Anal. Chem. 1982, 54, 1673-1677
The molecular ionization method in conjunction with time of flight mass spectroscopy will be extremely useful for the production and detection of isotopically distinct molecular ions. The identification of the isotopic composition of the produced ions makes it possible to separate distinct isotopic molecules, whose spectrail features overlap. A relevant example involves the 13C/12C substitution in aromatics where the spectral shift of the electronic origin 6v10 = 2 cm-l is small and, as already pointed. out herein, the LIF method is inapplicable. Recently, it was demonstrated that the laser molecular ionization, combined with time of flight mass spectrometry techniques, can be used by the isotopically selective production of aniline ions containing 13C and 12C, i.e., 12C6H5NH2 and 13C12C5NHz, respectively (42,43). This was accomplished by photoselective excitation at different energies along the rotational contour of the electronic origin of aniline. This isotopically selective ion production method will be of interest in isotopic anailysis.
ACKNOWLEDGMEWT This research was supported in part by the United States Army through its European Research Office. LITElRATURE CITED Bauer, H. H.; Christlan, G. D.; O’Reiliy, J. E. “Instrumental Analysis”; Aiiyn and Bacon: Boston, MA, 1978. Barnes, R. M. Anal. C,hem. 1972, 44, 122FI. Barns, R. M. Anal. Chem. 1974, 46, 150R. Jortner, J.; Levine, R. 1). ”Photoselectlve Chemlstry”; Jortner. J., Levine, R. D., Rice, S. A , Eds.; Wiley-Interscience: New York, 1981; Advances in Chemical Physlcs, Vol. 47, p 1. Byrne, J. P.; Ross, I . G. Can. J . Chem. 1965, 43,3253. Rebane, K. K. “Impurity Spectra In Solids”; Plenum: New York, 1970. Brown, J. C.; Duncanson, J. A.; Small, G. J. Anal. Chem. 1980, 52, 1711. Yang, Y.; D’Sllva, A. P.; Fassal, V. A. Anal. Chem. 1981, 53, 894. Birks, J. “Photophyslcs of Aromatic Molecules”. Gouterman, M. ”The Porphyrins”; Dolphin, I).,Ed.; Academlc Press: New York, 1978; Voi. 111. p 1. Levy, D. H.; Wharton. L.; Smalley, R. E. ”Chemical and Blochemical Appiicatlons of Laser”; Academic Press: lUew York, 1977; Vol. 2. Levy, D. H.; Wharton, I-.; Smalley, R. E. Acc. Chem. Res. 1977, IO, 134. Levy, D. H. Annu. Rev. Phys. Chem. 1980, 31, 197. Fitch, P. S. H.; Wharion, L.; Levy, D. H. Chem. Phys. 1979, 70, 2019. Fitch, P. S. H.; Hayman, C. A.; Levy, D. H. J Chem. Phys. 1980, 73, 1064.
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(16) Amlrav, A.; Even, U.; Jortner, J. J . Chem. Phys. 1979, 71,2319. (17) Amirav, A.; Even, U.;Jortner, J. Chem. Phys. 1980, 51, 31. (18) Beck, S. M.; Liverman, M. G.; Mouts, D. L.; Smalley. R. E. J. Chem. Phys 1979, 70 232. (19) Hopkins, J. 6.; Powers, D. E.; Smaiiey, R. E. J. Chem. Phys. 1980, 72 . - , -5039 - - -. (20) Beck, S. M.; Powers, D. E.; Hopkins, J. 6.; Smalley, R. E. J. Chem. Phvs. 1980. 73.2019. (21) Beck, S. M.; Powers, D. E.; Hopkins, J. 6.; Smalley, R. E. J. Chem. Phys. 1981, 74,43. (22) Hays, T. R.; Henke, W.; Selzle, H. L.; Schlag, E. W. Chem. Phys. Lett. 1981, 77,19. (23) Amirav, A.; Even, U.; Jortner, J. J. Chem. Phys. 1981, 75,3770. (24) Amlrav, A.; Even, U.; Jortner, J. Chem. Phys. Lett. 1980, 72,21. (25) Amirav, A.; Even, U.; Jortner, J. Chem. Phys. Lett. 1979, 69, 14. (28) Amirav, A.; Even, U.;Jortner, J. J. Chem. Phys. 1981, 74,3745. (27) Even, U.; Magen, J.; Jortner, J.; Levanon, C. J. Am. Chem. SOC. 1981, 103,4583. (28) Brown, J. c.; Hayes, J. M.; Warren, J. A.; Small, G. J. “Lasers in Chemical Analysis”; Hieftje, G. M., Travis, J. M., Lytie, F. E., Eds.; The Humana Press: Cllfton, NJ, 1981; p 237. (29) Hayes, J. M.; Chlang, I.; McGlade, M. J.; Warren, J. A.; Small, G. J. J. SOC.Photo-Pot. Insfrum. Eng. 1981, 286, 117. (30) Warren, J. M.; Hayes, J. A.; Small, G. J. Anal. Chem. 1982. 54, 138. (31) Amirav, A.; Even, U.; Jortner, J. Chem. Phys. Lett. 1981, 63,1. (32) Amirav, A.; Even, U.; Jortner, J.; Birss, F. A.; Ramsay. D. A. “Rotatlonai Temperatures of Anillne In Pulsed Axlsymmetric and Planar Jets”; to be submitted for publication. (33) Amlrav, A.; Even, U.; Jortner, J. Chem. Phys. Lett. 1979, 67,9. (34) Amirav, A.; Even, U.;Jortner, J. J. Chem. Phys. 1981, 75,2489. (35) Gentry, W. R.; Glese, C. F. Rev. Scl. Insfrum. 1978, 49,595. (36) Gentry, W. R.; Giese, C. F. J. Chem. Phys. 1977. 67,5389. (37) Beyllch, A. E. Paper 111 on the 12th Symposium on Rarefled Gas Dynamics, Charlottesvllie, 1980. (38) Beylich, A. E. 2.Flugwlss. Welfraumforsch. 1979, 3 , 48. (39) Ashkenas, A.; Sherman, F. S. “Rarefled Gas Dynamics”; de Leeuw, J. H., Ed.; Academic Press: New York, 1966; Vol. 2, p 84. (40) ”International Crltlcal Tables”; McGraw-HIII: New York. 1929. (41) Craig, D. P.; Phiipott, M. R. Proc. R. SOC. London, Ser. A 1988, A290, 583. (42) Leutwyler, S.; Even, U. Chem. Phys. Lett., in press. (43) Amirav, A.; Leutwyler, S.; Even, U.; Jortner, J. Ann. Isr. Phys. SOC. 1981, 4 ,3. (44) Dietz, T. G.; Duncan, M.: Liverman, M. G.; Smalley, R. E. J. Chem. Phys. 1980, 73,4816. (45) Dletz, T. G.; Duncan, M. A.; Liverman, M. G.; Smalley, R. E. Chem. Phys. Lett. 1980, 70,246. (46) Teller, E. Handb. Jahrib. Phys. Chem. 1934, 9, 141. (47) Sage, M. L.; Jortner, J. “Advances in Chemical Physics”; Wiiey-Intersclence: New York, 1981; Vol. 47, p 293. (48) Valda, V.; McCleliand, G. M. Chem. Phys. Lett. 1980, 71,436. (49) Henley, R. J.; Leopold, D. G.; Vaida, V.; Roebber, J. L. J. Phys. Chem. 1981, 85, 134.
.
I
RECEIVED for review October 23,1981. Resubmitted April 23, 1982. Accepted May 10, 1982.
Shpol’skii Effect in the Analysis of Sulfur-Containing Heterocyclic: Aromatic Compounds Anders
L. Colmsjo,” Yngve U. Zebuhr, and Conny E. Ostman
Department of Analytical IChemistry, Arrhenius Laboratory, University of Stockholm, S- 106 9 7 Stockholm, Sweden
A number of sulfur heterocyclic polyaromatic compounds (SPAC) have been studied with respect to their ability to emit well-resolved fluoresccrnce spectra at cry0 temperatures (Shpoi’skll fluorescence). I t has been observed that there is a high probability that a bay region sulfur substituted polyaromatic hydrocarbon will exhlbit Shpol’skll fluorescence if the corresponding parent compound shows the same ability under identical condltllons. The 0-0’ transition of those spectra can In many cases be regarded as being blue shtfted in a regular manner with respect to the 0-0’ transition of the PAH analogue. These types of compounds are also detected In carbon black samples.
The utility of the Shpol’skii effect as an analytical technique
has during the last decade been proved by the efficiency of the method for the qualitative analysis of certain chemical compounds at trace levels of concentration (I-5,7). The type of substances studied with this low-temperature fluorescence technique has mostly been pure hydrocarbons due to the fact that the well-resolved spectra derived from polyaromatic hydrocarbons (PAHs) in n-alkane solutions usually become drastically less well resolved when more polar atoms are introduced in the fluorescing molecule. This problem can partially be overcome by the aid of laser-excited spectroscopy if the band broading is dependent only on an increased number of sites of the fluorescing molecule in the solvent crystal (5). However, if the band broading isdependent basically on an increase in the phonon-wing, Le., an increase in the interaction with the solvent at an electronic transition,
0003-2700/82/0354-1673$01.25/00 1982 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 54, NO. 11, SEPTEMBER 1982
( i 3 b
Flgure 1. Fluorescence spectrum of 10,ll-epithiobenzo[a Ipyrene at 63 K (solvent, n-hexane). the only possibility of enhancing the resolution is either by selecting a more suitable solvent or by a decrease in temperature of the solvent system. The latter criteria are not easily achieved in practice, because only a few solvents are known which are suitable as Shpol'skii solvents and the usual temperature used in this field a t laboratories today varies between 4 and 77 K which can hardly be lowered further. Nevertheless, this paper deals with the application of the Shpol'skii effect in the analysis of pericondensed thiophenes. Sulfur-heterocyclic aromatic compounds are not known to exhibit quasi-linear fluorescence, but a number of observations during routine analysis of HPLC fractions by the Shpol'skii fluorescence led to the conclusion that if a sulfur atom is introduced at the peri position of a polyaromatic hydrocarbon the resolution of the low-temperature fluorescence spectrum can be of the same quality, or even better than that of the parent compound a t identical conditions. This assumption led to the investigation and synthesis of a number of bay region sulfur-substituted PAHs.
EXPERIMENTAL SECTION In order to obtain pure products by synthesis and to separate the carbon black sample, we used a Spectra-Physics HPLC chromatograph, Model 3500, equipped with a Schoeffel variable wavelength UV detector monitoring the effluent at 289 nm. Analysis of the HPLC fractions by Shpol'skii fluorescence and phosphorescence was made using a low-temperature spectrophotometer designed and built at the department (4). The spectrophotometer consists in the main of a 450-W high-pressure xenon arc lamp, an Oriel excitation monochromator,a sample cell for cryo temperatures, and a Jarrel Ash scanning 0.5-m monochromator as analyzer. Solid nitrogen was used as cooling medium, which gave a sample temperature of 63 K. Subsequent analysis with gas chromatographywas carried out with a modified Varian 3700 gas chromatograph equipped with an effluent splitter to perform simultaneousdetection using flame ionization (FID) and flame photometric (FPD) detectors (split ratio 1.21). UV spectra were obtained with a PYE SP-150 UV-VIS spectrophotometer, and room temperature fluorescence spectra were obtained with a Perkin-Elmer MPF-2A fluorescence spectrophotometer. Mass spectrometric analysis was performed on a JEOL JMS-DBOO mass spectrometer interfaced to a Finnegan Incos computer. When analyzing unfractionated samples on the mass spectrometer, a Carlo Erba Fractovap 2150 chromatographywith capillary column was connected. NOMENCLATURE The pericondensed thiophenes discussed in this paper are referred to as substituted PAHs and not as thiophenes in order to make easier the comparison between these groups and in order to give more comprehensible names, especially to the poly-sulfur-substituted PAHs. RESULTS AND DISCUSSION A number of low-temperature fluorescence spectra of bay region sulfur substituted PAHs in n-hexane were registered
460
4iO
420
430
4iO
*A
"~
Flgure 2. Fluorescence spectrum of l112-ep~hlobenzo [a]anthracene at 63 K (solvent, n-hexane).
Flgure 3. Fluorescence spectrum of 1,lP-epithiobenzo[e]pyrene at 63 K (solvent, n-hexane).
@s 00
Flgure 4. Fluorescence spectrum of 7,8-epithiobenzo[ghi]perylene at 63 K (solvent, n-hexane). a t 63 K. The resolution of the spectra of the compounds is in general very high and fully comparable with those of the parent compounds (6) which is quite unusual when dealing with Shpol'skii spectra of,heterocyclic compounds. The number of dominating sites or the multiplet characters are in most cases unchanged but have in the case of l0,ll-epithio [benzo[a ]pyrene (S-B(a)P) and 1,12-epithiobenzo[a]anthracene (S-B(a)A), Figures 1 and 2, increased considerably, but with preserved resolution, indicating that no increase in the phonon wing of the separate emission lines has occurred. Most of the spectra appear spectroscopically to be derived from that of the parent compound with some kind of substituent. The enhancement of the 0-0' transition can clearly be observed in the case of 1,12-epithiobenzo[e]pyrene(S-B(e)P), 7,8-epithiobenzo[ghi]perylene (S-B(ghi)Per), and 1,12-epithiotriphenylene(S-Tri) in Figures 3, 4, and 5, respectively. Furthermore, if the shift of the 0-0' transition on substitution is studied, the spectra can be regarded as blue
ANALYTICAL CHEMISTRY, VOL.
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nm
Figure 5. The weak fluorescence spectrum of 1112-epithiotriphenylene at 63 K (solvent, n-hexane). I
nm
Flgure 8. Fluorescence spectrum of 1,12:4,5-epidithiotriphenyIene at 63 K (solvent, n-hexane). I m
Fluorescence spectrum of 1,12-epithioperylene at 63 K (solvent, n-hexane). Flgure 6.
A 470
-
490
510
530
* h, nm
Flgure 9. Phosphorescence spectrum of l1l2:4,5-epkIithiotriphenylene at 63 K (solvent, n-hexane).
Flgure 7. Fluorescence spectrum of 4,bep1ithIochryseneat 63 K (solvent, n-hexane).
shifted in a much more regular manner compared with the 0-0' transition of the corresponding PAH analogue than if being regarded as red shifted spectra of thle parent compounds. The corresponding PAH analogue is defined as the compound derived if the thiophene ring is replaced with a benzene ring. This blue shift, calculated from the PAH analogue, varies between 12.2 and 18.2 mn (860-1270 cm-') which is much more uniform than the red sihift of 5.4-21.4 nm (390-1480 cm-l) when compared with the parent compound. 1,12-Epithioperylene (S-Per), Figure 8,must be regarded as an exception. Introduction of a sulfur atom in one of the peri positions of perylene leads to a strong blue shift of the 0-0' transition (29.3 nm) which indicates that the spectral character of the compound cannot be referred to as that of a substituted perylene. The sulfur atom gives rise to an effect resembling more that
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d
%
Flgure 10. Phosphorescence spectrum of l,lPepithiobenzo[e]pyrene at 63 K (solvent, n-hexane).
achieved when an ethylene bridge is introduced (the 0-0' transition of benzo[ghi]perylene exhibits a blue shift of 39.4 nm compared to that of perylene (6)). The fluorescence intensities of the quasi-linear spectra or the quantum efficiencies of the pericondensed thiophenes examined are in most cases in the same range as that of the parent compounds with the exception of 4,5-epithiochrysene (S-Chy),Figure 7. The latter compound exhibits an increased
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Figure 11. Phosphorescence spectrum of 7,8-eplthiobenzo[gh/]peryiene at 63 K (solvent, n-hexane).
I1 .$: 480
Figure 14. HPLC chromatogram of a carbon black soot sublimate. Collected fractions are marked out in the figure. Conditions: stationary phase, HC-ODs; solvent flow, 1.2 mL/min; initial mobile phase compositions, 50% water in acetonitrile; delay time, 1 min; sweep time, 30 mln; final mobile phase composition, 100% acetonitrile.
m
480
e 500
A nrn
Figure 12, Phosphorescence spectrum of 1,12-epithiotrIphenylene at 63 K (solvent, n-hexane). 3h-
'I; Figure 13. Fluorescence spectrum of pyreno[2,1-b]thiophene at K (solvent, n-hexane).
"rn
b
63
intensity of approximately 1 order of magnitude. A study has been made of two cases where PAHs have been sulfur-substituted in two peripositions. In the first case 1,12:4,5-diepithiotriphenylene(DS-Tri), Figure 8, has a fluorescence spectrum which shows a strong similarity to that of the monosubstituted compound and the parent compound. The red shift of the 0' transition is approximately twice the red shift for this transition of the monosubstitued compound and the resolution is basically unchanged. The second disubstitued compound studied was 4,5:10,1l-diepithiochrysene (DS-Chy)which did not show fluorescence. This effect might be explained by considering the easily influenced fluorescence intensity of chrysene when substituted in one peri position. A number of pericondensed thiophenes also exhibit wellresolved phosphorescence spectra, Figures 9-12. General
Figure 15. (a) Fluorescence spectrum of fraction 3 at 63 K (solvent, n-hexane). (b) Fluorescence spectrum of 4,5-epithiophenanthrene at 63 K (solvent, n-hexane).
conclusions are difficult to make because of the small number of compounds studied, but if the parent compound exhibits a well-resolved phosphorescence spectrum, the substituted compound might be expected to do the same. In the case of S-B(ghi)Per, however, a well-resolved phosphorescence spectrum can be registered, Figure 11,whereas B(ghi)Per does not show phosphorescence. (The PAH analogue coronene exhibits strong quasi-linear phosphorescence (6)). Analytical Applications. The analytical applicability of the Shpol'skii effect is best demonstrated by the analysis of prefractionated samples. Compounds present even at very low concentrations can be detected and identified by their low-temperature fluorescence spectra if prefractionation has
ANALYTICAL CHEMISTRY, VOL. 54,
F11
Figure 16. Fluorescence, spectrum of an unknown compound in fraction 11 at 63 K: rnoletcular weight, 282; elemental composition, C,H,S;
solvent, n-hexane.
been properly carried out by, for example, HPLC. Figure 14 shows the HPLC chromatogram of a carbon black sample monitored by means of the UV absorption at 289 nm. All the collected fractions contained quasi-linear-emitting compounds with the most characteristic spectra of pyrene, benzo[ghi]perylene, and coronene in fractions 3,13, and 18, respectively. Many of the fractions contained at the time of registering, well-resolved low-temperature fluorescence spectra of unidentified compounds. These compounds were analyzed by the aid of mass spectrometry and gas chromatogi~aphywith flame photometric detection which gave information about the presence of sulfur-containing compounds and also led to the assumption that a number of pericondensed thiophenes were present. A number of tentatively identified compounds were also confirmed by synthesis. Thus, S-B(g1hi)Per was showed to be present in fraction 17, S-I3(a)P in fraction 15, S-B(e)P in fraction 12, and S-Tri in fraction 7. It was found that the pericondensecl thiophenes eluted just prior to their respective PAH analogues, both on reversed-phase HPLC and nonpolar GC. This indicated that 4,5-epithiophenanthrene (S-Phe) should be eluted just prior to pyrene, or in this case because of the strong concentration of pyrene, in the pyrene peak. Figure 15 shows that this could be verified, because the location of the 0-0' transition of S-Phe is about 12 nm prior to that of pyrene, which made it possible to register the first part of the S-Phe spectrum, despite the very intense fluorescence of pyrene. Fraction 11 was intitially assumed to contain S-Per because of the molecular weight,,elemental composition, and retention times of the compound on HPLC
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and GC. This was shown not to be the case by comparing the Shpol'skii spectra of the synthesized product, Figure 6, and that of the unidentified compound, Figure 16. The compound exhibiting the Shpol'skii spectrum of fraction 11still remains unidentified. By synthesis it could be verified that fraction 12 contains S-B(e)P which is the same compound earlier reported to be present in commercial B(ghi)Per (14). Fraction 8, which was expected to contain S-Chy because of its retention times, molecular weight, elemental composition, and room temperature fluorescence spectrum (15) was shown by synthesis not to do so. The Shpol'skii spectra of S-Chy and fraction 8 are shown in Figures 7 and 13, respectively. The two spectra differ significantly and the compound was later identified as pyreno[2,1-b]thiophene by comparison with standard substances. With a few exceptions the bay region sulfur substituted PAHs exhibit regular spectroscopic and chromatographic behavior, these can be summarized as: (1)high ability to emit Shpol'skii fluorescence; (2) a blue shift of 12-18 nm of the 0-0' transition compared to the PAH analogue (exception, S-Per); (3) a chromatographic elution order on reversed-phaseHPLC and nonpolar GC just prior to the PAH analogue (exception, S-B(a)A which elutes after B(a)P on HPLC); (4) A typical mass fragmentation of [M - 451 (10) (exception, S-B(ghi)Per (1.2%)). ACKNOWLEDGMENT We thank W. Karcher for supplying the S-Phe and the S-B(a)Aand M. Lee for supplying the pyreno[2,1-b]thiophene. We also wish to thank J. Korostenski for supplying the carbon black soot sample and B. Holm for reviewing the manuscript. LITERATURE CITED (1) Shpol'skll, E. V.; Il'ina, A. A.; Klimova, L. A. Dokl. Akad. Nauk 1952, 8 7 , 935. (2) Colln, J. M.; Vion, G.; Lamotte, M.; Joussot-Dublen, J. J. Chromafogr. 1981, 204, 159. (3) Woo, C. S.; D'Sllva, A. P.; Fassel, V. A. Anal. Chem. 1980, 5 2 , 159. (4) Colmsjo, A.; Stenberg, U. Anal. Chem. 1979, 5 1 , 145. (5) Yang, Y.; D.'Silva, A.; Fassel, V. Anal. Chem. 1981, 5 3 , 894. (6) Colmsjo, A.; Ostman, C. "Atlas of Shpol'skll Spectra and Other Low Temperature Spectra of POM"; Unlversity of Stockholm, Sweden, 1981. (7) Colmsjo, A.; Stenberg, U. "Polynuclear Aromatic Hydrocarbons"; Jones, P. W., Lever, P., Eds.; Ann Arbor Science Publishers: Ann Arbor, MI, 1979; p 121. (8) Karcher, W.; Depaus, R.; van Eljk, J.; Jacob, J. "Polynuclear Aromatic Hydrocarbons"; Jones, P. W., Lever, P., Eds.; Ann Arbor Science Publishers: Ann Arbor, MI, 1979; p 341. (9) Karcher, W.; Nelen, A.; Depaus, R.; van Eijk, J.; Glaude, P.; Jacob, J. "Polynuclear Aromatic Hydrocarbons"; Cooke, M., Dennis, A., Eds.: Battelle Press: Columbus, OH, 1981, p 317. (10) Gallegos, E. J. Anal. Chem. 1975, 47, 1150.
RECEIVED for review October 27, 1981. Resubmitted April 27, 1982. Accepted May 21, 1982.
