Showing papers in "Applied Spectroscopy in 1992"
TL;DR: In this paper, a comprehensive analysis of the surface sum-frequency generation (SFG) spectrum has been presented to facilitate the analysis of a surface-fixed array system with a given experimental setup, where the electric field components of the SFG beam for a given setup have been related via appropriately defined Fresnel coefficients to the non-linear source polarization.
Abstract: Comprehensive expressions have been presented to facilitate the analysis of the surface sum-frequency generation (SFG) spectrum. The electric field components of the SFG beam for a given experimental setup have been related via appropriately defined Fresnel coefficients to the non-linear source polarization, which in turn has been related to the electric fields of exciting visible and infrared beams through the macroscopic SFG susceptibility tensor. The coefficients of transformation have been given to relate the laboratory-fixed Cartesian components of the SFG tensor to the components described in a surface-fixed axis system. The tensor components have been further related to the components of the microscopic hyperpolarizability tensor of surface species, and the explicit expressions (in terms of the Euler angles defining molecular orientation) of the transformation coefficients are presented to describe the Cartesian tensor components described in a surface-fixed axis system by the molecule-fixed components.
373 citations
TL;DR: In this article, the wavelength of the excitation laser was tuned into resonance with an electronic absorption band of only one molecular species, and the vibrational Raman scattering from this species can be selectively enhanced.
Abstract: Resonance Raman spectroscopy is a powerful technique for probing the vibrations of particular chromophores in multicomponent systems. By tuning the wavelength of the excitation laser into resonance with an electronic absorption band of only one molecular species, the vibrational Raman scattering from this species can be selectively enhanced. Thus, resonance Raman spectroscopy can provide structural information for chromophores in solution or biological chromophores within their functionally active protein environment. However, since the very nature of the experiment requires that the excitation light be absorbed by the sample, the measurement of resonance Raman spectra is often made difficult by a large fluorescence background in the same spectral region as the Raman scattering. The problem of fluorescence interference from intrinsic sample emission is often further exacerbated in biological samples, where low-concentration impurities with large fluorescence yields can be difficult to remove. Even weak fluorescence, with an effective fluorescence quantum yield of ≈10−4, completely overwhelms resonance Raman signals, which have typical quantum yields of ≈10−7.
319 citations
DSM1
TL;DR: In this article, the performance of the confocal Raman microscope can be described satisfactorily by geometrical optics, and measurements are performed to determine the depth resolution of the system for different combinations of objectives and pinholes.
Abstract: Raman microspectroscopy can be used effectively to study very small samples or to study small areas within a transparent sample. With the application of the technique of confocal microscopy to a Raman microscope, the depth resolution of the instrument can be enhanced considerably. Confocal microscopy uses a pinhole, placed in the back image plane of the microscope objective, to block light from outside the focal plane. In this way the signal from the small volume element one wants to study can be better separated from the signals arising from the surrounding material. In this paper we show that the performance of the confocal Raman microscope can be described satisfactorily by geometrical optics. Furthermore, we have performed measurements to determine the depth resolution of our system for different combinations of objectives and pinholes. Finally, we report on the applications of this technique to different polymer systems, such as multilayer foils, fibers, and fiber composites.
191 citations
TL;DR: In this article, a 2D statistical correlation of mid and near-infrared spectra is presented as a means to assist with qualitative spectral interpretation, which is applied to complex agricultural samples that differ in wax (cuticle), carbohydrate, protein, and lignin content.
Abstract: A novel approach, utilizing a two-dimensional (2D) statistical correlation of mid- and near-infrared spectra, is presented as a means to assist with qualitative spectral interpretation. The method utilizes cross-correlation by least-squares to assess changes in both regions that result from changes in sample composition. The technique has been applied to complex agricultural samples that differ in wax (cuticle), carbohydrate, protein, and lignin content. Dispersive near-infrared (NIR) and interferometric mid-infrared (FT-IR) diffuse reflectance spectra were obtained on each of the samples, and point-for-point 2D cross-correlation was obtained. The technique permits the correlation of the combination and overtone region of the NIR to the fundamental vibrations in the mid-infrared (MIR) region. This allows the determination of the most probable source of NIR signals and verification of the "real" information content of the purely statistically derived signals whose intensities currently are used for quantitative analysis in this spectral region.
177 citations
TL;DR: It is suggested that blood chemistry differences were sufficiently different for the four subjects to require that a larger number of subjects be included in the calibration for adequate prediction abilities to be obtained from near-infrared spectra of blood from subjects not included inThe calibration.
Abstract: Noninvasive monitoring of glucose in diabetic patients is feasible with the use of near-infrared spectroscopic measurements. As a step toward the final goal of the development of a noninvasive monitor, the near-infrared spectra (4250 to 6600 cm−1) of glucose-doped whole blood samples were obtained along with reference glucose values. Glucose concentrations and spectra of blood samples obtained from four subjects were subjected to multivariate calibration with the use of partial least-squares (PLS) methods. The cross-validated PLS standard errors of prediction for glucose concentration based on data obtained from each individual subject's blood samples averaged 33 mg/dL over the range from 3 to 743 mg/dL. Cross-validated standard errors for glucose concentration from PLS calibrations based on data from all four subjects were 39 mg/dL. However, when PLS models based upon three subjects' data were used for prediction on the fourth, glucose prediction abilities were poor. It is suggested that blood chemistry differences were sufficiently different for the four subjects to require that a larger number of subjects be included in the calibration for adequate prediction abilities to be obtained from near-infrared spectra of blood from subjects not included in the calibration.
154 citations
TL;DR: In this paper, a single-stage spectrograph and charge-coupled-device (CCD) detector were used to collect near-infrared (NIR) Raman spectra from intact human arterial tissue.
Abstract: We demonstrate the use of a single-stage spectrograph and charge-coupled-device (CCD) detector to collect near-infrared (NIR) Raman spectra from intact human arterial tissue. With 810-nm excitation, the fluorescence emission from human artery is sufficiently weak to allow observation of Raman bands more rapidly with the spectrograph/CCD system than with 1064-nm excited FT-Raman systems. We also present a method for removing the broad-band emission from the spectra by computing the difference of two emission spectra collected at slightly different excitation frequencies. Our results indicate that NIR Raman spectra can be collected in under one second with the spectrograph/CCD system and an optical fiber probe, opening the possibility of in vivo clinical applications.
144 citations
TL;DR: The NIR FT-Raman spectrum of old-leaf (about one year old) Japanese tea has been compared with that of its new leaf as discussed by the authors, indicating that the ratio can be used as a practical indicator for estimating the unsaturation level of a wide range of lipid-containing foods.
Abstract: The 1064-nm excited Fourier transform (FT) Raman spectra have been measured in situ for various foods in order to investigate the potential of near-infrared (NIR) FT-Raman spectroscopy in food analysis. It is demonstrated here that NIR FT-Raman spectroscopy is a very powerful technique for (1) detecting selectively the trace components in foodstuffs, (2) estimating the degree of unsaturation of fatty acids included in foods, (3) investigating the structure of food components, and (4) monitoring changes in the quality of foods. Carotenoids included in foods give two intense bands near 1530 and 1160 cm−1 via the pre-resonance Raman effect in the NIR FT-Raman spectra, and therefore, the NIR FT-Raman technique can be employed to detect them nondestructively. Foods consisting largely of lipids such as oils, tallow, and butter show bands near 1658 and 1443 cm−1 due to C=C stretching modes of cis unsaturated fatty acid parts and CH2 scissoring modes of saturated fatty acid parts, respectively. It has been found that there is a linear correlation for various kinds of lipid-containing foods between the iodine value (number) and the intensity ratio of two bands at 1658 and 1443 cm−1 (I1658/I1443), indicating that the ratio can be used as a practical indicator for estimating the unsaturation level of a wide range of lipid-containing foods. A comparison of the Raman spectra of raw and boiled egg white shows that the amide I band shifts from 1666 to 1677 cm−1 and the intensity of the amide III band at 1275 cm−1 decreases upon boiling. These observations indicate that most α-helix structure changes into unordered structure in the proteins constituting egg white upon boiling. The NIR FT-Raman spectrum of old-leaf (about one year old) Japanese tea has been compared with that of its new leaf. The intensity ratio of two bands at 1529 and 1446 cm−1 (I1579/I1446), assignable to carotenoid and proteins, respectively, is considerably smaller in the former than in the latter, indicating that the ratio is useful for monitoring the changes in the quality of Japanese tea.
141 citations
TL;DR: In this paper, a calibration transfer method called piecewise direct standardization (PDS) is applied to a set of gasoline samples measured on two different NIR spectrometers.
Abstract: Near-infrared (NIR) spectroscopy has been widely accepted as a quantitative technique in which multivariate calibration plays an important role. The application of NIR to process analysis, however, has been largely limited by a problem identified as calibration transfer, the attempt to transfer a well-established calibration model from one instrument (e.g., located in the central laboratory) to another instrument of the same type (e.g., located on an industrial process). A calibration transfer method called piecewise direct standardization (PDS) is applied to a set of gasoline samples measured on two different NIR spectrometers. On the basis of the measurement of a small set of transfer samples on both instruments, a structured transformation matrix can be determined and applied to transform spectra between two instruments, enabling the transfer of calibration models. The effect of spectrum preprocessing on standardization is studied with the use of a set of gasoline samples. In a separate study, the day-to-day instrument variation as observed from the change in the polystyrene spectrum is related to the prediction of moisture, oil, protein, and starch content in corn samples, and then the possibility of using such generic standards to replace real samples in a transfer set is explored. In all cases, a standard error for prediction comparable to full set cross-validation is obtained through standardization.
128 citations
TL;DR: Changes in spectrometer design or calibrations based on large numbers of subjects are expected to eliminate the presence of this bias and methods are demonstrated that significantly reduce the bias while retaining the sensitive outlier detection capabilities of the PLS methods.
Abstract: The multivariate calibration method of partial least-squares (PLS) was applied to the mid-infrared spectra of whole blood for quantitatively determining blood glucose concentrations. Separate calibration models were developed on the basis of spectra of whole blood obtained from six diabetic subjects from either in vitro glucose-supplemented blood or blood obtained from the same subjects in the post-prandial state during meal tolerance tests. The cross-validated PLS calibrations yielded average errors in glucose concentration of 11 and 13 mg/dL, respectively. It is desirable to use the calibration models based on the in vitro glucose-supplemented blood for determining glucose concentrations in unknown blood samples. However, when these multivariate calibration models based upon in vitro blood spectra were applied to the spectra of the post-prandial blood samples, a subject-dependent concentration bias was observed. The source of this bias was not identified, but when the glucose determinations were corrected for the bias, average concentration errors were found to be 14 mg/dL. Changes in spectrometer design or calibrations based on large numbers of subjects are expected to eliminate the presence of this bias. If these measures do not succeed in eliminating the bias, then methods are demonstrated that significantly reduce the bias while retaining the sensitive outlier detection capabilities of the PLS methods. These latter methods require that the infrared spectrum and reference glucose levels be obtained from a single blood sample from each subject.
124 citations
TL;DR: In this paper, a multivariate analysis of near-infrared spectra of gelatinized starch was performed using principal component regression (PCR) to identify the importance of spectral variations due to the effect of scattering.
Abstract: This paper describes an approach for studying collections of near-infrared spectra by using multivariate analyses. The method is illustrated with the use of two sets of spectra of gelatinized starch, recorded in the transmission mode between 650 and 1235 nm. The first set consisted of 99 spectra of partly gelatinized samples (from 24.5 to 100% gelatinization). Application of principal component analysis (PCA) made it possible to identify an outlying sample and to identify the importance of spectral variations due to the effect of scattering. Hence, it was possible to eliminate the scatter variations. From principal component regression (PCR), it was shown that the relationship between corrected spectra and gelatinization was not linear. Discriminant analysis was applied to seven classes of starch gelatinization. Only five samples out of 98 were incorrectly identified. The second set of samples was designed for studying the effect of temperature variation on the spectra of fully gelatinized starch samples. It was possible to show from PCR that the relationship between the spectra and temperature was linear. The "spectral patterns" assessed from discriminant analysis of starch gelatinization and from the PCR of temperature were compared.
116 citations
TL;DR: In this paper, the authors measured the UV resonance Raman spectra of Bacillus cereus, Bacillus megaterium and Bacillus subtilis endospores at various exciting wavelengths.
Abstract: UV resonance Raman spectra of Bacillus cereus, Bacillus megaterium, and Bacillus subtilis endospores have been excited at 222.7, 230.7, 242.5, and 251.1 nm, and spectra have been compared with those of vegetative cells. The resonance Raman spectra of aqueous solutions of dipicolinic acid and calcium dipicolinate have been measured at the same wavelengths. Spectra of endospores and their corresponding germinated spores show only modest differences when excited at 222, 231, and 251 nm. However, very substantial differences appear when excitation occurs at 242 nm. Difference spectra obtained at 242 nm by subtracting spectra of germinated spores of Bacillus cereus from spectra of their corresponding endospores are attributed almost entirely to dipicolinate. Vegetative cells and endospores show large spectral dissimilarities at all exciting wavelengths. These spectral differences, which vary strongly with exciting wavelength, appear to be the results of large differences in the amounts and composition of proteins and nucleic acids, especially ribosomal RNA. The very substantial resonance enhancement of Raman spectra has been obtained from aqueous solutions of pure dipicolinic acid and of sodium and calcium dipicolinate salts, as well as spores at the various exciting wavelengths. The strong enhancement of dipicolinate spectra in spores, however, was noted only with 242-nm excitation. Consequently, only with 242-nm light was it possible to selectively and sensitively excite and study calcium dipicolinate in spores. Resonance enhancement of the dipicolinate spectra with 242-nm excitation appears due primarily to resonance interactions with n-π* electronic transitions associated with the pyridine ring and/or the carboxylate group.
TL;DR: In this paper, an acousto-optic tunable filter (AOTF) is used to obtain high-fidelity Raman images and Raman spectra.
Abstract: In this communication, we describe a technique for obtaining high-fidelity Raman images and Raman spectra. The instrumentation provides the ability to rapidly collect large-format images with the number of image pixels limited only by the number of detector elements in the silicon charge-coupled device (CCD). Wavelength selection is achieved with an acousto-optic tunable filter (AOTF), which maintains image fidelity while providing spectral selectivity. Under computer control the AOTF is capable of μs tuning speeds within the operating range of the filter (400-1900 nm). The AOTF is integrated with the CCD and holographic Raman filters to comprise an entirely solid-state Raman imager containing no moving parts. In operation, the AOTF is placed in front of the CCD and tuned over the desired spectral interval. The two-dimensional CCD detector is employed as a true imaging camera, providing a full multichannel advantage over competitive Raman imaging techniques. Images and spectra are presented of a mixture of dipalmitoyl-phosphatidylcholine (DPPC) and L-asparagine, which serves as a model system for the study of both lipid/peptide and lipid/protein interactions in intact biological materials. The Raman images are collected in only several seconds and indicate the efficacy of this rapid technique for discriminating between multiple components in complex matrices. Additionally, high-quality Raman spectra of the spatially resolved microscopic regions are easily obtained.
TL;DR: In this paper, the electronic absorption spectra of more than 20 crude oils and asphaltenes were examined, and the spectral location of the electronic edge varies over a wide range, from the near-infrared for heavy oils, to the nearUV for gas condensates.
Abstract: The electronic absorption spectra of more than 20 crude oils and asphaltenes are examined. The spectral location of the electronic absorption edge varies over a wide range, from the near-infrared for heavy oils and asphaltenes to the near-UV for gas condensates. The functional form of the electronic absorption edge for all crude oils (measured) is characteristic of the "Urbach tail," a phenomenology which describes electronic absorption edges in wide-ranging materials. The crude oils all show similar Urbach widths, which are significantly larger than those generally found for various materials but are similar to those previously reported for asphaltenes. Monotonically increasing absorption at higher photon energy continues for all crude oils until the spectral region is reached where single-ring aromatics dominate absorption. However, the rate of increasing absorption at higher energies moderates, thereby deviating from the Urbach behavior. Fluorescence emission spectra exhibit small red shifts from the excitation wavelength and small fluorescence peak widths in the Urbach regions of different crude oils, but show large red shifts and large peak widths in spectral regions which deviate from the Urbach behavior. This observation implies that the Urbach spectral region is dominated by lowest-energy electronic absorption of corresponding chromophores. Thus, the Urbach tail gives a direct measure of the population distribution of chromophores in crude oils. Implied population distributions are consistent with thermally activated growth of large chromophores from small ones.
TL;DR: In this article, a program package for XAFS data analysis, especially of liquid and amorphous samples, has been developed and a consequent error propagation is presented for all functions to be calculated in the course of the data analysis.
Abstract: A program package for XAFS data analysis, especially of liquid and amorphous samples, has been developed. For the first time a consequent error propagation is presented for all functions to be calculated in the course of the data analysis. The structural investigation of the Grignard compound CH3MgBr in diethyl ether is taken as an example for the various steps of the data analysis.
TL;DR: In this article, a locally weighted regression (LWR) method is used for diffuse near-infrared transmittance spectroscopy (NIRTS) data from beef and pork samples.
Abstract: This paper presents an application of locally weighted regression (LWR) in diffuse near-infrared transmittance spectroscopy. The data are from beef and pork samples. The LWR method is based on the idea that a nonlinearity can be approximated by local linear equations. Different weight functions (for the samples) as well as different distance measures for “closeness” are tested. The LWR is compared to principal component regression and partial least-squares regression. The LWR with weighted principal components is shown to give the best results. The improvements with respect to linear regression are up to 15% of the prediction errors.
TL;DR: In this paper, preliminary results for the analytical use of electrospray mass spectrometry (ES-MS) for elemental analysis are presented, with the declustered plus-one ion (M+) as the dominant species for the alkali metals (Li, Na, K, Rb, and Cs).
Abstract: Preliminary results for the analytical use of electrospray mass spectrometry (ES-MS) for elemental analysis are presented. Spectra with the declustered plus-one ion (M+) as the dominant species have been measured for the alkali metals (Li, Na, K, Rb, and Cs) and for several transition metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, and Cd) in both aqueous and methanol solvents. A number of background ions are also observed including MH+, MO+, MOH+, and MOH(H2O)+. For vanadyl sulfate and uranyl nitrate, ES conditions can be adjusted to produce VO+ and UO2+ as the dominant ions in the mass spectra, indicating that direct speciation of inorganic solution components is possible. On the basis of these preliminary results, it appears that electrospray may offer a low-cost and simple generic ion source for elemental mass spectrometry.
TL;DR: In this article, laser-induced breakdown spectroscopy has been used to determine carbon content in steel with a precision of 1.6% and a detection limit of 65 ppm.
Abstract: Laser-induced breakdown spectroscopy has been used to determine carbon content in steel. The plasma was formed by focusing a Nd:YAG laser on the sample surface. With the use of time-resolved spectroscopy and generation of the plasma in nitrogen atmosphere, a precision of 1.6% and a detection limit of 65 ppm have been obtained. These values are similar to those of other accurate conventional techniques. Matrix effects for the studied steels are reduced to a small slope difference between the calibration curves for stainless and nonstainless steels.
TL;DR: In this paper, the emission spectra of a laser-generated plasma were obtained for copper and lead targets, and the two metals gave quite different sizes of plasma, the plasma formed with copper extending 2 mm, and that with lead extending 5 mm, above the metal surface.
Abstract: Spatial measurements of the emission spectra of a laser-generated plasma were obtained for copper and lead targets. Results showed that the two metals gave quite different sizes of plasma, the plasma formed with copper extending 2 mm, and that with lead extending 5 mm, above the metal surface. Excitation temperatures of the plasma ranged from 13,200 to 17,200 K for copper and 11,700 to 15,300 K for lead.
TL;DR: In this paper, the effects of pressure over the range 10 to 760 Torr and of atmosphere (air, argon, and helium) on an ArF-excimer laser (λ = 193 nm) ablated plasma created above the surface of a copper target was studied with the use of emission measurements.
Abstract: The effects of pressure over the range 10 to 760 Torr and of atmosphere (air, argon, and helium) on an ArF-excimer laser (λ = 193 nm) ablated plasma created above the surface of a copper target was studied with the use of emission measurements. These factors greatly influenced the shape, line-to-background (L/B) ratio, and temperature of the plasma. In general, the size of the plasma decreased with increasing pressure. In air or argon, and at pressures less than 50 Torr, the plasma consisted of two distinct regions. With the use of neutral copper [Cu(I)] lines, reduced pressure from 760 to 10 Torr resulted in a 7-fold increase in air and an 11-fold increase in an argon atmosphere. With the use of a helium atmosphere, the maximum line intensity was obtained at 50 Torr. This was a 1.5-fold increase over that obtained at 760 Torr. With a reduction in the pressure in air or argon, the position of maximum intensity (for copper atom and ion lines) moved away from the surface. For helium, the position of maximum intensity did not significantly vary in accordance with a reduction in the pressure. In general, the plasma temperature decreased with decreasing pressure.
TL;DR: In this paper, an acousto-optic tunable filter (AOTF) and charge-coupled-device (CCD) detector with an infinity-corrected microscope for operation in the visible and near-infrared (NIR) spectral regions is described.
Abstract: A new instrumental approach for performing spectroscopic imaging microscopy is described. The instrument integrates an acousto-optic tunable filter (AOTF) and charge-coupled-device (CCD) detector with an infinity-corrected microscope for operation in the visible and near-infrared (NIR) spectral regions. Images at moderate spectral resolution (2 nm) and high spatial resolution (1 μm) can be collected rapidly. Data are presented containing 128 × 128 pixels, although images with significantly larger formats can be collected in approximately the same time. In operation, the CCD is used as a true imaging detector, while wavelength selectivity is provided by using the AOTF and quartz tungsten halogen lamp to create a tunable source. The instrument is entirely solid state, containing no moving parts, and can be readily configured for both absorption and reflectance spectroscopies. We present visible absorption spectral images of human epithelial cells, as well as NIR vibrational absorption images of a hydrated phospholipid suspension, to demonstrate the potential of the technique in the study of biological materials. Extensions and future applications of this work are discussed.
TL;DR: In this paper, the interface of a Pt filament pyrolysis control unit and a rapid-scan FT-IR spectrometer is described that enables the thermal decomposition of a thin film of material to be studied isothermally after heating at 2000°C/s.
Abstract: The interface of a Pt filament pyrolysis control unit and a rapid-scan FT-IR spectrometer is described that enables the thermal decomposition of a thin film of material to be studied isothermally after heating at 2000°C/s. A model of the heat transfer of the Pt filament as a function of gas atmosphere and pressure is developed to help understand the instrument response. The control voltage of the Pt filament is highly sensitive to the thermochemistry of the thin film of sample. By simultaneously recording the control voltage and the rapid-scan IR spectra of the near-surface gas products, one learns considerable detail about chemical mechanisms relevant to combustion of a bulk material. The application of T-jump/FT-IR spectroscopy is illustrated with rapid thermolysis data for the energetic organoazide polymers azidomethyl-methyloxetane (AMMO), bis(azidomethyl)oxetane (BAMO), and glycidylazide polymer (GAP); the cyclic nitramine, octahydro-1,3,5,7,tetranitro-1,3,5,7-tetraazacine (HMX); and the nitroaromatic 1,3,5-triamino-2,4,6-trinitrobenzene (TATB).
TL;DR: In this paper, a similar technique combining a CCD camera with a double monochromator system with additive dispersion is presented, which can be universally applied to all spectroscopic methods where CCD detection is used.
Abstract: In continuation of work performed with the application of the scanning multichannel technique in combination with a photodiode array and a single monochromator we show in the present paper a similar technique combining a CCD camera with a double monochromator system with additive dispersion. Special emphasis is given to a discussion of the reproduction of spectral features with small bandwidth. Examples of applications of this technique are given in terms of high-resolution Raman spectroscopy of gases. This technique is not restricted to this type of optical spectroscopy, but can be universally applied to all spectroscopic methods where CCD detection is used.
TL;DR: In this paper, the FT-Raman spectra of polyiodides and of a series of D·I2 chargetransfer complexes, where D is a molecule containing the thione or selone groups as donors, are reported.
Abstract: FT-Raman spectra of some polyiodides and of a series of D·I2 chargetransfer complexes (where D is a molecule containing the thione or selone groups as donors), all characterized by x-ray diffraction, are reported. For the adducts with the thione compounds, which can be considered weak or medium-weak complexes, an empirical linear correlation between the frequency of the v(I-I) stretching vibrations and the d(I-I) bond distances has been found. Some polyiodides show FT-Raman spectra that are indistinguishable with respect to those displayed by the neutral complexes of weak or medium-weak strength; in such cases, the polyiodide can be regarded as a diiodine molecule, perturbed by an In- (n = 1, 3, ...) donor. Polyiodides of this type show Raman absorptions falling in the linear correlation.
TL;DR: An infrared (IR) emission cell which is capable of operation up to 1500°C is described in this paper, which is based on an atomic absorption graphite furnace and coupled with a Fourier transform infrared spectrometer.
Abstract: An infrared (IR) emission cell which is capable of operation up to 1500°C is described. The cell is based on an atomic absorption graphite furnace and is coupled to a Fourier transform infrared spectrometer. The spectrometer has been used to measure the emission spectrum of quartz from 200 to 1400°C, and the changes in the spectrum occurring with temperature can be related to the formation of cristobalite; transitions between low and high forms (alpha and beta forms) can also be monitored. Aragonite has also been analyzed through the temperature range 100 to 600°C, and the aragonite/calcite transition is clearly evident. The transformation of kaolinite to metakaolinite and through to mullite and cristobalite has also been studied with this in situ technique. The formation of mullite is evident in the spectrum at temperatures as low as 900°C, and the formation of cristobalite is clearly seen at 1200°C.
TL;DR: In this paper, a portable Raman system is described that has been developed for line-of-site spectral measurements of remotely located samples at intermediate ranges using a small f/4 image-corrected spectrograph with a liquid nitrogen-cooled CCD detector.
Abstract: A portable Raman system is described that has been developed for line-of-site spectral measurements of remotely located samples at intermediate ranges. Raman spectra were measured at distances up to 20 m with the use of a 40-mm-diameter collection optic (f/500) and at 16.7 m with a 22-mm-diameter collection optic (f/750). In all cases, low-power cw lasers were used with powers ranging from 23 to 100 mW. The system consists of a small f/4 image-corrected spectrograph with a liquid-nitrogen-cooled CCD detector and has been demonstrated with both an argon-ion laser, emitting at 488 nm, and an 809-nm diode laser. Applications of the system include monitoring of organic and inorganic compounds at toxic waste sites during remediation, process monitoring, and remote detection of highly toxic materials.
TL;DR: In this paper, the concentration of NaCl in aqueous solutions has been determined with the use of near-IR spectra between 1100 and 1900 nm, using linear and nonlinear regression with use of the absorbances at selected wave-lengths and with principal component regression (PCR) using entire spectra.
Abstract: The concentrations of NaCl in aqueous solutions have been determined with the use of near-IR spectra between 1100 and 1900 nm. Models expressing the concentration of NaCl are developed with linear and nonlinear regression with the use of the absorbances at selected wave-lengths and with principal component regression (PCR) using entire spectra. Temperature perturbations on water bands interfere with the measurement of NaCl but can be removed by linear or nonlinear regressions using the absorbances at the wavelengths where the temperature effects are zero, or they can be accounted for by PCR. Standard errors of 5 mM and a detection limit of 15 mM are obtained for NaCl. This technique can be applied for quantitative analysis of NaCl in the laboratory or can be readily adapted for continuous monitoring in process control.
TL;DR: In this article, the feasibility of direct quantitative analysis of styrene by Raman spectroscopy during an emulsion polymerization was examined, using a dispersive spectrometer fitted with an intensified diode array detector with excitation from the 514.5-nm line of an Ar-ion laser.
Abstract: The feasibility of a direct quantitative analysis of styrene by Raman spectroscopy during an emulsion polymerization is examined. A dispersive spectrometer fitted with an intensified diode array detector is used with excitation from the 514.5-nm line of an Ar-ion laser. The limits of detection are 0.26 weight percent styrene in the reaction mixture. Raman measurements are compared with those obtained by UV absorption measurements on extracted samples and found to give essentially the same results.
TL;DR: In this paper, a novel asynchronous time-resolved FT-IR spectrophotometer based on a conventional continuous-scan interferometer has been developed, which does not require the synchronization between the signal for time resolving and that for the sampling of the A/D converter.
Abstract: A novel asynchronous time-resolved FT-IR spectrophotometer based on a conventional continuous-scan interferometer has been developed. In contrast to the existing methods, this method does not require the synchronization between the signal for time resolving and that for the sampling of the A/D converter. The signal-processing assembly for time-resolved measurements consists of a pulse generator, a pulse delay circuit, a gate circuit, and a low-pass filter. This assembly can be attached to any conventional FT-IR spectrophotometer. By this method, time-resolved spectra without any spectral distortion or artifacts can be obtained for repetitive fast phenomena. As an application of this method, time-resolved FT-IR measurements have been carried out for the reorientation process in a ferroelectric liquid crystal induced by the reversal of external electric field, and a time resolution of 0.5 μs or less has been achieved. The present system is best suited for observing repetitive transient phenomena with lifetimes in the range from approximately 1 μs to 1 ms.
TL;DR: In this paper, the authors studied the plasma characteristics and excitation process of laser-induced plasma with the use of a TEA CO2 laser of 750 mJ pulse energy and 100 ns pulse width.
Abstract: The plasma characteristics and excitation process of laser-induced plasma with the use of a TEA CO2 laser of 750 mJ pulse energy and 100 ns pulse width are studied in different surrounding gases at reduced pressures. From the time-resolved spatial distribution, it is clear that in helium and argon atmospheres, two different excitation processes take place in forming the plasma. The first excitation process is due to the blast wave, while the second process is due to the metastable state of the noble gases. It is believed that this second process transfers metastable energy to the vaporized atoms of the target for emission, even long after the laser bombardment ends, thus giving total emission intensity that is higher in the noble gases than in air. The displacement of the front of the emission line under different atmospheres is also presented.
TL;DR: In this paper, the authors describe the optical analysis, construction, testing, and application of a cell for measuring in situ IR reflection spectra in the C-H stretching region of monolayer films of long-chain alkanethiolates on evaporated Au films beneath a thin overlayer (∼ 1 μm) of aqueous solution.
Abstract: This paper describes the optical analysis, construction, testing, and application of a cell for measuring in situ IR reflection spectra in the C-H stretching region of monolayer films of long-chain alkanethiolates on evaporated Au films beneath a thin overlayer (∼1 μm) of aqueous solution. The cell facilitates the interchange of sample (monolayer-coated) and reference substrates—a major improvement over previous designs. This allows the acquisition of an IR reflection spectrum of a monolayer without the application of electrochemical or polarization-modulation methods. The optical properties of the cell are analyzed within the context of classical electromagnetic theory; the effects of angle of incidence, solution layer thickness, and solution composition (H2O and D2,O) and the refractive indices of the IR-transparent window material on the observed spectrum are specifically examined. Calculations of both the mean-square electric fields and the reflection spectra for a monolayer of octadecanethiolate on Au are presented. From these results, conditions to achieve high surface detectability are identified, and optically induced alterations in the intensities and shapes of the monolayer spectrum are delineated. Spectra for the same monolayer are measured to test these predictions as well as to assess the practical limitations of the experimental technique.