Quantitative determination by temperature dependent near-infrared spectra

Near-infrared (NIR) spectra are sensitive to the variation of experimental conditions, such as temperature. In this work, the relationship between NIR absorption spectra and temperature was quantitatively analyzed and applied to the quantitative determination of the compositions in mixtures. It was found that, for the solvents such as water and ethanol, a quantitative spectra-temperature relationship (QSTR) model between NIR spectra and temperature can be established by using partial least squares (PLS) regression. Therefore, the temperature of a solution can be predicted by using the model and NIR spectrum. Furthermore, it was also found that the difference between the predicted results of different solutions is a quantitative reflection of concentration. The variation of intercept in the relationship of the predicted and measured temperature can be used to determine the concentration of the compositions. The mixtures of water, methanol, ethanol and ethylenediamine in a concentration range of 5-80% (v/v) were studied. The calibration curves are found to be reliable with the correlation coefficients (R) higher than 0.99. Both the QSTR and calibration model may extend the application of NIR spectroscopy and provide novel techniques for analytical chemistry.     

Quantitative analysis of arsenic in mine tailing soils using double pulse-laser induced breakdown spectroscopy

A double pulse-laser induced breakdown spectroscopy (DP-LIBS) was used to determine arsenic (As) concentration in 16 soil samples collected from 5 different mine tailing sites in Korea. We showed that the use of double pulse laser led to enhancements of signal intensity (by 13% on average) and signal-to-noise ratio of As emission lines (by 165% on average) with smaller relative standard deviation compared to single pulse laser approach. We believe this occurred because the second laser pulse in the rarefied atmosphere produced by the first pulse led to the increase of plasma temperature and populations of exited levels. An internal standardization method using a Fe emission line provided a better correlation and sensitivity between As concentration and the DP-LIBS signal than any other elements used. The Fe was known as one of the major components in current soil samples, and its concentration varied not substantially. The As concentration determined by the DP-LIBS was compared with that obtained by atomic absorption spectrometry (AAS) to evaluate the current LIBS system. They are correlated with a correlation coefficient of 0.94. The As concentration by the DP-LIBS was underestimated in the high concentration range (>1000 mg-As/kg). The loss of sensitivity that occurred at high concentrations could be explained by self-absorption in the generated plasma.     

Influence of TMAO as co-solvent on the gelation of silica-PNIPAm core-shell nanogels at intermediate volume fractions

We study the structure and dynamics of poly(N-isopropylacrylamide) (PNIPAm) core-shell nanogels dispersed in aqueous trimethylamine N-oxide (TMAO) solutions by means of small-angle X-ray scattering and X-ray photon correlation spectroscopy (XPCS). Upon increasing the temperature above the lower critical solution temperature of PNIPAm at 33 °C, a colloidal gel is formed as identified by an increase of I(q) at small q as well as a slowing down of sample dynamics by various orders of magnitude. With increasing TMAO concentration the gelation transition shifts linearly to lower temperatures. Above a TMAO concentration of approximately 0.40 mol/L corresponding to a 1 : 1 ratio of TMAO and NIPAm groups, collapsed PNIPAm states are found for all temperatures without any gelation transition. This suggests that reduction of PNIPAm-water hydrogen bonds due to the presence of TMAO results in a stabilisation of the collapsed PNIPAm state and suppresses gelation of the nanogel.     

β-环糊精与阿霉素相互作用荧光光谱

用荧光光谱技术确定了β-环糊精（β-CD）与阿霉素（ADM）之间的超分子包络物ADM-β-CD的形成。 研究了时间、浓度和温度对包络反应的影响,确定了包络物形成的化学计量比,计算了在不同温度下的包络常数和包络反应的热力学参数。 在33 ℃、pH=7.0时,包络常数K=2.98×106 L/mol,且包络常数随温度升高而变小,该包络反应属于焓驱动的自发的放热反应。 由于β-CD对ADM的天然荧光有增强作用,因此,ADM与β-CD形成超分子包络物后,荧光强度增大,荧光光谱是研究ADM与β-CD超分子包络反应的很好的技术。 求得β-CD增敏荧光法定量测定ADM的线性回归方程为:F=5.64×108c+47.26,相关系数r=0.9985,检测下限为6.30×10-8 mol/L。     

Direct orthogonal signal correction as data pretreatment in the classification of clinical lots of creams from near infrared spectroscopy data

Direct orthogonal signal correction (DOSC) is applied to correct for major variance sources such as temperature effects, time influences and instrumental differences in near infrared (NIR) data. The samples analysed are creams containing different concentrations of an active drug. The final aim is to classify the samples according to their concentration of active compound. Having performed DOSC on the data, it is not necessary anymore to apply sophisticated chemometric techniques to correct for temperature or time effects and to attribute the samples to their respective concentration classes. Moreover, the application of DOSC on the NIR spectra recorded on two different instruments shows that this method can be considered as a valuable alternative for the standardisation in classification applications. Since the applied algorithm tends to overfit, in a second part of this paper, a comparison is made with an algorithm designed by Westerhuis, which should overcome this problem. Although the calibration set results show that the overfitting has been partially corrected for by the latter algorithm, the test set results did not improve significantly.     

Solid-State Dynamics and High-Pressure Studies of a Supramolecular Spiral Gear

The structures and solid-state dynamics of the supramolecular salts of the general formula [(12-crown-4)₂ ⋅ DABCOH₂](X)₂ (where DABCO=1,4-diazabicyclo[2.2.2]octane, X=BF₄, ClO₄) have been investigated as a function of temperature (from 100 to 360 K) and pressure (up to 3.4 GPa), through the combination of variable-temperature and variable-pressure XRD techniques and variable-temperature solid-state NMR spectroscopy. The two salts are isomorphous and crystallize in the enantiomeric space groups P3₂2₁ and P3₁2₁. All building blocks composing the supramolecular complex display dynamic processes at ambient temperature and pressure. It has been demonstrated that the motion of the crown ethers is maintained on lowering the temperature (down to 100 K) or on increasing the pressure (up to 1.5 GPa) thanks to the correlation between neighboring molecules, which mesh and rotate in a concerted manner similar to spiral gears. Above 1.55 GPa, a collapse-type transition to a lower-symmetry ordered structure, not attainable at a temperature of 100 K, takes place, proving, thus, that the pressure acts as the means to couple and decouple the gears. The relationship between temperature and pressure effects on molecular motion in the solid state has also been discussed.     

Coupling of concentration fluctuations to viscoelasticity in highly concentrated polymer solutions

Photon correlation spectroscopy in the polarized geometry has been used to systematically investigate the complex dynamics of a highly concentrated entangled polymer solution in a nominally good solvent, poly(butylacrylate) in dioxane. In addition to the well known fast cooperative diffusion process, a slow virtuallyq-independent mode is detected, whereq is the scattering wavevector, in agreement with previous experimental works on semidilute solutions. This mode is attributed to the viscoelastic nature of the transient physical network, formed by the entanglements, which relaxes its elastic stress induced by the concentration fluctuations, as confirmed by small amplitude oscillatory shear measurements; the latter reveal a terminal relaxation time comparable to the characteristic time of the slow relaxation process. Results, especially in terms of concentration and temperature dependence, are evaluated and discussed in view of the existing theoretical treatments in the field, predicting the existence of the slow viscoelastic relaxation. The relationship between dynamic light scattering and mechanical spectroscopy is established.     

Generalized two-dimensional correlation spectroscopy-- Theory and applications in analytical field

Since the theory of generalized two-dimensional (2-D) correlation spectroscopy was proposed, it has been keenly concerned in scientific research and its analytical method has been widely applied in various analytical fields. The mathematical process to construct generalized 2-D correlation spectroscopy and the physical meaning of 2-D correlation spectral map are described, and three examples in the fields of chemical analysis and molecular biology are provided, such as the component analysis of organic solvent, the analysis of biological molecules in the solvent with different pH values and structural analysis of protein. The theory and analytical method of generalized 2-D correlation spectroscopy are also detailedly commented.     

FTIR isothermal cure kinetics and morphology of dicyanate ester resin/polysulfone blends

The isothermal cure of a dicyanate ester monomer by “in situ” Fourier transform infrared spectroscopy (FTIR) has been investigated. The degree of cyanate conversion and the kinetic parameters have been determined for cobalt catalyzed and uncatalyzed resin as well as for polysulfone (PSF) modified systems at different curing temperatures. The cyanate conversion increases with the increment of temperature and with the addition of a catalyst, but it does not vary with the addition of PSF. In all the systems studied, the rate of reaction showed a second-order dependence on the cyanate concentration in the kinetically controlled stage. Moreover, the addition of PSF generates a matrix with two-phases that changes in composition and morphology depending on the percent of added thermoplastic and curing temperature as observed by scanning electron microscopy.     

Thermal restraint on PEG-EG mixtures by FTIR investigations and wavelet cross-correlation analysis

The aim of the present work is to investigate the thermal response of PolyEthylene Glycol 1000 (PEG1000) and of its mixtures with the monomer Ethylene Glycol (EG). On purpose Attenuated Total Reflectance Infra-Red (ATR-IR) spectra were collected, in the spectral range spanning from 400 cm⁻¹ to 4000 cm⁻¹, on PEG1000 and on its mixtures with EG, as a function of concentration and temperature, through positive thermal scans, i.e. by increasing temperature. It will be shown that ATR-IR technique reveals a powerful tool for the characterization of the thermal response in polymeric systems. The registered spectra have been analyzed both on the whole investigated spectral range, as well as, separately, on the restricted intramolecular OH stretching vibrational contribution region. In the first case the displacement of the spectral features from the spectrum at the lowest temperature, taken as reference spectrum, shows a lower dependence for the mixture. As far as the intramolecular OH vibrational contribution is concerned, besides a conventional analysis in terms of band components, three different data analysis procedures have been applied, i.e. the characterization of the temperature dependence of the intramolecular OH stretching center frequency, of the spectral distance and of the wavelet cross correlation coefficient. The three applied data analysis approaches indicates that the addition of a small amount of pure EG to PEG1000 significantly influences the OH vibrational properties of the PEG1000 polymeric matrix. The three different methods furnish a unique coherent interpretative picture which supports the validity of the applied approaches. Furthermore, the analyses show the presence of a higher thermal restraint for the PEG + EG mixture which confirms that, within the three-dimensional networks of hydrogen bonded EG-PEG1000 mixtures, a key role is played by EG in determining an increase of the hydrogen bond network density.     

Spectroscopic study of the water-soluble organic matter isolated from atmospheric aerosols collected under different atmospheric conditions

The composition of the water-soluble organic matter from fine aerosols collected in a rural location during two different meteorological conditions (summer and autumn) was investigated by UV-vis, synchronous fluorescence (with Δλ = 20 nm), FT-IR and CPMAS-¹³C NMR spectroscopies. A seasonal variation in the concentration of total carbon, organic carbon and water-soluble organic carbon was confirmed, with higher values during the autumn and lower values during the summer season. The chemical characterisation of the water-soluble organic matter showed that both samples are dominated by a high content of aliphatic structures, carboxyl groups and aliphatic carbons single bonded to one oxygen or nitrogen atom. However, the autumn sample exhibits a higher aromatic content than the summer sample, plus signals due to carbons of phenol, ketones and methoxyl groups. These signals were attributed to lignin breakdown products which are likely to be released during wood combustion processes. The obtained results put into evidence the major contribution of biomass burning processes in domestic fireplaces during low temperature conditions into both the concentration and the bulk chemical properties of the WSOC from fine aerosols.     

Generalized two-dimensional correlation spectroscopy——Theory and applications in analytical field

After correlation analysis for general spectro- scopy, two-dimensional (2-D) correlation spectroscopy is obtained by extracting the information contained in the spectra in two dimensions, which is the function of two dependent spectral variables. 2-D correlation spectroscopy is initially regarded as an analytical data treatment method in the study of molecular interaction by using sinusoidal infrared sign[1]. In 1993, it was extended to generalized 2-D correlation spectroscopy, which used mo…     

Isothermal crystallization behavior of water in poly(vinyl methyl ether) aqueous solution investigated by infrared and two-dimensional infrared correlation spectroscopy

Isothermal crystallization behavior of water at −30 °C in PVME aqueous solution with the PVME concentration in the range of 40-60 wt% was investigated in detail by time-dependent infrared spectroscopy and two dimensional correlation analysis. The result suggests that when the PVME concentration is between 40 and 60%, the crystallization rate decreases with increasing PVME concentration, and the crystallization of water in low temperature is kinetically controlled. Of particular interest is that the so-called “unfrozen bound water” can be frozen slowly when PVME aqueous solution is annealed at a suitable low temperature. The crystallization mechanism of water in PVME/water system is elucidated by 2D correlation analysis.     

二维相关荧光光谱技术

从发展历史、计算方程、一般规则和特有性质等方面系统地介绍了近年来在二维相关荧光光谱技术方面的方法探索和应用进展。以不同的外扰方式,如浓度、激发波长、猝灭以及其他如pH等分类,举例阐述了二维荧光相关光谱的可操作性及其应用,并与普通一维荧光光谱比较,说明了二维荧光相关光谱技术的优势。     

Polarized and depolarized dynamic light scattering of concentrated polystyrene solutions

Polarized and depolarized dynamic light scattering have been used to examine the dynamics of concentrated polystyrene solutions in dioctyl phthalate and toluene. Time-temperature superposition of the depolarized intensity correlation functions gave master curves covering more than 10 decades on the time scale. Polarized correlation functions are resolved into relaxational and diffusive components having different temperature dependences. When the relaxation rate of the concentration fluctuations approaches the reorientational relaxation rate, the concentration fluctuations become q-independent i.e. the diffusional relaxation is rate-determined by the backbone mobility. With a small molecule solvent as toluene, however, a part of the concentration fluctuations relaxes faster than the orientational relaxation, i.e., the diffusion occurs in the free volume within the “frozen” network.     

Further studies of multiple nuclear spin relaxation and local motions is dissolved 1,1-dichloro-2,2-bis(4-hydroxyphenyl)ethylene polyformal

Deuterium, carbon-13 and proton spin-lattice relaxation times at two fields are reported for dilute solutions of 1,1-dichloro-2,2,-bis(4-hydroxyphenyl)ethylene polyformal. The carbon-13 and proton relaxation measurements were made at a concentration of 10% (w/w) in deuterated s-tetrachloroethane and as a function of temperature. A partially deuterated analog with deuterated methylene groups was used in order to remove cross-relaxation effects from the phenylene proton relaxation. In addition, deuterium relaxation measurements were made on this sample at a concentration of 10% (w/w) in tetrachloroethane as a function of temperature. The data are interpreted in terms of segmental motion arising within the bisphenol units and anisotropic internal rotations of the other structural components. Motions of the phenylene groups in the backbone are described by the Hall-Helfand segmental correlation function plus the Woessner anisotropic internal-rotation correlation function. Motions of the formal linkage are described by the same segmental correlation function plus an internal correlation function based on restricted double rotation about the two carbon/oxygen bonds. The local motion of the formal group is discussed in terms of confomational transitions that are likely in a polyformal in view of the conformational energy surface. A Helfand Type II motion of the formal group corresponding to a transition from gg′ to tg is identified as the most plausible rearrangement of this unit.     

Numerical simulation of laser-induced breakdown spectroscopy: Modeling of aerosol analysis with finite diffusion and vaporization effects

The application of laser-induced breakdown spectroscopy (LIBS) to aerosol systems has been shown to provide quantitative analysis of particle-derived species; however, the exact nature of the plasma/particle interactions remains to be fully understood. Although the plasma/particle interaction may be idealized within a framework of instantaneous vaporization and analyte diffusion throughout the plasma volume, experimental evidence suggests that these processes actually occur on finite time scales relative to the plasma decay times at which measurements are frequently taken. In the present work, a numerical simulation of the temperature and species concentration fields of a plasma containing a single particle, including dissociation and diffusion on semi-empirical finite time scales, is developed. Using these results, the intensity of analyte emission is calculated as a function of time, and the standard ion/neutral ratios typical of aerosol-derived LIBS signals are calculated. Furthermore, the ratio of ion/neutral ratios for two different species was used to assess the temperature homogeneity of the particle-derived analytes in comparison to the overall plasma temperature field. From this numerical study, it is shown that the finite time scale of evaporation and diffusion of aerosol material results in a non-uniform spatial distribution in concentration. This results, in turn, in temperature and free electron density gradients within the plasma, leading to variation between the local conditions surrounding aerosol mass and the bulk conditions of the plasma as a whole.     

二维红外相关光谱研究缠结对冷冻升华无规聚苯乙烯分子运动的影响

用冷冻升华法制备了浓度为1×10^－4 和2×10^－5 g/mL的单链无规聚苯乙烯(a-PS). 利用FTIR测试方法, 测定a-PS在等温处理时红外吸收峰的时间依赖性与温度依赖性, 研究样品中链缠结和链结构单元的堆积等因素对红外吸收峰的影响, 进而探讨链缠结对a-PS分子运动的影响. 同时, 也通过二维相关分析来研究a-PS等温实验过程中, 链缠结的变化情况以及官能团之间的变化顺序, 推断在a-PS等温时, 与链结构单元的堆积相联系的苯环振动首先发生, 其次才是与链缠结相关联的CH₂振动发生变化, 并由此确定缠结对冷冻升华a-PS分子运动的影响.     

Structure-Infrared Optical Property-Correlations of C,O,H-Polymers for Transparent Insulation and Greenhouse Applications

Summary. In this paper an understanding of the physical relationships between the material structure and the temperature dependent infrared optical properties of different transparent polymer films for solar applications is described. The infrared optical properties are relevant for the heat transport of e.g. greenhouse and transparent insulation structures. The properties were determined based on infrared transmittance measurements and the assumption of a constant index of refraction from the visible range. To establish structure-property-correlations molecular structure parameters such as the concentration of carbon-oxygen single bonds and carbon-hydroxyl groups were determined. For 50 μm thick films a good correlation between the concentration of the functional carbon-hydroxyl and the carbon-oxygen group and the infrared optical thickness as well as the hemispherical emittance was found. This correlation fits well for high and low infrared radiation absorbing polymeric materials consisting of carbon, hydrogen, and oxygen atoms. The carbon-hydroxyl group appears to be slightly more effective than the carbon-oxygen single bond. Interestingly, the correlation works for polymers with aromatic (PC, PET) and aliphatic (PMMA, CTA, ethylene copolymers) groups.     

Quantitative determination by temperature dependent near-infrared spectra: a further study

Quantitative spectra-temperature relationship (QSTR) between near-infrared (NIR) spectra and temperature has been studied in our previous work (Talanta, 2010, 82, 1017-1021). In this study, applicability of the QSTR model for quantitative determination is further studied using the spectra of aqueous ethanol samples in the temperature range of 31-40 °C and the concentration range of 1-99%. The results show that QSTR model can be built by using the spectra in a small temperature range and the quantitative analysis can be achieved by only two spectra at different temperatures. Moreover, calibration curves for different concentration ranges (1-5%, 20-70%, 95-99%, v/v) are investigated by using linear and nonlinear curve fitting, respectively. Both of the linear and nonlinear curves are found to be applicable within these concentration ranges. Therefore, the temperature dependent NIR spectra may provide a new way for quantitative determination and may have high potential in bio-fluids analysis or industrial practices.