OH Stretching Vibration Band Research Articles

Thermal Behavior of Clinoptilolite

Understanding the thermal properties of zeolites is crucial for their industrial applications. This study explores the thermal stability and dehydration process of clinoptilolite using high-temperature X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Clinoptilolite’s thermal decomposition was monitored from 25 °C to 1200 °C, with results analyzed based on its crystal structure. Principal components analysis (PCA) of the DRIFT spectra indicated progressive water removal and dehydration upon heating, leading to the formation of hydrogen bonds. Thermogravimetric analysis (TGA) revealed a two-step endothermic weight loss: initially, physically adsorbed water was lost up to 100 °C, followed by the removal of tightly bound water and hydroxyl groups until 800 °C. Clinoptilolite remained the dominant phase up to 800 °C, after which albite and cristobalite took over. Rietveld refinement showed that the sample initially contained 70% clinoptilolite, 24% albite, and 6% cristobalite. Above 800 °C, clinoptilolite disappeared, leaving 93% albite and 7% cristobalite. FT-IR spectra changes due to water loss were evident: drying of adsorbed water occurred up to 75 °C and minimal changes were observed from 75 °C to 135 °C, followed by further dehydration until 240 °C. Complete dehydration was confirmed by the disappearance of OH stretching vibration bands by 395 °C, consistent with TGA findings.

Hydration of N-Hydroxyurea from Ab Initio Molecular Dynamics Simulations.

N-Hydroxyurea (HU) is an important chemotherapeutic agent used as a first-line treatment in conditions such as sickle cell disease and β-thalassemia, among others. To date, its properties as a hydrated molecule in the blood plasma or cytoplasm are dramatically understudied, although they may be crucial to the binding of HU to the radical catalytic site of ribonucleotide reductase, its molecular target. The purpose of this work is the comprehensive exploration of HU hydration. The topic is studied using ab initio molecular dynamic (AIMD) simulations that apply a first principles representation of the electron density of the system. This allows for the calculation of infrared spectra, which may be decomposed spatially to better capture the spectral signatures of solute-solvent interactions. The studied molecule is found to be strongly hydrated and tightly bound to the first shell water molecules. The analysis of the distance-dependent spectra of HU shows that the E and Z conformers spectrally affect, on average, 3.4 and 2.5 of the closest H2O molecules, respectively, in spheres of radii of 3.7 Å and 3.5 Å, respectively. The distance-dependent spectra corresponding to these cutoff radii show increased absorbance in the red-shifted part of the water OH stretching vibration band, indicating local enhancement of the solvent's hydrogen bond network. The radially resolved IR spectra also demonstrate that HU effortlessly incorporates into the hydrogen bond network of water and has an enhancing effect on this network. Metadynamics simulations based on AIMD methodology provide a picture of the conformational equilibria of HU in solution. Contrary to previous investigations of an isolated HU molecule in the gas phase, the Z conformer of HU is found here to be more stable by 17.4 kJ·mol-1 than the E conformer, pointing at the crucial role that hydration plays in determining the conformational stability of solutes. The potential energy surface for the OH group rotation in HU indicates that there is no intramolecular hydrogen bond in Z-HU in water, in stark contrast to the isolated solute in the gas phase. Instead, the preferred orientation of the hydroxyl group is perpendicular to the molecular plane of the solute. In view of the known chaotropic effect of urea and its N-alkyl-substituted derivatives, N-hydroxyurea emerges as a unique urea derivative that exhibits a kosmotropic ordering of nearby water. This property may be of crucial importance for its binding to the catalytic site of ribonucleotide reductase with a concomitant displacement of a water molecule.

Water release from dacitic melts near the glass transition and implications for volcanic eruptions

To get insights in the mechanisms of magma degassing and fragmentation, we performed dehydration experiments at ambient pressure with dacitic glasses containing between 1.42 and 5.28 wt% H2O. The focus was on the degassing behavior in the range of glass transition, i.e., from temperatures 50 K below to 50 K above the glass transition temperature Tg. At each T the duration of the experiments was varied between 5 and 125 h. Water contents and initial water speciation was determined by FTIR spectroscopy. Diffusion depth profiles were measured by Raman spectroscopy. We developed an equation to calculate the total water content along the depth profiles from the ratio of the fundamental OH stretching vibration band at 3550 cm−1 and the T-O-T bending band near 500 cm−1. Glasses with high water content (4.66–5.28 wt%) showed huge alterations, i.e., crack formation below Tg and crystallization at and above Tg, but glasses with water contents up to 2.5 wt% were visually unchanged and suitable for water diffusion analysis.The measured profiles of total water content vs. distance can be fitted well by an error function, assuming that the water content in the glass does not decrease to zero at the surface. However, the apparent water concentration at the surface and the total water diffusivity derived from the error function fitting decrease with increasing duration of the experiment. This clearly shows that degassing of dacitic melts is not a simple out-diffusion mechanism. The model of Coumans et al. (2020) that explicitly considers the kinetics of the interconversion of water species can reproduce the temporal evolution of the total water concentration profiles very well. Our results show the importance of considering explicitly the interconversion kinetics of water species when modelling water diffusion in melts at high viscosities. Due to the slow interconversion of OH groups to much more mobile water molecules, dehydration is much slower in the range of glass transition than predicted by diffusion models based on experiments performed on stable melts at magmatic temperatures.

Structure and thermodynamics of water adsorption in NU-1500-Cr

Metal-organic frameworks (MOFs) are a class of materials with diverse chemical and structural properties, and have been shown to effectively adsorb various types of guest molecules. The mechanism of water adsorption in NU-1500-Cr, a high-performance atmospheric water harvesting MOF, is investigated using a combination of molecular dynamics simulations and infrared spectroscopy. Calculations of thermodynamic and dynamical properties of water as a function of relative humidity allow for following the adsorption process from the initial hydration stage to complete filling of the MOF pores. Initial hydration begins at the water molecules that saturate the open Cr3+ sites of the framework, which is then followed by the formation of water chains that extend along the channels connecting the hexagonal pores of the framework. Water present in these channels gradually coalesces and fills the hexagonal pores sequentially after the channels are completely hydrated. The development of hydrogen-bond networks inside the MOF pores as a function of relative humidity is characterized at the molecular level using experimental and computational infrared spectroscopy. A detailed analysis of the OH-stretch vibrational band indicates that the low-frequency tail stems from strongly polarized hydrogen-bonded water molecules, suggesting the presence of some structural disorder in the experimental samples. Strategies for designing efficient water harvesting MOFs are also proposed based on the mechanism of water adsorption in NU-1500-Cr.

Thermal Migration Behavior of Na+, Cu2+ and Li+ in Montmorillonite

The main aim of this paper is to study the cation fixation sites in montmorillonite after heating at different temperatures. Montmorillonite was used to adsorb cations (Na+, Cu2+ and Li+) in the solution, and the montmorillonite-adsorbed cations were heated at different temperatures (unheated, 100 °C, 200 °C and 300 °C) for 25 h. Subsequently, the basal spacing of montmorillonite treated at different temperatures was monitored by X-ray diffraction (XRD). The exchangeable cationic content (Na+, Cu2+ and Li+) in montmorillonite was determined based on an inductively coupled plasma emission spectrometer (ICP-OES). In addition, the stretching and bending vibration changes in the OH group and the Si-O bond in montmorillonite were detected by Fourier transform infrared spectroscopy (FTIR). The vibration changes were related to the cation fixation sites. The XRD data showed that when the heating temperature reached 200 °C, the structure of montmorillonite adsorbing Li+ and Cu2+ ions completely collapsed, but the layer spacing of montmorillonite adsorbing Na+ decreased slightly, which indicated that Li+ and Cu2+ were more easily able to enter the crystal structure. The ICP-OES results showed that the contents of exchangeable Na+, Cu2+ and Li+ in montmorillonite decreased with the increase in heating temperature, and Li+ was more easily fixed by montmorillonite than Na+ and Cu2+. The FTIR data showed that when montmorillonite adsorbed with Li+ was heated at more than 200 °C, a new OH stretching vibration band appeared at 3971 cm−1, which may be caused by the migration of Li+ into the octahedral vacancy to form a local trioctahedral structure. Na+ has a large radius; it can only be fixed near the OH group and may not enter the tetrahedron/octahedron of montmorillonite. The number of charges carried by Cu2+ is high and the dehydration enthalpy of hydrated Cu2+ is high. When the heating temperature was greater than 200 °C, Cu2+ mainly entered the hexagonal cavity of the tetrahedron and caused slight changes in the OH bending vibration. The vibration of the Si-O bond hardly changed after montmorillonite adsorbed Na+, but the stretching vibration peak of the Si-O bond moved to the high value region after adsorbing Cu2+ and Li+, which was speculated to be related to the migration of Cu2+ and Li+ into the crystal structure.

Mid-infrared spectroscopy of hemispherical water droplets

As an important component of atmospheric aerosols, water is profoundly related with aerosol hygroscopicity and provides a medium for atmospheric heterogeneous reactions. The quantitative analysis of water content in aerosol droplets is instrumental to understanding atmospheric chemistry, as well as to addressing the related environmental issues, such as air pollution and climate change. Fourier transform infrared (FTIR) spectroscopy has been widely adopted to quantify the amount of water content in atmospheric aerosols, which is based on the absorbance of OH functional group in proportion to water content. However, in the OH stretching vibration band around 3400 cm−1, spectral distortions may occur, making a quantitative analysis impossible. In addressing this issue, here we put forth a model to simulate the FTIR absorption of hemispherical water droplets, along with a quantitative description of the spectral distortion. Our model prediction was benchmarked with the microscopic-FTIR experiments conducted on sodium sulfate droplets, and good agreements between theoretical and experimental results were found. We observed that the absorbance spanning across the mid-wavenumber infrared region increases with water absorption coefficients; while such an increasing trend was not seen in the 3400 cm−1 band. We speculate that the spectral saturated absorption is related to the absorption coefficient of water and the ratio of the projected area of droplets to the aperture area. In addition, the effects of droplet size and number density on the absorption spectra were investigated. The waveband range of the saturated absorption broadens with an increase in droplet radius. On the other hand, as the number density of water droplets increases, the absorption at 3400 cm−1 is enhanced, and the characteristic peak of condensed water becomes increasingly sharper, asymptotic to the typical infrared spectra of water collected by the pressing method.

Hydrogen defects in feldspars: defect properties and implications for water solubility in feldspar

Hydrogen defects can strongly affect mechanical and chemical properties of feldspars. To get insight into the behavior of such defects, alkali feldspar and plagioclase of igneous origin were studied combining IR spectroscopy with heating experiments under well-controlled conditions. Near-infrared spectra show that OH groups are the predominant hydrous species in these feldspars but presence of minor amounts of molecular H2O cannot be excluded. Short-term annealing at 400–800 °C produces a small but significant irreversible change in the OH stretching vibration band which is attributed to relaxation of the feldspar structure. Polarized mid-infrared spectra of sanidine, adularia, and plagioclase recorded in situ at temperatures up to 600 °C show reversible shifts of maxima toward higher wavenumber and an overall decrease in integrated intensities. The pleochroic features of the OH vibration bands, i.e., the predominant orientation of OH dipoles along the crystallographic a axis in all feldspars and the additional band component perpendicular to the (010) plane in sanidine are still present in the high-temperature spectra. Different behavior during long-term annealing at high temperature was found for the alkali feldspars and the plagioclases. At 900–1000 °C, the Eifel sanidines rapidly lost about one quarter of the initial water content which is attributed to a weakly bound hydrogen species in the feldspar structure. The remaining hydrogen is very strongly bound and was still detectable in 0.7–0.9 mm thick sections after annealing for 108 days at 1000 °C in air dried by phosphorus pentoxide. In contrast, a 1-mm-thick section of plagioclase completely lost hydrogen during heating in air within 8 days at 1000 °C. After partial dehydration, the pleochroic behavior of the OH absorption bands of the feldspars was basically preserved except that the 3050 cm−1 band of the sanidine, oriented perpendicular to (010), becomes more pronounced than the 3400 cm−1 band, oriented parallel to the a direction. Annealing experiments at 1000 °C under controlled water pressures indicate equilibrium solubilities of several tens of ppm H2O in the plagioclases and more than 100 ppm H2O in the alkali feldspars already at 1 bar water pressure. The variation of the water content with H2O pressure and spectroscopic observations indicates that the water content in the feldspars is determined not only by the water pressure but also by already existing defects. Vacancies on alkali sites (VA1) may accommodate H2O molecules, possibly with subsequent hydrolysis of network bonds to minimize local stress. A likely explanation for the strongly bound hydrogen in the sanidine is a coupled substitution of H+ + Al3+ for Si4+ (AlOH defect) where the protons are located on interstitial sites. This incorporation model is supported by the complete recovery of the defects in H2O vapor after previous proton/alkali exchange in alkali chloride vapor at 1000 °C.

Characterization of the Influence of Hydrated Ions on the Oxygen–Hydrogen Stretching Vibration of Water by Raman Spectroscopy

The Raman OH stretching vibration band of liquid water is asymmetric and multimode superimposed and is susceptible to variations in salinity, pressure, and temperature. Ions have non-negligible influences on the Raman O–H stretching band of water because these ion–water interactions are stronger than those between water molecules. The determination of molecular-level details of hydration processes remains a great challenge, both experimentally and theoretically. The effects of 11 common ions on the O–H stretching band of liquid water are characterized with a skewing parameter introduced to describe the distortion caused by ion hydration. With increasing salt concentration, the symmetry of the Raman O–H stretching band decreases as the skewing parameter value increases. Therefore, ions primarily break the tetrahedral hydrogen bonding and promote the formation of partly hydrogen-bonded and free water molecules. Additionally, the effects of anions are much stronger than those of cations due to the asymmetric charge distribution in the dipoles of H2O. It is revealed that the influences of the common ions on the Raman OH stretching band of water are in the following order: I– > Br– > Cl– > F–, > K+ > Na+, and Sr2+ > Ca2+ > Mg2+. For ions with the same charge, the order of their effects on the Raman O–H stretching band of water is usually the same as the order of their ionic crystal radii but the reverse order of their hydrated radii.

Complex Defects in Mg-Doped Lithium Niobate Crystals Over a Wide Concentration Range and Their Manifestation in IR Absorption Spectra in the OH Stretching Vibration Region

Structural defects of nominally pure congruent and stoichiometric LiNbO3 crystals and a series of congruent crystals doped with 0.91–5.91 mol% MgO were compared and comprised two concentration thresholds at ~3.0 and ~5.5 mol% MgO. The main band parameters of OH stretching vibrations in IR absorption spectra (frequency, half-width, intensity) displayed abrupt changes near the concentration threshold at 5.5 mol% MgO. The OH stretching-vibration band shifted to higher frequency by ~50 cm–1 because of the formation of (MgLi)+–(MgNb)3––OH–complexes upon reaching the second Mg concentration threshold.

Raman Thermometry in Water, Ethanol, and Ethanol/Nitrogen Mixtures from Ambient to Critical Conditions.

We present investigations into remote liquid temperature sensing with Raman spectroscopy using different evaluation methods for the OH stretching vibration band. Water, ethanol, and ethanol saturated with nitrogen, all as liquids or liquid-like supercritical fluids, are pumped through a heated microcapillary system at elevated pressures. Raman spectra are recorded from the liquid inside the microcapillary and are evaluated with respect to the temperature sensitivity of the OH stretching vibration. The four approaches applied are (i) to evaluate the center position of the Raman OH-band, (ii) the integrated absolute difference spectrum, (iii) the intensity ratio of two regions of the OH-band, and (iv) the intensity ratio of two fitted Gaussian peaks. The temperature range investigated covers from ambient temperature to the component’s respective boiling temperature or critical temperature at sub- and supercritical pressures. Precision and robustness of the employed methods are characterized. It is shown that two out of the four methods feature temperature deviations smaller than 5 K at all pressures and that one method can also be applied to liquid mixtures of ethanol and nitrogen. Applicability to other liquids and mixtures is discussed.

Disentangling Coupling Effects in the Infrared Spectra of Liquid Water.

A quantitative characterization of intermolecular and intramolecular couplings that modulate the OH-stretch vibrational band in liquid water has so far remained elusive. Here, we take up this challenge by combining the centroid molecular dynamics formalism, which accounts for nuclear quantum effects, with the MB-pol potential energy function, which accurately reproduces the properties of water across all phases, to model the infrared (IR) spectra of various isotopic water solutions with different levels of vibrational couplings, including those that cannot be probed experimentally. Analysis of the different IR OH-stretch line shapes provides direct evidence for the partially quantum-mechanical nature of hydrogen bonds in liquid water, which is emphasized by synergistic effects associated with intermolecular coupling and many-body electrostatic interactions. Furthermore, we quantitatively demonstrate that intramolecular coupling, which results in Fermi resonances due to the mixing between HOH-bend overtones and OH-stretch fundamentals, is responsible for the shoulder located at ∼3250 cm-1 of the IR OH-stretch band of liquid water.

Quantification of distortion of the water OH-band using picosecond Raman spectroscopy

An anomalously large (~40 cm−1) blue-shift of the Raman OH stretching vibration band was observed when bulk water was probed by picosecond versus nanosecond pulses. The temperature distortion of the OH band contour (3200–3600 cm−1) was studied by both nanosecond and picosecond Raman techniques. It was observed that the OH band centroid shifted linearly with temperature (~0.87 cm−1 °C−1) for both nano- and picosecond pulses. This feature of the picosecond Raman spectra was explained by the dynamics of the non-equilibrium hydrogen bond structures in water.

To the Problem of the Water Transparency Bandwidth (1.8–11.2 eV) and Hydrogen Bonds

It is experimentally detected the gravity center of theOHband of Raman scattering (RS) of picosecond pulses in water shifts by ~40 cm−1 (~0.005 eV) to the high-frequency wing due to shortening the time of observation of the hydrogen bond restructuring in comparison with RS of nanosecond pulses. It was shown that declarative negation of hydrogen bonds and the introduction of the water transparency window half-width (5 eV) or (11.2 eV as seen in Fig. 1 of the paper by V. G. Artemov [Bulletin of the Lebedev Physics Institute 42, 187-191 (2015)] should be regarded as incorrect. These values multiply exceed the well known half-width in the range of 650–360 nm (~1.8 eV [1] which is defined by the fundamental absorption region and OH stretching vibration band overtones from the side of UV and IR regions, respectively.

An insight into the influence of hydrogen bond acceptors on cellulose/1-allyl-3-methyl imidazolium chloride solution

Although ionic liquids have been well established as effective solvents for the dissolution and processing of natural cellulose fibers, the detailed dissolution mechanism at the molecular level still remains unclear. Herein, the turbidimetric measurement showed that the solubility of cellulose in 1-allyl-3-methyl imidazolium chloride (AmimCl) decreased with increasing temperature. The temperature dependence of the OH stretching vibration band of cellulose in AmimCl was investigated by infrared spectroscopy. The interaction between AmimCl and different hydrogen bond acceptors were investigated by turbidimetry and NMR spectroscopy, which indicated that the excellent compatibility of the hydrogen bond acceptors with AmimCl provides more interaction sites for the hydroxyl groups of the cellulose. In addition, ionic liquids with a similar anionic structure of hydrogen bond acceptors have been synthesized. This study provides a green and safe guide for the preparation of ionic liquids with excellent solubility of cellulose.

Observation and Identification of a New OH Stretch Vibrational Band at the Surface of Ice.

We study the signatures of the OH stretch vibrations at the basal surface of ice using heterodyne-detected sum-frequency generation and molecular dynamics simulations. At 150 K, we observe seven distinct modes in the sum-frequency response, five of which have an analogue in the bulk, and two pure surface-specific modes at higher frequencies (∼3530 and ∼3700 cm–1). The band at ∼3530 cm–1 has not been reported previously. Using molecular dynamics simulations, we find that the ∼3530 cm–1 band contains contributions from OH stretch vibrations of both fully coordinated interfacial water molecules and water molecules with two donor and one acceptor hydrogen bond.

Structural investigation of hydrous sodium borosilicate glasses

The structural properties of a borosilicate glass with nominal 16mol% Na2O, 10mol% B2O3 and 74mol% SiO2 and water contents between 0 and 8wt% H2O (0–22mol% H2O) were investigated with IR, Raman and 11B MAS NMR spectroscopy. In addition to the pronounced OH stretching vibration band of weakly H-bonded species at 3580cm−1 the MIR spectra show a triplet at 2900, 2350 and 1750cm−1, similar as observed in water-bearing silicate glasses. These bands are assigned to OH groups and water molecules which are strongly H-bonded, to non-bridging oxygen. Water species contents determined from absorption bands in the NIR at 5200cm−1 (molecular H2O), 4700cm−1 (BOH), and 4500cm−1 (SiOH) indicate that hydroxyl groups dominate up to ~6wt% total H2O. Based on the absorption coefficients known from literature for silicate and borate glasses the BOH/SiOH ratio is estimated to be ≈0.8.As indicated by density, Raman and NMR data the incorporation of water has strong structural impacts in particular at low water contents up to 3wt% H2O. While the nominally dry glasses still contain a significant fraction (12%) of three-fold coordinated boron, almost all boron is four-fold coordinated in hydrous glasses.The increase of band components in the Raman spectra near 900cm−1 relative to the region>1050cm−1 gives evidence for depolymerization of the network upon hydration. Fitting of the spectra with Gaussians implies that silica tetrahedra with two non-bridging oxygen (Q2) are preferentially formed by reaction with water on expense of tetrahedra linked to four tetrahedra (Q4).

Quantifying Raman OH-band spectra for remote water temperature measurements.

Remote water temperature measurements by Raman scattering is a perspective tool for in situ and/or real-time studies for inaccessible areas such as the Arctic region. State-of-the-art laser remote temperature detection techniques are based on temperature-dependent transformation of the Raman OH stretching vibration band. This study compared different approaches quantifying Raman OH-band spectra transformation with temperature: the two-color technique, deconvolution procedure, Raman difference spectroscopy, and centroid technique. Distilled water was probed remotely by compact Raman LIDAR, and the results demonstrated that the Raman OH-band centroid technique achieved the best temperature measurement accuracy (±0.15°C).

Temperature and salinity effects on the Raman scattering cross section of the water OH-stretching vibration band in NaCl aqueous solutions from 0 to 300 °C

Water is often used as an internal standard in quantitative Raman spectroscopic measurements of dissolved species in aqueous solutions containing salts at varying temperatures. However, the effects of temperature and dissolved ions on the relative differential Raman scattering cross section (RSCS) of the OH-stretching vibration band of water at elevated temperatures and salinities are not well defined quantitatively. In this study, the Raman spectra of NaCl solutions with different salinity (from 0 to 5 mol NaCl/kg · H2O) at 20 °C at atmospheric pressure and from 0 to 300 °C at 30 MPa were studied. The relative RSCS of the OH-stretching vibration band of liquid water (σ(mNaCl, T, 30 MPa)/σ(Pure water, 20 °C, 30 MPa)) as a function of temperature (T, in °C) and salinity (mNaCl, in mol/kg · H2O) was established: σmNaCl,T,30MPa/σ(Pure water,20oC,30MPa)=fT,mNaCl=aT−20+b where a = 0.000089 × mNaCl1/2 − 0.001164; b = 0.0355 × mNaCl + 1; The RSCS of the OH-stretching vibration band of water in pseudo back-scattering geometry decreases linearly with increasing temperature, but increases with the addition of dissolved NaCl within the whole temperature range. The enhancement factor of the RSCS by dissolved NaCl increases with temperature. Such effects of temperature and salinity should be considered in quantitative Raman spectroscopic study of species concentration in aqueous solution at high temperature when using water as internal standard. Copyright © 2016 John Wiley & Sons, Ltd.

Crystalline structure and morphological properties of porous cellulose/clay composites: The effect of water and ethanol as coagulants

In this study, cellulose foams incorporated with surface-modified montmorillonite (SM-MMT) were prepared following NaOH dissolution and regeneration into water and ethanol. According to the SEM images, the type of coagulating agent significantly affected the morphological properties of composite foams. The crystalline parameters were evaluated using wide-angle X-ray diffraction (WAXD), which showed an increase in crystal size as the effect of SM-MMT; however, the crystal size decreased for the samples treated with ethanol. The distribution of hydrogen bond types was also investigated using Fourier transform infrared (FTIR). Resolving the hydrogen-bonded OH stretching band at around 3340 into five bands indicated that presence of SM-MMT caused the shift of OH-stretching vibration band to lower wave number due to new hydrogen bonds between cellulose and SM-MMT. In general, the results indicated a change in the contents of the intra- and inter-molecular hydrogen bonds when the coagulant was changed or SM-MMT was incorporated.

Raman spectra of water in fluid inclusions: I. Effect of host mineral birefringence on salinity measurement

Raman microspectrometry of water in individual aqueous fluid inclusions can provide chemical information about fluid composition, in particular the concentration of chloride ions. The regular method consists in correlating the deformation of the OH stretching vibration band of liquid water in the region assigned to hydrogen‐bonded OH groups with chloride concentration. In the present study, a set of seven different minerals with various birefringence properties (barite, calcite, celestine, fluorite, kyanite, quartz and siderite) was selected for the analysis of the water band of their hosted aqueous fluid inclusions. The comparison with microthermometry highlighted that any birefringent mineral may affect the determination of salinity carried out by the analysis of the Raman signal of water: the Raman salinity exposed sinusoidal variations when rotating the samples on the microscope stage. This phenomenon was explained by mineral birefringence, and by the polarization properties of the OH stretching vibration band of liquid water and of the spectrometers gratings. A good knowledge of the polarization properties of the optical devices of the Raman spectrometer and a correct positioning of the sample thus result in salinity (chloride concentration) measurements with the same accuracy as classic microthermometry. Copyright © 2015 John Wiley & Sons, Ltd.