glasses. This nondestructive technique offers a fast method to obtain qualitative information about the presence of iron oxides in glass. The effect of the iron content in glass samples is reflected on the topology of the Raman spectra: A strong link between the ratio of the Q₂/Q₃ vibration units of the silica tetrahedral structure is seen. If matrix effects are taken into account, also (semi)quantitative results can be obtained from the calibration lines. The linear calibration is based on the normalized band intensity at 980 cm⁻¹ (I₉₈₀/I₁₀₉₀) and the iron oxide concentration for similar glasses. In amber and dark colored glasses, an extra peak in the spectrum indicates the presence of a FeS chromophore. Different series of glasses of various origins (ancient and modern/industrial glass) have been considered. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman spectroscopy as a tool to the in situ study of three lichens species from Antarctica and Brazil

In this investigation the chemistry of the lichens Gondwania regalis, Teloschistes exilis and Xanthoria candelaria (Teloschistaceae) have been recorded by means of Raman spectroscopy. The non‐destructive analysis provided the recognition of parietin and conjugated polyenes, probably belonging to the carotenoid family for all the investigated specimens. Bands at ca. 1370 and 1600 cm⁻¹, respectively, assigned to the ν(C―O) and ν(CO) modes of the phenyl group of the anthraquinone compound, as well the bands at ca. 1005, 1158 and 1527 cm⁻¹, possibly assigned to the β‐carotene in the FT‐Raman spectra, have provided valuable spectroscopy data for the identification of the biomarkers for these lichen pigments. Thus, this is the first report of parietin and carotenoid in T. exilis and X. candelaria tissues even as the parietin anthraquinone for G. regalis tissues, which are effective pigments against free radicals from UV radiation. Copyright © 2014 John Wiley & Sons, Ltd.     

Drop coating deposition Raman spectroscopy as a potential tool for identification and determination of fructose in seminal plasma

The detection of fructose in the seminal plasma has significant value to evaluate the function of seminal vesicles and evaluate male fertility. In this study, drop coating deposition Raman (DCDR) method was utilized to quantitative determination of fructose in seminal plasma. Optimization of experimental parameters to achieve reagent‐free and rapid detection of fructose was also investigated. Different fructose concentrations within physiological level demonstrated a linear relationship with the band intensity of 627 cm⁻¹ (assigned to fructose), and the relative error of predicted fructose concentration was 10.23%. Our results show that DCDR method has the potential for the determination of fructose concentration. Copyright © 2014 John Wiley & Sons, Ltd.     

Chromatographic paper embedded with silver nanostructure as a disposable substrate for surface‐enhanced Raman spectroscopy and catalytic reactor

The high cost of regular diagnostic kits severely impeded its uses for routine clinical assay and fieldworks. A cost‐effective chromatography paper is chemically modified with Ag nanostructures using the simple electroless silver deposition, producing a scalable and disposable substrate for surface‐enhanced Raman spectroscopy, as well as a large scale of catalytic active sites over many chemical reactions. Synergetic measurement including surface‐enhanced Raman spectroscopy and laser desorption ionization‐mass spectrometry is performed on Ag decorated filter paper using a thiol containing compound as indicator, allowing for the acquisition of spatially correlated spectroscopy in the tandem mode. In addition, hydrophilic porous cellulose network that contains a certain amount of liquid naturally served as a chemical reactor for molecular transport and reaction. Positive results from catalytic reaction on metallized paper convincingly demonstrated that total microanalysis system on paper (μ‐TASoP), as a compelling alternative would find a wide breadth of applications in developing disposable medical devices and customary laboratory assays. Copyright © 2015 John Wiley & Sons, Ltd.     

A novel method for quantification of ethanol and methanol in distilled alcoholic beverages using Raman spectroscopy

In this study, direct quantification of ethanol and methanol in distilled alcoholic beverages using Raman spectroscopy was performed. Raman spectra of varying ethanol–methanol mixtures were obtained, baseline corrections were made, and the data were normalized using Raman scattering intensity of an internal standard (acetonitrile, 921 cm^–1). Then, calibration graphs were produced for ethanol and methanol concentrations in the ranges of 0–7 M and 0–10 M, respectively. Accurate R² values of the calibration graphs proved the notable linear correlations (0.998 for ethanol and 0.998 for methanol). The method was validated based on linearity, sensitivity, intraday and interday repeatability, and recovery tests. The limit of detection and limit of quantification values of the validated method were determined for ethanol concentration as 1.2 and 3.7 mM, and for methanol concentration as 3.4 and 10.3 mM, respectively. The ability of the developed method to detect ethanol and methanol concentrations in real samples was also investigated. The results of the developed method were compared with the experimental results from traditional method and high correlation value (R² = 0.926) was obtained. Besides being sensitive and cheap, the developed method is rapid with the analysis time of less than 30 s. Furthermore, it eliminates labor‐consuming operations, chromatographic separation, and measurement error due to the high number of experiment steps in the standard method. Copyright © 2012 John Wiley & Sons, Ltd.     

Use of a handheld Raman spectrometer for fast screening of microbial pigments in cultures of halophilic microorganisms and in microbial communities in hypersaline environments in nature

A compact handheld Raman spectrometer equipped with a 532 nm excitation laser was used to detect pigments as possible biomarkers in autotrophic (cyanobacteria and purple sulfur bacteria) and heterotrophic halophilic microorganisms (Archaea of the family Halobacteriaceae, Salinibacter). Common as well as less common carotenoids, including α‐bacterioruberin, salinixanthin, and spirilloxanthin derivatives were detected in cell pellets of model organisms belonging to the genera Haloferax, Haloarcula, Halobacterium (Archaea), Salinibacter (Bacteroidetes), and Ectothiorhodospira (Gammaproteobacteria). Direct measurements on such cultures provide fast and reliable identification of pigments. Bacterioruberin was detected as the dominant carotenoid in pellets of cells collected from the saltern crystallizer ponds in Eilat, Israel. Raman analysis of the colored layered microbial communities in a benthic gypsum crust in the saltern evaporation ponds showed signals consistent with the presence of myxoxanthophyll and echinenone carotenoids in the upper orange and dark‐green cyanobacterial layers. Chlorophyll a and phycocyanin expected in the green layer were not detected using the green excitation. Spirilloxanthin dominates the red layer below, inhabited mainly by purple sulfur bacteria. To our best knowledge, this is the first attempt to detect and identify pigments in natural microbial communities consisting of different types of halophilic microorganisms by direct Raman spectrometric measurements using light compact handheld devices. Copyright © 2013 John Wiley & Sons, Ltd.     

Quantitative detection of captopril in tablet and blood plasma samples by the combination of surface‐enhanced Raman spectroscopy with multiplicative effects model

With p‐thiocresol as internal standard, quantitative analysis of captopril, a synthetic angiotensin converting enzyme inhibitor, was achieved by the combination of the multiplicative effects model with surface‐enhanced Raman spectroscopy (SERS). The multiplicative effects model was adopted to correct the detrimental effects caused by the heterogeneity in the physical properties of enhancing substrate (i.e. Ag nano‐particles). Experimental results showed that the calibration model built on the SERS spectra of the calibration captopril samples prepared with ultrapure water could attain quite satisfactory concentration predictions for captopril in both real‐world tablet samples and plasma samples. The recovery rates were in the range of 94.3% to 109.8%, which were in substantial agreement with the corresponding results of LC‐MS/MS. The limit of detection and limit of quantification were estimated to be 0.149 and 0.451 μM, respectively. The proposed approach has advantages of relatively low cost, simplicity, high sensitivity and good accuracy and therefore can be further developed and extended to a routine method for the quantification of captopril in complex systems. Copyright © 2015 John Wiley & Sons, Ltd.     

Visible Raman spectroscopy for the discrimination of olive oils from different vegetable oils and the detection of adulteration

We have investigated the potential of Raman spectroscopy with excitation in the visible spectral range (VIS Raman) as a tool for the classification of different vegetable oils and the quantification of adulteration of virgin olive oil as an example. For the classification, principal component analysis (PCA) was applied, where 96% of the spectral variation was characterized by the first two components. A significant similarity between sunflower oil and extra‐virgin olive oil was found using this approach. Therefore, sunflower oil is a potential candidate for adulteration in most commercially available olive oils. Beside the classification of the different vegetable oils, we have successfully applied Raman spectroscopy in combination with partial least‐squares (PLS) regression analysis for very fast monitoring of adulteration of extra‐virgin olive oil with sunflower oil. Different mixtures of extra‐virgin olive oil with three different sunflower oil types were prepared between 5 and 100% (v/v) in 5% increments of sunflower oil. While in the present context the adulteration usually refers to the addition of reasonable amounts of the adulterant (given the similarity with the basic product), we show that the technique proposed can also be used for trace analysis of the adulterant. Without using techniques like surface‐enhanced Raman scattering (SERS), a quantitative detection limit down to 500 ppm (0.05%) could be achieved, a limit irrelevant for adulteration in commercial terms but significant for trace analysis. The qualitative detection limit even was at considerably lower concentration values. Based on PCA, a clear discrimination between pure extra‐virgin olive oil and olive oil adulterated with sunflower oil was achieved. The adulterant content was successfully determined using PLS regression with a high correlation coefficient and small root mean‐square error for both prediction and validation. Copyright © 2009 John Wiley & Sons, Ltd.     

Anti‐Stokes Raman spectroscopy as a method to identify the metallic and semiconducting configurations of double‐walled carbon nanotubes

Although Raman spectra reveal, as a signature of double‐walled carbon nanotubes (DWCNTs), two radial breathing mode (RBM) lines associated with the inner and outer tubes, the specification of their nature as metallic or semiconducting remains a topic for debate. Investigating the spectral range of the RBM lines, we present a new procedure of the indexing of the semiconducting or metallic nature of the inner and outer shell that forms the DWCNT. The procedure exploits the difference between the intensities of recorded anti‐Stokes Raman spectrum and the anti‐Stokes spectrum calculated by applying the Boltzmann formulae to the recorded Stokes spectrum. The results indicate that the two spectra do not coincide with what should happen in a normal Raman process, namely, that there are RBM lines of the same intensity in both spectra, as well as RBM lines of higher intensity that are observed in the calculated spectrum. This discrepancy results from the surface‐enhanced Raman scattering mechanism that operates differently on metallic or semiconducting nanotubes. In this context, the analysis of the RBM spectrum can reveal pairs of lines associated with the inner/outer shell structure of DWCNT, and when the intensities between the recorded and calculated spectra coincide, the nanotube is metallic; otherwise, the nanotube is semiconducting. Copyright © 2014 John Wiley & Sons, Ltd.     

In situ detection of cocaine hydrochloride in clothing impregnated with the drug using benchtop and portable Raman spectroscopy

This study describes the application of benchtop and portable Raman spectroscopy for the in situ detection of cocaine hydrochloride in clothing impregnated with the drug. Raman spectra were obtained from a set of undyed natural and synthetic fibres and dyed textiles impregnated with the drug. The spectra were collected using three Raman spectrometers: one benchtop dispersive spectrometer coupled to a fibre‐optic probe and two portable spectrometers. Despite the presence of some spectral bands arising from the natural and synthetic polymer and dyed textiles, the drug could be identified by its characteristic Raman bands. High‐quality spectra of the drug could be acquired in situ within seconds and without any sample preparation or alteration of the evidential material. A field‐portable Raman spectrometer is a reliable technique that can be used by emergency response teams to rapidly identify unknown samples. Copyright © 2009 John Wiley & Sons, Ltd.     

A comparison of noise models in a hybrid reference spectrum and principal components analysis algorithm for Raman spectroscopy

Raman spectroscopy exploits the Raman scattering effect to analyze chemical compounds with the use of laser light. Raman spectra are most commonly analyzed using the ordinary least squares (LS) method. However, LS is known to be sensitive to variability in the spectra of the analyte and background materials. In a previous paper, we addressed this problem by proposing a novel algorithm that models expected variations in the analyte as well as background signals. The method was called the hybrid LS and principal component analysis (HLP) algorithm and used an unweighted Gaussian distribution to model the noise in the measured spectra. In this paper, we show that the noise in fact follows a Poisson distribution and improve the noise model of our hybrid algorithm accordingly. We also approximate the Poisson noise model by a weighted Gaussian noise model, which enables the use of a more efficient solver algorithm. To reflect the generalization of the noise model, we from hereon call the method the hybrid reference spectrum and principal components analysis (HRP) algorithm. We compare the performance of LS and HRP with the unweighted Gaussian (HRP‐G), Poisson (HRP‐P), and weighted Gaussian (HRP‐WG) noise models. Our experiments use both simulated data and experimental data acquired from a serial dilution of Raman‐enhanced gold‐silica nanoparticles placed on an excised pig colon. When the only signal variability was zero‐mean random noise (as examined using simulated data), HRP‐P consistently outperformed HRP‐G and HRP‐WG, with the latter coming in as a close second. Note that in this scenario, LS and HRP‐G were equivalent. In the presence of random noise as well as variations in the mean component spectra, the three HRP algorithms significantly outperformed LS, but performed similarly among themselves. This indicates that, in the presence of significant variations in the mean component spectra, modeling such variations is more important than optimizing the noise model. It also suggests that for real data, HRP‐WG provides a desirable trade‐off between noise model accuracy and computational speed. Copyright © 2013 John Wiley & Sons, Ltd.     

SVD‐based method for intensity normalization,background correction and solvent subtraction in Raman spectroscopy exploiting the properties of water stretching vibrations

A semiautomated method combining intensity normalization with effective elimination of the solvent signal and non‐Raman background is presented for Raman spectra of biochemical and biological analytes in aqueous solutions. The method is particularly suitable for rapid and effortless preprocessing of extensive datasets taken as a function of gradually varied physicochemical parameters, e.g. analyte and/or ligand concentration, temperature, pH, pressure, ionic strength, time, etc. For intensity normalization, the strong Raman OH stretching band of water in the range of 2700–3900 cm⁻¹ recorded together with the analyte spectrum in the fingerprint region below 1800 cm⁻¹ is employed as internal intensity standard. Concomitant dependences of the solvent Raman spectra are taken into account and, in some cases, turned into advantage. Once the Raman spectra of the solvent are acquired for a particular range of the parameter varied, solvent contribution can be subtracted correctly from any analyte spectrum taken within this range. The procedure presented can be efficiently applied only for the analytes having their own Raman signal in the range of OH stretching vibrations much weaker than that of the solvent. However, this is the case for a great number of biochemical and biological samples. Accuracy, reliability and robustness of the method were tested under the conditions of spontaneous Raman, resonance Raman and surface‐enhanced Raman scattering. Serviceability of the method is demonstrated by several real‐world examples. Copyright © 2011 John Wiley & Sons, Ltd.     

Raman spectroscopy at different excitation wavelengths (1064, 785 and 532 nm) as a tool for diagnosis of colon cancer

Raman spectroscopy is structure sensitive non‐destructive method that allows observing the status of biological tissues with minimal impact. This method has a great potential in the diagnosis of various types of degenerative diseases including cancer damages. Near‐infrared Fourier transform (NIR‐FT)‐Raman (λ_ex ~1064 nm), NIR‐visible (Vis)‐Raman (λ_ex ~785 nm) and Vis‐Raman (λ_ex ~532 nm) spectra of normal and colorectal carcinoma colon tissue samples were recorded in macroscopic mode at 10–20 randomly chosen independent sites. In the cases of NIR‐Vis‐ and Vis‐Raman spectra, enhanced resonance effects were observed for tissue chromophores absorbing in the visible area. Evident spectral differences were noticed for Raman spectra of normal colon tissue samples in comparison with abnormal samples. The average Raman spectra of colon tissue samples were analysed by principal component analysis (PCA) to discriminate normal and abnormal tissues. PCA of combined dataset containing Raman intensities of chosen NIR‐FT, NIR‐Vis or Vis‐Raman bands led to discrimination of normal and abnormal colon tissue samples. Therefore, combination of these three Raman methods can be helpful for recognizing cancer lesions in colon for diagnostic purposes. Copyright © 2014 John Wiley & Sons, Ltd.     

A novel combinative Raman and SEM mapping method for the detection of exfoliation of graphite in electrodes at very positive potentials

The random exfoliation at very positive potentials (>5 V vs Li/Li⁺) of graphite (used as a conductive component in positive electrodes of lithium‐ion batteries) was investigated with in situ Raman microscopy and post mortem scanning electron microscopy (SEM). A novel semiautomated computational method for the data analysis of both characterization methods was developed to correlate Raman and SEM information with good lateral resolution, in order to locate exfoliated graphite particles. Proof is given that the exfoliating particles detected via the semiautomatic in situ Raman microscopy mappings correctly describes exfoliated areas, as confirmed via post mortem SEM pictures. Copyright © 2011 John Wiley & Sons, Ltd.     

FT‐Raman spectroscopy—a rapid and reliable quantification protocol for the determination of natural indigo dye in Polygonum tinctorium

In the recent years, Raman and IR spectroscopies have attracted increasing attention as fast, non‐invasive and widely applicable alternative analytical approaches for a variety of materials. Vibrational spectroscopy has been used in the analysis of herbal products, dyes and sensitive art objects, besides complex and aqueous biomaterials such as biopolymers or mammalian tissue. Compared to conventional analytical methods based on high‐performance liquid chromatography (HPLC) or gas chromatography, which often involves extensive and time‐consuming sample preparation, Raman or IR spectroscopy can avoid these procedures. The present work introduces a fast and reliable quantification method for the determination of naturally occurring indigo dye in dyer's knotweed (Polygonum tinctorium) based on Fourier transform (FT) Raman spectroscopy. The results were validated by HPLC‐UV, and the merits and drawbacks of the present method are elaborated. Besides the qualitative aspects of signal assignment and comparison to appropriate attenuated total reflectance Fourier transform infrared (ATR‐FT‐IR) measurements, the Raman spectrum of dihydro indigo, an important intermediate in the indigo dying process, is presented for the first time and discussed with regard to its spectroscopic behaviour. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman Spectroscopy for the Undergraduate Teaching Laboratory: Quantification of Ethanol Concentration in Consumer Alcoholic Beverages and Qualitative Identification of Marine Diesels Using a Miniature Raman Spectrometer

Raman spectroscopy has steadily gained popularity as a powerful tool in both the analytical lab and the undergraduate classroom. The technique is attractive because it allows for rapid, nondestructive qualitative or quantitative analyses of many analytes with little or no sample preparation requirements. The introduction of less expensive, smaller, and more powerful diode laser excitation sources and the recent availability of rugged, red‐sensitive, charge‐coupled device–based miniature modular spectrometers has prompted the integration of Raman spectroscopy into the undergraduate curriculum. We have evaluated the analytical utility of a small, portable Raman instrument for the qualitative and quantitative analyses of two “real” samples. The experiments in this paper were designed to be used as a laboratory component for undergraduate education and include the quantification of ethanol in consumer alcoholic beverages and the qualitative identification of marine diesel fuels that had been spilled on surface waters. In the case of the liquor samples, the ethanol concentration in colorless, odorless alcoholic beverages could be determined very rapidly, but colored and heavily scented liquors proved more difficult and required pretreatment with activated carbon to remove fluorescence that masked the Raman signal. Similarly, a high‐intensity fluorescence background was observed to mask characteristic Raman bands of the diesel fuels. Some reduction in the intensity of the fluorescence was observed after carbon pretreatment of the fuels. The set of undergraduate experiments described in this paper treat the concepts of quantitative and qualitative analysis using portable instrumentation, instrumental calibration by the standard addition and external curve methods, and method development for the analysis of real consumer and environmental samples.