Fourier transform infrared analysis of contamination by searching difference spectra against libraries of difference spectra

A method is presented for quickly identifying contaminants in a material. Fourier transform infrared (FT-IR) spectra are collected for anomalous and normal material using a method that gives highly reproducible absolute intensity, such as attenuated total reflection (ATR) spectroscopy of liquids or solids that contact the crystal perfectly. The difference spectrum is calculated as the point-by-point subtraction of absorbance values without the use of a variable subtraction factor, giving a spectrum with positive and negative spectral features. This spectrum is then searched against libraries of difference spectra, such as spectra of possible contaminants minus the spectrum of normal material. The key advantage of the method is that it removes subjective judgment in choosing the subtraction factor. It also provides information about the material that is depleted along with identifying the contaminant.     

Fourier transform infrared attenuated total reflection and transmission spectra studied by dispersion analysis

Fourier transform infrared transmission (FT-IR) and attenuated total reflection (ATR) spectra of water-ethanol mixtures are recorded and reconstructed thanks to a causal dispersion analysis technique. As expected, the Beer's law technique is an empirical approximate method that cannot account for complex spectral features. On the other hand, a rigorous analysis performed by using the theoretical optical paths for both experimental techniques and Gaussian dispersion analysis (GDA) allows the dielectric functions of the pure liquids to be calculated. Simulations of the whole mid-infrared spectra in the range 500-4000 cm(-1) match the experimental data very well, whatever the water-ethanol mixtures. This method is a powerful tool to quantify such model mixtures and more generally could be the first step toward software for assistance to the FT-IR spectrum analysis.     

A new method to obtain Fourier transform infrared spectra free from water vapor disturbance

Infrared absorption bands due to water vapor in the mid-infrared regions often obscure important spectral features of the sample. Here, we provide a novel method to collect a qualified infrared spectrum without any water vapor interference. The scanning procedure for a single-beam spectrum of the sample is divided into two stages under an atmosphere with fluctuating humidity. In the first stage, the sample spectrum is measured with approximately the same number of scans as the background. If the absorbance of water vapor in the spectrum is positive (or negative) at the end of the first stage, then the relative humidity in the sample compartment of the spectrometer is changed by a dry (or wet) air blow at the start of the second stage while the measurement of the sample spectrum continues. After the relative humidity changes to a lower (or higher) level than that of the previously collected background spectrum, water vapor peaks will become smaller and smaller with the increase in scanning number during the second stage. When the interfering water lines disappear from the spectrum, the acquisition of a sample spectrum is terminated. In this way, water vapor interference can finally be removed completely.     

Correlation between photoluminescence and Fourier transform infrared spectra in tetra-ethyl-ortho-silicate thin films

We report strong visible photoluminescence (PL) from thermally treated tetra-ethyl-ortho-silicate (TEOS) thin films at room temperature. High-resolution transmission electron microscope (HRTEM) studies showed that the PL originated from nanocrystalline-Si (nc-Si). HRTEM images showed that as-grown TEOS thin films had quasi-static amorphous (QSA) SiO(2) phases instead of the typical amorphous (TA) SiO(2) phases, and that they divided into small pieces of nc-Si after thermal treatment. In addition, Fourier transform infrared (FTIR) investigations showed that the QSA-SiO(2) phases were composed of three types of bonding modes (i.e., Si-O-Si bending, Si-O bending, and Si-O-Si stretching), which play important roles in the formation of the nc-Si at relatively lower annealing temperatures.     

Fourier transform spectroscopy of LaS in the infrared

We recorded the emission spectrum of diatomic lanthanum sulfide on the Los Alamos Fourier transform spectrometer. In the region 7500-16,000 cm(-1), we identified over 120 bands and assigned them to the A(2)∏(r)-X(2)Σ(+) and B(2)Σ(+)-X(2)Σ(+) transitions. Each of these bands is four headed.     

Comparative study of wine tannin classification using Fourier transform mid-infrared spectrometry and sensory analysis

Wine tannins are fundamental to the determination of wine quality. However, the chemical and sensorial analysis of these compounds is not straightforward and a simple and rapid technique is necessary. We analyzed the mid-infrared spectra of white, red, and model wines spiked with known amounts of skin or seed tannins, collected using Fourier transform mid-infrared (FT-MIR) transmission spectroscopy (400-4000 cm(-1)). The spectral data were classified according to their tannin source, skin or seed, and tannin concentration by means of discriminant analysis (DA) and soft independent modeling of class analogy (SIMCA) to obtain a probabilistic classification. Wines were also classified sensorially by a trained panel and compared with FT-MIR. SIMCA models gave the most accurate classification (over 97%) and prediction (over 60%) among the wine samples. The prediction was increased (over 73%) using the leave-one-out cross-validation technique. Sensory classification of the wines was less accurate than that obtained with FT-MIR and SIMCA. Overall, these results show the potential of FT-MIR spectroscopy, in combination with adequate statistical tools, to discriminate wines with different tannin levels.     

Fourier transform infrared analysis of gas composition in low-volume light bulbs

Fourier transform infrared spectroscopy has been used for in situ analysis of HBr, CH3Br, and CO within light bulbs at different stages of burning time. The interference fringes originated in the quartz walls of the bulbs have been eliminated by different methods. The NIPALS procedure yielded higher S/N ratio than the fringe-elimination method applied. The CO and HBr showed time-dependent concentration changes during the burning period. The maximum CO concentration (approximately 6 ppm) was detected after 30-50 s of burning time, and then it practically burned out after 5 h. The HBr concentration increased in the first 3 min of burning, and then its concentration stabilized at a 10-15 ppm level. After 5 s of illumination, the CH3Br concentration became undetectable.     

Fourier transform infrared detection in miniaturized total analysis systems for sucrose analysis

In this work, a flow system containing a micromachined lamella-type porous silicon reactor and a novel mid-IR fiber-optic flow cell were used for the enzymatic determination of sucrose in aqueous solution. The method relies on the enzymatic hydrolysis of sucrose to fructose and glucose catalyzed by β-fructosidase and on the acquisition of FT-IR spectra before and after complete reaction. β-Fructosidase was covalently bound to the porous silicon surface of the channels in the microreactor. The porous silicon was achieved by anodization of the silicon reactor in a HF/ethanol mixture. For the measurement of small amounts of aqueous solution, a miniaturized flow cell was developed which consisted of two AgCl(x)Br(1)(-)(x) fiber tips (diameter, 0.75 mm) coaxially mounted in a PTFE block at a distance of 23 μm. The flowing stream was directed through the gap of the two fiber tips which served to define the optical path length and to bring the focused mid-IR radiation to the place of measurement. Using this construction, a probed volume of ～10 nL was obtained. The calibration curve was linear between 10 and 100 mmol/L sucrose. Furthermore, the potential of this method was demonstrated by the analysis of binary sucrose/glucose mixtures showing no interference from glucose and by the successful determination of sucrose in real samples.     

Quantitative analysis of polyethylene blends by Fourier transform infrared spectroscopy

The quantitative analysis of binary polyethylene (PE) blends by Fourier transform infrared (FT-IR) spectroscopy has been achieved based on the ratio of two absorbance peaks in an FT-IR spectrum. The frequencies for the absorbance ratio are selected based on structural entities of the PE components in the blend. A linear relationship between the absorbance ratio and the blend composition was found to exist if one of the absorbance peaks is distinct to one of the components and the other peak is common to both components. It was also found that any peak resulting from short-chain branching in copolymers (such as linear low-density polyethylene (LLDPE) or metallocene-catalyzed LLDPE (mLLDPE)), is suitable for use as the peak that is designated as being distinct to that component. In order to optimize the linearity of the equation, however, the selection of the second common peak is the most important and depends on the blend system studied. Indeed, under certain circumstances peaks that are not spectrally distinct can be used successfully to apply the method. The method exhibits potential for the routine analysis of PE blends that have been calibrated prior to its application.     

Fourier transform infrared spectral analysis of degenerative cartilage: an infrared fiber optic probe and imaging study

A preliminary investigation into the diagnostic potential of an infrared fiber optic probe (IFOP) for evaluating degenerative human articular cartilage is described. Twelve arthritic human tibial plateaus obtained during arthroplasty were analyzed using the IFOP. Infrared spectra were obtained from IFOP contact with articular surface sites visually graded normal or degraded (Collins Scale grade 1 and grade 3, respectively). Comparisons of infrared spectral parameters (peak heights and areas) were made to elucidate spectral indicators of surface degeneration. IFOP spectral analysis revealed subtle but consistent changes between grades 1 and 3 sites. Infrared absorbance bands arising from type II collagen were observed to change with degradation. More degraded tissues exhibited increased amide II (1590-1480 cm(-1))/1338 cm(-1) area ratio (p=0.034) and decreased 1238/1227 cm(-1) peak ratio (p = 0.017); similar changes were seen with Fourier transform infrared imaging spectroscopy (FT-IRIS) analysis. Grades 1 and 3 cartilage showed consistent spectral differences in the amide II, III, and 1338 cm(-1) regions that are likely related to type II collagen degradation that accompanies cartilage degeneration. These results suggest that it may be possible to monitor subtle changes related to early cartilage degeneration, allowing for IFOP use during arthroscopy for in situ determination of cartilage integrity.     

Fourier transform infrared analysis of poly(ester-urethanes) at low temperature in-situ by using a newly constructed liquid nitrogen cooled sample stage

The design and use of an apparatus intended to cool samples for in-situ Fourier transform infrared (FTIR) spectroscopy study is described. Using liquid nitrogen as the cooling medium, a working sample temperature of −165°C was achieved. The combination of the cooling stage and FTIR spectroscopy allowed us to study the hydrogen bonding in polyurethanes at very low temperatures in-situ. Experimental results in the N-H and carbonyl absorption regions as a function of temperature are compared. This revised version was published online in November 2006 with corrections to the Cover Date.     

Absorption-mode: the next generation of Fourier transform mass spectra

The Fourier transform spectrum can be presented in the absorption-mode (commonly used in FT-NMR), magnitude-mode (FT-ICR), and power-mode (engineering applications). As is routinely used in FT-NMR, it is well-known that the absorption-mode display gives a much narrower peak shape which greatly improves the spectrum; recently, the successful solution of the phase equation allowed broadband phase correction which makes it possible to apply the absorption-mode routinely in FT-ICR. With the empirical evidence provided herein, it has been confirmed that in addition to the improvement on resolving power, compared to the conventional magnitude-mode, the new absorption-mode improves the signal-to-noise ratio (S/N) of a spectrum by 1.4-fold and can improve the mass accuracy up to 2-fold with no extra cost in instrumentation. Therefore, it is worthwhile to apply and promote absorption-mode in routine FT-ICR experiments.     

Effects of CaCl2 and MgCl2 on Fourier transform infrared spectra of lung cancer cells

The cations Ca2+ and Mg2+ are two important factors in the growth and maintenance of living cells. The addition of Ca2+ to living cells can cause a change in the three-dimensional (3D) structure of calcium binding proteins. Therefore, we decided to study whether the addition of CaCl2 and MgCl2 to three in vitro growing lung cancer cell lines could cause changes that could be measured by Fourier Transform Infrared Spectroscopy. The addition of CaCl2 or MgCl2 to lung cancer cells caused an increase in absorbance of the trough at 1410 cm(-1). This translated into an inversion of the 1410/1395 cm(-1) ratio following the addition of CaCl2 or MgCl2 for all three lung cancer cell lines. Also, the amide I peak shifted from around 1631 cm(-1) to lower wavenumbers when CaCl2 or MgCl2 was added to cancer cells. Furthermore, the addition of these two substances caused a shift of the peak between 3290 and 3395 cm(-1). Finally, while the addition of CaCl2 to lung cancer cells was associated with an increased cell death, this was not the case following the addition of MgCl2. This would confirm that the changes seen in the spectra of all three cell lines are due to metabolic and ionic shifts rather than cell death.     

Reproducibility of Fourier transform infrared spectra of compost, municipal solid waste, and landfill material

The reproducibility of infrared spectra from different waste materials such as compost, mechanically-biologically treated (MBT) municipal solid waste, and landfill materials was investigated. Reproducibility tests focused mainly on infrared spectra and parameter prediction from the spectrum developed for composts and MBT-waste, as well as band height ratio measurement for landfill materials in terms of practical applications. Compared to compost and landfill material, the reproducibility of infrared spectra from MBT-waste was considerably lower. Accordingly, sample preparation was modified and maximum mean deviation was minimized from 8.3% to 4.2%. The number of required spectra replicates was determined in consideration of practical aspects such as parameter prediction for composts and MBT-waste and the measurement of band height ratios (2925/1630 cm(-1)) of landfill materials. For composts two-fold measurements and for MBT-waste and landfill materials three-fold measurements were considered appropriate.