about ca. 1000-fold improvement ( I I ) , but a t considerable cost. (c) Data Processing. We have recently added a microcomputer with signal averaging facilities and a simple spectral stripping and integrating programs. The spectrometer scan has been reduced to 30 ms. Thus, fluctuations in sample pressure are insignificant and spectral purity can be checked easily by comparison of spectra obtained at different times. By using the data more efficiently, it should enable the sample size to be reduced by an order of magnitude. (This is also, of course, a valuable addition to the direct-insertion heated inlet system.) In our future work we shall use the GC-PES combination when warranted and take advantage of the greater sensitivity and ease of quantitative measurement provided by the microcomputer and the newly designed target chamber. ACKNOWLEDGMENT We are grateful t o the Lyons Central Laboratories for the loan of the gas chromatograph.
LITERATURE CITED (1)D. Betteridge, A. D. Baker, P. Bye, S.K. Hasanuddin, N. R. Kemp, D. I. Rees. M. S. Stevens. M. Thompson, and B. J. Wright, 2.Anal. Chern., 263, 286 (1973). (2)D. Betteridge. Analyst (London), 99, 994 (1974). (3)D. Betteridge, A. D. Baker, P. Bye, S. K. Hasanuddin, N. R. Kemp. and M. Thompson, J. Electron Spectrosc., 4, 163 (1974). (4)P. Bye and D. Betteridge. J. Electron Spectrosc., 7 , 355 (1975). (5)D. Betteridge, M. Thompson, A. D. Baker, and N. R. Kemp, Anal. Chem., 44,2005 (1972). (6) D. Ambrose, "Gas Chromatography". 2nd ed, Butterworths, London, 1961,p 159. (7)A. D. Baker, D. Betteridge. N. R. Kemp. and R. E. Kirby, Anal. Chern.,
44, 2005 (1972). ( 8 ) H. Lempka, private communication, April 13,1975. (9) N. R. Kemp, P h D Thesis, University of Wales, 1971. (10) D. W. Turner and D. P. May, J. Chem. Phys., 45,471 (1966). (11) D. Jones and D. Betteridge, unpublished studies, July 1975.
RECEIVEDfor review December 10, 1975. Accepted January 12, 1976. Grants for instrumentation were provided by the SRC and ARC.
Determination of Trace Aluminum in Urine by Neutron Activation Analysis A. J. Blotcky,' D. Hobson, J. A. Leffler, E. P. Rack, and R. R. Recker General Medical Research, Veterans Administration Hospital, Omaha, Neb. 68 105; Department of Chemistry, University of Nebraska, Lincoln, Neb. 68588; and Department of Medicine, Creighton University School of Medicine, Omaha, Neb. 68 102
Trace aluminum determination in biological material is difficult because of the very low levels generally present and the fact that significant quantities of aluminum are present in all reagents and the laboratory environment. A cation-exchange chromatography procedure is outlined for the simple and quantitative determination of trace amounts of aluminum (Le., 20.05 pg Al/ml urine) in biological material, employing 28AI neutron activation analysis. The procedure, utilizing a lowpower nuclear reactor (-3.1 X 10" n/cm2-s), consistsof a) wet digestion of the biologlcal material, b) cation-exchange chromatography employing 1 M nitric acid to remove the major radiocontaminantssodium, chloride, silicate, and phosphate ions, and c) irradiation and radioassay of the aluminum contained in the resin. The aluminum concentration in normal urine samples varied from
