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A N A L Y T I C A L CHEMISTRY, VOL. 51, NO. 1, JANUARY 1 9 7 9
Table I. Effect of Collision Gas on (M/M (M - H/M - 2 H ) Peak-Height Ratios (B/E Linkscan), for PAH Isomers PAH isomer
chrysene 1,2-benzanthracene 2,3-benzanthracene
collision gas pressure Torrn
(15)
0
128
0
189 6.6 7.3 5.8 (19) 63
2 x 10-6 (ion source)
1 x 10.6 2 x 10-6
H ) and
( M / M - (M - H/ H)b M - 2H) 78
0
2x (ion source)c
5x
-
(20)
7.2
0.44 (3.1) 2.4 0.39 (3.8) 1.5 0.48 0.43
LITERATURE CITED (1) M. L. Lee and R. A. Hites, J . A m . Chem. SOC., 99, 2008 (1977). (2) R. G. Cooks. J. H.Beynon, R. M. Caprioli, and G. R. Lester, Metastable Ions", Elsevier, Amsterdam, 1973. (3) T. L. Kruger, J. F. Litton, and R. G. Cooks, Anal. Chem., 48, 21 13 (1976). (4) J. H. McReynolds and M. Anbar, Inf. J . Mass Specfrom. Ion Phys.. 24, 37 (1977). (5) K. Levsen and H. D . Beckey, Org. Mass Specfrom., 9 , 570 (1974). (6) K. Levsen and H.-R. Schulten, Biomed. Mass Specfrom., 3, 137 (1976). (7) F. W. McLafferty, in "High Performance Mass Spectrometry: Chemical Applications", M. L. Gross, Ed., Am. Chem. SOC.Symp. Series, 1978. (8) A. F. Weston, K. R. Jennings, S. Evans, and R. M. Elliott, Inf. J . Mass Specfrom. Ion Phys., 20, 317 (1976). (9) R. K. Boyd and J. H. Beynon, Org. Mass Spectrom., 12, 163 (1977). (10) A. P. Bruins, K . R. Jennings, and S. Evans, Int. J . Mass Specrom. Ion Phys., 26, 395 (1978). (1 1) R. P. Morgan, C. J. Porter, and J. H. Beynon, Org. Mass Spectrom., 12, 735 (1977).
0.57 (ion source) (3.5) triphenylene 0 20.0 2 x 0.51 (ion source) (14) (2.8) a Indicated pressure on analyzer ion gage; differential pumping ratio between collision cell and analyzer is approximately 100:1. Highly irreproducible with collisional activation. Ratios observed in conventional E1 spectra.
Bori Shushan S t e p h e n H. S a f e R o b e r t K. Boyd* Guelph-Waterloo Centre for Graduate Work in Chemistry (Guelph Campus) University of Guelph, Guelph, Ontario, Canada, N1G 2W1
to establishing diagnostic analytical techniques and to investigating further the range of validity of the number of peri and/or benzo hydrogen interactions as a significant structural feature controlling PAH ion fragmentations.
RECEIVED for review September 5 , 1978. Accepted October 12, 1978. Research supported by the National Research Council of Canada. The award of a Province of Ontario Graduate Scholarship (to B.S.) is also gratefully acknowledged.
Potential Interferences in the Determination of Sulfur by Thermal Neutron Induced Prompt y-Ray Spectrometry Sir R e recently reported a technique for the quantitative analysis of S in complex matrices that measured the intensity of prompt rays produced by thermal neutron irradiation ( I ) . Analyses of standard materials showed that S abundances calculated using the 841-keV prompt 7 ray were accurate and precise. This y ray is the most intense one emitted from neutron irradiated S and appeared to be relatively free of interferences from y rays emitted by other elements. Although no interferences were actually observed, it was suggested that Ca and K were likely sources in materials with large K/Sor Ca/S abundance ratios. Interfering peaks were observed only in materials containing quantities of S that were very close t o the detection limits of the procedure. Subsequent to the publication of that work we attempted to measure S in chondritic meteorites using prompt y-ray spectrometry. These measurements revealed 7 rays which could perturb S abundances obtained using the 841-keV y ray T h e meteoritic spectra contained a y ray a t 847 keV from the decay of 56Mn.an isotope of Mn which is produced by the nuclear reaction i5Mn(n,y)56Mnand decays with a half life of 2.6 h. Because of its half-life, the intensity of the peak increases as a function of the length of irradiation. until i t attains radioactive equilibrium after several half-lives. The 847-keV line was well resolved from the 841-keY S -( ray by our spectrometer. I t should not directly interfere with the S analysis unless the sample has a relatively large Mn/S (>1) and the length of irradiation is several half-lives of jfiMn. Immediately adjacent to the 841-key peak on the low energy side, the meteoritic spectra contained a line we believe to be a prompt y ray emitted by Cr. Irradiation of Cr2(SOJ7 produced a prompt y ray a t 835 keV that was about three times more intense per unit weight of Cr than the mass normalized 841-keV S peak. This is roughly the same relative photon intensity per unit weight calculated for the two lines
-,
0003-2700/79/0351-0158$01 O O / O
in the meteoritic prompt 7 ray spectra using the appropriate abundances of Cr and S in meteorites (2). It is, however, about twice as large as the relative intensities per unit weight given by Hamawi and Rasmussen ( 3 ) . \Ve cannot account for this discrepancy, but we believe the correspondence between the Cr2(S04)3and the meteorites confirms the identification of Cr as the source of the 835-keV y ray in the meteoritic spectra. Again, the 835-keV -/ ray was well resolved from the 841-keV line and should interfere only with the S analysis in cases where the C r / S >I. As indicated in the original work ( I ) , association between an element and a prompt *, ray relies exclusively upon the energy of the photon. The analyst using this technique must continually be aware of the possibility of interferences. The integrity of the S y rays should always be determined by monitoring the ratio of the 841-keV 7 ray to the 2380-keV ray. The higher energy line should be used preferentially for S analysis of those materials that have M n / S or C r / S abundances greater than unity. LITERATURE CITED
-,
(1) E. T. Jurney, D. B. Curtis, and E. S. Gladney, Anal. Chem., 49, 174 i (1977). (2) "Handbook of Elemental Abundances in Meteorites", Brian Mason, Ed., Gordon and Breach Science Publishers, New York. 1971 (3) J. N. Hamawi and N. C. Rasmussen, "Neutron Capture Gamma Rays of 25 Elements in Terms of Increasing Gamma Ray Energy", Massachusetts Institute of Technology, Department of Engineering. MITNE-105 (1969).
David B. C u r t i s " E r n e s t S. Gladney E d w a r d T. J u r n e y
Los Alamos Scientific Laboratory Los Alamos, New Mexico 87545 RECEIVED for review September 5. 1978. Accepted October 23. 1978. c 1978 American Chemical Society
