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RECEIVED for review March 2, 1987. Accepted June 2, 1987.
Analysis of Geological Samples by Hollow Cathode Plume Atomic Emission Spectrometry R. K e n n e t h Marcus' a n d W. W. Harrison*
Department of Chemistry, university of Virginia, Charlottesville, Virginia 22901
The hollow cathode plume (HCP) was applied to the elemental analysis of geological materlais by atomlc emlssion. Graphlte, sllver, and copper were studled as matrix materials to produce conducting electrodes from geologlcal/matrlx mixtures. Data taken from a range of sample-to-matrix ratlos showed that a 10% sample composition was optlmum. Reproduclbllhy of HCP data was approximately 5 % . Slmulated analyses of NBS geologlcai samples were undertaken by the developed procedures.
The applicability of the hollow cathode plume (HCP) atomic emission technique to direct solids analysis of metal alloys has been illustrated previously (1, 2). The source is characterized by its ability to sputter large atomic populations of the cathode sample material into a stable, controlled, inert atmosphere plasma. Resultant emission spectra are atomic in nature with very low amounts of molecular band structure or background continua. A promising application of the technique is in the analysis of nonconducting materials such as soils, ores, catalysts, and the like. These materials often pose problems for solution analysis techniques because of time-consuming and possibly specialized fusion dissolutions. A considerable advantage would result by analysis directly in the solid state. In order to analyze these materials by HCP atomic emission, they must be modified such that they can act as the cathode, Le., the material must be made to conduct current by mixing with a conducting host matrix material. This type of matrix conversion was developed for arc discharge sources (3)in an attempt to obtain more uniform transport into the excitation region. Before this time, powders were routinely analyzed by placement into a hollowed graphite cup electrode and vaporization by the high-temperature arc ( 4 ) . Papp (5)extended this approach to analyzing nonconducting powders by binding the sample in a graphite matrix using phenol-formaldehyde resin. A method for compacting nonconducting samples for glow discharge analysis was first described by Dogan, Laqua, and Massman (6) using copper and graphite as host matrices. A range of sample-to-host ratios was studied. A subsequent report from the same laboratory (7) described sample preparation and plasma parameters affecting the use of compacted samples for glow discharge atomic emission analysis. Caroli and co-workers (8),in another glow discharge study, pressed powder mixtures to form a hollow cathode configuration. They used a complex matrix, designed to simulate a mineral residue. Present address: Department of Chemistry, Clemson University, Clemson, SC 29634.
Calibration curves were generated for a number of elements in order to perform quantitative analyses. Recently, Zimmer and co-workers (9) compared the analytical capabilities of ICP and glow discharge atomic emission for the analysis of medieval glasses. Glow discharge samples were prepared by mixing the pulverized sample (
