Showing papers in "Applied Spectroscopy in 1982"
TL;DR: In this paper, an algorithm for the computation of bandwidths and center of gravity and least-squares frequencies with maximum uncertainties of hundredths or thousandths of a wave number is presented.
Abstract: Algorithms for the computation of bandwidths, and center of gravity and least-squares frequencies are developed. The sources of error are discussed, and it is shown that the above parameters can be determined with maximum uncertainties of hundredths or thousandths of a wave number.
207 citations
TL;DR: In this paper, four weighted least-squares methods incorporating different baseline assumptions were investigated using FT-IR spectra of the three pure xylene isomers and their mixtures, and accurate results can be obtained using three of the fitting methods even when baselines are not cor- rected to zero.
Abstract: Improvements have been made in previous least-squares regression analyses of infrared spectra for the quantitative estimation of concentrations of multicomponent mixtures. Spec- tral baselines are fitted by least-squares methods, and overlap- ping spectral features are accounted for in the fitting procedure. Selection of peaks above a threshold value reduces computation time and data storage requirements. Four weighted least- squares methods incorporating different baseline assumptions were investigated using FT-IR spectra of the three pure xylene isomers and their mixtures. By fitting only regions of the spectra that follow Beer's Law, accurate results can be obtained using three of the fitting methods even when baselines are not cor- rected to zero. Accurate results can also be obtained using one of the fits even in the presence of Beer's Law deviations. This is a consequence of pooling the weighted results for each spectral peak such that the greatest weighting is automatically given to those peaks that adhere to Beer's Law. It has been shown with the xylene spectra that semiquantitative results can be obtained even when all the major components are not known or when expected components are not present. This improvement over previous methods greatly expands the utility of quantitative least-squares analyses.
152 citations
TL;DR: In this paper, the synchronous luminescence (SL) technique was used in multiscale analysis of complex organic samples, and the efficacy of SL was demonstrated in the direct determination of anthracene and 2-methylanthracene in a raw coal liquid.
Abstract: This paper discusses the figures of merit associated with the synchronous luminescence (SL) technique in multicomponent analysis of complex samples. Spectral interferences and experimental factors that influence the choice of experimental conditions are investigated. The efficacy of SL is demonstrated in the direct determination of anthracene and 2-methylanthracene in a raw coal liquid. The application of the second-derivative technique to the SL measurement of organic samples is shown. Special emphasis is directed toward the applicability of the SL technique as a practical and cost-effective screening procedure in the routine analysis of complex organic samples.
120 citations
TL;DR: In this paper, a linear combination of spectra of known constituents of ground wheat was used to approximate the near infrared (log 1/reflectance) spectra and the appropriate coefficients of these linear combinations were then linearly correlated with the protein and moisture content of the samples.
Abstract: Near infrared (log 1/reflectance) spectra of samples of ground wheat were approximated by a linear combination of spectra of known constituents, the approximation satisfying a least-squares criterion. The appropriate coefficients of these linear combinations were then linearly correlated with the protein and moisture content of the samples. Two extensions of previously reported curve-fitting techniques were made. First, multilinearly correlating several of the curve fit coefficients with the chemical data improved the standard errors. Second, using sample spectra as components, rather than pure constituent spectra, improved the standard errors to a point where they became comparable to those obtained by currently used derivative methods. The samples covered a protein range of 10 to 19%. Correlation coefficients reached 0.998 for protein, corresponding to a standard error of prediction of 0.15%. Parameters examined included spectral region, smoothing, and wavelength shifting. Results with reflectance spectra of sample sets with large particle size variation and high noise are also reported.
83 citations
TL;DR: A detailed study of the importance of various spatial dimensions in an ICP torch is described in this article, where it is shown that the annular spacing between the coolant (outer) and plasma (flared) tube is the most critical for plasma stabilization at low argon coolant flows and applied radio-frequency powers.
Abstract: A detailed study of the importance of various spatial dimensions in an ICP torch is described. Of the various dimensions which were examined, the annular spacing between the coolant (outer) and plasma (flared) tube is the most critical for plasma stabilization at low argon coolant flows and applied radio-frequency powers. Similarly, the inner diameter of the aerosol injection tube was found to be important, with the value of 1.0 mm chosen for a compromise between low-power, low-flow capability and routine analysis of high-solids sample solutions. A constriction at the inlet of the coolant argon was found not to affect plasma stability greatly, but altered significantly the applied powers and coolant flows which were necessary for plasma ignition. With these and other torch dimensions optimized, it was found to be possible to ignite a plasma at a coolant flow of 5 L/min and an applied radio frequency power of 450 W. Continued operation of the plasma during analysis of real samples or during aspiration of a 1% NaCl solution was found to be possible alternatively at 500 W (rf power) and 3.5 L/min coolant argon or 125 W and 5.5 L/min, respectively.
82 citations
TL;DR: In this article, an expression for the intensity in coherent anti-Stokes Raman spectroscopy (CARS) was derived by taking into account the linewidths and phase relation of the two laser beams, and simulation procedures suited for practical applications were developed.
Abstract: The expression for the intensity in coherent anti-Stokes Raman spectroscopy (CARS) was derived for scanning CARS by taking into account the linewidths and phase relation of the two laser beams, and simulation procedures suited for practical applications were developed. The CARS spectra of p-xylene and N2 gas were observed, and the results were compared with the simulation curves based on two extreme cases of the statistical property of the laser source. It was shown that the effect of laser linewidth becomes remarkable when the Raman linewidth is comparable to or smaller than the laser linewidth, and that the degree of coherence among the frequency components within the laser linewidth is an important factor in determining the spectral profile.
77 citations
TL;DR: Polarization modulation has been combined with Fourier transform infrared (FT-IR) spectroscopy to yield a sensitive method for obtaining infrared reflection-absorption spectra of monolayer films adsorbed on low-area metal surfaces as mentioned in this paper.
Abstract: Polarization modulation has been combined with Fourier transform infrared (FT-IR) spectroscopy to yield a sensitive method for obtaining infrared reflection-absorption spectra of monolayer films adsorbed on low-area metal surfaces. A 10-A film of cellulose acetate adsorbed on a polished copper coupon was examined and the results compared with spectra obtained on the same instrument without polarization modulation. The signal-to-noise ratio is significantly better with the polarization modulation approach. The new method has the additional advantage of being sensitive only to molecules adsorbed on the surface. IR absorption by background gases is not detected.
64 citations
TL;DR: In this article, the authors adapted a laser Raman microprobe to an under air study of the solid phase transformation of cobalt and nickel molybdates in which the molybdenum atoms are in tetrahedral oxygen environment ([a] phase) or in octahedral environment ([b] phase).
Abstract: Heating cells used in optical microscopy are adapted to a laser Raman microprobe to an under air study of the solid phase transformation of cobalt and nickel molybdates in which the molybdenum atoms are in tetrahedral oxygen environment ([a] phase) or in octahedral environment ([b] phase). In each case, the Co or Ni environment is octahedral. In the second part of this paper, a newly designed controlled-atmosphere and temperature cell is described. It permits the study of several problems particularly those related to the reactivity of Co or Ni-Mo-γ-Al2O3 hydrodesulfurization catalysts. Results on (1) sulfidation of the oxide precursor form catalysts by a H2-H2S mixture, (2) interaction with a model sulfided molecule: thiophene, and (3) pyridine chemisorption are reported.
64 citations
TL;DR: In this paper, the authors reported a simple method to derive the Lorentzian linewidth of a Raman line as well as its fraction of its fraction in terms of the fraction of the Lipschitz constant of the bandwidth at half maximum obtained from recorded Raman and plasma lines with same spectrometer slit settings.
Abstract: We report on a simple method to derive the Lorentzian linewidth of a Raman line as well as its fraction Lorentzian character The method is based on the experimental determination of the bandwidths at half maximum obtained from recorded Raman and plasma lines with same spectrometer slit settings From the ratio of the two half bandwidths, the Lorentzian Raman linewidth can be easily derived from the given table This table was compiled by explicit calculations of Voigt profiles The fraction Lorentzian character, needed for instance for Raman difference spectroscopy, can be obtained directly from this table to a good accuracy
60 citations
TL;DR: In this paper, the applications of electron spin resonance (ESR) to carbonaceous materials are reviewed, and the relevance to the carbonization process of the free radicals observed by ESR is also discussed.
Abstract: The applications of electron spin resonance (ESR) to carbonaceous materials are reviewed. The stable paramagnetic species observed in the products of low-temperature pyrolysis are odd-alternate neutral free radicals, whereas the unpaired spins of higher temperature carbons and graphites are primarily conduction electrons. The variety of ESR properties and phenomena requires special attention to techniques of measurement and interpretations of results. The relevance to the carbonization process of the free radicals observed by ESR is also discussed.
56 citations
TL;DR: In this article, a self-scanned photodiode array was used as a spectrometric multichannel detector for molecular absorption and molecular fluorescence spectrometry, and the performance of the diode array system was evaluated with a few typical chemical systems.
Abstract: A state-of-the-art self-scanned photodiode array, utilized as a spectrometric multichannel detector, was studied for its applicability to molecular absorption and molecular fluorescence spectrometry. Molecular absorption spectrophotometry requires detectors with high UV to near IR response, high dynamic range, linear response, low noise, and temporal as well as thermal stability. Molecular fluorescence spectrometry requires, in addition, sensitivity to low-light level signals. These requirements were satisfied by the systems under study. Other parameters that govern the overall performance of diode array-based spectrophotometers and spectrofluorometers include: photometric range, stray energy radiation and its effect on photometric accuracy, photometric precision, spectral resolution sensitivity, and signal-to-noise considerations. Various readout methods for the array detectors were examined including: real time, in-memory signal integration, on-target signal integration, variable integration time (VIT), diode grouping, and diode fast access (a pseudorandom access readout). Performance demonstrations of these multichannel spectrometers were made with a few typical chemical systems. The spectrophotometric performance of the diode array system was excellent, practically equal to that of conventional single-channel systems. Exceptions were higher amenability to the adverse effects of stray radiation energy and a dependency of the geometric (wavelength) accuracy on spatial fluctuations (wander) in the light source. Potential long-term UV degradation of diode arrays may present an inherent problem, but was not discussed here because data accumulated up-to-date was considered inconsequential. As a spectrofluorometer multichannel detector, the diode array showed an "unexpected" signal-to-noise (detectability) performance, closely matching that of conventional high gain detectors. However, this performance was achieved only if sufficiently long signal integration times (20 to 160 s) were feasible. Overall performance of the diode array has demonstrated that theoretical multiplex advantages are achievable, resulting in either a considerable improvement in signal-to-noise or a corresponding shortening in observation time.
TL;DR: In this article, the Mertz method and the symmetrization-convolution method were evaluated with respect to the accurate reproduction of a single-beam spectrum, and the variation in photometric accuracy with the number of points used in the phase calculation, and apodization in phase calculation was examined.
Abstract: Two approaches to phase correction in FT-IR spectroscopy are discussed. Using synthetic data, both the Mertz method and the symmetrization-convolution method are evaluated with respect to the accurate reproduction of a single-beam spectrum. The variation in photometric accuracy with (1) the number of points used in the phase calculation, and (2) apodization in the phase calculation is examined.
TL;DR: In this article, the authors reported the use of either a solvent removal technique or a flow cell technique in which interferometric spectrometers have been used as the detector, and the results showed that the combination of high performance liquid chromatography and infrared spectrometry can achieve state-of-the-art performance.
Abstract: Much work has been done in recent years on the combination of high performance liquid chromatography and infrared spectrometry. Such studies reported the use of either a solvent removal technique or a flow cell technique in which interferometric spectrometers have been used as the detector.
TL;DR: In this article, the application of factor analysis to reduce random noise in FT-IR spectra is described, by utilizing the total information content of all the spectra, it is possible to reduce the amount of random noise present in individual spectrum.
Abstract: The application of factor analysis to reduce random noise in FT-IR spectra is described. By utilizing the total information content of all the spectra, it is possible to reduce the amount of random noise present in individual spectrum.
TL;DR: In this paper, different high-frequency generators have been studied in the 5 to 56 MHz range in order to observe the influence of frequency on spectral characteristics of inductively coupled plasmas used in emission spectroscopy.
Abstract: Different high-frequency generators have been studied in the 5 to 56 MHz range in order to observe the influence of frequency on spectral characteristics of inductively coupled plasmas used in emission spectroscopy. Higher frequencies tended to yield decreased excitation temperatures and electron number densities and therefore decreased line and background continuum intensities. Signal-to-noise ratios were improved ranging from 1 to 8 MHz going from 27 to 56 MHz with similar improvements in detection limits. Precision, working curve linearity, chemical interferences, and the ability to atomize high salt concentration samples were unaffected by frequency.
TL;DR: In this paper, an examination of the use of cross-correlation in quantitative analysis under conditions that isolated peaks are not obtained is reported, and the properties of correlation that are relevant to this application are described.
Abstract: An examination of the use of cross-correlation in quantitative analysis under conditions that isolated peaks are not obtained is reported. Examples are taken from infrared absorption spectroscopy. The properties of correlation that are relevant to this application are described. A comparison between cross-correlation and peak measurement in made with emphasis on the effects of sample background and instrument noise. Results are presented to show that correlation allows substantial improvement of performance when spectra with complex backgrounds are involved. It affords a significant improvement when noisy signals must be handled.
TL;DR: This work uses the sequential simplex optimization technique to evaluate the performance of a proposed objective function in locating optimal instrumental operating conditions for simultaneous multiple-element determinations by inductively coupled plasma spectrometry.
Abstract: This work considers several composite objective functions and uses the sequential simplex optimization technique to evaluate the performance of a proposed objective function in locating optimal instrumental operating conditions for simultaneous multiple-element determinations by inductively coupled plasma spectrometry. The proposed objective function, combined with a generalized approach to optimization, can be applied to any group of analysis elements and is of value in routine optimization procedures for simultaneous multiple-element methods of analysis.
TL;DR: In this article, an Atlas of Spectral Information for Inductively Coupled Plasma, Atomic Emission Spectroscopy has been assembled to provide the analyst with the basic information concerning the analytical capabilities and the potential spectral interferences of the prominent spectral lines of 70 elements.
Abstract: A thorough knowledge of the spectral emission characteristics of the inductively coupled plasma is a prerequisite for its maximum utilization in atomic emission spectroscopy. Toward this end an Atlas of Spectral Information for Inductively Coupled Plasma, Atomic Emission Spectroscopy has been assembled to provide the analyst with the basic information concerning the analytical capabilities and the potential spectral interferences of the prominent spectral lines of 70 elements. The Atlas contains 232 wavelength scans of 70 elements covering the range of 189 to 517 nm (189 to 597 nm for sodium and the reference blank). The Atlas also contains a listing of 973 prominent lines with estimated detection limits and a detailed collection of coincidence profiles for 281 of the most prominent lines, each with profiles of ten of the most prevalent concomitant elements superimposed. This paper contains a survey of the spectral information contained in the Atlas.
TL;DR: In this article, a data compression technique using factor analysis and the Karhunen-Loeve transformation has been applied to a library of vapor phase infrared spectra, which results in a fivefold reduction in storage requirements for the spectral library and a corresponding reduction in search time.
Abstract: A data compression technique using factor analysis and the Karhunen-Loeve transformation has been applied to a library of vapor phase infrared spectra. Application of the compression algorithm results in a fivefold reduction in storage requirements for the spectral library and a corresponding reduction in search time. A search system based on the compression data has been evaluated and found to compare favorably with a search using the entire spectrum.
TL;DR: In this article, a two-crystal x-ray spectrometer with a wide scanning range (2° to 146° 2θ) under vacuum is described, which makes possible the observation of chemical shifts in xray spectra.
Abstract: The design and construction of a new two-crystal x-ray spectrometer are described together with the observed Mg Kα, Al Kα, Si Kα, S Kα, and Cu Kα1 spectra. The spectrometer is designed for x-ray fluorescence analysis and has a wide scanning range (2° to 146° 2θ) under vacuum. Excellent reproducibility of 0.4 s in are is attainable, which makes possible the observation of chemical shifts in x-ray spectra. Magnesium Kα was found to be influenced by the coordination number, proving that the spectrometer is useful for chemical state analysis.
TL;DR: In this paper, the effect of spectrometer resolution on the peak intensity and the full width at half maximum (FWHM) of a Lorentzian spectrum is obtained by evaluating the convoluted line shapes.
Abstract: The effect of spectrometer resolution on the peak intensity and the full width at half maximum (FWHM) of a Lorentzian spectrum is obtained by evaluating the convoluted line shapes. Spectrometer resolution functions (SRF) having Gaussian and triangular profiles are considered separately. Empirical relations to estimate the true peak intensity and the FWHM from the observed parameters are suggested. These relations are valid over an extended range of parameters with an accuracy better than that of other methods suggested earlier. As an application, the true FWHM's and peak intensities of the main component of the Raman active Ag mode of sulphate ion in potash alum at low temperatures are evaluated.
TL;DR: In this article, the authors used high-resolution infrared diode laser spectroscopy to determine line strengths, foreign-, and self-broadening coefficients for several transitions in the v2 band of H2O near 6 μm.
Abstract: High-resolution infrared diode laser spectroscopy has been used to determine line strengths, foreign-, and self-broadening coefficients for several transitions in the v2 band of H2O near 6 μm. Sources of systematic experimental error, most notably stray radiation from off-axis modes and thermal etalon effects, were detected and characterized. Their effects on the resulting line parameters were minimized by making appropriate corrections or adjusting experimental conditions such as laser current and temperature. Measured line strengths are found to agree to better than 5% with one published tabulation. Foreign-gas broadening coefficients compare favorably with theoretical values, whereas measured self-broadening coefficients were found to be systematically less.
TL;DR: A review of analytical applications of matrix isolation Fourier transform infrared spectroscopy is presented in this paper, along with practical techniques for obtaining analytically useful results, and a few studies relating to matrix isolation used in conjunction with Raman and conventional IR Spectroscopy are reviewed.
Abstract: A review of analytical applications of matrix isolation Fourier transform infrared spectroscopy is presented. The characteristics of matrix isolation spectroscopy are discussed along with practical techniques for obtaining analytically useful results. A few studies relating to matrix isolation used in conjunction with Raman and conventional IR spectroscopy are reviewed. The majority of analytical applications of matrix isolation vibrational spectroscopy has entailed the use of FT-IR techniques. Qualitative and quantitative results from a number of sample types are presented. The coupling of matrix isolation vibrational spectroscopy with chromatographic separations is reviewed.
TL;DR: In this article, Fourier transform IR photoacoustic (FT-IR-PAS) dichroism studies have been applied to determine molecular orientation from the surface of one-way drawn poly(ethylene terephthalate) film.
Abstract: Fourier transform IR photoacoustic (FT-IR-PAS) dichroism studies have been applied to determine molecular orientation from the surface of one-way drawn poly(ethylene terephthalate) film. When compared with attenuated total internal reflectance (ATR) dichroic spectra obtained with a modified, rotatable sample holder on the same sample, photoacoustic (PA) spectra show saturation effects in strong absorption bands near 1730, 1250, and 1100 cm−1, probably due to the greater penetration depth in the PA technique. The dichroic ratios (kx/ky) on the plane of the sample film have been calculated from PA spectra, only on bands which do not show saturation and compared with the analogous ratios determined from ATR dichroic spectra. For three well-known parallel bands at 1335, 975, and 795 cm−1 the dichroic ratio is greater than unity in both ATR and PAS, as expected from the drawing process. In general, somewhat lower dichroic ratios are observed by PA spectra than by ATR spectra with this sample. Possible reasons for this trend are discussed. This study demonstrates the potential of FT-IR-PAS dichroism as a complementary technique to ATR dichroism, especially on samples with rough or brittle surfaces.
TL;DR: In this paper, a Fourier transform spectrometer built with a photothermal beam deflection detector was used to record infrared spectra of organic and inorganic solids, and the total absence of sample-containing devices makes it possible to examine portions of the surfaces of objects which are very large in size.
Abstract: Infrared spectra were recorded of organic and inorganic solids with a Fourier transform spectrometer built to operate with a photothermal beam deflection detector. No sample preparation or cells per se is needed to examine milligram quantities of powder. The total absence of sample-containing devices makes it possible to examine portions of the surfaces of objects which are very large in size. Sample heating may occur, so that care must be taken with heat-sensitive materials.
TL;DR: In this paper, factor analysis has been used to resolve the overlapping XPS spectra obtained in the x-ray-induced transformation of Pt(en)2(OH)2Cl2 to Pt( en)2CL2, without prior knowledge of the data set nor the establishment of any initial curve fitting criteria.
Abstract: Factor analysis has been used to resolve the overlapping XPS spectra obtained in the x-ray-induced transformation of Pt(en)2(OH)2Cl2 to Pt(en)2Cl2. This is achieved without prior knowledge of the data set nor the establishment of any initial curve fitting criteria.
TL;DR: The spatial dependence of spectral and matrix interference effects known to affect ICP emission spectrometry has been studied in this paper, where the emissions of atoms, ions, and molecules were resolved on both a vertical and radial basis.
Abstract: The spatial dependence of spectral and matrix interference effects known to affect ICP emission spectrometry has been studied. The emissions of atoms, ions, and molecules were resolved on both a vertical and radial basis. Interference and sample volatility effects were found to be limited to specific spatial regions. Molecular background emission was dominated by the entrainment of air and was limited primarily to the outer radial regions of the plasma. In contrast, the radial displacement of analyte molecular emission from more slowly atomized samples varied with height. In the case of the easily ionized element interference on Ca atomic/ionic emission, evidence was found indicating at least two different mechanisms of interaction. The ability to attain radial resolution was instrumental in assigning causes to interference effects.
TL;DR: In this paper, the design of a furnace assembly for maintaining aqueous solutions at temperatures up to 300°C and controlled pressures of up to 15 MPa is described, and the apparatus is used to monitor the chemical processes taking place in high-temperature annealing solutions.
Abstract: The design of a furnace assembly for maintaining aqueous solutions at temperatures up to 300°C and controlled pressures of up to 15 MPa is described. The apparatus is being used to monitor the chemical processes taking place in high-temperature aqueous solutions. Spectra of the Zn(NO3)2/H2O system and the HCl/H2O system are presented as examples.
TL;DR: In this paper, the emission spectrum of the series limit of Al was used to estimate the electron number densities (ne) in inductively coupled Ar or Ar-N2 plasmas (ICP).
Abstract: The emission spectrum of the series limit of Al was used to estimate the electron number densities (ne) in inductively coupled Ar or Ar-N2 plasmas (ICP). The spectra of the series limit were recorded either with a silicon-intensified target vidicon detector or by a computer-controlled, scanning spectrometer. Background stripping was performed on the spectra recorded by both instruments to enhance signal recovery. Under comparable experimental conditions, the ne values in the Ar-supported ICP were higher than those observed in Ar-N2 plasma, when pure N2 was used in the outer flow. However, the ne value of the Ar ICP under the conditions commonly used in analytical laboratories (15 mm observation height and 1200 W forward power) was comparable to that found in pure N2 outer flow, Ar-N2 plasmas operated under conditions (5 mm observation height and 3000 W forward power) suitable for exciting spectral lines of high excitation energies. Whereas the use of higher, carrier gas flows tended to reduce the ne values of the Ar ICP substantially, this trend was not observed for the pure N2 outer flow Ar-N2 plasma.
TL;DR: In this paper, a helium-neon laser was used for the measurement of infrared absorption of condensed phase samples, and the average specific absorption coefficient for hydrocarbons at this wavelength was found to be 2.09 (± 0.09) 1 g−1 cm−1.
Abstract: Thermal lens calorimetry is applied to the measurement of infrared absorption of condensed phase samples. The unique trade offs encountered with longer wavelength lasers in thermal lens measurements are discussed. As a demonstration of the technique, the determination of hydrocarbons using a helium-neon laser operated at 3.39 μm is reported. The minimum detectable sample has an absorbance, A = 5 × 10−4, corresponding to 8 ng of 2,2,4-trimethylpentane within the beam volume in the sample. Interpretation of absorbance at the helium-neon laser transition is aided by the determination of functional group molar absorptivities from a series of normal, cyclic, and branched-chain hydrocarbons. The average specific absorption coefficient for hydrocarbons at this wavelength is found to be 2.09 (±0.09) 1 g−1 cm−1.