In situ monitoring of solid‐state transition of p‐aminobenzoic acid polymorphs using Raman spectroscopy

The purpose of this study is to investigate the mechanism of solid‐state polymorphic transition of p‐aminobenzoic acid (PABA) using in situ Raman spectroscopy measurement. The polymorphic transition experiments were conducted on a micro quartz vessel mounted on a microscope, hot and cold stage, under isothermal conditions. The temperature was precisely controlled by a standalone temperature controller equipped with liquid nitrogen cooling system. The Raman spectroscopy probe was positioned on the surface of the solid sample in the micro vessel. The polymorphic transition progression was in situ monitored and recorded by Raman spectroscopy. Based on the polymorphic transition rate resulted from the quantitative analysis of Raman spectra, the mechanism of solid‐state polymorphic transition of PABA was examined by various empirical kinetic models. An Arrhenius analysis was also performed to calculate activation energies from 134.7 kJ mol⁻¹ to 137.7 kJ mol⁻¹ for the transition. The results demonstrated that in situ Raman spectroscopy is a valuable and accurate technique to probe polymorphic transition process. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal micro‐Raman spectroscopic study of polymorphic transformation of famotidine under different compression pressures

The objective of this study was to investigate the effect of pressure and/or temperature on the polymorphic transformation of famotidine from form B to form A by using a thermal confocal Raman microspectroscopy. A compact with a wide transparent zone in the center and an opaque zone surrounding it was prepared by compressing a conical mass of famotidine form B. Two unique Raman peaks at 2897 and 2920 cm⁻¹ for famotidine forms B and A, respectively, were used as markers. The result indicates that the opaque zone in each compact was composed of famotidine from B, and it did not undergo any polymorphic transformation by preparing with higher compression pressure and/or by heating. The Raman peak intensity ratio of the 2920 cm⁻¹ and 2897 cm⁻¹ bands markedly increased starting from 120 °C for the transparent zone prepared by compressing with 19.61 × 10⁴ kPa pressure, but increased from 100 °C with 49.03 × 10⁴ kPa pressure, indicating the occurrence of thermally induced polymorphic transformation of famotidine from form B to form A. However, the transparent zone prepared by 9.81 × 10⁴ kPa compression pressure retained the same Raman spectrum as that of the famotidine form B, revealing that the thermally induced polymorphic transformation of famotidine was dependent on the pressure applied. There was no polymorphic transformation of famotidine in the transparent zone when it was prepared by a higher compression pressure at a lower temperature or by a lower pressure at a higher temperature. The combined effect of compression and temperature was found to accelerate the polymorphic transformation from form B to form A in the transparent zone of famotidine. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman microspectroscopic mapping or thermal system used to investigate milling‐induced solid‐state conversion of famotidine polymorphs

Confocal Raman microspectroscopy was used to nondestructively determine the polymorphic conversion of famotidine in the course of the milling process. A mapping system was applied to assess the blending uniformity of each polymorphic component in the milled mixture. Raman microspectroscopy combined with a thermal analyzer was also used to investigate the synergistic co‐effects of milling and heating on the polymorphic conversion of famotidine polymorphs. Famotidine has two polymorphs, forms A and B, the raw material of famotidine used was proved to be of form B. The Raman peak intensity ratio of the 2920 cm⁻¹ band for form A and 2897 cm⁻¹ band for form B was used to act as an indicator to evaluate the polymorphic conversion of famotidine form B to form A after different milling courses. The results indicate that the peak intensity at 2897 cm⁻¹ gradually decreased with the milling time, whereas the peak intensity at 2920 cm⁻¹ slowly enlarged, suggesting the polymorphic conversion of famotidine from form B to form A. The longer milling process might strongly induce and promote this polymorphic conversion of famotidine. Both polymorphic forms of famotidine were found to be well uniformly distributed within the milled samples due to their smaller varieties by using the Raman microscopic mapping system. The temperature effect could synergistically accelerate the polymorphic conversion of famotidine from form B to form A in the milled sample. The thermal‐dependent critical temperature for sharply enhancing the content of famotidine form A in each milled sample was also identified. Copyright © 2007 John Wiley & Sons, Ltd.     

In situ diagnostics of catalytic materials using tunable confocal Raman spectroscopy

A new Raman spectroscopic setup for in situ characterization of catalytic materials based on a tunable laser system and a confocal Raman microscope is described. The laser excitation wavelength is variable over a broad range from deep ultraviolet (UV) to near‐infrared allowing for targeted use of Raman diagnostics for catalyst characterization. By utilization of resonance effects, the sensitivity of the method can be strongly increased. The potential of the setup is illustrated by new in situ Raman results on dispersed vanadium oxide catalysts obtained at 217.5 and 280 nm UV laser excitation. Copyright © 2013 John Wiley & Sons, Ltd.     

In‐situ Raman spectroscopy of current‐carrying graphene microbridge

In‐situ Raman spectroscopy was performed on chemical vapor deposited graphene microbridge (3 μm × 80 μm) under electrical current density up to 2.58 × 10⁸ A/cm² in ambient conditions. We found that both the G and the G′ peak of the Raman spectra do not restore back to the initial values at zero current, but to slightly higher values after switching off the current through the microbridge. The up‐shift of the G peak and the G′ peak, after switching off the electrical current, is believed to be due to p‐doping by oxygen adsorption, which is confirmed by scanning photoemission microscopy. Both C–O and C=O bond components in the C1s spectra from the microbridge were found to be significantly increased after high electrical current density was flown. The C=O bond is likely the main source of the p‐doping according to our density functional theory calculation of the electronic structure. Copyright © 2014 John Wiley & Sons, Ltd.     

In situ monitoring of the solution‐mediated polymorphic transformation of glycine: characterization of the polymorphs and observation of the transformation rate using Raman spectroscopy and microscopy

The aim of this work was to investigate the mechanism and progression of the solution‐mediated polymorphic transformation and crystallization of glycine. The identification of the α‐ and γ‐forms of glycine crystals was performed using powder X‐ray diffraction (PXRD), Raman microscopy and in situ probe Raman spectroscopy. The influence of the addition of NaCl and of the process parameters such as saturation temperature, seed size and stirring speed on the transformation behavior from the metastable α‐ form to the stable γ‐ form was examined. In situ probe Raman spectroscopy was used to monitor the solid‐phase properties—polymorphic composition. Fourier transform infrared spectroscopy (FTIR) with a ZnSe window was used to track the liquid‐phase concentration at different times. Besides, the polymorphic transformation of glycine in the solvent was also examined in situ using a microscope with a heating/cooling stage. The integration of the different offline and in situ analytical measurement techniques greatly assisted in accurately and quantitatively perceiving the fundamental phenomena that govern the transformation process. Copyright © 2008 John Wiley & Sons, Ltd.     

Monitoring of the microstructure of ion‐irradiated nuclear ceramics by in situ Raman spectroscopy

Raman spectroscopy is an efficient technique for studying the evolution of microstructure of materials under irradiation. For that purpose, a Raman spectrometer has been recently installed at the JANNUS‐Saclay platform. In this paper, we describe the new setup for in situ experiments. These in situ experiments allowed following the microstructural evolution of different materials (SiC, ZrO₂ and B₄C) as a function of ion fluence on a single sample (either single crystal or polycrystalline ceramics) under the same irradiation conditions. Our results show that Raman spectroscopy is a versatile non‐contact technique for studying on‐line crystalline phase changes or amorphization of irradiated iono‐covalent solids. A detailed analysis of Raman spectra is provided for the three materials (SiC, ZrO₂ and B₄C) investigated in this study, revealing quite different behaviors upon irradiation. Basically, Raman spectroscopy gives insight on these evolutions at the level of bonds given by specific phonon modes, in good agreement with Rutherford backscattering channeling (RBS/C), X‐ray diffraction (XRD) or transmission electron microscopy (TEM) data, which provide information at a long‐range scale. Copyright © 2015 John Wiley & Sons, Ltd.     

Measurement and calculation of the Q‐branch spectrum of nitrogen using inverse Raman spectroscopy and cw Raman‐induced polarization spectroscopy

The techniques of inverse Raman spectroscopy, Raman‐induced polarization spectroscopy (RIPS), and optical heterodyne RIPS (OHD‐RIPS) are compared by probing the Q‐branch of the nitrogen molecule. The signal is measured employing either a photomultiplier tube (low background level–RIPS) or a photodetector (high background level–IRS and OHD‐RIPS). The measurements are performed using atmospheric mixtures of N₂ Ar with concentrations varying from 0 to 79% N₂. This strategy permits estimation of detection limits using the different techniques. Pump and probe energy levels are varied independently to study signal dependence on laser irradiance. A theoretical treatment is presented on the basis of the Raman susceptibility equations, which permits the calculation of spectra for all three techniques. Calculated Q‐branch spectra are compared with the measured spectra for the interactions of a linearly polarized probe beam with a linearly or circularly polarized pump beam. The polarizer angle in the detection path for OHD‐RIPS has a dramatic effect on the shape of the spectrum. The calculated and experimental OHD‐RIPS spectra are in good agreement over the entire range of investigated polarizer angles. Detection limits using these techniques are analyzed to suggest their applicability for measuring other species of importance in combustion and plasma systems. Copyright © 2007 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.     

In situ chemical analysis of modern organic tattooing inks and pigments by micro‐Raman spectroscopy

The chemical composition of tattooing pigments has varied greatly over time according to available technologies and materials. Beginning with naturally derived plant and animal extracts, to coloured inorganic oxides and salts, through to the modern industrial organic pigments favoured in today's tattooing studios. The demand for tattooing is steadily growing as it gains cultural popularity and acceptance in today's society, but ironically, increasing numbers of individuals are seeking laser removal of their tattoos for a variety of reasons. Organic pigments are favoured for tattooing because of their high tinting strength, light fastness, enzymatic resistance, dispersion and relatively inexpensive production costs. Adverse reactions have been reported for some organic inks, as well as potential complications, during laser removal procedures stemming from the unintentional creation of toxic by‐products. Currently, regulatory bodies such as the US Food and Drug Administration have not approved any coloured inks to be injected into the skin, and tattoo ink manufacturers often do not disclose the ingredients in their products to maintain proprietary knowledge of their creations. A methodology was established using micro‐Raman spectroscopy on an animal model to correctly identify the constituents of a selection of modern, organic tattoo inks in situ or post procedure, within the skin. This may serve as a preliminary tool prior to engaging in Q‐switched laser removals to assess the risks of producing potentially hazardous compounds. Likewise, the pigments responsible for causing adverse reactions in some patients may be quickly identified to hasten any corresponding treatment. Copyright © 2008 John Wiley & Sons, Ltd.     

Recent advances in linear and non‐linear Raman spectroscopy. Part III

Following the first two reviews on recent advances in linear and non‐linear Raman spectroscopy, the present review summarises papers mainly published in the Journal of Raman Spectroscopy during 2008. This again serves to give a brief overview of recent advances in this research field and to provide readers of this journal a quick introduction to the various sub‐fields of Raman spectroscopy. It also reflects the current research interests and trends in the Raman community. Copyright © 2009 John Wiley & Sons, Ltd.     

Recent advances in linear and non‐linear Raman spectroscopy. Part IX

This annual review is published to provide an overview of advances in the field of Raman spectroscopy as reflected in papers published each year in the Journal of Raman Spectroscopy (JRS) as well as in trends across related journals that have published papers in the broad field of Raman spectroscopy. The content is obtained from statistical data on article counts obtained from Thomson Reuters ISI Web of Science Core Collection by year and by subfield of Raman spectroscopy. Additional information is gleaned from presentations at the VIII International Conference on Advanced Vibrational Spectroscopy (ICAVS‐8) in Vienna, Austria in July 2015 and those featuring Raman scattering at SCIX 2015 organized by the Federation of Analytical Chemistry and Spectroscopy Societies (FACSS) in Providence, Rhode Island, USA, in September/October 2015. Coverage is also provided for topics from the conference ECONOS 2015 held in April in Leuven, Belgium. Finally, papers published in JRS in 2014 are highlighted and arranged by topics at the frontier of Raman spectroscopy. Taken from these various viewpoints, it is clear that Raman spectroscopy continues to be a rapidly expanding field that provides sensitive photonic information of matter at the molecular level in an ever‐widening arena of novel applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Analysis of seized drugs using portable Raman spectroscopy in an airport environment—a proof of principle study

The rapid identification for drugs‐of‐abuse in airports is of critical importance. In this study we demonstrate the viability of Raman spectroscopy for the rapid identification of illicit substances in their containers in an airport environment. Raman spectra of drugs‐of‐abuse in situ were collected using portable Raman spectrometers; this technique offers distinct advantages to government agencies, first responders and forensic scientists working in the security field. We have demonstrated that the spectrometers are able to collect the spectra of suspect powders, including cocaine HCl and d‐amphetamine sulphate with unknown constituents rapidly and with a high degree of discrimination. Copyright © 2008 John Wiley & Sons, Ltd.     

Melting temperature and enthalpy variations of phase change materials (PCMs): a differential scanning calorimetry (DSC) analysis

Differential scanning calorimetry (DSC) analysis is a standard thermal analysis technique used to determine the phase transition temperature, enthalpy, heat of fusion, specific heat and activation energy of phase change materials (PCMs). To determine the appropriate heating rate and sample mass, various DSC measurements were carried out using two kinds of PCMs, namely N-octadecane paraffin and calcium chloride hexahydrate. The variations in phase transition temperature, enthalpy, heat of fusion, specific heat and activation energy were observed within applicable heating rates and sample masses. It was found that the phase transition temperature range increased with increasing heating rate and sample mass; while the heat of fusion varied without any established pattern. The specific heat decreased with the increase of heating rate and sample mass. For accuracy purpose, it is recommended that for PCMs with high thermal conductivity (e.g. hydrated salt) the focus will be on heating rate rather than sample mass.     

Understanding guest and pressure‐induced porosity through structural transition in flexible interpenetrated MOF by Raman spectroscopy

Interpenetrating metal organic frameworks are interesting functional materials exhibiting exceptional framework properties. Uptake or exclusion of guest molecules can induce sliding in the framework making it porous or non‐porous. To understand this dynamic nature and how framework interaction changes during sliding, metal organic framework (MOF) 508 {Zn(BDC)( 4,4′‐Bipy)_0.5 · DMF(H₂O)_0.5} was selected for study. We have investigated structural transformation in MOF‐508 under variable conditions of temperature, pressure and gas loading using Raman spectroscopy and substantiated it with IR studies and density functional theory (DFT) calculations. Conformational changes in the organic linkers leading to the sliding of the framework result in changes in Raman spectra. These changes in the organic linkers are measured as a function of high pressure and low temperature, suggesting that the dynamism in MOF‐508 framework is driven by ligand conformation change and inter‐linker interactions. The presence of Raman signatures of adsorbed CO₂ and its librational mode at 149 cm⁻¹ suggests cooperative adsorption of CO₂ in the MOF‐508 framework, which is also confirmed from DFT calculations that give a binding energy of 34 kJ/mol. Copyright © 2015 John Wiley & Sons, Ltd.     

The first in situ Raman spectroscopic study of San rock art in South Africa: procedures and preliminary results

Southern Africa has a rich heritage of hunter‐gatherer, herder and farmer rock art traditions made by using both painted and engraved techniques. Until now, there have been only a handful of studies on the chemical analysis of the paint, as all previous types of analysis required the removal of pigment samples from the sites a practice which has been avoided. Raman spectroscopy is an ideal techniques to analyse the paint non‐destructively and also offers the possibility of in situ work with portable instruments. This article describes the procedures and reports the preliminary results of the first in situ Raman spectroscopic study of rock art in South Africa (also a first worldwide), where we, first, evaluate the capability of a Raman portable instrument in very difficult conditions, second, analyse the paints in order to contribute to a better knowledge of the technology used and, third, evaluate the possible contribution of in situ analyses in conservation studies. The paintings from two different rock art sites were studied. The instrument proved to be highly suitable for in situ analyses in physically very challenging conditions. Most of the pigments and alteration products previously detected under laboratory conditions were identified, thereby giving information on both the pigments and conservation state of the paintings. A layered structure of alteration products and pigment was identified in situ for the first time by controlling the laser power, thereby obtaining the same results as in mapping experiments of cross sections of paint. Copyright © 2010 John Wiley & Sons, Ltd.     

Characterization of polycyclic aromatic hydrocarbons using Raman and surface‐enhanced Raman spectroscopy

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous atmospheric pollutants and food contaminants, which exhibit potent carcinogenicity, mutagenicity, and teratogenicity. Vibrational spectroscopy techniques, especially Raman spectroscopy and surface‐enhanced Raman spectroscopy (SERS), can be potentially used as an alternative technique to liquid and gas chromatography in PAH analysis. However, there is limited information on the intrinsic Raman and SERS fingerprints of PAHs. In this study, we have acquired the Raman and SERS spectra of seven PAH compounds and compared their experimental spectra with theoretical Raman spectra calculated by density function theory (DFT). The vibrational modes corresponding to the Raman peaks have also been assigned using DFT. Characteristic Raman and SERS peaks have been identified for five PAH compounds, and the limits of detection were estimated. Such information could be useful for developing SERS assays for simple and rapid PAH identification. Copyright © 2014 John Wiley & Sons, Ltd.     

Probing reoxidation sites by in situ Raman spectroscopy: differences between reduced CeO2 and Pt/CeO2

Raman spectroscopy is a powerful technique for detecting peroxo (O₂)^2– and superoxo (O₂)^– species adsorbed on defect sites of ceria. These sites are probed by reducing CeO₂ at high temperature and then chemisorbing oxygen species at low temperature. In the present study, it is shown for the first time that such Raman characterization has to be achieved at very low laser power to avoid formation of oxygen species by photolysis and analyze only the chemisorbed species. Respecting this requirement, the (O₂)^2– and (O₂)^– species formed on 0.7% Pt/CeO₂ compound, and the CeO₂ support used to prepare it were compared after reduction for various times and at various temperatures. Superoxo species were more stabilized on reduced 0.7% Pt/CeO₂ after short reduction at 773 K than on reduced CeO₂. Additionally, the distributions of peroxo species adsorbed on defect sites of Pt/CeO₂ and CeO₂ were significantly different after long reduction at 773 K in spite of similar amounts. Indeed, less stable species were formed during the reduction of 0.7% Pt/CeO_2. These two features revealed that new sites were created during the preparation and reduction of Pt/CeO₂ compared to its bare support. Copyright © 2012 John Wiley & Sons, Ltd.     

高温高压下方解石相转变的拉曼光谱原位实验研究

用热液金刚石压腔装置结合拉曼光谱技术研究了高温高压下方解石的相变过程及拉曼光谱特征。结果表明:常温条件下,体系压力增至1 666和2 127 MPa时,方解石的拉曼特征峰155cm-1消失,1 087cm-1峰分裂为1 083和1 090cm-1两个谱峰、282cm-1峰突然降至231cm-1,证明其转变为方解石-Ⅱ和方解石-Ⅲ。在起始压力为2 761MPa和低于171℃的升温过程中,方解石-Ⅲ的拉曼散射的各个特征振动峰没有变化。当温度达到171℃,方解石晶体完全变成不透明状,其对称伸缩振动峰1 087cm-1、面内弯曲振动峰713cm-1和晶格振动峰155和282cm-1均发生突变,说明方解石-Ⅲ相变生成一种碳酸钙新相。体系降至常温,该新相一直保持稳定不变,表明高温高压下方解石向碳酸钙新相的转变过程是不可逆的。方解石-Ⅲ与碳酸钙新相之间的相变线方程为P(MPa)=9.09.T(℃)+1 880。碳酸钙新相的对称伸缩振动峰(ν1 087)随压力、温度的变化率分别为dν/dP=5.1(cm-1.GPa-1),dν/dT=-0.055 3(cm-1.℃-1)。