Coweeta is one of the oldest continuously operating laboratories of its type in the world. For the first time, a complete review and summary of more than 50 years study of the hydrological and ecological responses of baseline and managed Southern Appalachian hardwood forests at Coweeta is now supplied by this volume. The long-term research approach represents a continuum of theory, experimentation and application using watersheds as landscape units of investigation. Thus, the information encompasses a wide range of interpretations and interests. In addition to in-depth analyses of terrestrial and stream processes, the breadth of coverage includes historical perspectives and relevance of ecosystem science to management needs. In a broader sense, the Coweeta research effort is considered from a perspective of national and international forest hydrology and ecology programs.

Forest hydrology and ecology at Coweeta.

An inductively coupled plasma sustained in flowing argon and a permanently aligned all-glass coaxial pneumatic nebulizer are employed in the atomic emission mode with a direct-reading polychromator for simultaneous multielement determinations. The inductively coupled plasma is shown to be remarkably free from matrix and interelement effects by application for the determination of major (Na, K, P, Ca, and Mg) and trace (Fe, Cu, Zn, Mn, Pb, Cd, Co, Cr, Ni, V, Ti, Al, Sr, and Ba) elements in reference biologic materials and soil extracts. Wet-digestion and several dryashing sample preparation procedures are evaluated. Accuracy, precision, and sensitivity compare favorably with other multielement instrumental techniques (neutron activation analysis) energy dispersive x-ray fluorescence, solution-rotating disk atomic emission spectrometry) and with flame atomic absorption spectrometry. The directness of the method reported here is illustrated by use of one set of system operating conditions with one set of synthetic reference solutions used to establish a single calibration curve for each element.

Inductively Coupled Plasma-Atomic Emission Spectrometry: Analysis of Biological Materials and Soils for Major, Trace, and Ultra-trace Elements

Observed spectra normally contain spurious features along with those of interest and it is common practice to employ one of several available algorithms to remove the unwanted components. Low frequency spurious components are often referred to as 'baseline', 'background', and/or 'background noise'. Here we examine a cross-section of non-instrumental methods designed to remove background features from spectra; the particular methods considered here represent approaches with different theoretical underpinnings. We compare and evaluate their relative performance based on synthetic data sets designed to exemplify vibrational spectroscopic signals in realistic contexts and thereby assess their suitability for computer automation. Each method is presented in a modular format with a concise review of the underlying theory, along with a comparison and discussion of their strengths, weaknesses, and amenability to automation, in order to facilitate the selection of methods best suited to particular applications.

Investigation of selected baseline removal techniques as candidates for automated implementation.

Argon-supported inductively coupled plasmas operated at atmospheric pressures are excellent vaporization-atomization-excitation-ionization sources for analytical atomic emission spectroscopy. When a polychromator is used for observing the emitted spectra, the metals and metalloids can be determined simultaneously at the ultratrace, trace, minor, and major concentration levels under one set of experimental parameters. Alternatively, programmable scanning spectrometers may be utilized for sequential determinations. The atomization-excitation process is remarkably free of interelement interactions, the powers of detection are in the part per billion range for most elements, and sample manipulation requirements prior to analyses are often minimal. The technique meets the requirements of an analytical system for the simultaneous or sequential determination of the elements at all concentration levels to an unusual high degree.

https://science.sciencemag.org/content/sci/202/4364/183.full.pdf

Quantitative Elemental Analyses by Plasma Emission Spectroscopy

Plant Tissue Analysis in Micronutrients

The suppression of atomic excitation in a microwave-induced plasma due to the presence of sodium has been studied for three different nebulization systems. Evaluation of the factors affecting this effect has shown that its occurrence depends on the nature of the analytical aerosol introduced and the aerodynamic features of the sample nebulization system. The results indicate that the sodium suppression effects observed can be largely accounted for by reductions in the analyte transport efficiency due to changes in the aerodynamic characteristics of the aerosol resulting from variations in the salt content of the nebulized solutions. It is further shown that these effects may be generally predicted on the basis of fluid mechanical principles and that these may be used to design systems to eliminate the interferences. The study under-scores the essentiality of considering aerodynamic factors in formulating mechanistic explanations for interference effects in flames and plasmas.

Aerosols, Aerodynamics, and Atomic Analysis

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.

Characterization of a dc Plasma as an Excitation Source for Multielement Analysis

The analytical capabilities of a dc plasma used in combination with an echelle spectrometer have been evaluated. Measurements of the spectrometer resolution capabilities have demonstrated that they closely approximate the high values theoretically predicted but are ultimately limited by Doppler broadening effects occurring in the plasma. Investigations of possible ionization interference effects have shown that enhancements due to the addition of easily ionized elements are generally observed for elements having ionization potentials below approximately 8.5 eV; these may be compensated for by the addition of an excess of an easily ionized element. Evaluation of solute vaporization interference effects indicates that they also occur but can be negated by proper choice of operational conditions and/or the addition of releasing agents. Comparison of the detection capabilities of the system with those reported for other techniques shows that they are equivalent or superior to those characteristic of flame atomic absorption and often competitive with those obtained with the inductively coupled plasma, atomic emission system.

Evaluation of the Analytical Capabilities of a dc Plasma-Echelle Spectrometer System:

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.

A Dynamic Background Correction System for Direct Reading Spectrometry

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.

R. K. Skogerboe

Papers

Aerosols, Aerodynamics, and Atomic Analysis

Characterization of a dc Plasma as an Excitation Source for Multielement Analysis

Evaluation of the Analytical Capabilities of a dc Plasma-Echelle Spectrometer System:

A Dynamic Background Correction System for Direct Reading Spectrometry

Evaluation of the microwave-induced plasma for multielement emission spectrometric analyses