Royce K. Winge

Inductively Coupled Plasma-Atomic Emission Spectroscopy: Prominent Lines

The prominent lines of 70 elements as emitted in an inductively coupled plasma excitation source have been identified. The lines are listed alphabetically by element and numerically by wavelength. Detection limit capabilities are estimated for each spectral line.

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.

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.

High speed photographic study of wet droplets and solid particles in the inductively coupled plasma

Motion pictures of the ICP were taken at 4000 frames s–1 . An intact wet droplet containing yttrium causes the formation of a pale red cloud juxtaposed on the usual ambient emission structure of the plasma. Most of these droplet clouds are shaped like an oval or a comet. A few droplets produce small, bright spheres followed by faint, wispy streaks that point downstream. Such a spherical cloud is caused by some rapid event such as explosion of a droplet in the final stages of solvent evaporation. The faint streaks are some residue, perhaps small solid particles. In a particular frame, a number of these faint streaks protrude from the tip of the initial radiation zone (IRZ) into the normal analytical zone (NAZ). When wet droplets are introduced, that portion of the analyte that travels through the center of the plasma passes through three distinct regions (i.e., the IRZ, the streaks, then the NAZ), rather than directly from the IRZ to the NAZ. Groups of two or three droplets tend to appear together in the same time interval (≈0.12 ms) in the plasma. These droplet clouds are not seen, and the particle streaks are much less evident, when the solvent is removed before the aerosol is injected into the plasma. Aqueous slurries of Y2O3 in various particle sizes (0.1 or 3 µm mean diameter) produce white streaks along the center line of the plasma, which are attributed to individual solid particles. These observations also support the general precept that calibration of the response for slurries using aqueous solution standards is best accomplished by keeping the particle loading such that each wet droplet contains no more than one solid slurry particle.

Spatiotemporal characteristics of the inductively coupled plasma

A previously unrecognised source of noise in inductively coupled plasma (ICP) atomic emission spectrometry was identified with a combination of high-speed motion picture photography and noise spectrum analysis. The noise mechanism is a fluid mechanics phenomenon and involves axisymmetric oscillations of the plasma as the plasma gases flow from the torch into the surrounding static atmosphere. The oscillations develop into vortex rings with increasing height above the torch. As these plasma oscillations pass through the optical axis of the measurement system they produce periodic variations in the analytical signal, typically in the 100–600 Hz range. The frequencies of the oscillations observed in the films agreed with the frequencies of the major noise peaks in the noise power spectra. Knowledge of this noise phenomenon is relevant to studies of the fundamental properties of the ICP and its applications.

High speed photographic study of plasma fluctuations and intact aerosol particles or droplets in inductively coupled plasma mass spectrometry

Cine-films of the inductively coupled plasma were taken at 3000 frames s–1 while the plasma was sampled for mass spectrometry. The axial channel expanded and contracted periodically at frequencies of 260–300 Hz, depending on the operating conditions. The frequency of the observed fluctuations decreased as the separation between the torch and sampling cone increased. With a concentric nebulizer, emission from vapour clouds surrounding the aerosol droplets or particles was observed flowing along the axial channel and into the sampling orifice.

Direct Nebulization of Metal Samples for Flame Atomic-Emission and Absorption Spectroscopy

A device for transforming solid-metal samples into an aerosol of fine metal particles has been combined with a flame spectroscopic method for the determination of trace impurities and alloying elements in steels. The aerosol generator is a simple apparatus in which the sample serves as the cathode of a low-current dc-arc discharge. Constant movement of the cathode spot results in uniform sampling of a relatively large area. A flowing gas stream transports the aerosol particles from the arc discharge to the nitrous oxide–acetylene flame. Analytical curves for the determination of chromium, manganese, and nickel in steel are shown. The method provides a very rapid means of determining trace elements and alloy constituents in metals without the complications attendant to dissolution procedures.

Spectral line-diode registry effects with photodiode array detectors

A limitation of photodiode array detectors for spectroscopic intensity measurements relates to the spacing of the diodes and the errors generated when a spectral line is not in exact registry with the diode or diodes from which its intensity is being measured. These misregistry intensity errors, which may be as high as 25 to 30%, are documented for a range of spectral bandwidths and for single diode (pixel) intensities and multiple diode summations of intensities.

Comparative Complexity of Emission Spectra from ICP, dc Arc, and Spark Excitation Sources

A comparison of atomic emission spectra excited in high voltage spark and dc arc discharges and in an inductively coupled plasma revealed that the most complex spectra were emitted by the high voltage spark. The dc arc and the inductively coupled plasma yielded spectra of approximately equivalent complexity. These observations are not in accord with the impressions conveyed in the literature.