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(11) T. Y. Toribara, C. P. Shields, and L. Kovai, Talanta, 17, 1025 (1970). (12) F. A. Cotton and G. Wilkinson, "Advanced Inorganic Chemistry", Interscience, New York, 1966, p 621. (13) J. Halpern and H. B. Tinker, J . Am. Chem Soc., 89, 6427 (1967). (14) J. Chatt, Chem. Rev., 48, 7 (1951). (15) A. J. Green, T. J. Kemp. J. S. Littler, and W. A. Waters, J . Chem. Soc., 1964, 2723. (16) L. G. Makarova and A. N. Nesmeyanov, "The Organic Compounds of Mercury", North Holland Publishing Co., Amsterdam, 1967, pp 57-141. (17) J. C. Strini and J. Metzger, Bull. SOC.Chim. Fr.. 1966, 3150 (18) A. Y . Drummond and W. A. Waters, J . Chem. SOC.,1953, 2836. (19) J. S. Littler and W. A. Waters, J . Chem. Soc., 1959, 1299. (20) J. S. Littler, J . Chem. SOC.,1962, 827. (21) T. R. Crompton, "Chemical Analysis of Additives in Plastics", Pergamon Press, New York, 1971, pp 96-121. (22) M. S. Kharasch, E. V. Jensen. and W. H. Urry, J . Am. Chem. Soc., 69, 1100 (1947). (23) M. S. Kharasch, E. V. Jensen, and W. H. Urry, Science, 102, 128 (1945). (24) D.Jenkins, "The Differentiation, Analysis and Preservation of Nitrogen and Phosphorous Forms in Natural Waters". Adv. Chem. Ser., 73, 265 (1968). (25) W. R . Hatch and W. L. Ott, Anal. Chem., 40, 2085 (1968). (26) A. A. El-Awady, R. M. Miller, and M. J. Carter, Anal. Chem., 48, 110 (1976). (27) R . W. Heiden, and D.A. Aikens, Anal. Chem., 49, 668 (1977). (28) R. J. de Kock and P. A. H. M. Hol, Po/ym. Lett.. 2, 339 (1964). (29) J. N. Lomonte, Anal. Chem., 34, 129 (1962). (30) H. Waggon and D. Jehle, Nahrung. 4, 495 (1965). (31) "Standards Methods for the Examination of Water and Waste Water". 13th ed., American Public Health Association, New York, 1971 (32) G. A. Carlson, personal communication, New York State Department of Environmental Conservation, Albany, N Y., June 1977. (33) D. R. Rueda, F. J. Calleja, and A. Hidalgo, Spectrochim. Acta, Part A , 30, 1545 (1974). (34) S R . Koirtyohann and M. Khalil, Anal. Chem., 48, 136 (1976). (35) R. A . Carr and P. E. Wilkness. Envifon. Sci. Techno/., 7, 62 (1973). (36) R. E. Cranston and D. E. Buckley, Environ. Sci. Techno/.,6, 274 (1972).
(37) R . S. Reimers and P. A. Krenkel, J . Water Pollut. Control Fed., 46, 352 (1974). (38) R. L. Thomas, Can. J . Earth Sci., 9, 636 (1972). (39) J. D. Hem, U S . ,Geol. Surv. Prof. Pap., 713, 17-24 (1970). (40) R . W. Miller, J. E. Schindler, and J. J. Alberts, "Mobilization of Mercury from Fresh Water Sediments by Humic Acid" in "Mineral Cycling in Southeastern Ecosystems", CONF-7405 13-NTIS, Augusta, Ga., May 1-3, 1974, pp 445-451. (41) A. W. Andren and R. C. Harriss. Geochim. Cosmochim. Acta, 39, 1253 (1975). (42) P. Strohal and D. Huljev, Proc. Symp. Nucl. Techniques Environ. Pollut., October 26-30, 1970, Int. At. Energy Agency, Vienna, 1971, 439; Chem. Abstr., 75, 80049) (1971). (43) L. Hannerz, "Experimental Investigations on the Accumulation of Mercury in Fresh Water Organisms" Inst. of Freshwater Research, Drottningholm, Sweden, Report No. 48, 1968, p 120; Biol. Abstr., 50, 553 (1969). (44) R. V. Coyne and J. A. Collins, Anal. Chem., 44, 1093 (1972). (45) R. M. Rosain and C. M. Wai, Anal. Chim. Acta, 65, 279 (1973). (46) C. Feldman, Anal. Chem., 46, 99 (1974). (47) J. M. Lo and C. M. Wai, Anal. Chem., 47, 1869 (1975). (48) L. B. Weisfeld. G. A. Thacker, and L. Giamundo, "Effect of Stabilizers on the Melt Rheology of Polyvinyl Chloride". Adv. Chem. Ser., 85, 38 (1968). (49) B. Raney and J. F. Rabek. "Photodegradation Photooxidation and Photostabilization of Polymers", Wiley-Interscience, New York. 1975, pp 192-195.
23, 1978. Supported in part by a grant in aid from Allied Chemical Corporation. Presented a t the 19'78 Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. Cleveland, Ohio, March 2, 1978. R.W.H. gratefully acknowledges financial support through the Corning Graduate Fellowship in Chemistry. RECEIVEDfor review March 15, 1978. Accepted October
CORRESPONDENCE Mass Spectrometry of Polycyclic Aromatic Hydrocarbons by Linked-Scan Studies of Metastable Ions I
Sir: It is well known ( 1 ) that structural identification of isomeric polycyclic aromatic hydrocarbons (PAH) by mass spectrometry is a difficult problem, since their electron impact spectra are essentially indistinguishable, Recently (I) the use of a CH4--argon mixture as chemical ionization reagent gas was shown to differentiate between PAH isomers. T h e methane acts as a proton donor to form a protonat,er! molecular ion (M l ) +while , the argon participates in charge exchange reactions to yield mass spectra similar to those produced by electron impact. T h e ratio ( M + I ) / M . for a particular reagent gas composition. was found to be diagnostic for each isomer in a series. and to correlate well with the ionization potential of the P A H ( 7 ) . T h e purpose of this note is to describe a different approach t o the same general problem. T h e analytical power of observations of spontaneous and collisionally indiiced fragmentations of ions in field-free regions of sector mass spectrometers has been well documented (2). Such ions possess lower internal energy. on average. than do those fragmenting nn the time scale appropriate to an ion snurce. so that their fragmentation reactions are often more sensitive t o the structiire of the neutral precursor than are the latter This is true despite the increased possibility of isomerization reactions prior to fragmentation in the field-free regions. A further advant,age of studies of this type concerns the ability of certain techniques to pick out for study just one group of ions of rhosen m /e ratio. Instruments in which the magnetic sector precedes the electric sector were the first to he used
+
0003-2700/79/0351-0156$01 00iO
for this purpose (2) (the so-called MIKES or DADI experiments), and can vield unique daughter-ion spectra of parent ions preselected in terms of m / p ratio. T h e power rsf such methods in augmenting traditional pre-separation techniques such as gas chromatography, for the analysis of mixtures, has been emphasised (3-7). For the problem of differentiating between isomers, however. as for the PAH investigated here, pre-separation of the isomers is desirable in any case. For instruments in which the electric sector precedes the magnet. it is possible t o obtain a daughter-ion spectrum, of a parent of preselected ( m / e )ratio, via techniques in which two of the three fields of the instrument are scanned in a linked fashion (8-10). These methods have the advantage over the MIKES or DADI techniques of increased effective mass resolution in the daughter-ion spectra, but are susceptible to artifact peaks of various kinds. including interferences from daughter ions arising from parent ions of ( r n / ~ ratios ) clos~ t o that actually preselected ( I O , I I ) . The method used in the present work was that in which both R and E are scanner! so that (B/E) is held a t the constant value required to transmit stable parent ions of preselected ( r n / e ) ratio; in this wav fragment ions formed in the first field-free region, from the preselected parent ions, are successively transmitted T h e experiments were performed with a VG Micromass 7070F double-focusing mass spectrometer. T h e suitahlv amplified signal from a Hall effect probe installed in the magnetic field, normally used to drive the mass marker. was used to program the power supply for the electric sector when C 1978 A m w c a n Chemical Society
ANALYTICAL CHEMISTRY, VOL. 51, NO. 1, JANUARY 1979
\I
e
m/e
2lR
22'
226
-
12'
*I/F
Figure 2. Replicate B/E linked scans of M, M - H, and M - 2H peaks of chrysene (20 ng) injected via gas chromatograph Other conditions as for Figure 1
I1
i
JU I 6-4-Z:
?iNi Gr
>(IC
m.1
:li:
WII
ivy
i+r
194
19:
-~ - - .
~ 1 0 iili
180
c / c
Figure 1. First field-free region daughter-ion spectrum (no collisional activation) of molecular ion ( m l e = 228) of chrysene: B/E linked scan, source temperature 210 OC, nominal electron energy 70 eV. direct probe inlet
operating in the R / E linked-scan mode T h e entrance and exit slits were set for a mass resolving power of 1000 (10% valley) in the double-focusing mode, and the 8 slit (energy resolving slit) was positioned centrallv in the main beam and closed down until the main beam intensitv was just affected. Collision gas (helium) was introduced when required into a differentially pumped collision cell situated immediatelv after t h e entrance slit, in t h e first field-free region. A nominal electron energy of 50 eV was used in all experiments reported here. T h e P A H used in this study were four isomers of formula C18H17( m / e of molecular ion = 2281: 20 ng of each PAH isomer, dissolved in CH9C12,were introduced into the soiirce via gas chromatographv (Perkin-Elmer Sigma 111, 3% SE 30 on 80/100 mesh Chrnmosorb W-HMDS. 2-mm i d.. 2-m glasc column controlled a t 200 "C, helium flow rate 20 mI,/min. all-glass jet separator). Gas chromatograms were obtained by riqing the integrating ion monitor supplied with the mass spectrometer: this monitor was pre-set to integrate (1-s scans) only the intensities of the m / e 228 parent ion plus its daughter ions arising in the first field-free region. Eventuallv. only the M, (M 11, and iM - 2) ions were monitored. thus providing a gas chromatogram specific t o m / p = 228 ions. At the maximiim of a GC peak. a three-second linked-scan of the hl to M 2 region was obtained on an oscillographic ITV recorder Figure 1 shows a complete daughter-ion spectriim of the molecular ion of chrysene, obtained using a direct insertion probe, n o collision gas, and a scan time of 100 s Resides t h e peaks corresponding to M - H and M 2H daughter ions, the M CH? and M C,H2 fragments vield fairlv intense signals. other peaks are relatively weak Similar preliminarv work on t h e other isomers. using t h e direct probe inlet. showed that t h e M H and M 2H peaks offered the best analvtical pwsihilities T h e spectra shown in Figure 2 were obtained from 20 ng of PAH introduced via the GC. using the conditions described previouslv. with n o collision gas From t h e width of t h e GC peak. it was estimated that each spectriim was ohtained from 1 2 ng of PAH. These daughter-ion spectra of the four isomers show ronsirlerahle differences in the relatir e abundance. (peak heights) of the M (main beam). M H, and W - 2H ions the Istter two being t h e products of fragmentation of M ' ions in the firqt field free region One structural featrire. which &as found t o correlate well with the ( M / M HI and ('M H I M 2H)intensity ratios, was the number of hLdrogen atnms per mole( c a p a b l ~of h e n m interactions ic'orrelations of ~
1 1 1 ~
.
BF'.ZD
lrlERACTlON~
Figure 3. Correlation of relative peak height ratios f r o m B/E linked scan spectra of PAH isomers with number of hydrogen benzo interactions per molecule. Circles, ion source 210 O C ; triangles, 160 OC
similar quality were obtained if the number of peri interactions was used as a structural feature). T h e results are shown plotted against the number of benzo interactions per molecule in Figure 3; a weak dependence upon ion source temperature is evident for these unimolecular fragmentations T h e repeatability of these ratios was k5% in the worst case Thus, structural assignments of these PAI-I isomers can he readily cross-checked using t h e two correlations shown in Figure 3 All of t h e experiments described thus far were carried out with no collision gas; t h e indicated pressure on the ion gage fitted t o the analyzer section was 2 X 10 Torr. It is well known t h a t use of collision gas in the first field-free region increases appreciably the percentage of fragmentation occurring there This was confirmed in the present work. but the increased sensitivity thus ohtainahle must he balanced against a loss in diagnostic capahilitv in the present case T h e d a t a shown in Table T illustrate t h a t intensity ratios of collisionally induced reactions are much closer than are the corresponding ratios for the unimolecular case In addition, these ratios are sensitive to variations in collision gas pressure, and our equipment was unahle to reproduce and control this parameter enough to permit collisional activation to be a useful diagnostic tool in t h e present case. This work has illustrated once again the increased diagnostic rapabilities of studies of metastable ions over concentinnal eleLtron impdct mass spectra. This work is currentlv being extended to other serieL: of P A H isomers, with a view hoth
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ANALYTICAL CHEMISTRY, VOL. 51, NO. 1, JANUARY 1979
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
-
( M / M - (M - H/ H)b M - 2H) 78
0
2x (ion source)c
(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
5x
H ) and
(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 . Am. 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 (3.5) triphenylene 20.0 2 x 0.51 (ion source) (14) (2.8) a Indicated pressure o n 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. T h e award of a Province of Ontario Graduate Scholarship (to B.S.) is also gratefully acknowledged.
(ion source) 0
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 t h a t 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 t h a t were very close t o the detection limits of the procedure. Subsequent to the publication of t h a t 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 M n / 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 t h a t 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. T h e higher energy line should be used preferentially for S analysis of those materials t h a t 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. G l a d n e y 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
