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Showing papers in "Applied Spectroscopy in 1976"


Journal ArticleDOI
TL;DR: The measurement capability of a computer coupled photodiode array spectrometer based on a 1024 element array which is capable of simultaneously measuring over 50 nm (500 Å) of continuous spectral information anywhere from 200 to 1000 nm is illustrated.
Abstract: A rather large number of spectrochemical studies and analyses can be greatly facilitated by the simultaneous measurement of spectral information over a range of wavelengths. Of particular importance and interest to analytical spectroscopists is the development of simultaneous multielement analysis systems. The development and implementation of such analyses have been hampered by a lack of convenient and versatile multichannel spectrochemical measurement systems. New detector subsystems based on modern electronic image sensors are helping to overcome this obstacle. One type of electronic image sensor is the self-scanning linear array of silicon photodiodes. These arrays are available with densities of 1024 photodiodes per in and in lengths of up to 1 in. They are packaged in conventional dual-in-line integrated circuit packages complete with the necessary scanning circuitry. These sensors have simple and inexpensive control and measurement circuitry, and superior blooming and lag performance when compared to most other electronic image sensors. In addition, the signal integrating capability of the arrays is a flexible and powerful asset for many spectrochemical measurements. These and other operational characteristics of photodiode arrays are emphasized in this study. In addition, the measurement capability of a computer coupled photodiode array spectrometer based on a 1024 element array which is capable of simultaneously measuring over 50 nm (500 A) of continuous spectral information anywhere from 200 to 1000 nm is illustrated.

102 citations


Journal ArticleDOI
TL;DR: The effect of multiplexing in Fourier transform spectroscopy (FTS) and other coding techniques such as Hadamard transform spectral analysis (HTA) on the signal/noise ratio arises from two factors as mentioned in this paper.
Abstract: The effect of multiplexing in Fourier transform spectroscopy (FTS) (and other coding techniques such as Hadamard transform spectroscopy) on the signal/noise ratio arises from two factors. The first of these is a N½ improvement for a spectrum containing N resolution elements since each individual resolution element is now viewed for an N-fold longer time. The second factor is due to the simultaneous observation of all resolution elements, raising the signal level by a factor N for an uniform spectrum.

77 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present experimental evidence that stray light may produce substantial shifts in the background signal measured with some spectrometers when the total composition of the sample changes, and various methods for the reduction, elimination or correction of stray light effects are also discussed.
Abstract: When atomic emission spectroscopy is employed for the determination of trace elements at concentrations near the detection limit, the spectral background will normally be a large fraction of the total measured signal. Precise background corrections are therefore required if accurate analyses are to be achieved. Experimental evidence is presented to document the fact that stray light may produce substantial shifts in the background signal measured with some spectrometers when the total composition of the sample changes. The data presented have been obtained with the inductively coupled plasma as an excitation source; similar effects can be expected with other excitation sources as well. Examples of various forms of stray light originating from grating defects (ghosts, near and far scatter) and defects in the design of spectrometers are presented. Various methods for the reduction, elimination or correction of stray light effects are also discussed.

76 citations


Journal ArticleDOI
TL;DR: In this paper, a Fourier transform infrared spectrophotometer with the capability to measure diffuse reflectance (DR) from 5000 to 500 cm−1 (2 to 20 μm) in addition to the normal transmittance measurements is described.
Abstract: This paper describes a new Fourier transform infrared spectrophotometer with the capability to measure diffuse reflectance (DR) from 5000 to 500 cm−1 (2 to 20 μm) in addition to the normal transmittance measurements. The instrument has a true simultaneous double beam measurement mode and a high speed single beam mode. The system also takes advantage of many data manipulation and display features due to the built-in computer and 2.5 million word storage system. One of the objectives of this work was to produce a practical instrument which includes the DR capability; another was to introduce the qualitative and quantitative measurements of DR in the infrared to the analytical community. DR has been commonly available in the visible and near ir spectrum, but until this new instrument, has not been available in the ir. A brief survey of the background and history of DR and emittance measurements in the ir is given. The design details and operation of the instrument are generally examined. Brief examples are provided for a few transmittance, trace analysis, and microsampling applications, and a variety of DR results are shown. The addition of diffuse reflectance as a tool in the infrared opens new avenues for investigation and application in many fields.

67 citations


Journal ArticleDOI
TL;DR: In this paper, a method for the analysis of selenium and rsenic in surface water specimens by atomic absorption spectroscopy is described, which employs sodium borohydride for conversion of SE and arsenic compounds in specimens to hydrogen selenide and arsine.
Abstract: fully automated method for the analysis of selenium and rsenic in surface water specimens by atomic absorption spectroscopy is described. The technique employs sodium borohydride for conversion of selenium and arsenic compounds in specimens to hydrogen selenide and arsine. To increase the efficiency of hydride recovery for analysis, the reacted specimen is stripped using a heated column. The hydride gas and hydrogen evolved from the chemical reaction is then combusted in a tube furnace placed in the optical path of an atomic absorption spectrophotometer. Seventy specimens can be analyzed per hour with a detection limit of 0.019 μg/liter for selenium and 0.011 μg/liter for arsenic.

63 citations


Journal ArticleDOI
TL;DR: In this paper, a simple correction formula is presented for obtaining true Lorentzian halfbandwidths from convolutions with triangular slits, and the correction is shown to be applicable to a number of other convolutions.
Abstract: A simple correction formula is presented for obtaining true Lorentzian half-bandwidths from convolutions with triangular slits. The correction is shown to be applicable to a number of other convolutions. Also, the dependence of the depolarization ratio in terms of peak heights on slitwidth is investigated.

61 citations


Journal ArticleDOI
TL;DR: Inelastic electron tunneling spectroscopy (IETS) has been used extensively in analytical chemistry and surface interactions as discussed by the authors. But the application of IETS to analytical chemistry has not been discussed.
Abstract: The technique of inelastic electron tunneling spectroscopy (IETS) is reviewed. The physical principles involved, the theoretical status, and the experimental techniques necessary to obtain tunneling spectra are presented. The details of sample preparation and the necessary measuring circuits are discussed thoroughly. The application of IETS to analytical chemistry and surface interactions is illustrated through a review of the spectra that have been obtained from 1966 to the present.

53 citations


Journal ArticleDOI
TL;DR: In this article, Raman and site selection fluorescence spectra were compared when these spectra have been measured with conventional fixed wavelength excitation and with modulated wavelength excitations, and simple analysis of signal/noise ratios from these different experimental techniques show modulation methods can give improvements under particular conditions.
Abstract: Raman and site selection fluorescence spectra are compared when these spectra have been measured with conventional fixed wavelength excitation and with modulated wavelength excitation. The samples were solutions of benzene and of chlorophyll. The modulated wavelength method records the differential spectra. Simple analysis of signal/noise ratios from these different experimental techniques show modulation methods can give improvements under particular conditions. These conditions are discussed.

52 citations


Journal ArticleDOI
TL;DR: In this paper, a set of peak wavenumbers, Vm = m/2nd (1) where m is the sample refractive index, and d, its thickness, is given for thin film solid samples and ΔT = 4 (n − n 0/n + n 0)2 (3) for samples contained between windows of n 0.
Abstract: Thin samples in spectroscopy often show disturbing "channel spectra" due to interference fringes produced by reflections at the sample surface. These fringes will be characterized by a set of peak wavenumbers, vm as Vm = m/2nd (1) where m = 0, 1, 2, ... ; n is the sample refractive index, and d, its thickness. The intensity of these peaks, ΔT, is given by ΔT = 4 (n − 1/n + 1)2 (2) for thin film solid samples and ΔT = 4 (n − n0/n + n0)2 (3) for samples contained between windows of index n0.

52 citations


Journal ArticleDOI
TL;DR: In this paper, an ion-sputtering source was installed and evaluated as an emission spectrographic source for the analysis of metal surfaces and for the determination of in-depth concentration profiles.
Abstract: An ion-sputtering source was installed and evaluated as an emission spectrographic source for the analysis of metal surfaces and for the determination of in-depth concentration profiles. This source generates a direct current glow discharge in a low-pressure argon atmosphere between a hollow stainless-steel anode and the sample (the cathode) and sputters material at a controlled rate from the sample surface. The resultant spectrum of the sputtered material is recorded photographically, and the analysis is completed by conventional spectrographic techniques. The power supply of the source can be operated in either a constant dc mode or a square-wave dc mode, but better repeatability and accuracy have been achieved with the square-wave dc mode. Before any significant sputtering occurs with this source, the voltage must exceed 240 Volts, the threshold sputtering voltage. The sputtering rate increases with both source current and voltage. This source has been used for the quantitative analysis of the surface of steel products and the determination of changes in composition with depth below the surface.

52 citations


Journal ArticleDOI
TL;DR: The stripping of photoresists from a silicon wafer using an rf oxygen plasma has been monitored using the optical emission from electronically excited OH and CO species in the ultraviolet region of the spectrum as discussed by the authors.
Abstract: The stripping of photoresists from a silicon wafer using an rf oxygen plasma has been monitored using the optical emission from electronically excited OH and CO species in the ultraviolet region of the spectrum. The band systems at 283.0 nm (CO*, OH*), 297.7 nm (CO*), and 308.9 nm (OH*) are intense and spectrally isolated from other systems and arise from plasma-induced oxidation of the polymeric photoresist material. The endpoint of plasma stripping and the amount of stripped material is easily determined quantitatively. In addition, variations in stripping rate of photoresist as a function of wafer position in the reaction chamber can be detected.

Journal ArticleDOI
TL;DR: In this paper, the authors made a theoretical comparison of ICP discharges in argon and nitrogen with the objective of evaluating their relative spectrochemical usefulness for decomposition of Al2O3 particles.
Abstract: Using a recently developed numerical procedure for the solution of energy and magnetic flux density equations for inductively coupled plasma (ICP) discharges with diatomic gases, we made a theoretical comparison of ICP discharges in argon and nitrogen with the objective of evaluating their relative spectrochemical usefulness. Nitrogen discharges operating at powers between 3 and 7 kW and argon discharges of powers between 0.6 and 6 kW are investigated for a three-concentric gas flow arrangement now popular in spectrochemical analysis. Although the argon discharge temperatures are higher and the linear velocity of the central gas stream lower, nitrogen provides a more effective discharge for decomposition of Al2O3 particles. Two-dimensional temperature distributions, velocity profiles, and power loss relationships are described.

Journal ArticleDOI
TL;DR: In this paper, the use of wavelength modulation for background correction in graphite furnace atomic emission spectrometry is shown to improve detection limits in some cases by several orders of magnitude and to increase its applicability to sample analysis.
Abstract: The use of wavelength modulation for background correction in graphite furnace atomic emission spectrometry is shown to improve detection limits in some cases by several orders of magnitude and to increase its applicability to sample analysis. An HGA-2100 graphite furnace atomizer is used in conjunction with a ¾-m monochromator equipped for wavelength modulation. A discussion of analytical growth curves, detection limits, scatter, and optimization of signal/noise ratio is presented. Copper is analyzed in botanical samples and the results are compared to analysis by atomic absorption and molecular absorption spectrophotometry.

Journal ArticleDOI
TL;DR: In this paper, a commercial dc plasma has been evaluated as an excitation source for multielement spectrometric analyses, and the results indicate that precise multiellement analyses can be carried out at low concentration levels comparable to those that can be obtained by flame atomic absorption methods.
Abstract: A commercial dc plasma has been evaluated as an excitation source for multielement spectrometric analyses. Plasma temperatures have been measured and typical excitation profiles determined. Detection limits have been determined using a direct reading spectrometer equipped for simultaneous background correction measurements. The results indicate that precise multielement analyses can be carried out at low concentration levels comparable to those that can be obtained by flame atomic absorption methods.

Journal ArticleDOI
TL;DR: Fourier transform techniques in spectroscopy have been shown to offer significant improvements over classical dispersive methods in the study of infrared spectral features both in astronomical measurements and in laboratory studies as discussed by the authors.
Abstract: Fourier transform techniques in spectroscopy have been shown to offer significant improvements over classical dispersive methods in the study of infrared spectral features both in astronomical measurements and in laboratory studies. These improvements result from now well known principles including spectral multiplexing, high etendue or throughput, and a significantly improved wave number scale.

Journal ArticleDOI
TL;DR: In this paper, the electron beam is crossed by a molecular jet, the electrons are scattered (Fig 1) at some distance from the scattering center (the nozzle, Fig 1) one can observe the scattering pattern, a system of concentric rings (Fig 2) these rings have varying intensities The intensity distribution is a function of the structure of the scattering molecules
Abstract: If an electron beam is crossed by a molecular jet, the electrons are scattered (Fig 1) At some distance from the scattering center (the nozzle, Fig 1) one can observe the scattering pattern, a system of concentric rings (Fig 2) These rings have varying intensities The intensity distribution is a function of the structure of the scattering molecules This is the basis of electron diffraction as a tool of structural chemistry

Journal ArticleDOI
TL;DR: In this article, the results from a preliminary series of such controlled degradation conditions with on-line monitoring of the volatile products by automatic gc analysis and Fourier transform infrared (FT-ir) spectroscopy were reported.
Abstract: Thermal degradation studies conducted on a wide variety of polymeric materials necessitate sensitive and informative analytical techniques. Studies of thermal degradation under carefully controlled pyrolytic (inert) and combustive (air) conditions have been reported in which the major volatile products were monitored by gas chromatography (gc). With the use of data obtained by this method, details in polymer microstructure and degradation mechanisms have been deduced. We now report the results from a preliminary series of such controlled degradation conditions with on-line monitoring of the volatile products by automatic gc analysis and Fourier transform infrared (FT-ir) spectroscopy.

Journal ArticleDOI
TL;DR: A number of signal processing operations can be carried out on spectra using a digital filter based on a simple trapezoid function, applied to the Fourier transform of the spectral signal.
Abstract: A number of signal processing operations can be carried out on spectra using a digital filter based on a simple trapezoid function. The filter is applied to the Fourier transform of the spectral signal. Several signal processing examples are presented to illustrate the capabilities of this filter. These examples include filtering and diagnosis of high frequency noise on a signal, removal of fixed frequency noise, minimization of quantization noise, and differentiation and approximate deconvolution for the purpose of resolution enhancement.

Journal ArticleDOI
A. Danielsson1, P. Lindblom1
TL;DR: The Image Disjoint Echelle Spectrometer (IDES) as discussed by the authors is a state-of-the-art multielement spectrometer with high resolution and high dispersion.
Abstract: The image dissector echelle spectrometer system consists of a stigmatic, coma-compensated echelle spectrograph with high resolution and high dispersion, an image dissector tube with specially designed focusing and deflection coils and a minicomputer with 16K memory. The whole spectral range, i.e., from 200 to 800 nm, is focused on the photocathode of the image tube in 91 spectral segments (spectral orders). The measurement of the spectrum, involving wavelength selection and intensity measuring through single-photon counting, is performed by the computer. The standard software contains programs for focusing, wavelength calibration, scanning, and spectrochemical analysis. IDES is a multipurpose and multielement spectrometer which can be adapted for any application in analytical spectroscopy by utilizing the appropriate software program. The fields of application of the IDES system are; emission from combustion and electrical flames; dc arcs; hollow cathodes and glow discharges; atomic absorption; and fluorescence with line and continuous light sources.

Journal ArticleDOI
TL;DR: In this article, a direct reading emission spectrometer system is described which permits dynamic background correction measurements at each analytical wavelength, and a laboratory computer controls the system, receives the data, and performs the background subtraction.
Abstract: A direct reading emission spectrometer system is described which permits dynamic background correction measurements at each analytical wavelength. The system utilizes a refractor plate mounted on a tuning fork as a rapid means for square-wave shifting the spectral band pass from each analytical wavelength to the adjacent background wavelength position. A laboratory computer controls the system, receives the data, and performs the background subtraction. Evaluation of the system has shown that photon counting statistics are applicable and that reliable background corrections are obtained. Comparisons of this correction approach with others that have been used have further demonstrated its advantages for multielement analysis by emission spectrometry.

Journal ArticleDOI
TL;DR: A survey of the application of laser-Raman spectroscopy in structural studies of viruses and model nucleoproteins is given in this article, where the major constituents of viruses-nucleic acid and protein molecules-exhibit Raman spectra which differ greatly from one another, both in the spectral ranges that contain vibrational frequencies of conformational interest and in relative intensities of Raman scattering of their respective subgroups.
Abstract: A survey is given of developments leading to the application of laser-Raman spectroscopy in structural studies of viruses and model nucleoproteins. The major constituents of viruses-nucleic acid and protein molecules–exhibit Raman spectra which differ greatly from one another, both in the spectral ranges that contain vibrational frequencies of conformational interest and in the relative intensities of Raman scattering of their respective subgroups. These features, not common to the infrared spectra, allow laser-Raman spectroscopy to be exploited for the study of viral assembly and nucleoprotein interactions. Examples considered here are the RNA-containing virus MS2, the DNA-containing viruses Pfl and fd, and the complex of polylysine with DNA.

Journal ArticleDOI
TL;DR: In this article, a model system for coal-derived asphaltenes was proposed and the equilibrium constant of the 1:1 complex between the OH proton of o-phenylphenol and the nitrogen electron donor of pyridine (Py) was determined.
Abstract: Proton, carbon, and nitrogen-14 nuclear magnetic resonance studies are reported of hydrogen bonding between the OH proton of o-phenylphenol (OPP) and the nitrogen electron donor of pyridine (Py). Data are also reported on the hydrogen bonding of the acid and base components of coal-derived asphaltenes with the model system. Determination was made of the equilibrium constant of the 1:1 complex between OPP and Py from the proton NMR studies. Qualitative results are reported from the 13C and 14N studies of the model system (OPP-Py) with the individual asphaltene fractions. Because of the recent renewed interest in coal liquefaction this investigation may provide a starting point for future research.

Journal ArticleDOI
TL;DR: A microwave-induced argon plasma has been evaluated as a spectro-chemical excitation source for multielement analyses of solutions as discussed by the authors, and results for 12 elements indicate that detection capabilities are typically better than 0.01 μg/ml.
Abstract: A microwave-induced argon plasma has been evaluated as a spectro-chemical excitation source for multielement analyses of solutions. Results for 12 elements indicate that detection capabilities are typically better than 0.01 μg/ml. Analyses of food composite samples indicate that matrix effects occur but these are cancelled by the use of the internal standard method.

Journal ArticleDOI
TL;DR: In this article, a least squares algorithm suitable for a small memory-size programmable desk calculator is proposed for smoothing and deconvoluting electron spectroscopy for chemical analysis spectra.
Abstract: A least-squares algorithm suitable for a small memory-size programmable desk calculator is proposed for smoothing and deconvoluting electron spectroscopy for chemical analysis spectra. Smoothing with quadratic polynomial passing through nine points is shown to be the most convenient. The same procedure is applied to compute derivatives of spectra; power and limitations of this extremely simple method are discussed, in relation to a reexamination of gold valence band spectra, revealing significant features.

Journal ArticleDOI
TL;DR: In this paper, the Fourier transform system was used for absorption subtraction in ir spectroscopy, which has become an important interpretation procedure in the last few decades due both to the availability of instruments containing a built-in minicomputer and to the quantum jump in IR spectrometer performance.
Abstract: Absorbance subtraction has recently become an important interpretation procedure in ir spectroscopy. This is due both to the availability of instruments containing a built-in minicomputer, and to the quantum jump in ir spectrometer performance due to the introduction of Fourier transform systems.

Journal ArticleDOI
TL;DR: In this paper, relative radiances of the Hβ, Hγ, and Hδ spectral lines of hydrogen were measured sequentially at various lateral positions in an inductively coupled rf argon-hydrogen plasma operated at atmospheric pressure (12 kW, 9 MHz).
Abstract: Simultaneous relative radiances of the Hβ, Hγ, and Hδ spectral lines of hydrogen were measured sequentially at various lateral positions in an inductively coupled rf argon-hydrogen plasma operated at atmospheric pressure (12 kW, 9 MHz). Measurements to take self-absorption into account were also performed. By applying an Abel integral inversion, a radial radiance profile for each line was obtained. With the two-line temperature method, simultaneous temperature profiles were obtained from each of the three line-pairs. The difference between these three sets of values and the negative values obtained for the Hγ:Hδ pair indicates that thermal equilibrium does not exist in this plasma.

Journal ArticleDOI
TL;DR: In this article, the vibrational spectra of species adsorbed on thin layer chromatography (TLC) plates have been studied by Fourier transform infrared (FT-ir) and Raman spectrometry.
Abstract: Methods of measuring the vibrational spectra of species adsorbed on thin layer chromatography (TLC) plates have been studied by Fourier transform infrared (FT-ir) and Raman spectrometry. Previous measurements of the transmittance spectra of species separated by TLC (with the adsorbent deposited on AgCl plates) showed poor signal/noise ratio at high frequency due to scattering by the adsorbent. Scattering has been minimized in these experiments by treating the TLC plate with Fluorolube, an infrared mulling oil whose refractive index closely matches that of the adsorbent. Spectra of chlorinated hydrocarbon pesticides on silica gel and alumina adsorbents measured in this way show differences which can be correlated with the mechanism of adsorption. FT-ir spectra of compounds on TLC plates can be obtained from microgram quantities of sample but Raman spectrometry is not as sensitive, requiring at least 200 μg of sample. The Raman bands of adsorbed pesticides are weak and considerably broadened with respect to the corresponding bands in the spectra of the pure samples.

Journal ArticleDOI
TL;DR: In this paper, the thickness effect is treated using a simplified form for the window function and the absorption edge and it is shown that for the low absorbing portion of the K edge the relative error caused by the tail of the window functions becomes larger, rather than vanishing, in the limit of zero thickness foils.
Abstract: The thickness effect is treated using a simplified form for the window function and the absorption edge. It is shown that for the low absorbing portion of the K edge the relative error caused by the tail of the window function becomes larger, rather than vanishing, in the limit of zero thickness foils. A means is described and experimentally demonstrated for separating changes in K absorption edge fine structure due to alloying from those due to the thickness effect.

Journal ArticleDOI
TL;DR: In this article, the design and construction of a computer-controlled Raman spectrophotometer for the determination of difference spectra among up to four samples is described, and the advantages of control by a minicomputer compared to a microcomputer or a hard wired controller are discussed.
Abstract: The design and construction of a computer-controlled Raman spectrophotometer for the determination of difference spectra among up to four samples is described. The advantages of control by a minicomputer compared to a microcomputer or a hard wired controller are discussed. Conditions for the attainment of good signal/noise ratios with aqueous solutions of nucleotides in the 1 to 25 mM range are examined for the case of excitation in the visible spectrum to minimize radiation damage. Applications to studies of dilute aqueous solutions of biological molecules are discussed. The interactions of small molecules with biopolymers, particularly, are examined.

Journal ArticleDOI
TL;DR: In this article, a photochemical-fluorimetric method was proposed for measurement of original vitamin K1 concentration using two different readout methods: (1) digital integration of the fluorescence increase due to the photoproduct at 431 nm; and (2) analog recording of photoplroduct fluorescence as a function of irradiation time.
Abstract: Vitamin K1 (2-methyl-3-phytyl-1,4-naphthoquinone) is not naturally fluorescent, but yields a fluorescent photochemical product upon ultraviolet irradiation. Among several solvents, dioxane was found to be the most suitable for the determination of vitamin K1. A photochemical-fluorimetric method is proposed for measurement of original vitamin K1 concentration using two different readout methods: (1) digital integration of the fluorescence increase due to the photoproduct at 431 nm; and (2) analog recording of photoproduct fluorescence as a function of irradiation time. The two methods gave limits of detection of 5 ppb, with a better precision for the digital procedure. Limits of detection and speed of analysis are shown to be more satisfactory for the determination of vitamin K1 than in previously reported analytical methods. The specific data obtained depends greatly on the quality of the solvent and excitation-photolysis source used.