Curing kinetics of the epoxy system diglycidyl ether of bisphenol A/isophoronediamine by Fourier transform infrared spectroscopy

The curing reaction of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE, n = 0) and isophoronediamine (IPD), was studied by Fourier transform infrared spectroscopy (FTIR). The degree of conversions and the reaction rates at different isothermal curing temperatures were calculated from the infrared spectra using a method derived from Beer's law. This method is based on the ratio of the height of the characteristic absorbance peak to reference absorbance peak. A kinetic model proposed by Sourour and Kamal has been used to fit experimental data. Copyright © 2008 John Wiley & Sons, Ltd.     

Hierarchical clustering of infrared spectra

The generation of a hierarchical tree of 500 infrared spectra, using the recently proposed fractal or 3-distances-clustering method is described and discussed. The objects of clustering are infrared spectra of polymer compounds which are represented as sets of 80 complex Fourier coefficients, obtained by fast Fourier transformation of digitized absorbance spectra. The generated hierarchical tree, with a maximum height of 20 and an average height of 12 levels, yields a very satisfactory clustering scheme with respect to the structure of the compounds involved. In addition to very good clustering, a 100% retrieval (prediction) ability was obtained. This was achieved by the use of an iterative procedure after the initial tree had been generated. Additionally, the tree was tested with 240 infrared spectra of different compounds which were taken into account during the generation of the tree. The retrieval success of these test runs is discussed with respect to the structural similarity of the compounds to which the “unknown” spectra were linked.     

Construction and application of a novel library: Fourier transform infrared wavelet coefficients library

This article aims at designing a wavelet alternative to Fourier transform infrared spectra (FTIR). In order to select the most suitable wavelet parameters to perform, several decomposition levels and 53 wavelets were tested by trial and error approach, respectively. The result indicated that discrete meyer wavelet (dmey) associated with its third decomposition level was very efficient for this purpose. On the base of it, a novel library named as Fourier transform infrared wavelet coefficients library (FTIR-WC) has been constructed. Finally, two tools such as library search and structure elucidation were developed to evaluate the capability of the new library system. The results obtained were also compared with those from FTIR library by a variety of indices. The results suggested that the new library performed better but with less volume. This work is expected to propose a novel and practical strategy in infrared spectroscopic analysis.     

IR Spectrum Data Bank System

The infrared spectra of pure compounds of ninety thousands, poly compounds of twelve thousand, drugs of one thousand were included in the data bank. All of them can be searched out according to their serial number, chemical name, commercial name, amount of each atoms, or molecular formula, as well as their spectrum peak appearances. Program for spectrum information inputting, program for spectrum information search and program for spectrum peak appearance search were included in the system; in addition, spectrum information data bank, spectrum peak code data bank and spectrum figure data bank were attached to the system. System program was written by Visial Basic, and run under Windows system. The spectrum information data bank and spectrum figure data bank were administrated by Microsoft Access.The program for spectrum message inputting can be used to add message data and spectrum figure of some new compounds into the data banks by users themselves. The program for spectrum message search was designed to find out all the message data and spectrum figure of interested compound according to someone of the message data. The program for spectrum peak search was designed to find out some spectra most similar in peak shape with unknown spectrum by peak to peak comparison. When the wavenumbers and transmittances of main peaks in the spectrum of unknown sample were entered, the spectrum peak search was performed and several hits with higher similarity were reported including their similarity scores, spectrum serial numbers, sample's states,melt points, molecular formulas as well as spectrum images. If the search result was not satisfactory,some methods to modify spectrum parameters were reminded and search was performed again.     

Development of an on-site screening system for amphetamine-type stimulant tablets with a portable attenuated total reflection Fourier transform infrared spectrometer

We tried to develop a library search system using a portable, attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectrometer for on-site identification of 3,4-methylenedioxymethamphetamine (MDMA) and 3,4-methylenedioxyamphetamine (MDA) tablets. The library consisted of the spectra from mixtures of controlled drugs (e.g. MDMA and ketamine), adulterants (e.g. caffeine), and diluents (e.g. lactose). In the seven library search algorithms, the derivative correlation coefficient showed the best discriminant capability. This was enhanced by segmentation of the search area. The optimized search algorithm was validated by the positive (n = 154, e.g. the standard mixtures containing the controlled drug, and the MDMA/MDA tablets confiscated) and negative samples (n = 56, e.g. medicinal tablets). All validation samples except for four were judged truly. Final criteria for positive identification were decided on the basis of the results of the validation. In conclusion, a portable ATR-FT-IR spectrometer with our library search system would be a useful tool for on-site identification of amphetamine-type stimulant tablets.     

傅里叶变换红外光谱体表无创探测乳腺肿瘤

利用傅里叶变换红外(FTIR)光谱仪联合衰减全反射(ATR)探头的中红外光导纤维对46名健康志愿者及113名乳腺肿物患者的体表皮肤进行无创红外光谱测定, 并从分子水平比较、分析了正常乳腺和有肿物乳腺体表皮肤的红外光谱特征. 结果表明, 健康志愿者乳房皮肤8个FTIR光谱测定部位的图谱趋于一致; 正常乳腺体表与有肿瘤乳腺体表的吸收峰差异明显, 而1080 cm^-1处核酸相关吸收峰的变化对鉴别肿瘤的良、 恶性有重要意义.     

Crosslinking mechanism of an anhydride-cured epoxy resin as studied by fourier transform infrared spectroscopy

Fourier transform infrared spectra, including absorbance difference spectra, are presented which indicate that the accepted mechanism of tertiary amine-catalyzed copolymerization of cyclic anhydrides and epoxy resins requires modification. Results also show that the kinetic model is complicated by the lack of steady-state concentrations of the active species. The effect of silica filler and silane coupling agents on the reaction are also examined.     

Library search for HPLC diode array detection based on spectral interpolation

Summary A new method for spectral library search based on the dependences of absorbance on the modifier contents in binary mobile phases was developed. The normalisation of spectra by absolute and relative maximum and with respect to the area was tested. The correlation coefficient and the Euclidian distance were used to compare the spectra. The new method of library search allows interpolation of spectra at every composition of eluent in the model range. The range is bracketted by the upper and lower content of modifier in the eluent. In this range five reference spectra were recorded. For validation 34 spectra of pharmaceutical substances in water/methanol and water/acetonitrile mixtures were recorded. In the best case 97 % of spectra were identified correctly. The main problems encountered are that very similar substances e.g. dexa- and betamethasone, have similar spectra as well as similar spectral dependences on the composition of the mobile phase.     

Spectroscopic Investigation for Purity Evaluation of Detonation Nanodiamonds: Experimental Approach in Absorbance and Scattering

Nanodiamond powders have excellent mechanical, chemical, physical, and optical properties. In this research, two non-pure groups of nanodiamond particles labeled as ND1 and ND2 have been selected for purity evaluation by means of absorbance and scattering analysis. The nanodiamond powders have been used for Raman and dynamic light scattering (DLS), Fourier transform infrared (FTIR) and UV–Vis absorbance approaches. The Raman spectra show a weak diamond signal in ND2 as purity and 4 basic set of bands. FTIR absorbance spectroscopy was used in the spectral range of 400–3600 cm^?1. The results show that ND2 is almost non-absorbance with wavelength. It means that the diamond phase purity of ND2 is greater than ND1, and ND2 shows a better structure of diamond. UV–Vis absorption spectra of the sample have been recorded in the spectral range of 200–800 nm by means of nanodiamond suspended in methanol (NDM). The UV–Vis absorbance of NDM1 is stronger than NDM2 at the same concentration. Therefore the diamond phase purity of ND2 is greater than ND1. Particle size distribution and zeta potential of DNDs were investigated by DLS method. Finally the structure and phase of samples have been evaluated by X-ray diffraction (XRD) for confirmation.     

Recent developments in a computerized information system for organic chemistry

The configuration of a computerized information system for organic chemistry is outlined. Data banks for infrared, ¹³C-NMR, mass and x-ray diffraction spectra are accessed individually or from a central structure-handling and search system. Other facilities include a Chinese chemical documentation system, accessible in English or Chinese, and data analysis by multivariate techniques.     

Discriminating five Polygonatum medical materials and monitoring their chemical changes associated with traditional process by FT-IR spectroscopy coupled with multivariate analysis

Several Polygonatum species are important medicinal materials as tonic to cure disorders in China. Because of their different medical effects, it is desired to distinguish them at species level. In addition, to ensure and control their medical quality, it is also important to monitor their chemical changes associated with traditional process. Taking the advantages of Fourier transform infrared spectroscopy (FT-IR) and multivariate analysis, we developed a convenient, fast and reliable approach to discriminate and quality control these materials. Despite similar absorption patterns, each species also presented spectral differences, especially on the FT-IR fingerprint range of 1800-600 cm⁻¹. Second derivative method obviously enlarged those differences and then showed more species-specific features. These spectral differences could be used as powerful discriminating points to distinguish them. PCA results showed that each species separated clearly with their biological replicates grouped together, which indicated that the variance between species is greater than within species, therefore, these species could be distinguishable. Using this approach, the five herbal materials were discriminated successfully in their raw, processed and ethanol extracted formats. On the other hand, visual inspecting infrared spectra of samples from 1 to 9 process steps, absorbance near 1737, 1259, 817 and 780 cm^-1 increased gradually but decreased gradually at 927 cm⁻¹. Besides, spectral contour near 1050 cm⁻¹ changed sharply with process treatment. These spectral changes indicated that hydrolyzing polysaccharides into oligo- and mono-saccharides, especially glucose and fructose, are the main chemical changes associated with traditional process. This is consistent with the traditional experience that the processed materials are dark as night and sweet as malt sugar. Meanwhile, our results also indicated that their chemical constituents changed profoundly after process, which might be the chemical basis for raw and processed materials have different medical effects. Based on absorbance at 817 and 780 cm⁻¹ and the color, taste, smell of processed materials followed by energy efficacy, raw materials had to be processed more than 21 h to ensure their quality. This research shows the potential of FT-IR spectroscopy coupled with multivariate analysis to discriminate different herbs and to monitor chemical changes with process and then control their quality. This could be very helpful to ensure the quality, safety, and efficacy of herbs on clinical practices.     

Robust absorbance computations in the analysis of glucose by near-infrared spectroscopy

Procedures for data acquisition and data processing are evaluated for the optimal computation of absorbance values based on Fourier transform near-infrared transmission spectra. Samples consisting of physiological levels (1–20 mM) of glucose in an aqueous matrix of variable levels of bovine serum albumin and triacetin are studied in the combination spectral region (5000–4000 cm⁻¹). The weak glucose signals in this region define a challenging analysis that is extremely sensitive to the effects of instrumental drift. The impact of different procedures for obtaining absorbance estimates is evaluated in the context of multivariate calibration models based on partial least-squares (PLS) regression. Replicate calibration and prediction data acquired over 6 months are used to study the robustness of PLS models with respect to time. The recommended protocol for the absorbance calculations is based on the collection of a large group of individual background spectra during the instrumental warm-up period. Seven procedures are tested for obtaining optimal backgrounds for use with either the calibration or prediction data sets. When the developed methodology is employed, standard errors of prediction are maintained in the range of 1.0 mM for spectra acquired up to 6 months after the collection of the calibration data. This level of performance compares favorably to daily internal cross-validation errors of 0.5–0.9 mM.     

Effect of modified organic–inorganic hybrid materials on thermal properties of cotton fabrics

Phosphorus-modified siloxanes monomer DOPO-IPDI-AMEO (DIA) was synthesized and characterized by ¹H nuclear magnetic resonance (H NMR), ³¹P NMR, and Fourier transform infrared spectra (FTIR). It hydrolyzed and grew an organic–inorganic hybrid coating on the surface of cotton fabrics via sol–gel process. The conversion of gel reaction was characterized by solid-state ²⁹Si NMR. The effect of the modified organic–inorganic hybrid materials on thermal properties of cotton fabrics was investigated by thermogravimetric (TG) analysis, real time Fourier transform infrared (RT-FTIR), and microscale combustion calorimetry (MCC) experiments. In addition, thermogravimetry-Fourier transform infrared spectra (TG-FTIR) were used to investigate the released degradation products. The characterization information represented that DIA has been prepared successfully. Also the conversion of gel reaction was fairly high. The TG data showed that char residues increased with the addition of the DIA coating. While the peak heat release rate (PHRR) decreased with the presence of the coating in MCC test. Moreover, the flammable degradation products dropped obviously, which can be observed from the data of TG-FTIR.     

Detection of weathering in stockpiled coals by Fourier transform infrared spectroscopy

The process of natural oxidation of two low-rank coals exposed to the atmosphere for 11 months has been studied by Fourier transform infrared (FT-IR) spectroscopy. The study was carried out on samples taken at different time intervals and additionally from zones where signs of high oxidation and self-ignition were detected. The aliphatic hydrogen (3000-2800 cm⁻¹) and oxygen-containing structures (1800-1500 cm⁻¹) regions of the spectra were examined by curve-fitting analysis and a series of structural parameters based on ratios of integrated absorbance areas of curve-fitted bands were established. The aliphatic hydrogen content of samples tended to decrease with increasing time of storage and carboxyl groups only increased slightly under conditions of low pile activity. When oxidation and self-ignition processes took place, the structural changes were more significant. Aliphatic structures decreased drastically and net production of oxygen-containing structures was observed. Aliphatic hydrogen content evaluated from integrated absorbance measurements of normalized spectra and the CO/aliphatic hydrogen ratio seemed to be very sensitive in detecting signs of weathering even at very low levels of activity.     

Kisik — a combined chemical information system for a minicomputer

A minicomputer-oriented chemical information system (CIS) based on three different Spectrometries, i.e. infrared, mass, and ¹³C-n.m.r., is described and discussed.The system has roughly the same characteristics as CIS's implemented on large mainframe computers: substructure search, library searches on various files, file manipulation, statistical handling of retrieved data, etc. The source package is very suitable and simple for moving the entire CIS from one computer to another. In addition, the system has the Option UPDATE that enables the user to create his own fεles and modify them easily; this is rather difficult and expensive to implement on larger systems because of the very high disk-space price to frequency-of-access ratio. However, the quantity of data is strongly dependent on the disk space. At the moment the system handles 1016 compounds, each of which is described by a chemical name, molecular formula and weight, two-dimensional structure image, infrared, mass, and ¹³C-n.m.r. spectra. All these data for one compound are linked on-line via the identity number of the compound so there is no delay in accessing any of the items mentioned. The entire data bank together with the program package has a 1.8 Mbyte requirement which fits well within the 2.5 Mbyte space available on the small disk used by a PDP $\text{11}\text{34}$ minicomputer.     

Fine-structure enhancement--assessment of a simple method to resolve overlapping bands in spectra

A simple mathematical procedure--fine-structure enhancement--has been assessed on its ability to resolve overlapping bands in spectra. Its advantages and limitations have been explored using synthetic and experimental spectra. Fine-structure enhancement involves smoothing the original spectrum, multiplying the smoothed spectrum with a weighting factor and subtracting this spectrum from the original spectrum. As a result, the fine-structure of the original spectrum is enhanced in the processed spectrum and bands that overlap in the original spectrum appear as distinct bands in the processed spectrum. To be resolved by fine-structure enhancement, Lorentzian lines have to be separated by more than their quarter width at half maximum, Gaussian lines by more than their half width at half maximum. A comparison of fine-structure enhancement and Fourier self-deconvolution shows that Fourier self-deconvolution has in theory a higher potential to resolve overlapping bands. However, this depends crucially on the correct choice of the parameters. In practice, when parameters commonly used are chosen for Fourier self-deconvolution, fine-structure enhancement leads to similar results. This is demonstrated at the example of the infrared absorbance spectrum of the protein papain, where the amide I band components could be resolved similarly with both methods. Thus, fine-structure enhancement seems to be a simple alternative to Fourier self-deconvolution that does not require specialised software.     

Curve-fitting of Fourier manipulated spectra comprising apodization, smoothing, derivation and deconvolution

We present a general method for curve-fitting Fourier manipulated spectra, comprising apodized, smoothed, derivatised and deconvoluted spectra. The analytical expressions of Fourier manipulated bands in the spectral domain, needed for the curve-fitting, are usually very complex or do not even exist; hence an accurate curve-fit of Fourier manipulated spectra becomes unfeasible. Our strategy is to construct both the model and their derivatives in the Fourier domain, where they have simple and general expressions, and then Fourier transform them back to the spectral domain. The first benefit of this approach is the accurate curve-fitting of Fourier deconvoluted spectra, a main step in the secondary structure estimation of proteins by FTIR spectroscopy.     

Infrared spectra of phthalic acid, the hydrogen phthalate ion, and the phthalate ion in aqueous solution

The infrared spectra of a series of aqueous solutions containing phthalic acid (1,2-benzenedicarboxylic acid) and varying pH were examined using attenuated total reflection Fourier transform infrared spectroscopy and potentiometry. The basis spectra of phthalic acid, the hydrogen phthalate ion, and the phthalate ion were isolated using a factor analysis in which the absorbance of these species varies with pH and total phthalate concentration according to equilibrium and mass balance relations. Assignments of these basis spectra were made by comparison with spectra calculated ab initio. The conditional formation constants of phthalic acid and the hydrogen phthalate ion were determined at 25.0+/-0.1 degrees C in 0.6 M NaCl ionic media using infrared spectroscopy and in 1.5 M NaCl ionic media using both infrared spectroscopy and potentiometry.     

Recent advances in the hyphenation of chromatographs and FT-IR spectrometers

A common approach to measuring on-line infrared spectra of species eluting from gas, supercritical, and high performance liquid chromatographs is described. The eluites are deposited as very small spots on a moving ZnSe window and are passed through a microbeam of a Fourier Transform infrared spectrometer shortly after deposition. Identifiable spectra can be obtained from subnanogram quantities of each analyte. Spectra measured in this way are very similar to KBr-disk reference spectra.