with t h e relative costs. Single-channel wavelength-dispersive s p e c t r o m e t e r s are typically e m p l o y e d b o t h for rou t i n e a n d n o n r o u t i n e analysis of a wide range of p r o d u c t s , including ferrous a n d nonferrous alloys, oils, slags a n d sinters, ores a n d minerals, t h i n films, a n d so on. T h e s e single-channel sys t e m s are very flexible, b u t relative t o the multichannel spectrometers, they are s o m e w h a t slow. T h e m u l t i c h a n n e l wavelength-dispersive i n s t r u m e n t s a r e used solely for r o u t i n e , h i g h - t h r o u g h p u t analyses where t h e g r e a t n e e d is for fast, a c c u r a t e analysis, b u t where flexibility is of n o i m p o r t a n c e . E n e r g y dispersive s p e c t r o m e t e r s have t h e great a d v a n t a g e of being able t o dis play information on all e l e m e n t s a t t h e same t i m e . A benefit h e r e is t h a t t h e d a t a displayed n o t only show t h e elements t h a t a r e p r e s e n t , b u t also en able one t o d e t e r m i n e which e l e m e n t s are n o t present. T h i s " n e g a t i v e " infor m a t i o n is especially useful in, for ex a m p l e , q u a l i t a t i v e p o w d e r diffractom e t r y , where t h e object is t o reconcile p h a s e s revealed b y t h e diffraction m e t h o d with e l e m e n t a l composition. A l t h o u g h energy-dispersive s p e c t r o m eters a r e s o m e w h a t lacking in resolu tion c o m p a r e d w i t h t h e wavelengthdispersive systems, t h e y find g r e a t a p plication in q u a l i t y control, t r o u b l e s h o o t i n g p r o b l e m s , a n d so on. T h e y
h a v e been p a r t i c u l a r l y effective in alloy sorting a n d forensic science. P r o b a b l y t h e biggest r e m a i n i n g p r o b l e m i n X - r a y fluorescence spec t r o m e t r y t o d a y is t h e need for fast, re p r o d u c i b l e s p e c i m e n p r e p a r a t i o n pro c e d u r e s , p a r t i c u l a r l y for powder anal ysis. A m o d e r n m u l t i c h a n n e l wave l e n g t h - d i s p e r s i v e s p e c t r o m e t e r is able t o collect c o u n t s on u p t o 28 different e l e m e n t s , a p p l y corrections, a n d p r i n t o u t c o n c e n t r a t i o n s , all in < 9 0 s. I n t h i s t i m e scale a s a m p l e p r e p a r a t i o n proce d u r e t h a t r e q u i r e s 5-10 m i n is already u n r e a s o n a b l e . C o n t i n u i n g research on t h e e x t e n s i o n of t h e r a n g e of t h e fluo rescence s p e c t r o m e t e r t o cover t h e very low a t o m i c n u m b e r e l e m e n t s will e n h a n c e t h e usefulness of t h i s a l r e a d y versatile m e t h o d even further. References (1) Roentgen, W. C. Ann. Phys. Chem. 1898, 64, 1. (2) Moseley, H.G. J. Phil. Mag. 1912,26, 1024. (3) Freidrich, W.; Knipping, P.; von Laue, M. Ber. Bayer. Akad. Wiss. 1912, 303. (4) Jenkins, R. Norelco Rep. 1978, 25,12. (5) Jenkins, R. In "Proceedings of the XXI International Spectroscopy Collo quium"; Cambridge, U.K.; Heyden: Lon don, U.K., 1978; pp. 37-48. (6) Jenkins, R.; Gould, R. W.; Gedcke, D. A. "Quantitative X-ray Spectrome try"; Dekker: New York, N.Y., 1981. (7) Kikkert, J. N.; Hendry, G. Adv. X-Ray
Anal., in press. (8) Nicolosi, J. Α.; Jenkins, R. Norelco Rep., in press.
Ron Jenkins is principal scientist at Philips Electronic Instruments, Mahwah, N.J., where he is involved with the development of instrumen tation and techniques for materials analysis. He received a licentiate de gree in chemistry from Oxford Poly technic in England and a doctorate in chemical physics from Brooklyn Poly technic. He has been actively involved in the application of X-ray spectrographic and diffraction techniques since the late 1950s and has pub lished six books and about 100 papers on these methods. He is also the au thor of the ACS Audio Course, "Xray Spectrometry," and is editor-inchief of the I n t e r n a t i o n a l J o u r n a l of X-Ray Spectrometry.
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