Diffuse reflectance Fourier transform IR spectroscopy

Fourier transform infrared (FTIR) spectroscopy has greatly enhanced the utility and range of applications of infrared (IR) spectroscopy in chemistry. Until the development of routine FTIR instrumentation, applications of IR were essentially limited to direct transmission measurements. Newer sampling methods in FTIR spectroscopy can be successful with less than 1% throughput of the infrared radiation and yet yield a spectrum with acceptable signal-to-noise ratio. The decreasing cost of FTIR spectrometers has made a number of such sampling techniques accessible for routine applications without compromises in performance. This article will describe one of these, diffuse reflectance.     

衰减全反射傅里叶变换红外光谱法同时测定叔丁醇和二叔丁基过氧化物

分别应用914 cm-1和875 cm-1处的甲基特征峰作为叔丁醇和二叔丁基过氧化物的定量分析峰,使用峰面积作为吸光度的评估方法,得到的标准曲线的相关系数(R2)分别是0.9987和0.9952,叔丁醇的加标回收率在95％～110％之间,应用衰减全反射傅里叶变换红外光谱法测定3个样品,计算结果的F值、t值和p值,数据表...     

Investigation of water diffusion process in ethyl cellulose-based films by attenuated total reflectance Fourier transform infrared spectroscopy and two-dimensional correlation analysis

Two-dimensional correlation spectroscopy (2Dcos) analysis on the time-resolved attenuated total reflectance Fourier transform infrared spectroscopy has been employed to investigate the diffusion behavior of water in ethyl cellulose/triethyl citrate (EC/TEC) films with varied TEC content. The diffusion coefficients of water in the EC-based films are calculated from the diffusion curves according to the Fickian Diffusion Model. And they are observed to increase with TEC content, possibly caused by the increased free volume in the film matrix. In the 2Dcos analysis, the broad O–H stretching vibration region is split into at least four bands, which can be assigned to four different states of water molecules, that is, bulk water, cluster water, relatively free water and free water. Moreover, it is found that as water molecules disperse into the EC-based films, cluster water with moderate hydrogen bonds diffuses faster than bulk water with strong hydrogen bonds. The relatively free water and free water are formed during the diffusion process due to their interactions with the films matrix, which makes water molecules confined and restricted in limited space.     

A novel vertical attenuated total reflectance photochemical flow-through reaction cell for Fourier transform infrared spectroscopy

A unique photochemical cell design and two experiments are presented, which illustrate the usefulness of flow-through attenuated total reflectance (ATR) Fourier transform infrared (FT-IR) spectroscopy as a technique for investigating photochemical reactions at the mineral-water interface. The kinetics of the photolysis reaction of potassium oxalate (K(2)C(2)O(4)) in a ferric iron solution and oxalate adsorbed onto goethite (alpha-FeOOH) were investigated to show the capabilities of the cell. Due to complicated kinetics, the adsorption experiment demonstrates not only the types of complex problems, that may exist at the mineral-water interface, but also the ability for this novel cell design to address them.     

Diffusion measurements with fourier transform infrared attenuated total reflectance spectroscopy: Water diffusion in polypropylene*

The diffusion of pure liquid water into a commercial polypropylene (PP) film at 278–348 K was studied with Fourier transform infrared attenuated total reflectance spectroscopy. Abnormal diffusion behavior was indicated by a significant deviation between the experimental data and a Fickian diffusion model with the conventional saturated boundary condition applied at the water/PP interface. This deviation was observed at all the temperatures studied. With a modified boundary condition that took into account a mass‐transfer resistance at the water/PP interface, the Fickian model was able to represent the experimental data satisfactorily. The average water diffusion coefficient varied between 1.41 and 7.64 × 10^?9 cm²/s, with an activation energy of diffusion of about 19.3 kJ/mol. The interfacial mass‐transfer resistance was represented by an exponential model with an empirical relaxation parameter. The relaxation parameter β increased as the temperature increased and reached an apparent plateau. The infrared spectrum indicated a positive chemical shift of 18 cm^?1 for the less strongly hydrogen‐bonded component of the broad hydroxyl stretching band with respect to pure liquid water, indicating that hydrogen‐bonding interactions were weakened or broken when water molecules diffused into the PP matrix. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 980–991, 2002     

Complexation of polyacrylates by Ca2+ ions. Time-resolved studies using attenuated total reflectance Fourier transform infrared dialysis spectroscopy

The attenuated total reflectance Fourier transform infrared dialysis technique is introduced for the time-resolved investigation of the binding processes of Ca2+ to polyacrylates dissolved in water. We observed transient formation of intermediates in water with various types of coordination of the carboxylate group to Ca2+ throughout the complexation steps. Time-resolved changes in the spectra were analyzed with principal component analysis, from which the spectral species were obtained as well as their formation kinetics. We propose a model for the mechanisms of Ca2+ coordination to polyacrylates. The polymer chain length plays an important role in Ca2+ binding.     

Fourier transform spectroscopy using image sensors

Multichannel Fourier transform spectrometers utilizing image sensing devices are reviewed along with the instrumental design concepts. Although the idea itself is fairly simple, a photographic plate in holographic spectroscopy is replaced by an image sensor, there are stringent requirements to be satisfied in order to realize the system for field use. Mainly two types of the instrument, which are characterized by the Sagnac common-path interferometer and the polarization interferometer optics, respectively, are described with regard to their system performances. Examples of the system operation introduced show that Fourier transform spectrometers without mechanical moving parts play an important role in a variety of spectroscopic applications under severe surroundings. In a summary, methods for the resolution enhancement and comments on the signal-to-noise ratio are also included.     

Optimization of some instrumental factors in diffuse reflectance infrared Fourier transform spectroscopy

The effects of some instrumental factors on infrared spectroscopy analysis were investigated in the case of diffuse reflectance infrared Fourier transform (DRIFT) mode. It is usually said that quantitative analysis is possible only if both particle size distribution and sample density are perfectly controlled. However, even if these conditions are checked, instrumental factors are of great interest for the goodness of a curve fitting procedure, which is often necessary in solid sample studies. A factorial design achieved on anthron made it possible to obtain major trends concerning the required values for one instrumental parameter (resolution) and two mathematical treatments (zero filling and Savitsky-Golay (S-G) smoothing). Resolution was found to have the greatest effect on measured responses. A value of 2 cm(-1) according to the corresponding aperture is sufficient to approach the real width of bands for powdered samples. The use of a zero filling factor (ZFF) improves the apparent resolution by data interpolation. The best values found for instrumental parameters were applied to an anthron-anthracen mixture. The optimization of spectral features made it possible to obtain semi-quantitative results quite easily, in good agreement with the data corresponding to each pure compound.     

Diffuse reflectance infrared Fourier transform spectroscopy as a tool to characterise water in adsorption/confinement situations

We present experimental data acquired by diffuse reflectance infrared spectroscopy in the mid-IR (4000-400 cm(-1)), on micrometric-sized mineral grain powders. The spectral evolution of the OH-stretching band is followed when the adsorbed water film is thinned under dry conditions, from high to low hydration states. The IR bands are found to be characteristic of the degree of adsorption/confinement of the liquid water. The OH-stretching band is shifted toward shorter wavenumbers than in bulk water, showing that a significant portion of adsorbed water has a higher intermolecular bonding energy. Complementary treatment of the kinetics of water desorption, varying with the surface forces in the water film, confirms the relationships of these bands with the constrained water state. We distinguish different water types obeying liquid-liquid interactions (free and capillary water) or dominated by solid-water interactions (confined and adsorbed water). Part of this study is devoted to mesoporous silica MCM-41, of interest due to the restricted geometries of its mesopores (4.7 nm) favouring the confined water state. The methodology allows us to distinguish bulk and adsorbed/confined water, using spectral analysis coupled with an understanding of the dynamic behaviour of the desorption process.     

Direct and rapid determination of sulphate in environmental samples with diffuse reflectance Fourier transform infrared spectroscopy using KBr substrate

The feasibility of employing diffuse reflectance Fourier transform infrared spectroscopy (DRS-FTIR) as a sensitive tool in the submicrogram level determination of sulphate (SO₄²⁻) was checked in this work. This paper presents the development of a new, rapid and precise analytical method for ppb levels of sulphate (SO₄²⁻) in environmental samples like coarse and fine aerosol particles, dry deposits and soil. The determination of submicrogram levels of sulphate is based on the selection of a quantitative analytical peak at 617 cm⁻¹ among the three observed vibrational peaks and preparing calibration curve using different known concentrations of sulphate by diffuse reflectance-Fourier transform infra red spectrometric (DRS-FTIR) technique. Pre-weighed and ground IR grade KBr was used as substrate over which remarkably wide range of known concentration of sulphate was sprayed and dried. The dried sample was analysed by DRS-FTIR. Three calibration curves for three different concentration ranges of sulphate were prepared for samples containing low and relatively higher sulphate contents. The relative standard deviation (n = 8) for the sulphate concentration ranges, 2.5-35.5, 25.5-165, 55-1000 μg/0.5 g KBr, as used to prepare calibration curves, were 2.4%, 2.1% and 1.5%, respectively. The relative standard deviation for the sulphate concentration in real samples were found to be in the range, 3.11-5.76% (n = 16), 4.05-7.75% (n = 16) and 1.48-3.52% (n = 10) for aerosol, dry deposits and soil, respectively. The LOD of the method is 0.20 μg/g SO₄²⁻. The F- and t-tests were performed to check the analytical quality assurance test. The noteworthy feature of the reported method is the non-interference of any of the associated anions and cations. The results were compared with that of ion-chromatographic method with high degree of acceptability. The method can be applied in wide concentration ranges. A method for sulphate determination was introduced that did not require pretreatment of samples. This method employed the direct determination of the sulphate. The method is reagent less, nondestructive, very fast, repeatable, and accurate and has high sample throughput value.     

Quantitative aqueous attenuated total reflectance Fourier transform infrared spectroscopy : Part II. Integrated molar absorptivities of alkyl carboxylates

A quantitative attenuated total reflectance Fourier transform infrared (ATR-FT-IR) spectroscopic method is developed for the analysis of total carboxylate concentration, [COO⁻], in aqueous solution. The short (12–13 μm) and highly reproducible pathlength of the ATR cell permits quantitative subtraction of the water peak at 1640 cm⁻¹. Carboxylate quantitation is based on the area of the asymmetric stretching peak, which is nearly independent of compound structure. The molar absorptivity of alkyl carboxylates in water is 438 ± 58 l mol⁻¹ cm⁻¹, and the integrated molar absorptivity is 2.95 ± 0.08 × 10⁴ l mol⁻¹ cm⁻² (n = 15 compounds, 0.1 M ≤ [COO⁻] ≤ 1.5 M). The [COO⁻] in solutions of mixed carboxylates is measured with a root mean square error of 2.4% and a small (+1.5) positive bias. The accuracy of the method is limited by the assumption that integrated absorbance is constant for all COO⁻ groups.     

Fourier transform raman spectroscopy using a bench-top fourier transform infrared spectrometer

The use of a bench top FTIR spectrometer for near infrared Fourier transform Raman spectroscopy is demonstrated. The use of near infrared excitation results in fluorescence free Raman spectra allowing previously difficult samples to be measured.     

Some consequences of the Fourier transform in Fourier transform Raman spectroscopy

This paper reviews some of the differences between dispersive and Fourier transform (FT) Raman spectroscopy with the goal of highlighting some of the advantages and disadvantages of FT-Raman spectroscopy. In particular, the use of filters, Connes advantage, trading rules and the size of the multiplex and throughput advantages are discussed.     

Determination of total sterols in brown algae by Fourier transform infrared spectroscopy

A procedure is proposed for the determination of the total amount of sterols in brown algae Bifurcaria bifurcata, Cladostephus hirsitus, Dictyota dichotoma and Cystoseira sedoides, globally determined as fucosterol, which is the major sterol contained in these algae. The method involves the use of cholesterol as reference standard and a correction factor of 1.259 ± 0.003, which represents the ratio between the slopes of calibration lines obtained from fucosterol and cholesterol. The method provides precise and accurate results for the IR analysis of real samples.     

The vinyl + NO reaction: determining the products with time-resolved Fourier transform spectroscopy

We have studied the vinyl + NO reaction using time-resolved Fourier transform emission spectroscopy, complemented by electronic structure and microcanonical RRKM rate coefficient calculations. To unambiguously determine the reaction products, three precursors are used to produce the vinyl radical by laser photolysis: vinyl bromide, methyl vinyl ketone, and vinyl iodide. The emission spectra and theoretical calculations indicate that HCN + CH2O is the only significant product channel for the C2H3 + NO reaction near room temperature, in contradiction to several reports in the literature. Although CO emission is observed when vinyl bromide is used as the precursor, it arises from the reaction of NO with photofragments other than vinyl. This conclusion is supported by the absence of CO emission when vinyl iodide or methyl vinyl ketone is used. Prompt emission from vibrationally excited NO is evidence of the competition between back dissociation and isomerization of the initially formed nitrosoethylene adduct, consistent with previous work on the pressure dependence of this reaction. Our calculations indicate that production of products is dominated by the low energy portion of the energy distribution. The calculation also predicts an upper bound of 0.19% for the branching ratio of the H2CNH + CO channel, which is consistent with our experimental results.     

Surface study of hexagonal boron nitride powder by diffuse reflectance Fourier transform infrared spectroscopy

The surface chemistry of hexagonal boron nitride powder is examined. Surface functional groups are found to consist of a mixture of primary and secondary amine groups as well as hydroxyl groups. The surface has a net basic character indicating that the amine contribution to the overall surface chemistry is greater than that of the acidic hydroxyl contribution. A chemical surface treatment also is performed to modify the surface chemistry of hexagonal boron nitride powder. Copyright © 2005 John Wiley & Sons, Ltd.     

Fourier transform microwave spectroscopy and Fourier transform microwave-millimeter wave double resonance spectroscopy of the ClOO radical

Pure rotational spectra of the ClOO radical for the (35)Cl and (37)Cl isotopomers have been observed using Fourier transform microwave and Fourier transform microwave-millimeter wave double resonance spectroscopy. The rotational, centrifugal, spin-rotation coupling, and hyperfine coupling constants have been determined by least-squares fits of the observed transition frequencies. The molecular constants indicate that the electronic ground state is 2A". The r(0) structure is determined to be r(0)(ClO)=2.075 A, r(0)(OO)=1.227 A, and theta;(0)(ClOO)=116.4 degrees . Several highly accurate ab initio calculations have also been performed. Some of them turned out to be inaccurate because it is necessary to take into account both static and dynamic electronic correlations. Only multireference (single and double) configuration interaction calculations with large basis sets reproduce the present experimental results. The anharmonic force constants obtained by the ab initio calculations are used to determine the r(e) structure, r(e)(ClO)=2.084(1) A, r(e)(OO)=1.206(2) A, and theta;(e)(ClOO)=115.4(1) degrees . Unique features of the ClOO radical have become clear by the present experiment and the ab initio calculations.     

Determination of soil properties using Fourier transform mid-infrared photoacoustic spectroscopy

Photoacoustic spectroscopy (PAS) is based on the absorption of electromagnetic radiation by analyte molecules, and this technique has emerged as a valuable tool for the study of materials like biological, chemical and geological samples. In this paper, Fourier transform mid-infrared photoacoustic spectroscopy (FTIR-PAS) was used in the prediction of soil properties. Air-dried soil samples (n = 56) from Fengqiu Ecology Experimental Station Chinese Academy of Sciences were involved in this experiment, and FTIR-PAS spectra of these soil samples were recorded. These FTIR-PAS spectra indicated abundant soil information, but overlapping of absorption made it difficult to make direct measurement of soil properties. Partial least squares (PLS) models based on soil FTIR-PAS spectra was developed to predict available nitrogen (N), phosphorus (P), potassium (K) and organic matter content of soil. 42 soil samples were firstly used in leave-one-out cross-validation, and calibration error, calibration coefficient, validation error and ratio of standard deviation to prediction error (RPD) were obtained to optimize the PLS factor number; then based on the optimized PLS models the soil properties of the other 14 soil samples were predicted. The calibration statistics showed that the PLS model was suitable to use in the prediction of available N, P, K and organic matter content of soil. This prediction technique was non-destructive, and no sample pre-treatment was needed, which made FTIR-PAS a very promising method for fast evaluation of soil properties as well as soil quality.     

A modified diffuse reflectance infrared Fourier transform spectroscopy cell for depth profiling of ceramic fibers

A modified diffused reflectance infrared Fourier transformed spectroscopy (DRIFTS) accessory was used to analyze the surface properties of alumino-silicate fibers. The modifications are simple and involve a different way of performing depth-profiling from traditional DRIFTS by removing approximately 2 mm of salt from a full cup prior to placing the sample in for depth profiling. This method proved successful in elucidating the effects of quenching alumino-silicate fibers in mineral oil versus quenching in an air stream.     

Study of the aerosol fragrances of eugenol derivatives in Cananga odorata using diffuse reflectance infrared Fourier transform spectroscopy and gas chromatography

The purpose of this study was to develop and test a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) method, a fast and non-destructive method without extraction, and compare it with the standard gas chromatography (GC) method currently used. A micro-orifice uniform deposit impactor (MOUDI) was used to sample all the size distributions of the aerosol particles of essential oils to investigate the relation between size distributions and the indoor concentration distributions of ylang essential oils. Correlation coefficients for DRIFTS and GC were 0.9904, 0.9910, 0.9913, and 0.9983 for eugenol, isoeugenol, methyl ether, and eugenyl acetate, respectively. The results showed that the concentrations of the four eugenol derivatives of smoke were approximately three times higher than those of mist. Additionally, the major size distributions of aerosol were 0.19 μm and 1.8 μm for the smoke and mist methods, respectively. Because these two methods produce similar results, DRIFTS is a practical method for assessing these fragrances in aerosols.