Edward L. DeKalb

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.

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.

OPTICAL EMISSION SPECTROSCOPY AS AN ANALYTICAL TOOL

For many years the characteristic line spectra emitted by the elements in flames and arc, spark, or gaseous discharges have provided a relatively simple, convenient, and objective means for the detection and determination of trace impurities. Since no other analytical technique provides so much information with so little effort, these spectra are destined to find increasing application in trace or micro analyses. t The principles and practices of optical emission spectroscopy and its analytical applications have been adequately discussed in several books’ ’” and chapters in treatise~,’~.’’ and reviewslR 2 2 on recent developments have appeared a t regular intervals. We will, therefore, not concern ourselves with details of various standard operating procedures, techniques, and experimental facilities. Rather, we will focus our attention on special problems encountered in expanding the scope of application of these spectra to the quantitative determination of trace impurities a t ever decreasing concentration levels. Before considering these special problems, it is appropriate to note a few general characteristics of optical emission spectroscopic methods which directly affect their present and potential scope of application. These spectra are capable, under optimal excitation conditions, of detecting trace amounts of all the elements in solids, liquids, or gaseous samples. In most instances, these detection limits are as low as a few parts per million, and, under ideal conditions, the limits may be as low as a few parts per billion. These detection limits can normally be obtained on samples weighing only a few milligrams with little or no prior chemical treatment. The advantages inherent in the latter are often not readily apparent, but it must be remembered that impurities in chemical reagents may contaminate the original sample to such an extent that the trace impurity content is completely masked. Also, the possibility that trace impurities may be lost during chemical processing is ever present.

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.

The ames laboratory facility for the emission spectroscopic study of alpha-emitting radionuclei: The design and operating history

A commercially available inductively coupled plasma (ICP) radio-frequency power generator was adapted to operate within a stainless steel glove box and was used for optical emission spectroscopic studies of hazardous alpha-emitting materials. This ICP apparatus has been successfully used to determine plutonium in complex chemical mixtures and to analyze plutonium isotopically in solution. The finely divided particulates generated by the ICP emission source were removed by filtration of the exhausted gas stream via a train of three high-efficiency particulate air (HEPA) filters. The light from the glove-box-enclosed ICP was passed through a window set into a common wall to a separately ventilated spectrometer laboratory. Testing of the apparatus with nonhazardous materials revealed design flaws that were easily corrected prior to studying the emission spectroscopy of plutonium. An unnoticed error in construction that caused a serious problem after the glove box had become contaminated was less easily remedied.