Showing papers in "Applied Spectroscopy in 1983"
TL;DR: In this article, a computer-aided measurement of absorption line strengths from high-resolution spectra greatly improves the accuracies to which relative line strengths can be determined, by fitting simultaneously absorption line positions, strengths, linewidths, and continuum parameters.
Abstract: Computer-aided measurement of absorption line strengths from high resolution spectra greatly improves the accuracies to which relative line strengths can be determined. This article describes a computer program written for interactive use on a Prime minicomputer to fit simultaneously absorption line positions, strengths, linewidths, and continuum parameters. Application to the methane spectrum indicates that relative line strengths have been measured with accuracies of 2% or better for single isolated absorptions. Line strengths from the Q branches of the v4 and v1 + v4 bands of methane are reported and compared to calculated values given in the 1980 Air Force Geophysical Laboratory (AFGL) Compilation of Molecular Parameters.
98 citations
TL;DR: In this article, a new method is described and tested for background correction in atomic absorption spectrometry, which is based on the broadening which occurs in a hollow-cathode spectral line when the lamp is operated at high currents.
Abstract: A new method is described and tested for background correction in atomic absorption spectrometry. Applicable to flame or furnace atomizers, the method is capable of correcting back-grounds caused by molecular absorption, particulate scattering, and atomic-line overlap, even up to an absorbance value of 3. Like the Zeeman approach, the new method applies its correction very near the atomic line of interest, can employ single-beam optics, and requires no auxiliary source. However, no ancillary magnet or other costly peripherals are required and working curves are single-valued. The new technique is based on the broadening which occurs in a hollow-cathode spectral line when the lamp is operated at high currents. Under such conditions, the absorbance measured for a narrow (atomic) line is low, whereas the apparent absorbance caused by a broad-band background contributor remains as high as when the lamp is operated at conventional current levels. Background correction can therefore be effected by taking the difference in absorbances measured with the lamp operated at high and low currents. The new technique is evaluated in its ability to correct several different kinds of background interference and is critically compared with competitive methods.
88 citations
TL;DR: In this paper, the authors developed procedures to determine 12 trace elements, Al, As, Be, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, and V, in natural water using the stabilized temperature platform furnace.
Abstract: We have developed procedures to determine 12 trace elements, Al, As, Be, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, and V, in natural water using the stabilized temperature platform furnace. Suitable matrix modifiers were tested. Confirmation of the techniques was obtained by recovery experiments at four different concentration levels. Only simple aqueous standards were required and the method of additions was not used. A simple recovery experiment was satisfactory confirmation of freedom from chemical interferences. The detection limits in the natural waters were less than 1 μg/liter, closer to 0.1 μg/liter for most of the elements. The precision was 10 to 15%. The work did not require clean-room facilities.
82 citations
TL;DR: In this paper, the authors reviewed the application of self-deconvolution for band resolution enhancement in the Fourier transform infrared spectra and showed that the results confirm those reported by Kauppinen et al. at Ottawa, but the need for caution in applying self-Deconvolutions in routine laboratory measurements is stressed.
Abstract: The directly observable information in a digitally encoded spectrum can be selectively enhanced by deconvolution with an appropriate filter operator. This may be carried out on the frequency (wavenumber) domain spectrum or on its Fourier transform. Depending on the choice of the filter, one may achieve: (1) reduction in the random noise, (2) reduction of systematic instrumental errors, (3) enhancement of the resolution. These general deconvolution procedures are briefly reviewed in terms of this classification. Recent work at the National Research Council of Canada at Ottawa has emphasized the application to band resolution enhancement (self-deconvolution), principally with respect to Fourier transform infrared spectra. Experience in our laboratory with infrared data generated on dispersion spectrometers is described. Our results confirm those reported by Kauppinen et al. at Ottawa, but the need for caution in applying self-deconvolution in routine laboratory measurements is stressed.
70 citations
TL;DR: The microwave-induced plasma (MIP) has become increasingly popular as a method of producing elemental emission as discussed by the authors, using helium or argon primarily as support gases, resulting in the sensitive spectroscopic determination of a large number of elements including nonmetals, such as halogens.
Abstract: During the last 20 years, the microwave-induced plasma (MIP) has become increasingly popular as a method of producing elemental emission. Using helium or argon primarily as support gases, these discharges are characterized by high spectral temperatures, resulting in the sensitive spectroscopic determination of a large number of elements including nonmetals, such as halogens. The primary focus of work in this area has dealt with the utilization of the MIP as an element-selective detector in gas chromatography. Various applications of the MIP appear in several current review articles.
66 citations
TL;DR: In this paper, positive ions were extracted from the axial channel of an inductively coupled plasma (ICP) in which the outer gas flow was Ar, N2, or a mixture of Ar and N2.
Abstract: Positive ions were extracted from the axial channel of an inductively coupled plasma (ICP) in which the outer gas flow was Ar, N2, or a mixture of Ar and N2. Addition of N2 to the outer gas decreases the electron number density (ne) in the axial channel. Ar+2, O2+, and ArH+ react with N-containing species in the plasma and/or during the ion extraction process. Ar+ remains abundant even if there is no Ar in the outer gas, which indicates the probable occurrence of charge transfer reactions between N2+ and Ar. The present work corroborates two general concepts upon which several theories of the origin of suprathermal ionization in ICPs are based: (a) species are physically transported from the induction region to the axial channel; and (b) these species may react with and ionize neutral species in the axial channel. Ionization temperatures (Tion) measured from the ratio Cd+/I+ were 5750 to 6700 K for a N2 outer flow ICP at a forward power of 1.2 kW. This Tion range is significantly below that obtained for an Ar outer gas ICP under otherwise similar operating parameters.
63 citations
TL;DR: In this paper, the authors used pure vitreous silica and liquid cyclohexane as reference materials of choice for determining the appropriate spectral corrections applicable to the spectrophotometric data.
Abstract: The problem of measuring equilibrium vibrational temperatures in materials by using Raman spectroscopy has been analyzed theoretically and experimentally One major problem is the determination of the corrections, due to the Raman instrument response, that must be applied to raw data to obtain the temperature Normally a "standard" lamp is used for this purpose but the problems that can arise are legion Methods for determining spectral response and temperature response function corrections that must be applied to raw Raman data, for ultimately deriving the equilibrium temperatures of various materials, have been developed such that standard lamps are not required Instead pure vitreous silica and liquid cyclohexane, which are both readily available in all spectroscopy laboratories, are selected as reference materials of choice for determining the appropriate spectral corrections applicable to the spectrophotometric data The results were tested against data obtained from other transparent materials, namely CCl4, CHCl3, CH3PCl2, GeCl4, GeBr4, and CS2 GeBr4 and CS2 were poor choices because of the proximity of the melting point of the former to room temperature and laser-induced photolysis of the latter Detailed statistical analyses of the results indicate a marked lowering of systematic errors over those yielded by standard lamp calibrations Shortcomings of both methods are also discussed, including several lesser known spectral abnormalities arising from the use of a standard lamp
60 citations
TL;DR: In this article, a systematic study of interpolation of Fourier transform (FT) spectra is reported, where interpolation errors are examined for both frequency determination and intensity determination for different interpolation procedures for both absorption mode and magnitude mode FT spectra.
Abstract: A systematic study of interpolation of Fourier transform (FT) spectra is reported. Interpolation errors are examined for both frequency determination and intensity determination for different interpolation procedures for both absorption mode and magnitude mode FT spectra. The errors are presented in both analytical and graphical form as functions of the number of zero-fillings and (T/τ), the ratio of the acquisition time to the relaxation time of the time domain signal. For interpolation of absorption mode spectra, parabolic interpolation is superior to Lorentzian interpolation if T/τ 2, Lorentzian interpolation is superior. For small values of T/τ, both parabolic interpolation and Lorentzian interpolation of the absorption line shape give greater errors than no interpolation. For interpolation of the magnitude lineshape, interpolation with the
59 citations
TL;DR: In this article, the authors used Gauss-Jordan linear algebra to predict the concentration of one or more of the chemical species in a sample at several discrete wavelengths and evaluated the correlations for percent protein in wheat flour and percent benzene in hydrocarbons.
Abstract: Near-infrared reflectance analysis is an analytical technique that uses the near-infrared diffuse reflectance of a sample at several discrete wavelengths to predict the concentration of one or more of the chemical species in that sample. However, because near-infrared bands from solid samples are both abundant and broad, the reflectance at a given wavelength usually contains contributions from several sample components, requiring extensive calculations on overlapped bands. In the present study, these calculations have been performed using an approach similar to that employed in multi-component spectrophotometry, but with Gauss-Jordan linear algebra serving as the computational vehicle. Using this approach, correlations for percent protein in wheat flour and percent benzene in hydrocarbons have been obtained and are evaluated. The advantages of a linear-algebra approach over the common one employing stepwise regression are explored.
59 citations
TL;DR: In this paper, a review of high-resolution NMR techniques developed for 13C solids is presented, focusing on the most general interest for organic polymers and the experimental procedures are explained briefly and the provision of new information in various areas of polymer science by 13C NMR solids.
Abstract: Systematic research concerning synthetic polymers requires an understanding of molecular-level influences on macroscopic behavior. Chemical structure, morphology, orientation, and chain dynamics, which are known to have important effects on bulk material properties, have all been characterized by various forms of molecular spectroscopy. Despite such efforts, we do not have a complete understanding of the relationship between macroscopic and microscopic properties. Two general problems remain: (1) the requirement of special sample preparation for many types of spectroscopy; and (2) the limited scope of common spectroscopic techniques. Differences in sample preparation, variations in sensitivity, and ambiguities in interpretation combine to complicate the study. Recently developed NMR techniques for high-resolution in solids have demonstrated the potential to solve such problems in many cases. This review focuses on the high-resolution NMR techniques developed for 13C, the nucleus of most general interest for organic polymers. The experimental procedures are explained briefly and the provision of new information in various areas of polymer science by 13C NMR solids is discussed. Specific examples are used and some indication of future potential is presented.
54 citations
TL;DR: In this article, a bakeable high-vacuum cell based on a modification of a commercial diffuse reflectance infrared cell is described along with means for controlling the gaseous and thermal environment.
Abstract: Measurement of the reaction of water vapor and carbon dioxide with lithium compounds such as LiH and LiOH has been carried out in situ using diffuse reflectance infrared Fourier transform (DRIFT) Spectroscopy. The bakeable high-vacuum cell, based on a modification of a commercial diffuse reflectance infrared cell is described along with means for controlling the gaseous and thermal environment.
TL;DR: In this paper, the utility of a photodiode array based spatial emission profiling system has been enhanced by using a method for performing an Abel inversion on asymmetric lateral data which preserves the asymmetry in the radial emission profiles.
Abstract: The utility of a photodiode array based spatial emission profiling system has been enhanced by using a method for performing an Abel inversion on asymmetric lateral data which preserves the asymmetry in the radial emission profiles. This procedure has been implemented with an APPLE II plus computer, coupled with a Reticon RL-1024S photodiode array that has been masked with a narrow exit slit. The method has been tested with a theoretical set of lateral data and with actual measured spatial emission profiles.
TL;DR: In this article, target factor analysis error criteria are applied to the UV spectra of unresolved liquid chromatographic fractions to determine the number of components contributing to an unresolved chromatogram peak and individually verify the presence of suspected components without requiring any knowledge of the other components.
Abstract: Target factor analysis error criteria are applied to the UV spectra of unresolved liquid chromatographic fractions. The method is used not only to determine the number of components contributing to an unresolved chromatographic peak but also to individually verify the presence of suspected components without requiring any knowledge of the other components. An actual experimental example is presented using mixtures of o-xylene, ethylbenzene, and p-xylene. Factor analysis criteria are used to indicate which one of the fractions contains a UV-absorbing impurity(ies).
TL;DR: In this article, a simple cryostat was designed to obtain resonance Raman spectra via 135° backscattering directly from the surface of a frozen protein solution, which is the most successful technique when used to investigate the low-frequency region.
Abstract: A frequent problem encountered in resonance Raman studies of aqueous protein solutions is that of protein denaturation due to localized heating by the laser beam. The problem has been circumvented, with varying degrees of success, by using spinning cells, flowing solutions through capillary tubes (both 90° scattering geometry), or by backscattering from cooled, spinning NMR tubes (135° scattering geometry). In our experience the latter technique is most successful. However, it has limitations when used to investigate the low-frequency region (0 to 500 cm−1), because broad nonresonant Raman scattering from the glass or quartz NMR tubes produces an ill-defined envelope of bands between 300 and 500 cm−1. These bands often dominate resonance Raman spectra in this region, obscuring weak sample bands (e.g., see Fig. 2). These difficulties have led us to design a simple cryostat that can be used to obtain resonance Raman spectra via 135° backscattering directly from the surface of a frozen protein solution (Fig. 1.)
TL;DR: In the 15-year period between 1966 and 1981, detection limits for atomic spectroscopic methods of analysis have decreased by an average of 3 orders of magnitude as mentioned in this paper, and the current state of the art for the atomic techniques in general use is presented and the methods compared using the detection limits as the figure of merit.
Abstract: In the 15-year period between 1966 and 1981, detection limits for atomic spectroscopic methods of analysis have decreased by an average of 3 orders of magnitude. The current (1982) state of the art for the atomic techniques in general use is presented and the methods compared using the detection limits as the figure of merit.
TL;DR: In this paper, a new criterion was proposed for the choice of convolution function in terms of the degree, number of convolutions points, and number of passes of the convolution through the data.
Abstract: General expressions have been derived for the effects of convolution on a set of experimental data, from which the noise reduction may be predicted quantitatively. From these, a new criterion is proposed for the choice of convolution function in terms of the degree, number of convolution points, and number of passes of the convolution function through the data. This criterion gives maximal noise reduction with minimal signal distortion, and is particularly applicable in resolution enhancement applications. The new criteria have been tested with experimental data.
TL;DR: In this paper, the sensitivity limiting factor in thermal lens spectroscopy with a chopped pump laser was shown to be random, while thermal lens signals are shown to have a small periodic component caused by stirring.
Abstract: Thermally induced solution stirring can cause periodic signal fluctuations which can be the sensitivity limiting factor in thermal lens spectroscopy with a chopped pump laser. Pump and probe laser fluctuations are shown to be random, while thermal lens signals are shown to have a small periodic component caused by stirring. The problem is serious in dilute solutions because of the high solvent background absorbance.
TL;DR: In this article, the Raman spectra of 5.196 m aqueous zinc nitrate solution have been measured at a pressure of 11 MPa and temperatures ranging from 25 to 300°C.
Abstract: Raman spectra of 5.196 m aqueous zinc nitrate solution have been measured at a pressure of 11 MPa and temperatures ranging from 25 to 300°C. A band at 386 cm−1, assigned to the hexaaquazinc(II) cation, decreases in intensity and increases in frequency as the temperature rises. These observations are consistent with the replacement of water molecules in the primary solvation shell of Zn2+ by a nitrate ion. Changes in the spectrum of nitrate ion support this interpretation. Evidence is also presented which suggests that the octahedral configuration around Zn2+ is being changed to a tetrahedral configuration. Estimates are made of the populations of inner sphere and outer sphere nitrate; from the plots of log Qm vs 1/T estimates are made of ΔH and ΔS for the ion association. The plots are remarkably linear over 275 degrees of temperature.
TL;DR: In this paper, spatial profile studies are used to determine the interference effects of matrix elements on the observed emission of alkali analyte elements in the inductively coupled plasma, referred to as intra-alkali matrix effects.
Abstract: Spatial profile studies are used to determine the interference effects of alkali matrix elements on the observed emission of alkali analyte elements in the inductively coupled plasma. These interferences are referred to as intra-alkali matrix effects. It is found that significant enhancement of the analyte emission occurs low in the plasma in the initial radiation zone where atomic emission is most intense and that a slight downward shift in the vertical position of the emission peak is caused by the presence of the alkali matrix. A
TL;DR: In this paper, the authors used Fourier transform infrared spectroscopy and solid state 13C NMR spectroglobalization to measure the hydroxyl groups in coal and found that the proportion of phenolic to alkyl OH is approximately constant for the coals used in this study.
Abstract: Fourier transform infrared spectroscopy and solid state 13C NMR spectroscopy have been used to measure the hydroxyl groups in coal. The methodology depends upon measuring the intensities of bands and resonances assigned to the products of acetylation reactions. In the infrared three separate bands, assigned to acetylated phenolic OH, alkyl OH, and NH groups, can be identified. In NMR, we used the methoxy carbon to determine the total OH. Spectroscopic measurements demonstrate that not only does the total OH content of coals but also the individual types of OH groups vary systematically as a function of rank. The proportion of phenolic to alkyl OH is approximately constant for the coals used in this study.
TL;DR: In this paper, a sample introduction method involving the formation of volatile species in solution and subsequent pneumatic nebulization for inductively coupled plasma atomic emission spectrometry is proposed.
Abstract: We propose a sample introduction method involving the formation of volatile species in solution and subsequent pneumatic nebulization for inductively coupled plasma atomic emission spectrometry. A study of osmium oxidized to OsO4 and preliminary results for mercury reduced to the elemental form suggest that enhancements in sensitivity by a factor of 10 to 100 are achievable without degradation in analytical precision, in comparison with pneumatic nebulization of solutions containing the element of interest in a nonvolatile form. We discuss the physical basis for the method and support it by a brief theoretical treatment. The technique promises a broad applicability to elements capable of existing in a volatile form in solution. For the elements studied, no modifications of a commercial ICP spectrometer or sample introduction system are required.
TL;DR: In this paper, the use of an opaque (i.e. very thick) sample as a reference eliminates the distortions in the bandshapes of the IR emittance of liquids relative to a blackbody.
Abstract: The IR emittance of liquids relative to a blackbody is dependent on the reflectivity at the surface of the sample. This dependency leads to distortions in the bandshapes except when the absorption coefficient or the sample thickness is very low. The use of an opaque (i.e. very thick) sample as a reference eliminates the distortions in the bandshapes. A new emittance ɛ* = (emission of a thin sample)/(emission of an opaque sample) has been introduced. A theoretical analysis as well as experimental work on chloroaluminate melts demonstrate that the emittance ɛ* gives a better representation of the ideal sample property of interest, i.e., the internal transmittance of the sample, than the usual emittance with a blackbody as a reference.
TL;DR: The tangential-flow torch was evaluated as part of an atomic emission microwave plasma detector for gas chromatography as discussed by the authors, and the results showed that the chemical matrix has little effect on the relative degree of atomization.
Abstract: The tangential-flow torch was evaluated as part of an atomic emission microwave plasma detector for gas chromatography. Emission intensities for the elements carbon, sulfur, and bromine in a variety of organic molecules were studied. Calibration plots showed good linearity, indicating that the chemical matrix has little effect on the relative degree of atomization.
TL;DR: In this article, a sensitive method for the determination of trace amounts of tin, based on continuous sodium borohydride reduction of tin in solution to gaseous stannane, is described.
Abstract: A sensitive method is described for the determination of trace amounts of tin, based on continuous sodium borohydride reduction of tin in solution to gaseous stannane. The stannane generated is introduced into a relatively low-powered (1.6 kW) inductively coupled argon plasma source. The effects of a range of acids and interelement effects are investigated. Mixtures of nitric and succinic acids and of nitric and malic acids are the most suitable reaction media, especially in the presence of interferents. The method of standard additions is recommended for accurate tin determination. Compared to a conventional solution nebulization, the present system gives a sensitivity increase of a factor of approximately 3 orders of magnitude. The detection limit for tin is 0.05 ng/ml and precision values at 20 and 50 ng/ml Sn are less than 3% relative standard deviation. The linear calibration range spans nearly 5 orders of magnitude. The proposed method is applied to the determination of tin in low alloyed steels and in National Bureau of Standards standard reference materials (Cu-Ni alloy, orchard leaves, wheat flour, and rice flour).
TL;DR: The rates of solid-solid phase transitions have been measured by nonspectroscopic techniques, such as differential thermal analysis (DTA), dilatometry, and x-ray powder diffraction as discussed by the authors.
Abstract: The rates of solid-solid phase transitions have been measured by nonspectroscopic techniques, such as differential thermal analysis (DTA), dilatometry, and x-ray powder diffraction. With DTA, the accuracy of the activation energy is rarely better than ±15% in part because good thermal contact between the sample and, the pan is difficult to maintain. Dilatometry measures the volume change accompanying a thermodynamic first order phase transition. Crystal decomposition and out-gassing of trapped solvent molecules complicate the method. High temperature x-ray powder diffraction is restricted to relatively slow phase transformations. If the solid phase transition is quenched and the intensity of a characteristic peak measured, errors can be incurred in determining the concentration. Internal standards may alleviate this problem, but sample homogeneity becomes an issue.
TL;DR: In this paper, a microprocessor-controlled graphite rod direct sample insertion device for use with an inductively coupled plasma is described and the accompanying software design is illustrated; the system is shown to be suitable for trace element determinations in small liquid samples or directly with small solid samples.
Abstract: A microprocessor-controlled graphite rod direct sample insertion device for use with an inductively coupled plasma is described and the accompanying software design is illustrated. The energy of the rf field and the plasma itself is used to carry out the programed sample drying and ashing stages prior to analyte vaporization. The rod position for drying aqueous solutions and for ashing an aqueous solution containing organic material has also been investigated. Automation of the graphite rod insertion device in the manner described improves the precision attainable by this technique; the system is shown to be suitable for trace element determinations in small liquid samples or directly with small solid samples.
IBM1
TL;DR: Good chromatographic resolution, low nanogram sensitivity, and compound identification are demonstrated and applications to the analysis of a petroleum distillation fraction and to a polymer sample, analyzed after pyrolysis, are presented.
Abstract: In this work, we describe the interfacing of a high-resolution chromatographic system featuring narrow bore gas chromatographic columns to a Fourier transform infrared spectrometer. Excellent chromatographic resolution, low nanogram sensitivity, and compound identification are demonstrated. Applications to the analysis of a petroleum distillation fraction and to a polymer sample, analyzed after pyrolysis, are presented. A vapor-phase library search system is used to identify compounds in both samples.
TL;DR: In this paper, the coherent anti-Stokes Raman spectroscopy spectrum of H2O has been measured in a heated optical cell and in laboratory flames, and the experimental spectra with a theoretical model have been used to infer information about the unknown Raman linewidths of H 2O.
Abstract: The coherent anti-Stokes Raman spectroscopy spectrum of H2o has been measured in a heated optical cell and in laboratory flames. Comparisons of the experimental spectra with a theoretical model have been used to infer information about the unknown Raman linewidths of H2O. In the test cell, excellent agreement has been obtained between theory and experiment in terms of physically realistic linewidths. Agreement between experiment and theory in laboratory flames is also good.
TL;DR: In this paper, the Rozenberg and Pitts-Giovanelli methods are applied to diffusely reflecting samples that fail to conform to the Kubelka-Munk theory.
Abstract: Previous studies have shown that the Rozenberg and Pitts-Giovanelli methods are useful alternatives that may be applied to diffusely reflecting samples that fail to conform to the Kubelka-Munk theory. These studies are extended in the present work to include samples of three additional types, namely, those which incorporate the absorber in solid solution within the scattering particles, those in which the absorber is adsorbed on the surface of the scattering particles, and those consisting of a dye spotted on chromatographic papers. No single method of analysis is superior in all cases. Although the Pitts-Giovanelli method gives a much better fit in some cases, it fails to converge in others. For this reason the Kubelka-Munk and Rozenberg methods are preferred, particularly when applied to diffusers in a medium of refractive index n = 1. For such systems the Rozenberg equation reduces to a simple form that is as easy to apply as the Kubelka-Munk equation.
TL;DR: In this paper, two models for treating long samples of variable absorbance and enhancement are presented, one based on an approximation that such samples will behave according to the integrated position dependence of a thin lens and a more complex model, requiring numerical evaluation, including the effects of sample refractive index and lens element coupling.
Abstract: Laser-induced thermal lens calorimetry as applied to small absorbance determinations has traditionally relied upon the approximation that the sample behaves optically as a thin lens. The choice of a cell length which is not ideal for theory may be necessary for increased sensitivity. Two models for treating long samples of variable absorbance and enhancement are presented. The simpler of these is based on an approximation that such samples will behave according to the integrated position dependence of a thin lens. A more complex model, requiring numerical evaluation, includes the effects of sample refractive index and lens element coupling. The numerical model is verified experimentally and used to establish the limits of accuracy of the thin lens and integrated position dependence models. The consequences of using long path length samples in analytical thermal lens measurements are discussed in light of the numerical model results.