Detection of petroleum-based accelerants in fire debris by target

Anal. Chem. 1991, 63,1964-1971

1964

(20) Olson, L. K.; Story, W. C.; Creed, J. T.; Shen. W. L.: Ceruso, J. A. J . Anal. At. Specbwn. lSS0, 5 , 471-475. (21) Covey, 1. R.; Lee, E. D.; Brulns, A. P.; Henion, J. D. Anal. Chem. in118. .- - - , 59. - - , i. 4.-~..i. ~.-.-i .4. .e. i ~ . (22) Satzgef, R. D. Anal. Chem. 1988, 60, 2500. (23) Satzger, R. D.; Frlcke, F. L.; Caruso, J. A. J . Anal. A t . S p e d ” . 1888, 3, 319.

(24) Satzger. R. D.; Brueggemeyer, T. W. h4#”. Acta 198% 3 , 239-248.

for review November 29, 1990*Accepted June 7, 1991.

Detection of Petroleum-Based Accelerants in Fire Debris by Target Compound Gas ChromatographyIMass Spectrometry Raymond 0. Keto* and Philip L. Wineman Forensic Science Laboratory, Bureau of Alcohol, Tobacco, and Firearms, US.Department of the Treasury, 1401 Research Boulevard, Rockville, Maryland 20850

A gas chromatography/mser spectrometry (GWMS) method has been developed for the analyrls and IdenttflcaUon of beM o d pett”+elated target compomh In hiahty contaminated extracts of flre debrls. The process effectively -paratescompoundrofInteresthwncoduHngvdatlesorlglnatlng from the pyrolysls of substrate materials at the flre scene. Flks for the MentHlcatlon of gasollne, medlum petroleum dWlllate, and heavy petroleum dlstlliate are used to obtain remlquantttatlvepeak areas for the target .From these data, reconstructed “target compomd c)womatograms” are generated for vlwal comparison wlth standard petroleum samples treated In the same manner. Background patterns for pyrolysls products common to flre scenes have shown dlsrknlarltles to petroleum pattem and pose no r k k of false ldentllcatlons.

INTRODUCTION Gas chromatography has been the method of choice for the characterization of accelerants from suspected arson scenes for some 30 years (1-5). The technique involves visual comparison of chromatograms of fire debris extracts with those of known accelerants (typically petroleum products such as gasoline, lighter fluid, kerosine, etc.) to determine their presence. In many instances, the presence of an accelerant can neither be established nor be disproved due to coeluting substances obscuring the chromatographic pattem. Pyrolysis of common floor coverings such as carpet and vinyl flooring during a fire can produce a complex mixture of volatile compounds that interfere with low-level detection of common accelerants (6-9). Sample cleanup prior to GC analysis by acid stripping (8) or selective adsorption (10) is time consuming and not always successful because the requisite structural differences between the contaminants and analyte are minimal. Moreover, many frequently observed pyrolysis products are hydrocarbons of the type present in petroleumbased accelerants (8, 9, 11, 12). Replacement of the nonspecific GC detector by a mass spectrometer provides a means of greatly reducing these interferences (5, 7, 9, 12, 13). As a GC detector, the mass spectrometer can be used to identify and quantitate a significant number of compounds known to be components of accelerant fuels (11). Semiquantitative peak areas can then be used to generate a pattern referred to in this laboratory as a “target compound chromatogram” or TCC. This pattem is essentially a reconstructed chromatogram showing the re-

tention time and relative amount for each target compound. Visual pattem recognition is used to c o n f i i the fit to TCC’s of known accelerants for the identification of an unknown. The generation of extracted ion profiles or “mass chromatograms” (14) is another approach used in this laboratory as an adjunct to target compound analysis. Mass chromatography is generally limited to weak samples where the base ion is all that is available for the identification of a particular target compound or class of compounds. It is not used on a routine basis because the number of different mass chromatograms generated is burdensome, and the results are still subject to interpretation when interfering compounds also contain the extracted ion of interest. Target compound analysis is preferred because it displays all of the accelerant-related compounds on a single reconstructed chromatogram, thereby facilitating comparison to known accelerant patterns. Any compound known to be present in the type of accelerant sought can be used as a target. Desirable targets are those that remain detectable when the accelerant is highly evaporated, diluted, and contaminated with high levels of coeluting substances. Because of the uncertainties in this type of analysis, targets were initially selected on a tentative basis. The initial choices were modified over time as a result of experience with actual arson samples. Current targets are what we feel to be the best choices for accelerant identification. We have used the target compound approach for several years for extricating accelerant profiles from otherwise unidentifiable samples. Three quantitation files (ID files) have been developed for the detection of residual gasoline, medium petroleum distillate (MPD), and heavy petroleum distillate (HPD) in arson samples. M P D s contain hydrocarbons in the n-octane through dodecane boiling range (15) and include mineral spirits, charcoal lighter fluid, thinners for oil-base paint, and some dry cleaning solvents (i.e., Stoddard). H P D s contain hydrocarbons in the n-nonane through tricosane boiling range (15) and include fuel oils, kerosine, jet fuel, and some lamp oils. A library of TCC’s for petroleum products, fresh and in successive stages of evaporation, has been developed and used for the identification of accelerants in arson debris extracts. TCC’s have also been generated for pyrolysis products typically found in arson debris to ensure the detectability of accelerants against background.

EXPERIMENTAL SECTION The GC/MS system consisted of a Hewlett-Packard Model 5988A running the RTE-A software (HewletbPackard,Avondale, PA). Operating parameters are listed in Table I. Reagent grade

This article not subject to U.S. Copyrlght. Published 1991 by the Amerlcan Chemical Society

ANALYTICAL CHEMISTRY, VOL. 63, NO. 18, SEPTEMBER 15, 1991

Table 111. ID File for MPD Target Compounds

Table I. W/MS Operating Parameters DB-1, nonpolar capillary, 0.32-mm i.d. X 60 M, 0.25-pm methylsilicone bonded phase (J&W Scientific, Folsom, CA) carrier gas helium at 20 psig (138 P a ) , 2.0 cm3/min at 70 "C, 42 cm/s linear velocity split/splitless in splitless mode, 0.6-min splitless injector time, temp 260 OC transfer line 250 O C

column

method 1 (GASOLINE/MPD) temp programs initial temp initial hold first ramp rate intermediate temp intermediate hold second ramp rate final temp final hold run time mass spectrometer scan range start time scan cycle source temp ionization electron energy emission current PM tube voltage threshold

70 OC none 2 OC/min 130 "C 0.2 min 30 OC/min 260 OC 3 min 38 min

method 2 (HPD) 70 OC none 2 OC/min 130 O C 0.2 min 10 OC/min 260 O C 10 min 54 min

50-200 amu 4.00 min 1.25 s (16 A/D samples) 200 O C electron impact 70 eV 300 pA 1700 V 20 counts

Table 11. ID File for Gasoline Target Compounds target compd

retention m!z re1 time, min of ion abundance

1. 1,3,5-trimethylbenzene

6.8


7.6


8.4

4. indane

8.8

5. 1,2,4,5detramethylbenzene

12.3

6. 1,2,3,5-tetramethylbenzene

12.5

7. 5-methylindane

13.2

8. 4-methylindane

13.7

9. dodecane

17.5

105 120 105 120 105 120 117 118 115 119 134 119 134 117

132 117 132 57 71

10. 4,7-dimethylindane

19.1

11. 2-methylnaphthalene

21.2


22.0

13. ethylnaphthalenes (mixed) 14. 1,3-dimethylnaphthalene

27.7 28.5

15. 2,3-dimethylnaphthalene

29.6

lS65

85 131 146 142 141 142

141 141 156 141 156 141

100 50 100 45 100 45 100 55 35 100

50 100 50 100 40 100 40 100 65 50 100 40 100 80 100 85 100 100 90 100 90

carbon disulfide (J.T. Baker, Phillipeburg, NJ)was used as diluent for accelerant samples and extracting solvent for charcoal tubes. The charcoal tubes contained 50/200-mesh activated carbon (Fisher Scientific, Pittsburgh, PA) previously heated at 275 "C for 1 h. Gasoline, kerosine, and diesel fuel were obtained from local service stations. Paint thinner, charcoal lighter fluid, and mineral spirits were obtained at local hardware stores. Interior

target compd

retention m[z re1 time, min of ion abundance

1. nonane

5.4

2. propylcyclohexane


6.1 6.8


7.6

5. decane

8.2

57 85 71

83 105 120 105 120 57 71


8.4

7. n-butylcyclohexane

9.3

8. trans-decalin

10.0

9. undecane

12.4

85 105 120 83 82 138 96 81 57 71


12.5

11. n-pentylcyclohexane

13.8

12. Cl1hydrocarbon

15.5

13. dodecane

17.6

14. C12hydrocarbon

18.4

15. n-hexylcyclohexane

19.5

85 119 134 83 82 55 57 71

57 71 85 57 71

83 82 55

100 50 35 100 100 50 100 45 100 40 30 100 45 100

70 100 65 55 100 55 35 100 50 100 80 70 100 40 100 65 50 100 40 100 80 BO

grade plywood (s/4-in.American softwood),white vinyl floor tile, brown cut-pile Nylon carpeting with jute backing, and polyurethane foam carpet padding were on-hand and used without further preparation for generation of pyrolysis products. Weathered gasoline, kerosine, diesel fuel, and mineral spirits were produced by warming the fresh liquid in shallow containers until the desired degree of evaporation (by volume) had been attained. Pyrolysis products were produced by placing plywood chips, floor tile fragments, and carpet swatches with padding in separate 1-gal metal paint cans and sealing with lids having a 6-mm (1/4-in,)diameter vent hole. The cans were heated strongly over a Meker burner until heavy smoke was observed escaping from the vent. After cooling, the vapors within each can were collected by the charcoal tube adsorption method (16,17) and then eluted with carbon disulfide. Liquid petroleum products were diluted to approximately 1% (v/v) before analysis. For the performance tests, pyrolysis product extracts were spiked with weathered petroleum products at an approximate 0.1 % level. The evaporation of petroleum samples, preparation of pyrolysis products, and dilution of samples were carried out in a fume hood to prevent respiratory exposure to smoke and hazardous chemical vapors. Raw GC/MS data were quantitated by using one of the three ID files shown in Tables 11-IV, as appropriate for the type of petroleum product run. The resulting peak area data were fed into a user-generated program (procedure file) to produce the target compound chromatogram. Target compound chromatograms of petroleum products, both fresh and in progressive stages of evaporation, were collected and used as comparison patterns for the identification of unknown samples.

RESULTS AND DISCUSSION Accelerant Profiles. Total ion chromatograms (TIC'S) and the corresponding target compound chromatograms for typical accelerants (gasoline and diesel fuel) are shown in

ANALYTICAL CHEMISTRY, VOL. 63,NO. 18, SEPTEMBER 15, 1991

1966

4

2

'188

IO8OOe-

dV

*@

assso-

-75

10

asses-

10

1-

, 1400007'

de

1

40008-

1ge

,

2qe

,

sge

,

4qe

,

sge

,

Kgfl

,

7ge

I

,

ege

sge

, lege

,

11pe

2

,

12p0

, -ieo -30

-60 -71 -60

11 6

l3

1

8

I

5 E -4E

Flgure 2. TIC and TCC for 80% evaporated gasoline. Numbers on TCC refer to compounds listed In Table 11.

Figures 1-5. The numbers on the TCC's denote target compounds listed in Tables 11and IV. Figure 1was obtained on a blend of 18 fresh gasolines, and Figures 2 and 3 were obtained on the same gasoline evaporated to 20 and 4% of

ita original volume, respectively. Figures 4 and 6 were obtained for fresh diesel fuel and diesel fuel evaporated to 20% of ita original volume, respectively. As an accelerant evaporates during a fire (or in the interval between extinguishment and

ANALYTICAL CHEMISTRY, VOL. 63,NO. 18, SEPTEMBER 15, 1991 ,

ige

2q0

,

,

380

,

,

4ge

sq0

,

6q0

,

7q0

I

140003

10000

,

8q0

,

sq0

lIg0

lag0

,

,

12g0

1867

13g0

I

i

2 4 0 0 0-

11

-100 -98

-80

18000-

7 0

-60 12000-

12

5 0

-440 6

6088-

'50

8 5

14

10

7

2

13

1

3 4

. . . . , . . , . , . . . ' , , . 1 . . , .! . ' . , . . , . ,

0

h .

2 0

-1 0

15

., . . , . I . . . . , . . . . , . . . . . . . . , . . . . , . . . . , . . . . , . . . . ,I . . . . , . . . . , . . I. . , . . . . , . . . - - e

32888

24000-

d0 10000-

5 0

I

-4 0 -30

-20 -1 0

4

I

6

,

2qo

IO

12

,

14

,

dq8

10

70

16

6q0

,

22

24

,

spe

4 LA

30

76

26

,

rope

12po

4

1

-1;-23

6

12

I 'crc I6 I4 10

20

72

24

13

L 20

32 I

I

34

S I

,

lap0

40

38

1spo

,

44

42

,

raps

46

i0pe

48

,

50

nope

I 18

LL-4-LLL1 36

56

40

42

44

'

46

l

50

Flguro 4. TIC and TCC for fresh diesel fuel (fuel oil 2). Numbers on TCC refer to compounds listed in Table IV.

sample collection),the preferential volatization of lower boiling compounds results in the enhancement of later eluting GC peaks. This effect is self-evident in the chromatograms shown. T o ensure the proper identification of samples with unknown

histories, it is essential to have a reference library of TCC's for accelerants in various stages of evaporation. Analytical Methodology. In this laboratory,routine arson samples are screened by GC using a flame ionization detector.

1968


Table IV. ID File for HPD Target Compounds target compd

re1 retention m!z time, min of ion abundance

1. decane

8.2

2. n-butylcyclohexane

9.3

3. trans-decalin

10.0

4. undecane

12.4


12.5

6. n-pentylcyclohexane

13.8

51 71 85 83 82 138 96 81

7. dodecane

17.6

8. n-hexylcyclohexane

19.5


21.2


22.0

11. tridecane

23.6

12. n-heptylcyclohexane

25.6

13. 1,3-dimethylnaphthalene

28.5

14. tetradecane

29.7

15. n-octylcyclohexane

31.7

16. 2,3,5-trimethylnaphthalene 17. pentadecane

33.8 34.0

18. n-nonylcyclohexane

35.1

19. hexadecane

36.5

20. heptadecane

38.4

21. pristane

38.6

22. octadecane

39.8

23. phytane

40.0

24. nonadecane

41.1

25. eicosane 26. heneicosane

42.1 43.2

57 71 85 119 134 83 82 55 57 71 85 83 82 55 142 141 142 141 57 71 85 83 82 156 141 57 71 85 83 82 170 57 71 85 83 82 57 71 85 57 71 85 57 71 85 57 71 85 57 71 85 57 71 85 57 71 85 57 71 85

100 40 30 100 70 100 65 55 100 55 35 100 50 100 80

70 100 65 50 100 80 60 100 80 100 85 100 65 40 100 85 100 90 100 65 50 100 90 100 100 70 50 100 80 100 70 50 100 80 55 100 80 40 100 80

55 100 75 60 100

75 60

100 80

55 100 80 55

Questionable or uninterpretable chromatogramsare evaluated to determine which of the two GC/MS methods, listed in Table I, is to be used. The longer method is used if the GC/FID trace supports the possible existence of HPD or for mixtures of HPD with gasoline and/or MPD. The shorter

method is chosen if only gasoline or MPD is sought. Splitless injections are used to ensure the introduction of detectable quantities of trace accelerant components and to avoid possible sample segregation that can occur in split injections of solutes having wide boiling point differences (18). The relatively short mass spectral scan range of 150 m u , while incapable of detecting molecular ions for many of the target compounds, is nevertheless sufficient to cover the major ions in the target compounds for all three classes of petroleum producta. The scan range was kept to a minimum to "ize the dwell time per ion within an overall scan cycle of approximately 1s. Sensitivity was thereby increased without sacrificing "chromatographic" resolution. The target compounds listed in Tables II-IV were selected on the basis of resolution, relative size, and distribution of prominent peaks in chromatograms of each respective accelerant type. Components more volatile than nonane (bp 151 "C) were excluded for lack of persistence at fire scenes and to avoid simpler molecules that are often products of pyrolysis. Although this limited the amount of detectable gasoline to less than 20% of its full-range composition (191, these later eluting components were deemed both necessary and sufficient for gasoline identification. A homologous series of alkanes was the starting point for MPD and HPD identification and provided the "bell"-shaped peak envelope characteristic of petroleum distillate. Naphthenic hydrocarbons (alkylcyclohexanes)were added to ensure against false positives from polyolefin pyrolyzates, which also contain homologous series alkanes (20). The isoprenoids pristane and phytane provide additional insurance for HPD identification because of their recognition as biological markers in crude oil (21). The homologous series alkanes (nonane and higher) do not make good patterns with gasoline due to low concentrations and coelution with gasoline aromatics. Isomer pairs for aromatic compounds were included, where practicable, in all three accelerant files because our experience has shown that the abundance ratios of these compounds to their respective isomers are fairly consistent in petroleum distillates. Other sources for a target compound would not, in all likelihood, produce its isomer in the same relative amount. Naphthalene, an obvious target for petroleum identification, was found to be too common in pyrolysis products to be useful. The ions chosen for identification purposes consist of the base ion for each target with one or two other strong ions where their inclusion significantlyincreases selectivity without seriously affecting sensitivity. In this regard, ions having intensities less than 30% of the base ion were not considered. The ion intensities reflect the actual performance of the instrument during a GC/MS run. A target compound chromatogram is a bar graph of base ion peak area versus peak retention time for each target compound identified. The comparison of relative intensities for neighboring target compounds is an important aspect of accelerant pattern recognition. The further apart the compounds, the greater the tolerance for intensity mismatches due to evaporation or incomplete sample recovery. The ordinate on a TCC, being in terms of peak area for each compound's base ion, is not directly comparable to the ordinate on a TIC, which is in terms of total detector response. Performance Tests. The ability to extract usable target compound profiles from highly contaminated accelerant samples was tested, on a qualitative basis, by spiking laboratory-generated pyrolysis products with weathered accelerants at levels adjusted so that the accelerant's chromatographic pattern would be obscured. Figures 6 and 7 show representative chromatograms of pyrolysis products spiked with gasoline and diesel fuel, respectively. In both instances the presence of the petroleum product in the TIC of the spiked


20000?A

I

2 2I

1969

-lee(

24

9 0

-e8

-7 8

20000-

-60

19

*e 12008-

-4 8

-30

17 161

e-

-28

I

4080-

-1 0

. , . , . , . , . , . , . , . , . , . , . , . , . , . , . , . , . , . , . , . , . , . , . , . , . , . ; . , . , . , ,!. ! ,, ! ,

77-

Figure 5. TIC and TCC for 80% evaporated diesel fuel (fuel oil 2). Numbers on TCC refer to compounds listed In Table IV. ,

ige

deem,-..

-

" "

,

,

1qe

2qe

'

,

2qe

-

3 p

. ' . ' .'

sq0

,

,

rge

,

5qe

,

,,

,6qe,

,

7qe

,

sqe

,

aqe

iepe

,

,

iige

,

iepe

ispe 't

, sqe

690

,

,

6g8

,

7gE

,

eqe

348

,

lapa

,

11pe

,

,,

, ,__. , ,

,

12pe

ispe

2

14~00-

18880-

11

6

6000-

I,,

3

12

2888

,

, , , . , , , , -:,

6,8

I

6.8

, 8.8

;,.

10

9

,,

, , I , , , , , , , , : , ,

18.8

lP.8

,

:,a,, 16.8

,.,

,,,,,,,,,,,,I,, ,.A,, ,,

16.8

18.0

l4

13

,

, , ,,.,

28.8

,, , ,. , ,, , , , ., 22.8

24.8

26.8

15

!, , , . I , , , ,,, , , , 28.8

,

38.8

,,

,

, ) ,,

32.8

Figure 6. TIC and TCC for plywood pyrolyzate spiked with weathered gasoline (compare Flgure 2).

Potential interferencea to the target compound method were

pyrolyzate is not obvious. The TCC profiles, however, leave little doubt as to their presence (compare with Figures 2 and

visualized by chromatagraphing the pyrolysis samples without

5).

added accelerant and processing the data for gasoline, MPD


1970

1600

l20M

tr

1

5 8

5

e 5

e 5

0

4000

0 4

6

8

I

2qs

I2

10

,

14

491

I

16

bgS

20

18

,

24

22

,

b)O

lap0

26

78

,

33

30

iapo

,

34

iape

SO

,

38

l6PD

40

42

,

ispo

22

I24

44

,

46

2ape

48 1

SO

22po

Fbure 7. TIC and TCC for carpetlpadding pyrolyzate splked wtth weathered dlesel fuel (compare Figure 5).

4

25

B

11

17 14

20

t:

10

I I

4

16884

9

15

I

I

&-II.,, 4

, , , . , . 1. , .

6

8

I8

I

I I

I

.1I2 . , ,1,4 , , .16, . , ,18, , .28, .I, .22I , . , I 24 . , , , . , , , .,I., , , , , , , 26 28 38 32 ,

.

lL 18

41

Fburr 8. (A) Gasoline target compounds present In plywood pyrolyzate. (6) HW target compounds present in carpet/padding pyrolyzate.

and HPD. The resulting patterns had little resemblance to TCC's for petroleum products and posed no risk for false identification of a residual accelerant. Figure 8 shows TCC's

for plywood pyrolyzate processed for gasoline and carpet/ padding pyrolyzate processed for HPD. The contribution of these patterns to the spiked sample TCC's can be seen in

Aml. Chem. 1991, 63, 1971-1978

Figures 6 and 7. The extent to which these random target compounds exist in pyrolysis products from an arson scene establishes a limit below which accelerant patterns would become unrecognizable.

LITERATURE CITED D. M. J . ~ o n m s l ~ IBW, ~ d . 5,236-247. Parker, B. P.; Rajeswaran, P.; Kkk, P. L. M”. J . 1862, 8 , L-S,

31-36. Mldklff, C. R.; Washington, W. D. J . Assoc. Otf. Anal. CY”. 1072, 55, 840-845. Yip, I . H. L.; Clalr, E. G. a n . Soc. Fawrplc Sd. J . 1078, S,75-80. Bertsch,W.;Sdbrs,C.S.J.Hk3,R~.CYwomefog*.Clvomefog*. Commun. 1888, 9 , 657-661. DeHaan. J. D.; Bonarlus, K. J . F m s b Sd. Soc. 1888, 28, 299-309. Smith, R. M. Anel. Chem. 1082, 54, 1399A-1409A. Juhela. J. A. A m Anel. New. 1070, 3 , 1-19, Hober, 0.; Bertsch, W. Am. Lab. 1088, 20, 15-19. Aldrldge, T. A.; OeteS, M. J . Fwenslc Sd. 1886, 31, 666-686. Wlneman, P. L. (unpublished work) Symposium on Recent Advanes In Arson Analysh and Detection, Lee Vegas, NV, 1985. Bertsch, W.; Sellers, C. S.; Babln, K.; Mer, G. J . M& RSSOM. chroma-. chsomew. COmmM. 1888, 1 1 , 815-819. Kelly, R. L.; Mae, R. M. J . FcmMslc Sd. 1084, 20, 714-722. HWes, R. A.; Blemann, K. Anel. Chem. 1070, 42, 855-860. Fwenslc Sclence and Englneerkrg Commmee of the Intematknel Association of Arson Inwstlgators. Rg Areon Invesf@rOr 1888, 98 (4), 45-48. Chrostowski, J. E.; Holmes. R. N. Arson Anel. New/. 1878, 3 (5), 1-17. Tontarskl, R. E.; Strobel, R. S. J . FonmslC Sd. 1082. 27, 710-714. &ob, K. CIesSicel Sph end Spnmness In)sction In &pI&ry Q.C, 2nd ed.;Huthlg: New Yak, 1968; pp 56-58, 97. Sanders, W. N.; Maynard, J. 8. Anal. 0”.1868, 40, 527-535. Irwin, W. J. Anel)arcelpyrdysls; Marcel Dekker: New York, 1982; pp 133- 134. Hunt, J. M. P e m &oChedsby end oedogy;W. H. Freeman and CO.: San Franclsco, CA, 1979; pp 89, 101.

CONCLUSIONS Target compound analysis is a useful approach to the identification of residual petroleum products in fire debris. The generation of target compound chromatogramsfacilitates this process. Target compound patterns for fresh and weathered gasoline, MPD, and HPD are sufficiently specific to allow their identification in high-background arson samples. Registry No. 1,3,5-Trimethylbenzene, 108-67-8; 1,2,4-trimethylbenzene,95-63-6; 1,2,3-trimethylbenzene,52673-8; indane, 496-11-7; 1,2,4,5-tetramethylbenzene,95-93-2; 1,2,3,5-tetramethylbenzene, 527-53-7; 5-methylindane,874-35-1; 4-methylindane, 824-22-6;dodecane, 112-40-3; 4,7-dimethylindane,668271-9; 2-methyhphthalene, 91-57-6,l-methylnaphthalene,90-12-0; ethylnaphthalene,27138-19-8; l,%dimethylnaphthalene,575-41-7; 2,3-dimethylnaphthalene,581-40-8; decane, 124-18-5; n-butylcyclohexane, 1678-93-9; trans-decalin, 493-02-7; undecane, 1120-21-4;n-pentylcyclohexane,4292-92-6; n-hexylcyclohexane, 4292-75-5;tridecane, 629-50-5; n-heptylcyclohexane, 5617-41-4; tetradecane, 629-59-4; n-octylcyclohexane, 1795-15-9;2,3,5-trimethylnaphthalene,2245-38-7; pentadecane, 629-62-9; n-nonylcyclohexane, 2883-02-5; hexadecane, 544-76-3; heptadecane, 629-78-7; pristane, 1921-70-6; octadecane, 593-45-3; phytane, 638-36-8; nonadecane, 629-92-5; eicosane, 112-95-8; heneicosane, 629-94-7.

1971

RECEIVED for review January 17,1991. Accepted June 7,1991.

Charge Determination of Product Ions Formed from Collision- Induced Dissociation of Multiply Protonated Molecules via Ion/Molecule Reactions Scott A. McLuckey,* Gary L. Glish, and Gary J. Van Berkel Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6365

of bn/mokcule reactknr lnvolvlng muttiply protomid bnsdorlved from dectmpray for the detennhakn of the c h a r m of product bns fonned from colkkn-lnducd d b dation b The expwlmenb are carded out wiih a quadrupole Ion trap capable of muttlple siages of mass spectrometry. The approach k W a i d wlth proton transfer from a product Ion from quadruply proionaied meliiiln, and 20H)* lon from horse from a product b n from ihe (M myOgMlh, io l,edhhohex8nO. The major product ion hwn quadruply proionaied bovine lnsulln Is used io lllusiraie the use of a clustering reaw h 1,tkllamlnOhexane. The Ion trap Is shown io be a parilcularly useful tool for employing both collkknal acthraibn and bw-energy lon/mdecule reactknr hthe”eexp.rhmtiodet.mrlnproduct ioncharge. T)n w#)

+

INTRODUCTION Fenn and co-workers fiit demonstrated the propensity for multiple cationization of poly(ethy1eneglycols) (1) and biopolymers, such as peptides and proteins (2,3),via electrospray (ES).Since then, numerous examples of the usefulness of ES as a source of multiply charged ions for mass spectrometry 0003-2700/9 1/0363-197 1$02.50/0

have appeared. Much of this work has recently been reviewed (4-8). Biopolymers, in particular, show a strong tendency for multiple protonation (e.g., proteins) or deprotonation (e.g., oligonucleotides), resulting in highly charged ions. Although the ability to form highly charged ions provides new opportunities for mam spectzometry, the analysis of these ions poeee new challenges. Among these is the establishment of ion charge. Most maas spectrometersprovide the ion mass/charge ratio or some property proportional to mass/charge, such as momentum/charge or kinetic energy/charge. The majority of ionization methods provide predominantly singly charged ions, which makes trivial the determination of mass. The number of charges aasociated with ions formed via ES,on the other hand, is highly variable and can range up to many dozens of charges. Fortunately, a distribution of charge states is typically observed with ES for molecules that tend to form multiply charged ions. Furthermore, little or no fragmentation is typically observed for ions derived from ES. As a result, the ES masa spectrum of a multiply protonated polymer shows a series of peaks, each of which differs from its adjacent peaka by 1unit charge, and by 1Da. The procedure for obtaining the molecular weight of the polymer from the ES mass spectrum is straightforward and has been described (3,9,10). 0 I991 Amerlcan Chemical Soclety

Detection of petroleum-based accelerants in fire debris by target

Recommend Documents