Near-infrared Emission Spectroscopy Research Articles

Near infrared emission spectroscopy for rapid compositional analysis of Portland cements

Near infrared emission spectroscopy (NIRES) has been investigated to yield a new analytical method for determination of CaO, SiO2, Al2O3, Fe2O3, MgO, and SO3 in Portland cement samples. The analyses were accomplished by correlation of the second derivative NIRES spectra with reference elemental analyses made by X-ray Fluorescence (XRF), using Partial Least Square (PLS) regression models. Four different types of cements (type II, III, IV and V) were included in the models. The results show RMSEP from 0.18 to 1.67% (m/m) (which represents 8.6 to 2.8% of the mean value parameters, respectively) and precision (repeatability) from 0.12 to 1.49% (m/m). The worse performance of prediction [RMSEP = 0.18% (m/m), r2 = 0.63] was found for Fe2O3 determination due its low variability in the samples employed in the calibration and validation set, usual low content in cements, and high correlation with the weak emitting C4AF phase. However, the paired t-test at 95% confidence level demonstrated that the analytical results obtained by NIRES multivariate models are equivalent to measurements performed by XRF for all oxides analyzed. The cost, speed and safety aspects are improved in comparison with the XRF method. The method based on NIRES requires no sample preparation and speed up the cement analysis (6 min) about 5 times when compared with the method based on XRF presently employed by cement industries.

Near infrared emission photometer for measuring the oxidative stability of edible oils

Near infrared emission spectroscopy (NIRES) allows the determination of the induction time (IT) of edible oils in accelerated oxidation experiments by monitoring the emissivity of a band at 2900nm, which corresponds to the formation of hydroperoxides. In this work, a new near infrared emission photometer dedicated to the determination of oxidative stability is described. The photometer presents several advantages compared to the previously reported NIRES instrument, such as lower cost and extreme simplicity of design and maintenance. The results obtained in the evaluation of the proposed instrument were compared with the official Rancimat method and instrument. The significant advantages include: faster analysis, lower sample consumption and operational simplicity. It is demonstrated that the procedure for determination of oxidative stability of oils can be significantly simplified and performed by measuring the sample emission at only one spectral region centered at 2900nm. Also, the proposed instrument and method present precision equivalent to the Rancimat method (coefficient of variation=5.0%). A significant correlation between the methods has been found (R2=0.81).

Comparison of near‐infrared emission spectroscopy and the Rancimat method for the determination of oxidative stability

AbstractThis work presents a comparison between a new method for the determination of the oxidative stability of edible oils at frying temperatures, based on near‐infrared emission spectroscopy (NIRES), and the Rancimat method at 110 °C. In the NIRES‐based method, the induction time (IT) is determined by means of the variation of the emission band at 2900 nm during heating at 160 °C. The comparison between the IT values obtained with the two methods for 12 samples of edible oils shows some correlation for samples of the same type once there is an agreement on the sequence of highest to lowest IT values between the methods, but a poor correlation considering all samples (correlation coefficient of 0.78). This lack of correlation demonstrates that the results obtained with the Rancimat method cannot be used as an indication of the oxidative stability, or the resistance to degradation, of edible oils at frying temperatures. The difference in the heating temperatures used in the two methods leads to 20–36 times higher IT values for the Rancimat method in relation to the NIRES‐based method, but with similar repeatabilities (2.0 and 2.8%, respectively).

Use of near infrared emission spectroscopy in the study of supporting materials and stationary phases for liquid chromatography

Near infrared emission spectroscopy (NIRES) has been investigated in the study of different materials employed in liquid chromatography. The samples were heated in a nitrogen atmosphere and the emission spectra were obtained using a lab-made NIRES instrument. Through principal component analysis (PCA) using the raw emission spectra, it was possible to distinguish different materials according to their physical and/or chemical characteristics. Linear relationships between emissivity spectra and the contents of the coating material or the specific surface areas was observed for stationary phases or bare silicas, respectively. Furthermore, the thermal stability of stationary phases could be followed in real time.

A new method for determination of the oxidative stability of edible oils at frying temperatures using near infrared emission spectroscopy

This work proposes a new method for determination of the oxidative stability of edible oils at frying temperatures using near infrared emission spectroscopy (NIRES). The method is based on heating an oil sample at a fixed temperature, followed by the acquisition of the emission spectra with time using a home-made spectrometer with an acousto-optical tunable filter (AOTF) as monochromator. The induction time, related to the oxidative stability, is determined by means of the emission band at 2900 nm and its increase and broadening during the heating time. After the induction period, this band also provides information related to the oxidation rate of the sample. Twelve samples of edible oils, of different types and from different manufacturers, were analyzed for oxidative stability with mean repetitivity of 3.7%. The effects of nitrogen insertion, heating temperature and the presence of antioxidant compounds on the oxidative stability were evaluated.

Near-Infrared Emission Spectrometry Based on an Acousto-Optical Tunable Filter

A spectrometer has been constructed to detect the radiation emitted by thermally excited samples in the near-infrared spectral region extending from 1500 to 3000 nm. The instrument employs an acousto-optical tunable filter (AOTF) made of TeO2 and attains maximum sensitivity by making effective use of the two diffracted beams produced by the anisotropic AOTF. The full exploitation of the transmitted power of the monochromatic beams is reported for the first time and became possible because the detector does not saturate when employed for the acquisition of the weak emission signal in the NIR region, even when exposed to the total (nondiffracted) beam. Thus, modulation and lock-in-based detection can be employed to find the intensity of the diffracted beams superimposed on the nondiffracted beam. The resolution is slighted degraded in view of the small (approximately 10 nm) difference in the wavelength diffracted in the ordinary and extraordinary beams. The instrument has been evaluated in terms of signal-to-noise ratio, effect of sample thickness, and excitation temperature and for its potential in analytical applications in monitoring high-temperature kinetics, for qualitative identification of inorganic solids, for use with a closed cell to obtain spectra of species that evaporate at the temperatures (> 150 degrees C) necessary for sample excitation, and for quantitative purposes in the determination of soybean oil content in olive oil. The feasibility of near-infrared emission spectroscopy has been demonstrated together with some of its advantages over mid-infrared emission spectroscopy, such as greater tolerance to sample thickness, suitable signal-to-noise, and its use in the investigation of kinetic phenomena and phase transitions at high temperatures.

Synthesis and Nonlinear Optical, Photophysical, and Electrochemical Properties of Subphthalocyanines

Novel boron(III) subphthalocyanines (SubPcs) soluble in organic solvents containing a variety of donor and acceptor substituent groups have been synthesized by boron trihalide-induced cyclotrimerization of adequately substituted derivatives of phthalonitrile in 1-chloronaphthalene. The choice of the substituents on the 1,2-dicyanobenzene derivatives has been made taking into account the high reactivity of the Lewis acid BCl3 toward many functional groups. Considering this limitation, we set out to synthesize phthalodinitriles equipped with iodo, nitro, alkyl- or arylthio, alkyl- or arylsulfonyl groups that are sufficiently stable under the required reaction conditions and also provide an easily accessible set of acceptor/donor substituents. The quadratic and cubic hyperpolarizabilities of these compounds as well as their linear optical and electrochemical properties have been measured by several techniques, including EFISH (at two wavelengths), HRS, and THG, steady-state and time-resolved absorption and fluorescence, laser-induced optoacoustic calorimetry, time-resolved near-infrared emission spectroscopy, and cyclic voltammetry. βHRS has been measured at 1.46 μm, where the contamination from the multiphoton-induced fluorescence can be ruled out. βHRS reachs high values that markedly depend on substitution. It shows a clear enhancement with the acceptor character of the substituents, the highest values being obtained for the compounds bearing the strongest acceptor groups. They are comparable or even superior to many efficient second-order compounds. A main outcome of these results is that an adequate choice of the substituents offers a promising route for optimization of the quadratic response of the SubPcs. This kind of compounds is less prone to aggregation than their expanded analogues, the phthalocyanines, fluoresces with quantum yields ca. 0.25, lower than those typical for phthalocyanines, and has larger triplet quantum yields. The triplet-state lifetime is in the 100-μs time range, long enough for efficient oxygen quenching. Indeed, subphthalocyanines sensitize singlet molecular oxygen, O2(1Δg), with quantum yields ranging from 0.23 to 0.75. The ground-state oxidation potentials are similar to those of phthalocyanines, while the reduction potentials are clearly more negative; i.e., they are more difficult to reduce. In contrast, electronically excited subphthalocyanines are more easily oxidized than the corresponding phthalocyanines by ca. 500 mV which results in lower photostability, especially in polar solvents.