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dehydroxylation takes place at the same time (16-19).
ACKNOWLEDGMENT Thanks are due t o H. Beyer for supplying the chabazite standard and the results of chemical analysis. We thank G. Schay for t h e thorough reading of the manuscript and for helpful discussion.
(7) (8) (9) (10) (1 1) (12) . . (13) (Id)
LITERATURE CITED D. R. Beaman, and J. A. Isasi, "Electron Beam Microanalysis". ASTM STP 506, American Society for Testing and Materials, Philadelphia, Pa. 1972. C. E. Hall, "Introduction to Electron Microscopy", McGraw-Hill Book Co., New York, N.Y., 1953. J. C. Russ, %-Ray Spectrom., 6, 37-55 (1977). E. P. Bertin, "Theory and Practice of X-Ray Spectroscopy". Academic Press, New York/London, 1975, p 980. C. J. Powell, Rev. Mod Phys., 48, 33-48 (1976). G. G. Johnson, Jr., and E. W. White, "X-Ray Emission Wavelengths and keV Tables for Nondiffractive Analysis", ASTM Data Series DS 46, American Society for Testing and Materials, Philadelphia, Pa., 1960.
(15) (16) (17) (18) (19)
J. C. Russ, EDAX Editor, 5 (3), 3 - 6 (1975). A. Jdnossy, E. CzBrdn, and J. Papp, Magy. K6m. Foly., 83, 289 (1977). H. A . Kramers, Phil. Mag., 46, 836 (1923). D. G. W. Smith, C. M. Gold, and D. A. Tomkinson, X-Ray Spectrom., 4, 149 (1975). A . JBnossy. Unpublished work. J C. Russ, "Thin Section Microanalysis", J. C. Russ and El. J. Panessa. Ed., Proc Symp St. Louis, 1973. (a) A Hendricks, EDAXEditor, 5 (3). 7 (1975); (b) ibid.. p. 13. T A. Hail, "The Microprobe Assay of Chemical Elements", in "Physical Techniques in Biological Research", G. Oster, Ed., Academic Press, New York. N.Y.. Vol. I / A . 1971. DD 157-275. A. Jdnossy, Unpublished work. H. Beyer, J. Papp, and D. Kallb. Acta Chim Acad Sci. Hung.. 84, 7 (1975). A. P. Bolton, Exp. Methods Catai. Res., 1976, Vol. 2. D. W. Breck. "Zeolite Molecular Sieves", John Wiiey, New York, N.Y., 1974. J. A . Rabb, Ed., "Zeolite Chemistry and Catalysis", ACS Monogr.. 171, (1976).
RECEIVEEfor review December 12, 1977. Accepted May 3, 1978.
Energy-Dispersive X-ray Spectrometric Analysis of Environmental Samples after Borate Fusion P. A. Pella,' K. E. Lorber,' and K. F. J. Heinrich Institute for Materials Research, Analytical Chemistry Division, National Bureau of Standards, Washington, D.C. 20234
I n order to overcome particle-size and sample inhomogeneity effects in the analysis of environmental samples by energydispersive x-ray spectrometry, an automated borate fusion procedure was investigated and applied to the analysis of NBSSRM 1633 Fly Ash and NBSSRM 1648 Particulate Matter. Twelve elements in each sample were determined and the rewtts are in agreement with NBS certified values and/or those of other workers, usually within & 5 to 10% for most elements over the concentration range from 70 ppm to 15 %. Fly Ash samples were fused with the heavy absorbers La2O, or WO, and analyzed using a linear calibration curve, assuming no matrix effects. The particulate samples, however, were fused with lithium tetraborate only and the data were corrected for x-ray absorption and K x-ray line interferences by a NBS mathematical procedure. The limits of detection of this procedure for most of the elements analyzed in the sample were between 10 to 100 ppm.
T h e elemental composition of environmental samples such as particulates collected from urban aerosols can be quantitatively determined by energy-dispersive x-ray fluorescence spectrometry (EDXRF). Such samples have been analyzed by other workers ( I , 2). Ambient air aerosols can be collected on thin filter substrata and then measured directly by E D X R F , using thin specimens of known elemental composition for calibration. Since particulate matter collected from aerosols can penetrate t h e filter medium, significant attenuation of both incident and fluorescent x-rays by t h e filter can take place, especially for light elements. Absorption effects within the larger collected particles may also be significant, resulting in systematic error ( 3 ) . When particle size effects are appreciable, fusion methods of sample preparation with Present address, Technical llniversity of Graz, Gra7, Aiistrin
lithium tetraborate become an attractive alternative. Fusion methods have been applied to the analysis of geological materials ( 4 -8). These can be classified as (a) fusion of the sample followed by a separate casting operation t o produce a glass disk for direct x-ray analysis, (b) fusion and grinding where the samples are fused, ground, and pelleted, and (c) fusion and direct solidification where the fused sample solidifies directly in the crucible from which the solid glass disk separates. With the availability of the 95% Pt-5% Au alloy crucible, commercial automated fusion devices have recently been developed, and disks can be prepared by method ( : (9). T h e present work was performed to determine whether environmental samples could be analyzed with good accuracy with automated fusion as a n alternative to nondestructive sample p r e p a r a h n methods. Two samples consisting of NBS-SRM 1633 Fly Ash and NBS-SRM 1648 Particulate Matter were each analyzed for 12 elements. Monochromatic excitation of the sample was provided by three secondary target x-ray emitters. Several workers (7, 10) have reported on the use of heavy absorbers such as lanthanum oxide to minimize x-ray absorption effects in thick samples. This technique has been applied mainly to the determination of light elements below atomic number 26 in mineral specimens. Its principal advantage is t h a t the x-ray intensity from t h e analyte element approaches a linear function of its concentration in the glass disk, and corrections of x-ray absorption effects b.y digital computations are, in principle, not required. T h e heavy absorber method was used in this work in the analysis of the NBS-SRM 1633 Fly Ash to determine if acceptable results could be obtained for elements whose x-ray fluorescence lines cover a broad range of energies from 2.0 to 14.0 keV. In order to avoid severe x-ray line interferences h e h e e n the analyte x-ray lines and lines of the absorber, lanthanum oxide was used in the analysis of zinc, lead, and strontium, and tungsten oxide for all other elements. Interferences by x-ray lines of the analyte were corrected in an
This article not subject to U.S. Copyright. Published 1978 by the American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 9, AUGUST 1978
empirical manner with standards containing noninterfering elements and the heavy absorber. T h e NBS-SRM 1648 particulate sample was analyzed wit,h a digital computation procedure developed a t NBS (11) t o correct for x-ray absorption and K x-ray line interferences. T h e analytical results reported herein are compared t o NBS certificate values a n d / o r those obtained by other workers where certified values were not available. T h e theoretical limits of detection were calculated in order to characterize the sensitivity of this method.
EXPERIMENTAL Reagents. All materials used to prepare standards were Analytical Reagent quality and dried at 100 "C for 2 h before use, except calcium carboriat,e which was dried at 260 O C . The compounds used to prepare the standards were finely ground powders of A1203,Sios,KN03, CaCOS,Cr203,Mn02,Fe203,NiO, CuO, ZnO, and Pb(NO&. All grinding was performed in a noncontaminating boron carbide mortar. Lithium tetraborate (Spex Industries, Lot 176) was dried at 500 "C for 2 h. The purity of the Li2B40iblank was determined by EDXRF, and detectable amounts of iron, copper, zinc, and lead were found. However, the concentration of these elements in the blank was low (e.g.,
