and Campbell (16). Considering the peak to background ratio, the best value found for magnesium, of about 700 was better than the figure of 100 obtained by Wyckhoff (21) who also used a windowless x-ray spectrometer.
10090
-
80 : 70
LITERATURE CITED
-
(1) Campbell, W. J., Brown, J. D., ANAL.CHEM.36, 312 R (1964). (2) Dolby, R., Brit. J . Appl. Phys. 1 1 , 64 (1960). (3) Dunne, J. A., Pittsburgh Conference
60-
Z
=2I 5 0 -
on Analytical Chemistry and Applied Spectroscopy, 1964. ( 4 ) Fonda, G. R., J . Am. Chem. SOC.
4 I-$
40-
55. 55, 123 (1933). __,_ Fonda, G. R., R., Collins, G. B., J . ~ Am.m . (5) E'onda, Chem. SOC.53, 113 (1931). (6) Fox, J. C. hl., J . Znst. M e t . 91, 239 ( 1962-1 963 ), ( 7 ) Glocker, It., Schreiber, H., Ann. Phys. 85, 1089 (1928). ( 8 ) Henke, B. L., Bdvan. X-Ray .4naE. 6 . 3- 6- -2 f1962) 6,362 (1962). (9) Henke, B. L., White, R., Lundberg, B., J . A p p l . Phys. 2 8 , 98 (1957). (10) Hevesy, Von, G., Coster, D., Nature 111, 79 (1923). (11) Holliday, J. E., J . Appl. Phys. 33, 3259 11963). (12) Michaelis, R. E., Alvarez, R., Kilday, B. A., J . Res. Nut. Bureau of Stds. 65'2-1, 71 (1961). (13) Pechiney. Centre de Recherches j -
ep 30 20 -
- 7
10
-
n -
~
I
H He L i
I
I
I
Be'B C
I
I
N 0
I
I
I
I
I
F Ne NaMg AI
I
I
SI
P S C1
I
I
I
Figure 5. Calculated x-ray transmission characteristics of different detector-window materials in the 4 to 70 A. region
1 - - - - 1 .
hfetallurgiques de Chambery, France,
ence of traces of rhenium on the surface of the aluminum sample by x-ray fluorescence analysis. As a precaution during the analysis, the samples were left the same time under the electron bombardment. Nevertheless a complete elimination of the eventual rhenium contamination is possible by deflecting the electron beam from a helical rhenium cathode situated below the anode, as used by Henke (8). DISCUSSION
Quantitatire determination of low atomic number elements by direct electron excitation has given good results. The limits of detection of light elements in various matrixes are better than those found by x-ray fluorescence and of the same order of magnitude using the Henke tube associated with very thin detector windows and recently developed analyzing crystals. However, no liquid or volatile samples can be analyzed by this method as comparing by the two latter techniques. Further improvements in lowering the limit of detection can be obtained in the future by various technics1 modifications. Recently developed crystals have stronger reflecting power and preliminary studies on the Na K a of an XaC1 sample, have shown (with a KAP instead of a mica crystal) a n increase of
714
ANALYTICAL CHEMISTRY
the peak to background ratio by a factor of 2 and of 4 for the figure of merit. dlso, new thinner window materials are very promising as for example nitrocellulose of 1.000 to 2.000 A. thickness. Figure 5 indicates what improvements can be expected from various window materials, their mass absorption coefficients being calculated from Victoreen (20) and Henke's (9) data. It is possible to eliminate the window by using windowless photomultipliers such as the Bendix h l 306. But some preliminary work with this photomultiplier har shown a peak to background ratio of only 3 for the A1 K a line. By the use of direct electron spectrograph as a windowless x-ray tube spectrometer some experiments were performed to compare the two techniques in the case of the K a ,Mg line from a pure magnesium sample. For the fluorescence excitation three different anode materials, Cr, hIo, and W, were employed. Results showed obviously the superiority of electron excitation with a figure of merit of 3.200. A t the other hand the hlo anode was a little more efficient than Cr and W for the excitation of magnesium, the figures of merit being for Mo, 970, for W, 920, and for Cr, 840. The same order of efficiency was found for aluminum excitation by these three anodes, in contrast to the results given by Thatcher
1962. (14) Spielberg, N., Bradenstein, M., Appl. Spectr. 17, 6 (1963). (15) Stoddard, K. B., Phys. Rev. 46, 837 i 1924) j - l _ -
(16) Thatcher, J. W., Campbell, W. J., Advan. X-Ray Anal. 7, 519 (1964). (17) Toussaint, C. J., Vos, G., Anal. Chim. Acta. 33, 279 (1965). (18) VOS, G., Toussaint, C. J., European $1. Energy Commun. EUR-21 f (1962). (19) Vos, G., Tonssaint, C. J., 26th Congress of GAMS, Paris, 1964. (20) Victoreen, J. A., J . Appl. Phys. 20, 1141 (1949). (21) Wyckhoff, W. G., Davidson, F. D., Rev. Sci. Znstr. 35, 381 (1964).
RECEIVEDfor review April 15, 1965. Accepted February 15, 1966. Work performed in the field of the ORGEL Program, presented at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, hlarch 1-5 (1965).
Correction Improved Extraction Method for the Isolation of Trivalent Act inide-Lan t ha n ide Elements from Nitrate Solutions I n this article by Fletcher L. Moore [ANAL. CHEM.38, 510 (1966)) three errors appear on page 511 in column headings for Table 11. The headings for columns 3, 7 , and 10 should read z44Cm, 148Pm,and l7oTm, respectively.
