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Si and presumably representing surface contaminants left from the initial alumina polishing process. At this point, a definitive identification of the Cu/C1 surface microstructure has not been possible. X-ray diffraction spectra obtained for the crystals either intact on the glassy carbon surface or scraped off and collected for separate analysis have not yet been able to be matched with diffraction patterns of known Cu- and C1-containing crystalline species. At present, more extensive characterization of the modification mechanism and specific surface structure of the Cu CME is continuing, and it is hoped that these investigations may lead to an improved understanding of the chemistry involved in its formation and operation. In the meanwhile, it is apparent that the CME offers impressive capabilities for the constant-potential flow detection of a wide variety of polyhydroxy compounds and an improved compatibility with a useful range of anion-exchange chromatography mobile phases.
ACKNOWLEDGMENT We thank P. Luo for providing useful insights regarding the electrode modification procedure and J. R. Richardson and G. A. Lager for advice and assistance in carrying out X-ray diffraction characterization of the Cu CME surface.
LITERATURE CITED (1) Hughes, S.; Johnson, D. C. Anal. Chim. Acta 1981, 132, 11-22. (2) Hughes, S.; Johnson, D. C. J. Agric. Food Chem. 1982, 3 0 , 7 12-714.
(3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)
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RECEIVED for review May 19, 1989. Accepted July 21, 1989. This work, which was presented in part at the 197th National Meeting of the American Chemical Society in Dallas,TX, was supported by the National Science Foundation through EPSCoR Grant 86-10671-01 and by Burdick & Jackson Research Grant BJ8807.
Determination of Osmium and Osmium Isotope Ratios by Microelectrothermal Vaporization Inductively Coupled Plasma Mass Spectrometry Takafumi Hirata, Tasuku Akagi, Hiroshi Shimizu, and Akimasa Masuda*
Department of Chemistry, Faculty of Science, The University of Tokyo, Hongo 113, Tokyo, Japan
A new merging lntroductlon technlque has been developed for Os analysk wtth lnductlvely coupled plasma mass spectrowetry (ICP-MS). The sample was placed In a mkroheater cell In a merglng chamber and vaporized OsO, was carried to the ICP wlth a blank matrlx mlst flow sprayed from a nebulizer. I n the merglng lntroductlon, the best operatlonal parameters could be obtalned by the usual optlmlzation using a standard solution. The 1870s/18eOsratio and the Os abundance were measured slmuttaneausly by spiklng 1020s. The preclslons of the ratlo and abundance measurements using 0.8 ng of Os were 5 and 4 % , respectlvely. The detection llmlt of Os by this method was lower than 100 fg, which Is almost onetwelfth of that obtalned by conventlonal nebulization lntroductlon.
Mass spectrometry using inductively coupled plasma as an ion source (ICP-MS) is a new technique for elemental and isotopic analysis. However, nebulizers commonly used in ICP-MS transport only 2-370 of a sample solution into the ICP. Several techniques have been developed to enhance the efficiency of sample introduction to the ICP torch; e.g., the use of a recirculating nebulizer, a microconcentric nebulizer 0003-2700/89/036 1-2263$01.50/0
(I), direct insertion (Z),electrothermal vaporization (ETV) techniques (3,4),and vapor generation introduction (5-8). The 1s7Re-1s70sisobaric pair is a promising isotopic system in the fields of geo- and cosmochemistry. However, the difficulty in Os isotopic analysis, due mainly to the high ionization potential of Os and the low abundance in common silicate rocks, has limited the use of this system. Methods with high performance in obtaining detection limits, including secondary ion mass spectrometry (9-1I), accelerator mass spectrometry (IZ),and resonance ionization mass spectrometry (13),have been applied to Os isotopic analysis. With ICP-MS, we have succeeded in measuring the Os isotope ratios for natural metallic samples containing Os at parts per million (ppm) levels (14).A further enhancement of sensitivity is, however, required in order to measure the isotope ratio of Os for silicate rocks. In this study, we put forward a new introduction technique using a miniature heater placed in a merging chamber (abbreviated to “microheater/merging introduction”). This method assures the effective introduction of Os to the ICP torch. EXPERIMENTAL SECTION The ICP-MS used in this study is a VG PlasmaQuad type I. The operational conditions are listed in Table I. Ion optical 0 1989 American Chemical Society
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Table I. Instrumental Operation Conditions 1. ICP Settings
incident power 1.35 kW reflected power
