1780
Anal. Chem. 1082, 5 4 , 1786-1792 I
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spectrum stripping prior to the direct spectral analysis and data reduction.
1
SAMPLE RADIOACTIVE STEEL NO 4 EXCITATION A8 SECONDARY SOURCE LIVETIME 8 3 m m
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ACKNOWLEDGMENT The authors express their appreciation to E. A. Lepel and D. J. Hayes for their assistance and a special thanks to Ned A. Wogman for his helpful review. LITERATURE CITED
Mn X - R A Y S I FROM qa COMPTON CONTINUUM FROM HIGH ENERGY GAMMA RAYS
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SPECTRUU FROM RADIOACTIYiTY ONLI IX-RAY TUBE OFF>
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Flgure 4. Illustration of the observed EDXRF spectrum with sample radioactlvity, and the component due only to the radloactivity.
manganese X-rays. However, the analysis for heavier elements such as niobium would not be significantly affected. In summary, the direct analysis of steels of varying physical form and chemical composition can be accomplished accurately and precisely in comparison with the statistical counting errors normally associated with EDXRF analysis of steels. The use of a general-purpose multielement spectrometer calibration in these analyses obviates the need for specialized calibration standards of matching chemical composition or physical form. The present analyses were rapid, requiring less than 8-10 iterations or about 30 s of computer time using a PDP-11/34 computer operating under RSX-11M,version 3.1. The method is well-suited to minicomputer usage, either with the sm3 program or a simpler, more specific program written specifically for steel analysis. Corrections for low-energy X-ray and Compton continuum interferences due to sample radioactivity were also demonstrated to be feasible using simple
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)
(12) (13) (14) (15) (16) (17) (18)
Rasberry, S. D.; Heinrich. K. F. J. Anal. Chem. 1974, 48, 81-89. Lucas-Tooth, H. J.; Pyne, C. Adv. X-ray Anal. 1964, 7 , 523-541. Beattie, H. J.; Brissey, R. M. Anal. Chem. 1054, 26, 980-983. Lachance, G. R.; Traiil, R. J. Can. Spectrosc. 1966. 1 1 , 43-62. Ciaisse, F.; Quintin, M. Can. Spectrosc. 1967, 12, 129-146. Giiiam, E.; Heal, H. T. Brlt. J . Appl. Phys. 1952, 3 , 353-358. Sherman, J. Spectrochlm. Acta 1955, 7 , 283-306. Shlraiwa, T.; FuJlno, N. Jpn. J . Appl. Phys. 1966, 5 , 886-899. Criss, J. W.; Birks, L. S.;Gllfrich, J. V. Anal. Chem. 1978, 50, 33. Harmon, J. C.; Wyid, 0. E. A.; Yao, T. C.; Otvos, J. W. Adv. X-ray Anal. 1979, 22, 325-335. Nleison, K. K.; Sanders, R. W. "The SAP3 Computer Program for Quantitative Multlelement Anaiysls by Energy Dispersive X-ray Fluorescence"; Pacific Northwest Laboratory Report to US. Department of Energy, PNL-4173, April 1982. Nielson, K. K. Anal. Chem. 1077, 4 9 , 641-648. Nielson, K. K. X-ray Spectrom. 1978, 7 , 15-22. Nielson, K. K.; Wogman. N. A. I n "Computers In Activation Analysis and Gamma Ray Spectroscopy"; 1979; CONF-780421. pp 166-176. Clark, B. C. Adv. X-ray Anal. 1974, 17, 258-268. Sparks, C. J. Adv. X-ray Anal. 1976, 19, 19-52. McMaster, W. H.; Dei Grande, N. K.; Mallett, J. H.; Hubbell, J. H. "Compilation of X-ray Cross Sections"; 1969; UCRL-50174, Sec. 11, Rev. 1. Bambynek, W.; Craseman, B.; Fink, R. W.; Freund, H.-U.; Mark, H.; Swift, C. D.; Price, R. E.; Rao, P. V. Rev. Mod. Phys. 1072, 4 4 , 7 16-81 3.
RECEIVEXI for review February 8,1982. Accepted June 7,1982. This report was prepared in conjunction with research performed for the U.S.Nuclear Regulatory Commission under a related services agreement with the U.S. Department of Energy (Contract No. DE-AC06-76RLO 1830).
Quantitative Surface Analysis of Steel Furnace Dust Particles by Secondary Ion Mass Spectrometry M. Van Cram, D. F. S. Natusch,' and F. Adams" Department of Chemistty, University of Antwerp (U.LA.), 8-2610 Wiirflk, Belgium
Secondary ion mass spectrometrlc (SIMS) analysis has been used for the determinationof the enrichment of various elements at the surface of electric steel furnace dust particles. Depth profile analyses were performed and surface concentrations were calculated wlth matrlx corrected sensltlvlty coefflclents. Bulk concentrations of the dust partlcles were calculated by use of SIMS and tube-excled energydlsperslve X-ray fluorescence analysls (XRF). The resuls show that the elements Cr, Mn, Co, Cu, Zn, and Pb are enrlched at the surface of these dusts.
For the last several years, the use of secondary ion mass spectrometry (SIMS) has become increasingly widespread. The combination of surface analysis, depth profile, and spatial Permanent address: Colorado State University,Fort Collins, CO
80523.
0003-2700/82/0354-1786$0 1.2510
analysis capabilities, together with extremely high sensitivity, has found application in the fields of metallurgy ( I ) , geology and geochemistry (Z), microelectronics and semiconductor technology (3), and biology (4). For the most part these applications have involved qualitative analyses since quantitative analysis, although possible by SIMS, is not straightforward. Applications of SIMS to the study of environmental samples have been few and no truly quantitative work has been reported. This is due, in part, to the generally poor electrical conductivity of environmental samples, their chemical complexity, and the insufficient spatial resolution achievable for studies of heterogeneous samples. SIMS has, however, been applied to studies of the surface composition of coal fly ash (5-7) and automobile exhaust (7)particles in conjunction with several other microanalyticaland surface sensitive techniques including electron microprobe analysis, Auger electron spectroscopy, and ESCA. The results of these studies are of considerable importance from the standpoint of environmental 0 1982 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 54, NO. 11, SEPTEMBER 1982
chemistry and demonstrate the need for quantitative determination both of particle surface concentrations and of elemental depth profiles. It is the purpose of this paper to present a case study of the utility of SIMS for providing quantitative measurements of surface concentrations and depth profiles in an environmental sample. The sample chosen for this study is a dust derived from an electric steel making furnace and the necessary prerequisites for quantitation are that the sample is conductive and that the primary ion beam is adjusted so that a small selected area of a composite particle can be analyzed. EXPERIMENTAL SECTION Secondary Ion Mass Spectrometry(SIMS). The CAMECA IMS-300 ion analyzer employed is described in detail elsewhere (8). It is equipped with a11electrostatic sedor analyzer for energy discrimination of the secondary ions (SI). The primary ion source is operated with pure argon with a less than 5 ppm total impurity torr. The Ar+ ions bombard the level at a pressure of 1.5 X sample at a current density of less than 100 mA/cm2 at 6 keV for positive SI and 15 ke’V for negative SI. For surface analysis,thle beam was focused to an approximately 7 pm diameter probe. ‘The widths of the diaphragms in the immersion lens and at the entrance of the magnetic field were 12 and 750 fim,respectively. The minimum pressure in the sample chamber was about 8 X 1O4 torr. Secondary ions in the energy bandwidth of 4 eV were measured,which ensures a mass resolution of typically about M/AM = 2500 for positive ions. The spectrometer is equipped with automated data acquisition and processing capabilities (9, 10). Depth Profile Analysis. One of the most important analytical requirements for determmation of depth profiles by SIMS is to establish that the observed SI intensity variations reflect relative differences in elemental concentrations with depth and are not due to sputtering or signal processing artifacts. For minimum artifacts from edge effects, the primary ion beam was rastered over a 100 pm diameter =lea, while the area viewed by the detector was kept considerably smaller by a reduction of the diameter of the SI beam with diaphragms. For this purpose a 12-pm slit in the immersion lens and a 750 fim diameter field diaphragm were used. The high oxygen concentration in the sample eliminated the need for extra oxygen flooding. All positive SI intensities were normalized to the Fe+ signal to allow a direct comparison of depth profiles for different elements and also to be able to compare different profiles. This internal standard element &o allows compensation for variations in the primary ion current density during analysis. Fe was chosen as a reference as it is apparent from depth profiles that it is homogeneously distributed within the particles. %Fe+was chosen for the normalization because %Fe+and 57Fe+have contributions respectively, and the 5BFe+ peak from nA12+, @CaOH+and SAFeH+, was often too intense to be measured. The possible contribution of 58Ni+to 58Fe+was found to be insignificant (4
4.0
4.4
2.9
1.25 f 0.55 0.57 f 0.14 2.1 i 0.1 2.0 f 0.35 0.34 f 0.12 5.0 f 0.3 193 f 42 5 6 6 f 200 0.22 f 0.04 8.4 f 1.8 51f 4 4.9 + 1.7 0.12 f 0.02 2-7 9 7 + 18 3.8 f 0.8
0.45
260 900 0.21 9.4 59 3.0 0.13 2.5
11
9.0
-
In this work the Fe2+/Fe+ratio was chosen. SFs for Al, Si, Ti, V, Cr, Mn, Co, Cu,riind P b were calculated from I x CFe f x SFx = ---
IFe cx fFe
where f is the isotopic abundance of the chosen isotopes (16). Since the elements Na, C1, K, Ca, Zn, and Ba are not certified in the standard, no SFs could be obtained directly. However, for these elements it appears that semiquantitative results can be calculated, using the linear relationship between the de-
termined SFs and the elemental ionization potentials at specific matrix ion species ratios, as is shown in Figure 8 for Fe2+/Fe+= 0.037. The accuracy of this procedure is estimated to be *50% for Na, Ca, Zn, and Ba. Due to the extreme ionization potentials of C1 and K, estimation of SFs from Figure 8 is difficult and errors of a factor 2-3 are suggested by comparison with spark source mass spectrometry (SSMS) (16). The iron concentration can be assumed to be 70% in the bulk sample, if the particles are assumed to be Fe203. The quantitative procedure using both MISR and calculated ion yields allows determination of the surface concen-
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Table 11. Mean and Extreme Surface Enrichment Factors (SEF) for Some Elements in Electric Furnace Dust SEF element
mean
Al
0.95
Si
0.7 1.6
c1 Ca
1.25 1.2 1.15 1.5 2.25
0.7 0.7 1.5 2
Mn Fe
co cu
Zn Pb
tration of the elements Na, Mg, Al, Si, C1, K, Ca, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Ba, and Pb. Table I summarizes quantitative data for the sample surface (
