Anal. Chem. 1989, 61,689-694
absolute reduced mobility scale, the values reported are within 1% of the given value. Agreement with available data is good in most cases, which indicates that this estimation of the error is reasonable. ACKNOWLEDGMENT I thank M. J. Cohen, R. F. Wernlund, and R. M. Stimac of PCP, Inc., for their help, and Z. Rappoport from Jerusalem for his cooperation. Registry No. Methylamine, 74-89-5; ethylamine, 75-04-7; formamide, 75-12-7; dimethylamine, 124-40-3; n-propylamine, 107-10-8; trimethylamine, 75-50-3; diaminoethane, 107-15-3; ethanolamine, 141-43-5; imidazole, 288-32-4; isopropylamine, 75-31-0;NJV-dimethylformamide,68-12-2; diethylamine,109-89-7; sec-butylamine, 13952-84-6;isobutylamine, 78-81-9; tert-butylamine, 75-64-9; pyridine, 110-86-1;pyridazine, 289-80-5; pyrazine, 290-37-9; 1,2,4-triazole,288-88-0; butylamine, 109-73-9;triazine, 290-87-9;N-methylimidazol, 616-47-7;N,N-dimethylacetamide, 127-19-5; morpholine, 110-91-8; n-pentylamine, 110-58-7; tertpentylamine, 594-39-8; 3-picoline, 108-99-6;aniline, 62-53-3; 4picoline, 108-89-4;2-picoline, 109-06-8;4-hydroxypyridine, 62664-2; 3-hydroxypyridine, 109-00-2; cyclohexylamine, 108-91-8; triethylamine, 121-44-8;dipropylamine, 142-84-7; diisopropylamine, 108-18-9; hexylamine, 111-26-2; (dimethylamino)-1119064propane, 926-63-6;N,N-dimethyl-1,2-propanediamine, 99-2; 3-cyanopyridine, 100-54-9;diethanolamine, 111-42-2;2,4lutidine, 108-47-4; 2-toluidine, 95-53-4; benzylamine, 100-46-9; N-methylaniline, 100-61-8;3-toluidine, 108-44-1;1,2-phenylenediamine, 95-54-5; 1,3-phenylenediamine, 108-45-2; 1,4phenylenediamine, 106-50-3; 2,6-dimethyipyrazine, 108-50-9; 2,5-dimethylpyrazine, 123-32-0;2,3-dimethylpyrazine,5910-89-4; heptylamine, 111-68-2; hexamethylene diamine, 124-09-4;indoline, 496-15-1; 2-acetylpyridine, 1122-62-9; 2,4,6-collidine, 108-75-8; N-ethylaniline, 103-69-5; N,N-dimethylaniline, 121-69-7; 2ethylaniline, 578-54-1; 2,4-&methylaniline,95-68-1;3-chloroaniline, 108-42-9;2-chloroaniline, 95-51-2;N&-dimethylcyclohexylamine, 98-94-2;quinoline, 91-22-5; diisobutylamine, 110-96-3;dibutylamine, 111-92-2; isoquinoline, 119-65-3; octylamine, 111-86-4; quinoxaline, 91-19-0;cinnoline, 253-66-7; phthalazine, 253-52-1; 2-isopropylaniline, 643-28-7; benzyldimethylamine, 103-83-3; 4-tert-butylpyridine, 3978-81-2;salicylamide, 65-45-2; m-nitro-
689
aniline, 99-09-2; o-nitroaniline, 88-74-4; hexamine, 131-73-7; 1naphthylamine, 134-32-7;tripropylamine, 102-69-2;triethanolamine, 102-71-6; diethylaniline, 91-66-7; 2-phenylpyridine, 1008-89-5;4-phenylpyridine, 939-23-1; 2,2’-dipyridyl, 366-18-7; 2,4’-dipyridyl, 581-47-5; 2,3’-dipyridyl, 581-50-0; 4,4‘-dipyridyl, 553-26-4; decylamine, 2016-57-1; 4-amino-N,N-diethylaniline, 93-05-0; diphenylamine, 122-39-4; acridine, 260-94-6; dicyclohexylamine, 101-83-7;2,4-dinitroaniline, 97-02-9;tributylamine, 102-82-9; dihexylamine, 143-16-8; dodecylamine, 124-22-1; dibenzylamine, 103-49-1; bromoquinoline, 119007-62-4; tetradecylamine, 2016-42-4;hexadecylamine, 143-27-1;trihexylamine, 102-86-3; tribenzylamine, 620-40-6; trioctylamine, 1116-76-3; triisooctylamine, 25549-16-0; didodecylamine, 3007-31-6;tridodecylamine, 102-87-4. LITERATURE CITED Karpas, 2.; Cohen, M. J.: Stimac, R. M.; Wernlund, R. F. Int. J . Mass Spectrom. Ion Processes 1988, 7 4 , 153. Karpas, 2.; Stirnac, R. M.; Rappoport, 2. Int. J. Mass Spectrom. Ion Processes 1988. 83, 163. Lenga, R. E. The Skma -AMrlch Library of Chemlcal Safety Data ; Sigma-Aldrich Corp.: Milwaukee. WI, 1985. Shumate, C.: St. Louis, R. H.; Hill, H. H., Jr. J. Chromatogr. 1088. 373, 141. Karasek, F. W.; Kim, S. H.; Rokushika, S. Anal. Chem. 1978, 50,
152. Karasek, F. W.; Kim, S. H.; Rokushika, S. Anal. Chem. 1978, 50,
2013.
Hagan, D. F. Plasma Chrometography: Carr, T . W.. Ed.: Plenum Press: New York, 1984; Chapter 4. Lubman, D. M.; Kronlck, M. N. Anal. Chem. 1083, 55, 867. Lubman, D. M. Anal. Chem. 1084, 56, 1298. Kolaitls, L.; Lubman, D. M. Anal. Chem. 1088, 58, 1993. Kolaitis, L.; Lubman, D. M. Anal. Chem. 1988, 58, 2137. Lawrence, A. H. Anal. Chem. 1088, 58, 1269. Lawrence, A. H. Forensic Scl. Int. 1087. 3 4 , 73. Lias, S. G.; Liebman. J. F.; Levln, R. D. J. Chem. Phys. Ref. Data 1984. 13, 695. Dewar, M. J. S.; Dieter, K. M. J. Am. Chem. SOC.1088, 708, 8075. Karpas, 2.; Berant, 2.; Stlmac, R. M. Sfruct. Chem., in press. Revercomb, H. E.: Mason, E. A. Anal. Chem. 1075. 4 7 , 970. Berant, 2.; Karpas, 2. J. Am. Chem. Soc., in press. Parent, D. C.; Bowers, M. T. Chem. Phys. 1981, 6 0 , 257. Hagler, A. T.; Karpas, 2.; Klein, F. S. J. Am. Chem. SOC.1979, 701,
2191.
RECEIVED for review February 2, 1988. Accepted December 7, 1988.
Photodissociation of Laser-Desorbed Ions as a Structure Determination Tool Lydia M. Nuwaysir and Charles L. Wilkins* Department of Chemistry, University of California, Riverside, Riverside, California 92521
Laser desorptlon Fourler transform mass spectrometry (LD/ FTMS) of porphyrlns, metalloporphyrlns,and alkalolds Is used to lnvestlgate XeCl exclmer laser photodlssoclatlon of trapped Ions as an alternatlve to collision-induced dlssoclatlon for structure analysis purposes. I t Is shown that the presence of an approprlate metal enhances photodissoclatlon and that In stlu metal attachment durlng the laser desorption event may be a useful analytical strategy. Iron-, manganese-, and chromium-attached specles are examined In order to assess the effect of metal upon the propenslty for photodissoclatlon with 308-nm excitatlon.
Laser desorption has been used extensively in mass spectrometry for desorption and ionization of nonvolatile samples (1-5). It is a relatively soft ionization technique and usually
yields high abundances of molecular ions or cation-attached molecular ions, allowing facile determinations of molecular weight. Laser desorption also results in fragment ions, depending upon the nature of the sample (6,7).However, more fragmentation often is required in order to allow inference of molecular structure. I t is therefore desirable, if laser desorption is used, to have available a means of readily dissociating ionic species to provide requisite structural information. Collision induced dissociation (CID) is the means most commonly employed for this purpose in both mass spectrometry/mass spectrometry (MS/MS) applications and for laser-desorbed species (8-1 1). Most such applications involve low mass ions ( m / z C6H6]* 587 IM-CI-2H2.C6H61+ 185
400
450
500
MASS I N A . M U
600
650
C) IM.CI.2H2-C6H61+ S 8 S IM-CI-3H2.C6H61+ 583 IM-CI-C6H6-C2H61+SS9 IM-CI-2(C6H611tS I I 400
4 0
500
MASS
550
IN A M U.
I " " " " ' I " " " " ' I
600
650
700
Flgure 4.
Laser desorptlon/photodlssociation spectra of tetraphenylporphyrin manganese chloride: (a) photodissociatlon daughter ion spectrum from m l z 667; (b) photodissociation daughter ion spectrum with ejectbn sweeps to isdate m l z 585,587, and 589 bns; (c) photodissociation daughter ion spectrum from m / z 585, 587, and 589.
added potassium chloride, are under way. Metal-Containing Samples. Metalloporphyrins were examined as the first step in investigating the feasibility of transition-metal ion attachment for induction of 308-nm photodissociation in nonabsorbing compounds. Iron, manganese, and chromium tetraphenylporphyrin chloride ions (Fe[TPP]Cl, Mn[TPP]Cl, and Cr[TPP]Cl, respectively) photodissociate with successive loss of one and two phenyl substituents (as C,&) from the porphyrin nucleus. Figure 4a contains the laser desorption daughter ion spectrum from the [M - C1]+ ions of the manganese porphyrin. In addition to the ion resulting from c&& loss (m/z 589))fragments that could arise from loss of one and two molecules of hydrogen from that species are also apparent ( m / z 587 and 585). Future experiments involving continuous ejection of m/z 589 daughter ions will determine whether they or the original [M - C1]+ ions are precursors of the m / z 585 and 587 product ions. Other fragment ions with m / z 513 can be attributed to [M - C12(C6HS)]+.The appearance of these ions suggests that elimination of a single C6H6group from [M - C1]+ might compete
with C,& loss; however, isotopic abundances do not support this interpretation. A number of less abundant ions resulting from elimination ,c] and [M - C1- 2(c&&)] are also of C,H, from [M - C1- & present. The single C& loss daughter ion ( m / z589) and the corresponding dehydrogenated ions ( m / z 587 and 585) were isolated for further photodissociation (Figure 4b) with the result depicted in Figure 4c, elimination of a second C&& Note that rn/z 513 ions ([M - C1- 2(C6HS)]+)are not produced, supporting the earlier conclusion that elimination of a single C6H5 moiety is not a major fragmentation pathway. It is also noteworthy that the m/z 585 ions appear in greater relative abundance than the m / z 587 and 589 ions, whereas, before photodissociation, the m / z 589 ions were the most abundant. This obbservation, along with the appearance of m / z 583 ions (loss of three molecules of hydrogen) in the granddaughter ion spectrum (Figure 4c) and dehydrogenated [M - C1]+ ions in the daughter ion spectrum of Figure 4a (m/z 659,661,663, and 665)) indicates that photodissociation can result in loss of hydrogen without subsequent (or prior) loss of phenyl. Iron tetraphenylporphyrin chloride daughter ions [M - C1 - C~HS]'do not undergo further photodissociation. In contrast, chromium tetraphenylporphyrin chloride is similar to the manganese complex in its behavior, in that a photo-induced second C6H6 loss to produce granddaughter ions does occur. Laser desorption/ photodissociation of the non-metal-containing porphyrin, tetrapyridylporphyrin (TPyP) molecular ions ([MI+ ( m / z 618)) produces daughter ions resulting from loss of one and two pyridines. To test the possibility of in situ metal derivatization, a sample was prepared by deposition upon a stainless steel probe tip previously covered with a layer of FeC13. Iron was chosen as the metal for these cationization experiments because it appeared that the iron-containing porphyrin molecular ions examined earlier photodissociated to a greater extent than the analogous manganese- and chromium-containing porphyrin ions. Photodissociation of the metal-attached molecular ion species ([M - H2 Fe]+ and [M - H Fe + C1]+) once more resulted in formation of daughter ions by loss of pyridyl substituents (formally, as pyridine). However, the relative efficiency of the process clearly increased as a result of metal derivatization. Table 11summarizes the ion abundance data for LD/PD of tetrapyridylporphyrin in the presence and absence of the FeC13
+
+
ANALYTICAL CHEMISTRY, VOL. 61, NO. 7, APRIL 1, 1989
694
Table 11. Relative Daughter Ion Abundances in the Photodissociation Spectra of TPyP in the Presence and Absence of FeCls
FeCl, absent (parent ion: [MI+) daughter ion
mlz
% re1 abund
mlz
100 38 15
672 594 516
[MI+ [M - CbHdN]+ [M - 2(C~H~N)1+
618 540 462
FeCl, present (parent ions: [MI+, [M - H2 + Fe]+, [M - H + Fe + Cl)+") daughter ion % re1 abund [M - Hz + Fe]+ [M - Hz + Fe - C5H4N]+ [M - Hz + Fe - 2(C6H4N)]+
100 76 69
"Relative abundances of these ions before photodissociation: [MI+, 10%; [M - Hz + Fe]+, 100%; [M - H + Fe + C1]+,56%.
140 [M+Fc-H2]+
450
~ . 450
c)
500
'
I
'
'
500
550
~
~
~
toactive species, enabled production of structurally informative ions by 308-nm photodissociation. Subsequent work will attempt to extend these promising first results to the larger molecules which provide the motivation for pursuing these studies.
ACKNOWLEDGMENT
~
~
~
~
"
'
'
'
l
"
" "' ' "" "
6 0
'
"
'"'
7d0
""
l, A 740
800
We thank Thomas C. Bruice, University of California, Santa Barbara, for providing several of the porphyrins used in this study.
LITERATURE CITED Ijames, C. F.; Wilkins, C. L. J. Am. Chem. SOC. 1988, 770, 2687-2688. Nuwaysir, L. M.; Wilklns. C. L: Anal. Chem. 1988, 60, 279-282. Brown, R. S.; Wikins, C. L. Anal. Chem. 1986, 5 8 , 3196-3199. Brown, C. E.; Kovacic, P.; Welch, K. J.; Cody. R. 8.; Hein. R. E.; Klnsinger, J. A. J. Porn. Scl.: A : Poly. Chem. 1988, 26, 131-148. Shorn, R. E., 11; Chandrasekaran, A.; Marshall, A. G.; Reuning, R. H.; Robertson, L. W. Biomed. Envtron. Mass Spectrom. lg68, 75, 295-302. Lam, Z.; Comlsarow, M. B.; Dutton. G. 0. S.; Well, D. A.; Bjarnason, A. RapH Commun. Mass Spectrom. 1987, 7 , 83-86. Coates, M. L.; Wlikins, C. L. Anal. Chem. 1987, 59. 197-200. Cody, R. B. Anal. Chem. 1988, 60, 917-923. Tandem Mass Specfromeby, McLafferty, F. W., Ed.; John Wiley and Sons, Inc.: New York, 1983. Johnson, J. V.; Yost, R. A. A w l . Chem. 1985, 5 7 , 758A-788A. Hunt, D. F.; Shabanowitz, J.; Yates. J. R., 111; McIver. R. T., Jr.; Hunter, R. L.; Suka. J. E. P.; Amy, J. Anal. Chem. 1985, 5 7 , 2733-2735. Sheil, M. M.; Denick, P. J. Olg. Mass S p e c m . 1988, 23,429-435. Blemann, K.; Martin, S. A.; Scoble, H. A.; Johnson, R. S.: Papayannopoubs, I.A.; Biller, J. E.; Costelb, C. E. I n Mass Specwomeby In the A n a W of Large Mdecrrles; McNeal, C. J., Ed.; John Wiley and Sons, Ltd.: Chichester. 1986 pp 131-149. Comisarow, M. B. Int. J. Mass Spectrom. Ion Phys. 1978, 26, 389-378. Bowers, W. D.; Delbert, S. S.; Hunter, R. L.; McIver. R. T., Jr. J . Am. Chem. SOC. 1984, 106, 7288-7289. Bowers, W. D.; Delbett, S. S.; McIver, R. T., Jr. Anal. Chem. 1986, 5 8 , 972-974. Hunt, D. F.; Shabanowitz, J.; Yates, J. R., I11 J . Chem. SOC.,Chem. Gnnmun. 1987, 548-550. Fukuda, E. K.; Campana, J. E. Anal. Chem. 1985. 5 7 , 952-954. Fukuda. E. K.; Campana, J. E. Int. J . Mass specborn. Ion procesSes 1985, 65, 321-328. Watson, C. H.: Bavkut, G.; Eyler. J. R. Anal. Chem. 1987, 5 9 , 1133-1 138. Watson, C. H.; Baykut, 0.; Battiste, M. A.; Eyler, J. R. Anal. Chim. Acta 1985. 778. 125-136. Cassady, C. J.; Frelser, B. S. J . Am. Chem. Soc. 1986, 706, 6 178-81 79. Hettlch. R L.; Frelser, B. S. J. Am. Chem. SOC. 1988, 108, 2537-2540. Hettich, R. L.; Jackson, T. C.; Stanko, E. M.; Freiser, B. S. J. Am. Chem. SOC. 1986, 708, 5088-5093. Hettlch, R. L.; Frelser, B. S. I n FoukK Transform &ss Spectrmby; Buchanan, M. V., Ed.; American Chemlcal Society Symp. Series No. 359; American Chemical Soclety: Washington, DC, 1987; pp 155-1 74. Comisarow, M. 8. I n Transfom, Techniques in Chemistty; Wffiths, P. R., Ed.; Plenum Press: New York, 1978; pp 257-284. The Merdc Index, An EncydopWa of Chemicaband 9th ed.; Windholr, M.. Ed.; Mer& 8 Co.,Inc.: Rahwey. NJ, 1976. Brown, R. S.; Wllkins. C. L. I n Fowler Tmnsfm Mass Spectrmby; Buchanan. M. V., Ed.; American Chemical Society Symp. Serles No. 359; American Chemical Society: Washington, DC, 1987; pp 127- 139. Nuwaysir, L. M.; Wklns, C. L. Presented at 14th Annual FACSS Meeting, Detroit, MI. October 4-9, 1987, Abstract No. 429.
Poo 550
M6A8:
IN
A MdU
IMtFc H2l+ 740
i M i F e H ~ . C ~ H S F ]644 +
lM+Fc 2H2 C ~ H S F ] +642
lM+Fc H2 ~ I C ~ H ~ F 548 I]+
450
IM+Fc.3H2-C6H5FI+
550 [M+Fe-2(C6H5F)li Mi:% IN A
8'8
[M+Fc-3H21t 136
Flgure 5. Laser desorption/photodisswiation spectra of tetrakid4 fluoraphenyf)pwphyrln: (a) laser desorption, no FeCb present (b) laser desorption, Feci, present: (c) photodissociation daughter bn spectrum, FeCI, present.
substrate. Abundances of daughter ions (relative to undissociated parent ions) resulting from loss of one pyridine group are doubled for the spectrum obtained in the presence of metal vs those for the spectrum in the absence of metal (compare m/z 594 (76% relative abundance) for the metal species with m/z 540 (38% relative abundance) for the nonmetal species). Daughter ions arising from loss of two pyridines are 5 times more abundant (compare m/z 516 (69% relative abundance) with m / z 462 (15% relative abundance). Figure 5a contains the laser desorption mass spectrum of tetrakis(4-fluoropheny1)porphyrin[FTPP] desorbed from a stainless steel probe tip. Only molecular ions are detected, with no structurally informative fragment ions. Photodissociation of the molecular ion species does not occur with 308nm irradiation. When the sample is prepared upon an iron chloride surface, laser desorption again yields only molecular ion species. However, because of the presence of iron, these are iron and iron chloride attached species (Figure 5b). Photodissociation of the Fe-attached and FeC1-attached molecular ions results in successful photodissociation to yield daughter ion spectra, revealing ions corresponding to loss of both one and two fluorophenyl groups (Figure 54, as C6H5F. This is an encouraging verification of the premise that in situ metal ion attachment may activate target analytes toward 308-nm photodissociation for structural analysis purposes.
CONCLUSIONS Provided sufficient numbers of trapped ions are present, it is possible to perform multiple stage analysis by FTMS, using successive photodissociation steps, to probe the structures of complex molecules. This principle is illustrated here with daughter and granddaughter ion spectra of several of the compounds studied. Furthermore, successful in situ metal derivatization enhanced daughter ion abundances for one non-metal-containing compound, while metal derivatization of a nonphotodissociating species, converting it to a pho-
RECEIVED for review August 24,1988. Accepted December 6, 1988. Support for this research was provided by the National Institutes of Health under Grant GM-30604, which is gratefully acknowledged.
