Richard N. Kniseley

Excitation temperatures and electron number densities experienced by analyte species in inductively coupled plasmas with and without the presence of an easily ionized element

Spatially resolved radial excitation temperatures and radial electron density distributions experienced by analyte species in the observation zone of 15 to 25 mm above the load coil of a toroidally shaped, inductively coupled argon plasma are presented and related to the analytical performance of these plasmas. A comparison of radial temperatures measured with support gas (Ar I) lines and with a typical analyte thermometric species (Pe I) at 15 mm above the load coil is given. Radial (Fe I) excitation temperatures obtained at three observation heights are compared for aerosol carrier flows of 1.0 and 1.3 liters/min. The addition of a large amount of an easily ionized element (6900 µg of Na per ml) did not significantly change Fe I excitation temperature distributions at the respective aerosol carrier flows and observation heights. A comparison of radial electron density distributions measured with Saha-Eggert ionization and with Stark broadening methods is given for an observation height of 15 mm above the load coil. The differences between electron density values obtained by these methods is discussed. The effect of addition of 6900 µg of Na per ml on Saha-Eggert electron density distributions at three observation heights is also discussed.

Ultratrace Analyses by Optical Emission Spectroscopy: The Stray Light Problem

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.

Inductively coupled plasma-optical emission spectroscopy: Excitation temperatures experienced by analyte species

Abstract Spatially resolved, radical excitation temperature distributions experienced by analyte species injected into the axial channel of a toroidally shaped, inductively coupled argon plasma are presented. Typical axial temperatures experienced by the thermometric species (FeI) ranged from 6500 K to 5500 K in the analytical zone of 15–25 mm above the load coil. A comparison of temperatures calculated with different sets of transition probabilities is also given.

Evaluation of spectral continua as primary sources in atomic absorption spectroscopy

Abstract The results of a critical and systematic evaluation of the feasibility of employing spectral continua as primary sources in atomic absorption spectroscopy are presented. Useful sensitivities were observed for most of the metallic elements in the periodic system. For 32 elements, the sensitivities observed for a spectral continuum primary source were either comparable to or exceeded those presently obtained with sharp-line primary sources. Recordings of typical spectra are presented as well as several analytical curves illustrating the quantitative analytical applications.

Photoacoustic spectroscopy with condensed samples

A discussion of the photoacoustic spectroscopy of condensed matter is presented with emphasis on the role of the sample and the sample cell in the photoacoustic signal waveform. The spectrometer and sample cell are described, and an experimental evaluation of the system performance is given. Data on various samples are reported, and sample geometry, signal saturation, and scattered light effects are analyzed. The relationship between photoacoustic spectra and absorption and reflection spectra is developed.

Theoretical principles of internal standardization in analytical emission spectroscopy

Abstract The principles which affect the choice of analysis and internal standard lines in analytical atomic spectroscopy are explored theoretically using a computer-based model. The spectral source chosen for the model was the induction-coupled argon plasma fed with a water solution of metallic salts. The effect of excitation energy, ionization energy, partition functions and electron density on the analytical line pair intensity ratio is explored. Examples are presented which illustrate the contribution of each variable to the intensity ratio over the 3000–15000°K temperature range, allowing the reader to assess the importance of each based on a knowledge of the properties of his own source. Finally, some of the problems encountered in the course of this study are discussed.

Determination of trace elements in soft, hard, and saline waters by the inductively coupled plasma, multi-element atomic emission spectroscopic (ICP-MAES) technique

Abstract Analytical methods capable of determining natural and aberrant concentrations of the chemical elements in our nations water resources are essential for maintenance of the water qualities required for public water supplies, for habitat of aquatic biota, and for industrial and agricultural use. Simultaneous determinations of 20 or more elements at trace concentration levels may be required in real time to provide adequate protection of water supplies and to detect discharge of noxious materials into various water systems. The ICP-MAES technique allows quantitative determinations, without preconcentration, of most elements at concentrations below EPA recommended criteria levels for public water supplies and for continuous use irrigation water. Stray light problems arising in the analyses of hard waters are discussed and the effect of stray light on the various analyte lines are quantitated.

Signal saturation effects in photoacoustic spectroscopy with applicability to solid and liquid samples

A simple model of the interaction between the optical and thermal properties of the sample is shown to predict signal saturation in photoacoustic spectroscopy in excellent agreement with measurements on a methylene blue dye solution. The measured onset of signal saturation as a function of the absorption is accurately predicted by the model from the sample’s thermal properties. The effect of light reflection by the sample on the photoacoustic signal is discussed.

Spectroscopic flame temperature measurements and their physical significance—I. Theoretical concepts—A critical review

Abstract In this review the basic theoretical principles of temperature measurements of completely uniform flames (with no temperature or concentration gradients of the thermometric species) by the line reversal, emission-absorption, slope, and two-line Spectroscopic techniques are first presented. Since there have been no unifying accounts on the extension of the basic theoretical concepts to more realistic non-isothermal, non-homogeneous flames, a major portion of this review is devoted to a systematic examination of the validity of temperature data obtained by Spectroscopic techniques for these flames. This examination reaffirms several well known, as well as several less familiar, limitations of the temperature values obtained for real flames. Thus, the values obtained depend on: (a) the measurement method employed; (b) the energy of the quantum states involved in the line producing transition (s); (c) the particular temperature gradient in the flame; and (d) the concentration distribution of the thermometric species. Moreover, the values observed do not represent either the average or a weighted average flame temperature, but correspond to an apparent temperature that yields the ratio of the total number of particles in the relevant quantum states found within the viewing field of the spectrometer, i.e., where T app is the apparent temperature, q and p refer to the two quantum states, g is the degeneracy, n x is the particle density and E is the energy of the quantum level. This result is quite different from the Boltzmann equation which defines the temperature T x at the point x in the flame.

Flame spectra of the rare-earth elements

Abstract The rare-earth elements, including scandium and yttrium, emit intense line spectra when absolute ethanol solutions of rare-earth halide or perchlorate salts are aspirated into fuel-rich, oxy-acetylene flames. Recordings of the spectra are given, along with the exact wavelengths of about 1200 of the strongest lines. A discussion of the analytical utility of the stronger lines and excitation processes which may account for the appearance of these spectra is included.