Showing papers in "Applied Spectroscopy in 1974"

Quantitative Analysis of Glass Structure with the Use of Infrared Reflection Spectra

Abstract: It is predicted theoretically and justified experimentally that infrared reflectances are proportional to the concentrations of the vibrational species causing them. In the binary Li2O-, Na2O-, and K2O-SiO2 glasses used in this study, the reflection peaks have been assigned to vibrations of single silicon-oxygen tetrahedra in different symmetry environments caused by the presence of alkali ions. Care has been taken here in recording the spectra of high alkali glasses to prevent chemical reactions with water vapor in the atmosphere. The influence of phase separation on reflection spectra is also discussed.

The Backscattering Geometry for Raman Spectroscopy of Colored Materials

Abstract: Quantitative laser Raman spectroscopy on colored substances is considered, and it is shown that sample positioning and concentration are less critical when 180° illumination is used in place of the more common 90° illumination. In addition, the correction of Raman intensities for sample absorption is easily accomplished for data collected via backscattering (180° geometry), and the appropriate equations are presented. A spinning sample cell and holder are described for 180° illumination. The design utilizes simple and inexpensive sample tubes which are conveniently employed with standard liquids and solids as well as volatile, air-sensitive, and corrosive compounds. Provision for sample heating and cooling is described.

An Improved Pneumatic Nebulizer for Use at Low Nebulizing Gas Flows

Abstract: The common flames and electrical plasmas used for atomic absorption, emission, or fluorescence analytical techniques require a device to convert the solution to be analyzed into an aerosol, which is subsequently transported into the flame or plasma. Pneumatic nebulizers have been extensively employed for this purpose. In some systems, particularly those associated with inductively coupled plasmas, it is necessary to employ nebulizers that function efficiently at low nebulizing gas flow rates of about 1 liter/min. Although batch-type ultrasonic nebulization systems offer a potential solution to this problem, they are less convenient to use and more complex in construction. Direct impingement ultrasonic nebulizers are more convenient to use, but solutions of high salt and/or acid content may erode the coating on the piezo-electric crystal or the transducer transfer plates.

The Physical Basis for Analysis of the Depth of Absorbing Species Using Internal Reflection Spectroscopy

Abstract: Internal reflection spectroscopy is discussed for a nonuniform distribution of an absorbing species. Although some distributions cannot experimentally be distinguished from others, if one assumes a distribution, information about depth and concentration can be obtained by making measurements at several angles of incidence. A practical method is proposed and demonstrated for obtaining thickness and concentration for an assumed step profile.

A Method for Automatic Scanning of the Depolarization Ratio in Raman Spectroscopy

Abstract: A simple technique and an electronic system are described which allow an automatic scanning of the depolarization ratio in Raman spectroscopy. As a check the "parallel" and "perpendicular" spectra of the scattered Raman light can be recorded simultaneously with the depolarization ratio. The system performance is demonstrated for liquid carbon tetrachloride and carbon disulfide and the Q branch of nitrogen in air.

Laser-excited Resonance Raman Spectra of Small Molecules and Ions—A Review

Abstract: Laser-excited resonance Raman spectra of molecular vibrations in the gaseous, liquid, and solid state are reviewed. A short summary of the recently developed Raman techniques for absorbing materials is also given. A bibliography is added in an appendix which covers the literature of laser-excited resonance Raman spectra of molecular vibrations of more complicated molecules, mostly of biological interest.

The Raman scattering of uranyl and transuranium V, VI, and VII ions

Abstract: The Raman scattering of U(VI), Np(VI), Pu(VI), Am(VI), and Np(V), Am(V) in HClO4 solutions and Np(VII) in a NaOH medium is reported. Direct observation of the polarized v1 vibration (D∞h symmetry) is observed for the transuranium MO2n+ ions in the V and VI oxidation states. The spectroscopic evidence is consistent with a linear MO2n+ structure for the Np(VII) ion in basic solutions. The trend of the v1 frequency and the MO stretching force constants with the oxidation is discussed and is correlated with the bond strengths and the stability of the MO2n+ ions.

Rotating Surface Scanning Technique for Raman Spectroscopy

Abstract: The difficulty in recording Raman spectra of highly absorbing samples has been circumvented recently by the introduction of the rotating Raman sample technique. This technique appears to be a general solution for the study of highly absorbing materials which would decompose because of the localized heating of the focused laser beam if the conventional static excitation method were employed. Because of its simplicity the rotating Raman sample technique is very useful for laser-excited resonance Raman studies where excitation within strong absorption bands of the molecule under investigation is required. However, in some cases—for instance, at very low temperatures—it is complicated or even impossible to rotate the sample and keep it cold at the same time. Some developments have been made in this direction for moderately low temperatures.

A Method for Analysis of Plant Tissue by Direct Reading Spark Emission Spectroscopy

Abstract: A procedure was developed for the rapid quantitative determination of K, P, Ca, Mg, Mn, Fe, Cu, B, and Zn content in plant tissue by direct reading emission spectrometry using spark excitation and the rotating disc electrode technique. Aliquots of standard reference material, ground to pass a 40 mesh screen, are weighed into high form porcelain crucibles and ashed at 450°C for 6 h. Five milliliters of an internal standard-buffer solution (0.2% cobalt and 0.5% lithium in 1 N HCl) are added to the remaining ash. The resulting solution is subjected to a 30-sec burn on the spectrometer, and the intensity ratios for each element are recorded. Known concentrations (X) and intensity ratio units (Y) are entered into a stepwise regression computer program, and the linear, quadratic, and cubic regressions of Y on X are determined. Sample values are entered as Y into the appropriate regression equation which is then solved for X. If quadratic or cubic regression equations are used, the program will select the appropriate root. Relative standard deviations for samples determined over a several-day period generally were less than 10%.

Absorption Corrections and Concentration Optimization for Absorbing Samples in Resonance Raman Spectroscopy

Abstract: For Raman scattering studies of absorbing samples, e.g., in resonance Raman spectroscopy, it is frequently important to optimize the concentration and to correct for self-absorption effects on the observed intensities. These question are explored for 90°

Digital Least Squares Smoothing of Spectra

Abstract: We show that the most significant parameter in digital smoothing of spectra by least squares fitting to a cubic polynomial is the length of the smoothing range, and to avoid loss of resolution we recommend that the smoothing range be chosen approximately 0.7 FWHH (full width at half-height) of the narrowest single lines or components. Multiple use of digital smooths is shown not to be equivalent to a least squares fit of the original data but gives nearly the same response curve in smoothing of Gaussian lines.

Crystals for stellar spectrometers

Abstract: Crystal evaluation as it applies to instrumentation employed in X-ray astronomy is reviewed, and some solutions are offered to problems that are commonly encountered. A general approach for selecting the most appropriate crystals for a given problem is also suggested. The energy dependence of the diffraction properties of (002) PET, (111) Ge, (101) ADP, (101) KAP, and (001) RAP are reported.

Spectroscopy at High Pressures—Status Report and Update of Instrumental Techniques:

Abstract: A status report and update of the instrumentation necessary to obtain spectra of molecules at high pressures are presented. The optical pressure cells used, the spectrophotometer needed to obtain the spectra, the optical link between the two, high pressure spectroscopic windows, pressure calibration methods, and future outlook of the technique will be determined. The use of the high pressure cells with the interferometric technique and for Raman spectroscopy is outlined.

Gas Chromatography Mass Spectrometry: A Report on the State of the Art

Abstract: Instrumental and technical aspects of the combination gas chromatograph mass spectrometer are discussed, with emphasis on the various ways in which the mass spectrometer can serve as a detector for the gas chromatograph. A number of examples of applications are presented, in which the gas chromatograph mass spectrometer is used in its various instrumental modes. Computerized data processing is reviewed, and examples of applications are presented. Most of the examples of applications are taken from pharmacology and toxicology. Special attention is given to stable isotope analysis and to the role of stable isotopes in quantitation by gas chromatography mass spectrometry of samples in the subnanogram range.

Simultaneous Determination of Trace Wear Metals in Used Lubricating Oils by Atomic Absorption Spectrometry Using a Silicon-Target Vidicon Detector

Abstract: A multichannel atomic absorption spectrometer with a silicon-target vidicon detector was used for the simultaneous determination of trace metals in aqueous solution and in used lubricating oils. In most cases sensitivities were similar to those obtained by conventional single channel atomic absorption. Iron, magnesium, copper, and silver were simultaneously determined in lubricating oils, and, although precision was somewhat poorer than that normally attained by atomic absorption, it was adequate for this application. Good correlation was obtained between the vidicon method and a single channel method using a commercial atomic absorption spectrometer.

Application of X-ray Photoelectron Spectroscopy to the Study of Fiberglass Surfaces

Abstract: The application of x-ray photoelectron spectroscopy (ESCA) to the study of fiberglass surfaces is reported. Qualitatively, ESCA has been used to show the change in concentration of elements at the surface when fiberglass is subjected to heat and/or acid treatment. Diffusion of calcium to the surface as a function of temperature has been studied. Similarly, leaching of aluminum by acid as a function of pH is reported. The ability of ESCA to detect organic functional groups attached to fiberglass surfaces has been demonstrated for nitrogen and sulfur. Fiberglass coated with organic groups having chelating properties has been shown to extract metals from solution. It has also been demonstrated that ESCA can follow reactions of organic functional groups on glass surfaces, namely sulfonation of an amine.

Atomization Chambers for Atomic Absorption Spectrochemical Analysis: A Review

Abstract: Four types of atomization chambers for atomic absorption are reviewed. Advantages and dis-advantages of each are considered. The effects of chamber dimensions and sample introduction system are considered in relation to accuracy, sensitivity, and convenience. Relative sensitivity is more significant for real samples than absolute sensitivity. When peak heights are measured, the relative sensitivity is proportional to the atomizer chamber length. When peak area is measured, the relative sensitivity is proportional to the third power of the atomizer chamber length. Matrix materials in general affect the accuracy of determinations by changing the rate or time of atomization. Matrix effects are less serious with long tight tubes than they are for tubes with openings near the center.

Trace Metals Analysis in Petroleum Products by Atomic Absorption

Abstract: To provide information for customers who have regional environmental obligations, it was necessary to develop an analytical procedure to analyze for 25 metals in the range from 1 ppb to greater than 5 ppm in petroleum products. Atomic absorption is employed to determine 23 of the elements, namely: Al, Sb, Ba, Be, Bi, Ca, Cd, Co, Cr, Cu, Fe, K, Pb, Mg, Mn, Mo, Ni, Na, Si, Sn, Ti, V, and Zn. The general procedure is to ash the appropriate amount of sample by absorbing liquid samples on magnesium sulfonate ash aid (Conostan, Conoash M) or potassium sulfonate. Add 5 drops of H2SO4, heat to white fumes, fire, and ash at 650°C. The sulfonated ash is dissolved in dilute acid to provide the aspiration solution. Recovery studies on aluminum, antimony, beryllium, cadmium, and lead in the microgram per gram range are presented.

Radiative and Electrical Properties of Exploding Silver Wires

Abstract: The radiative properties of silver wires exploded by capacitive discharge are studied using time-integrated and time-resolved spectroscopy. Discharge current measurements are obtained from a calibrated current shunt and are correlated with time-resolved spectra to obtain a model for the current conduction processes during wire explosions. Two basic explosion mechanisms are described, both of which begin with the conversion of the wire from a conducting solid to a rapidly expanding dielectric cylinder of metal vapor. This results in a rapid reduction of discharge current. Current then may resume in one of two ways. In He at atmospheric and reduced pressure and in air at reduced pressure dielectric breakdown of the gas surrounding the wire occurs with current conduction peripheral to the expanding metal vapor cylinder. In air at atmospheric pressure, dielectric breakdown occurs through the metal vapor. This results in current conduction along the vapor cylinder axis. The advantages of peripheral current conduction for the analysis of metals electroplated on the surface of silver wires are discussed. Parametric studies with Cd-plated silver wires indicate that the intensity of the background continuum can be reduced by nearly 2 orders of magnitude with little effect on Cd line intensities by reducing the pressure from 730 Torr to 50 Torr in He where peripheral current conduction occurs.

A Study of Na 2 O-TiO 2 -SiO 2 Glasses by Infrared Spectroscopy

Abstract: The infrared absorption spectra of six Na2O-TiO2-SiO2 glasses in the frequency range of 1600 to 200 cm−1 are reported. These glasses, having a SiO2/Na2O molar ratio of 1.67 to 3.54, and containing 20 or 25 mole % TiO2, demonstrate two main absorptions at ~950 cm−1 and at ~450 cm−1. A weak absorption at ~790 cm−1 becomes progressively weaker in intensity, and a weak shoulder at 1050 cm−1 appears with increasing Na2O content. The frequency of the absorption band at ~950 cm−1 is found to decrease markedly and systematically with a decrease in the SiO2/Na2O molar ratio, whereas the frequency of the band at ~450 cm−1 shows a slight increase. The infrared results may be interpreted in terms of a lowering of symmetry occurring for the SiO4 units. The effect of TiO2 content on the relationship between vibrational frequency is discussed. The frequency composition curves for glasses containing 20 and 25 mole % of TiO2 intersect at SiO2/Na2O ratio ~2. A reversal in the frequency vs SiO2/Na2O ratio relation was also found at SiO2/Na2O ~2 for the sodium silicate glasses.

Resonance Raman Spectroscopy of Reaction Intermediates by a Rapid Mixing, Continuous Flow Technique

Abstract: Raman spectroscopy is potentially of great value in elucidating the structure of intermediates in chemical reactions. However, its utility in this regard has been limited because of the time required to scan a spectrum using a conventional spectrometer and static sample techniques. If one wishes to obtain a spectrum of an aliquot of a reaction mixture, while negligible concentration changes occur in the reactants, intermediates, and products, then clearly the half-life of the chemical reaction must be long compared to the spectral scan time. Since 10 min may be considered a typical time required to scan a 1000 cm−1 Raman spectrum, ordinary (static) sample handling techniques will yield satisfactory spectra of intermediates only for very slow reactions. Another disadvantage of static sample techniques, in Raman spectroscopy of reaction intermediates, occurs when one attempts to exploit the resonance Raman effect. In this situation, localized sample heating by the exciting radiation will generally cause a manifold increase in reaction rate and a concomitant decrease in the lifetimes of the intermediates. We now report a technique which allows one to obtain Raman spectra of reaction intermediates, with little determent due to reaction rate or sample heating.

A Programmed Cell Instrument for Digital Raman Difference Spectroscopy

Abstract: An instrument for digital Raman difference spectroscopy which uses a programmed sample carrier for automated alternate positioning of reference and sample cells in the laser beam is described. Conventional single photon counting equipment is employed with its attendant advantages over dc analog methods. Signal processing is done with a digital computer. There are relatively few limitations on the types of sample cells which may be used. Applications to studies of dilute aqueous solutions of biological molecules, particularly, are discussed.

A Circulating Sample Cell for Temperature Control in Resonance Raman Spectroscopy

Abstract: Localized sample heating by the exciting radiation is a constant problem in Raman spectroscopy of absorbing solutions. Static temperature control devices such as the Miller-Harney cell are ineffective when the sample has significant absorbance at the wavelength of excitation. Previous workers have circumvented this difficulty by employing either rotating or stirred sample cells. These methods allow the use of high exciting energy while maintaining sample temperature near ambient. However, these methods do not allow control of the sample temperature, without resorting to rather complicated accessories and scattering geometries. Furthermore, we find that the rotating cell technique sometimes leads to baseline instability in resonance Raman spectra of samples having appreciable background fluorescence.

A Tantalum Foil-Lined Graphite Tube for the Analysis of Arsenic and Selenium by Atomic Absorption Spectroscopy

Abstract: Methods for the carbon rod analysis of selenium and arsenic in wastewaters which employ commercially manufactured graphite atomizers have recently been described. The selenium studies were performed with the graphite minifurnace described by Matousek and Stevens (Varian Techtron model 61 CRA), while the arsenic studies employed a 9 mm × 3 mm i.d. graphite tube as the atomization chamber (Varian Techtron model 63). A major advantage in using the carbon tube was the ability to increase the optimal sample volume from 0.5 μl to 5.0 μl, thus improving relative detection limits. A serious drawback was an accompanying increase in nonspecific background absorption, which in this case was attributed to scattering effects from the sample matrix. In order to overcome the scattering problems, the samples were subjected to precipitation/ion exchange to lower the salt concentrations in order to facilitate the use of a hydrogen continuum lamp as a reliable means of background correction.

A Quantitative Method for Infrared Spectroscopy of Surface Species

Abstract: A quantitative method for studying surface species by infrared spectroscopy has been described. The solid particles are not subjected to high pressures or contacted with any extraneous substance during sample preparation. The method is quantified by using the solid substrate as an internal standard. Reproducibility measurements on surface concentration of trimethyl-chlorosilane adsorbed on silica gel and Aerosil gave 3.29 and 3.49% standard errors, respectively. Quantitative measurement of surface hydroxyl groups in open systems is also described.

Pressure-Temperature Relationships for Fe(II) Complexes of 1, 10-Phenanthroline and 2,2'-Bipyridine

Abstract: The complexes of the type Fe(phen)2X2 and Fe(bipy)2X2 (phen = 1, 10-phenanthroline, bipy = 2,2'-bipyridine) exist in high spin states (X = Cl−, Br−, N3−, NCO−, OAc−, HCOO−) or low spin states (X = CN−, CNO−, NO2−) or can exhibit the phenomenon of magnetic spin crossover. A recent study of the effect of pressure on the Mossbauer spectra for this type of complex indicates that high pressure is capable of partial conversion of the high spin state to the low spin state. However, there is still some disagreement concerning the interpretation of the Mossbauer data in systems which are in spin state equilibrium, as evidenced by some recent work on Fe(III) complexes with N, N-dialkyldithiocarbamates. High pressure studies have also been made on these Fe (III) dithio chelates. The results of these investigations on the solution electronic spectra indicate that the spin state is again pressure-sensitive.

A Simple Technique for Coating Carbon Atomic Absorption Atomizer Components with Pyrolytic Carbon

Abstract: Recent literature is replete with evidence that carbon nonflame atomizers used for atomic absorption or atomic fluorescence analysis are improved by the use of pyrolytically coated graphite or vitreous carbon in lieu of the more common (and cheaper) forms of carbon. The reasons lie in the permeability of the usual spectroscopic graphites to gases and solutions. This permeability allows actual loss of sample atoms through the walls of the atomization chamber and shortens the effective residence time of atoms within the optical path. Analyte material from solutions partially absorbed into the graphite substrate before drying enters the optical path more slowly upon application of the atomization current than will material on the surface. This causes a broadening and lowering of the peak absorption signal.

Studies of Gaseous Flame Combustion Products by Raman Spectroscopy

Abstract: Combustion products from various hydrocarbon-oxygen flames have been examined in the laboratory using the techniques of laser Raman spectroscopy and phase-sensitive detection. Instrumentation, techniques, and spectral results are described.

Electron Impact-induced Fragmentation of 4-Aminoazobenzene Dyes and Relationship with Photochemical Stability

Abstract: Relative abundance of daughter ions resulting from cleavage of 4-aminoazobenzene dyes across the C-Nα and C-Nβ bonds of the azo group can be related to the photochemical stability of these dyes on synthetic fibres.

Studies of Polymeric Bond Failure on Aluminum Surfaces by X-ray Photoelectron Spectroscopy (ESCA)

Abstract: X-ray photoelectron spectroscopy (ESCA) has been used to identify very thin layers of polymeric species remaining on aluminum plates after the polymer was cured and stripped from the aluminum. Two polymers were studied. In one, the residual polymeric carbon was used as the tracing signal; in the other, the polymeric silicon was used. In both cases, the polymeric species was partially sputtered from the aluminum surface by an argon ion gun. A reduction in the polymeric signal relative to a standard signal was noted. The results of this study show that, when the polymers studied were mechanically pulled from the aluminum substrate, the failure was a cohesive separation within the polymer, rather than failure at the polymer-aluminum interface. Scanning electron microscopy was used to show that the residual polymer does not remain on the surface as "clumps" or "islands," but rather as a smooth surface a few atomic layers thick.