The eight new USGS standard rocks have been analyzed for barium by the stable isotope dilution technique. Duplicate portions from three bottles of the rocks were analyzed in random order. No departures from homogeneity for these randomly selected bottles of samples were observed. The average barium contents are, in parts per million: STM-1, 584; RGM-1, 822; QL0-1, 1,401; SDC-1, 641; MAG-1, 476; SCo-1, 570; SGR-1, 286; and BHV0-1, 132.5. The analytical error is. generally less than 1 percent whereas the absolute accuracy of the technique for barium is approximately 2 percent. INTRODUCTION As part of a program to standardize a new series of rocks, the elemental abundance of barium in STM1, RGM-1, QL0-1, SDC-1, MAG-1, SCo-1, SGR-1, and BHV0-1 was determined by the stable isotope dilution technique using solid-source mass spectrometry. Three bottles, randomly selected from the stock of each rock, were analyzed in duplicate to provide a one-way experimental design with the three bottles as the variable of classification. The determination of barium in silicate samples is often imprecise and sometimes of doubtful accuracy by emission spectroscopy and other analytical techniques. Fleischer ( 1969) has summarized new data on the standard rocks G-1 and W-1 but is still unable to recommend a value for the barium content of these rocks with any confidence. Flanagan (1969) has provided a compilation of analytical data on the major, minor, and trace constituents of the new series of samples recently prepared by the U.S. Geological Survey. The barium determinations cover a wide range of abundances for each of the six rocks, and under the circumstances, the average values listed for barium are of questionable significance. The stable isotope dilution technique is for some elements potentially more accurate and precise than many other analytical methods and has been adopted in this project in an attempt to provide accurate barium data for this new series of USGS standard rocks. EXPERIMENTAL METHODS The elemental abundance of barium in each rock sample was determined by using a barium nitrate tracer enriched to approximately 94 percent in the isotope of mass 135. The isotopic composition of this tracer as obtained from Oak Ridge National Laboratory ( ORNL) is listed in table 49, together with the isotopic ratios as measured by the mass spectrometer used throughout the project. The isotopic composition of natural barium as measured in the Western Australian Institute of Technology (WAIT) laboratory is also listed. The measured ratios are uncorrected for mass spectrometer fractionation. We have taken the atomic weight of natural barium to be 137.327 as calculated by Eugster, Tera, and Wasserburg (1969). The atomic weight of the Ba tracer has been calculated from the measured isotopic composition to be 135.04, using isotopic weights according to the C :! = 12 scale (Mattauch and others, 1965). An accurately weighed sample of the Ban" (NO:!):! tracer was used to prepare a gravimetric solution in 6 M HCI. The concentration of this solution was determined using the isotope dilution technique itself to calibrate the tracer against an accurate gravimetric standard made up from a spectroscopically pure sample of BaCO:l (obtained from Johnson, Matthey & Co.) . The measured concentration of the tracer solution agreed with the gravimetric value within experimental error. The adopted concentration was the average of a number of calibrations t Dep:1rtment of Phy8ics, Western Australian Institute of Technology, South Bentley, Western Australia.

Descriptions and analyses of eight new USGS rock standards

Time shifts and double peaks for lead caused by chemisorbed oxygen in electrothermally heated graphite atomizers

The determination of germanium by atomic absorption spectrometry with a graphite tube atomizer

Atomic absorption and fluorescence spectroscopy with a carbon filament atom reservoir: Part VI. a study of some matrix effects

Atomic absorption and fluorescence spectroscopy with a carbon filament atom reservoir: The determination of gold by atomic fluorescence and atomic absorption spectroscopy with an unenclosed atom reservoir

L.A. Wolfe

Papers

An x-ray fluorescence spectroscopic method for the determination of total manganese in rocks and marine sediments