694
Anal. Chem. 1987, 59, 694-699
Determination of Double Bond Position in Diunsaturated Compounds by Mass Spectrometry of Dimethyl Disulfide Derivatives Marco Vincenti,* Gianfranco Guglielmetti, Giorgio Cassani, a n d Cristina Tonini
Istituto Guido Donegani S.p.A., Via Fauser, 4, 28100 Novara, Italy
A method for determining the double bond locations in 24 diunsaturated compounds has been investigated. The diene system is reacted with dimethyl disulfide and a stoichiometric amount of iodine in CS, (or without solvent). The derivatization leads to either linear or cyclic polythioethersdepending on the number of -CH,- groups separating the two double bonds. The mass spectra of the derlvatizatlon products show fragmentation which is strongly influenced by the sulfurated groups introduced, so that the original position of the double bonds is easily deduced. Only conjugated dienes give derivatives with scarcely meaningful mass spectra. The derivatization is proved to have only a moderate antistereoseiectivity when cyclic poiythioethers are obtained, since several diastereomers can be distinguished with gas chromatography. No conciuslve statement Is possible about the stereochemistry of the derivatirationleading to linear poiythioethers, where a different reaction mechanism is observed.
Determining the position of a double bond in unsaturated compounds by using mass spectrometric methods is a widely studied problem. In fact, olefins, unsaturated fatty acids, acetates, and alcohols are of great importance in biology and biochemistry. Unfortunately, electron impact (EI) mass spectra of underivatized olefins show rearrangements and extensive fragmentation, making it difficult to distinguish among the isomers. However, some methods exist which allow one to locate the double bond position based on the relative intensity of ions in the mass spectrum of the underivatized compounds and on the chromatographic retention time (1-3). Collisionally activated mass spectra obtained through chemical ionization (CI) (4) or fast atom bombardment (FAB) (5) experiments provide more reliable information, but they require specific and expensive instrumentation. In some cases, CI conditions allow one to determine the double bond position in monounsaturated or polyunsaturated compounds without previous derivatization. Vinyl methyl ether (VME) has been the most widely used reagent gas (6-8) but isobutane (9, l o ) , NO ( I l ) , and mixtures of gases (12, 13) have also been employed. The most common approach to overcome the difficulties arising from the rearrangements in E1 mass spectra is to derivatize the double bonds before analysis. Epoxydation, ozonolysis, silylation, and oxidation with OsOl are well-assessed derivatization methods. More recently, reactions yielding Diels-Alder ( 2 4 ) , amino alcohol (15), or dimethyl disulfide (DMDS) (16-19) adducts have been investigated. The latter method has recently been studied with increasing interest, but reactions with polyunsaturated compounds have riot been reported yet, whereas methoxylation (20) and epoxydation (21) have. We investigated the reaction of DMDS with compounds containing two double bonds so that the applicability and feasibility of the method could be assessed. In this paper, we
Table I. Analyzed Diunsaturated Compounds Z,Z-7,13-octadecadien-l-ol acetate Z,Z-3,9-octadecadien-l-ol acetate E,Z-2,9-octadecadien-l-o1 acetate Z,Z-2,13-octadecadien-l-o1 acetate E,Z-2,13-octadecadien-l-ol acetate Z,E-2,13-octadecadien-l-ol acetate E,E-2,13-octadecadien-l-ol acetate Z,Z-3,13-octadecadien-l-ol acetate Z,Z-3,14-octadecadien-l-o1 acetate Z,Z-3,12-octadecadien-l-o1 acetate E,Z-3,13-octadecadien-l-ol Z,Z-5,1l-hexadecadien-l-ol 1,7-octadiene Z,Z-5,9-octadecadien-l-ol acetate Z,Z-6,9-octadecadien-1-01acetate Z,Z-4,9-octadecadien-l-ol acetate Z,Z-3,8-octadecadien-l-ol acetate Z,Z-7,11-hexadecadien-l-ol acetate Z,E-7,11-hexadecadien-l-ol acetate Z,Z-5,9-octadecadien-l-ol Z,Z-8,12-octadecadienoicacid methyl ester Z,Z-7,9-octadecadien-l-ol acetate E,Z-3,5-tetradecadien-l-o1 acetate E-9,11-dodecadien-1-01acetate
Z,Z-7,13-C18Ac Z,Z-3,9-C18Ac E,Z-2,9-C18Ac Z,Z-2,13-C18A~ E,Z-2,13-C18Ac Z,E-2,13-C18Ac E,E-2,13-C18Ac Z,Z-3,13-C18Ac Z,Z-3,14-C18Ac Z,Z-3,12-C18Ac E,Z-3,13-C18Al~ Z,Z-5,11-C16Alc Z,Z-5,9-C18Ac Z,Z-6,9-C18Ac Z,Z-4,9-C18Ac Z,Z-3,8-C18Ac Z,Z-7,11-C16Ac Z,E-7,11-C16Ac Z,Z-5,9-C18Alc Z,Z-8,12-C18Est Z,Z-7,9-C18Ac E,Z-3,5-C14Ac E-9,11-C12Ac
show the changes required to amplify the applicability of the previously described derivatization method (17). The products arising from the reaction are discussed and their use in locating the position of the double bonds is evaluated. The goal was easily achieved with 16 acetates and 3 alcohols, whereas 3 acetates with conjugated double bonds gave derivatives with mass spectra that required a more complex interpretation. Some mechanistic aspects involved in the derivatization are also discussed. EXPERIMENTAL SECTION Reagents. The diunsaturated compounds listed in Table I were synthesized in our laboratory and were shown to be 9599% pure by capillary gas chromatography using a Carbowax 20M column. Carbon disulfide and hexane (Carlo Erba RPE-ACS) and dimethyl disulfide (Fluka AG) were distilled in an all-glass apparatus. Iodine and Na2S203were used as received. Derivatization. A 200-500-ng portion (0.4-1.0 nmol) of a diunsaturated compound was solubilized in 50 pL of DMDS and 50 pL of carbon disulfide added with 300 pg (1.18 pmol) of iodine. The reaction mixture was kept at 60 "C for 40 h in small-volume sealed vials. The reaction was quenched with aqueous Na2S2O3 (3 X M). The organic phase was extracted and evaporated to dryness under a nitrogen stream. The residue was dissolved in hexane and analyzed by gas chromatography-mass spectrometry (GC-MS). Z,Z-3,13-Octadecadien-l-ol acetate and Z,Z-7,11-hexadecadien-1-01acetate were also reacted in higher amounts. In these cases, 0.5 g of starting material (approximately 1.5 mmol) was treated with 6 mL (64 mmol) of DMDS in the presence of a catalytic amount of iodine (30 mg, 0.118 mmol). Three 100-mg (0.39 mmol) aliquots of iodine were added progressively only to Z,Z-7,11-hexadecadien-l-ol acetate. Both mixtures were heated at 50 "C and stirred for 4-6 h; water was subsequently added to the mixtures followed by extraction with ether. The organic layer
0003-2700/87/0359-0694$01.50/00 1987 American Chemlcal Society
ANALYTICAL CHEMISTRY, VOL. 59, NO. 5, MARCH 1, 1987
695
Scheme I1
Scheme I
SCH3
7H3 CH3COO-(CH&-CH
I
& CH -(CH2),,-
1
I
CH + C H - ( C H Z ) ~ - C H ~
1
SCH3
I
?H3
I
[A]L-!--[BC]'
[AB]'--!-+CIt
[A]'=
CH3COO- (CH&-
0 CH = S-CH3
[C]'=
CH3-(CH2)y-CH
= S-CH3
[AB]+=
CH3COO-(CH2),-CH-CH-(CH2),-CH I
0
SCH3
=0 5-CH3
I
SCH3
was washed with 10% aqueous Na2S203,dried over Na2S04,and evaporated yielding the tetrasubstituted adduct (approximate yield 80%). Instrumentation. Mass spectra were obtained with a Varian-MAT 112s double-focusing mass spectrometer, interfaced to a Varian 3700 gas chromatograph. The spectra were recorded in the E1 mode with an ionizing voltage of 70 eV (source temperature 250 "c; scan range 29400 amu in 1.5 s; resolution 1oOO). The sample was injected on-column with a Carlo Erba Strumentazione injector. Two columns were used: a 25 m X 0.32 mm OV-1 glass capillary column programmed from 80 to 300 "C at 10 "C/min and a 30 m X 0.32 mm SP2340 fused silica column programmed from 80 to 270 "C at 12 "Clmin, isothermal at 270 "C for 20 min. The tetrasubstituted linear high-boiling derivatives were not eluted on the latter column. The gas chromatograms were obtained with a Carlo Erba StnunentazioneHRGC 5300 Mega chromatograph under the same conditions and with the same columns described for the GC-MS analysis. A flame ionization detector was used. 13C and lH NMR spectra were obtained with a Bruker AM 300 and a Jeol GX 270189 spectrometers. Samples were contained in 5-mm tubes and CDC13 was used as a solvent. Solvent resonances were normally used as secondary standards and converted to the Me,Si scale.
RESULTS AND DISCUSSION The structures of the DMDS derivatives of molecules containing a diene system depend on the number of carbon atoms lying between the two double bonds; they are summarized in Scheme I. The expected adducts, resulting from the addition of two molecules of DMDS to a diene, are formed only when there are at least four methylene groups separating the two double bonds. When the double bonds are separated by only one, two, or three methylene groups, the reaction with two molecules of DMDS gives, respectively, four-, five-, and six-membered cyclic thioethers which are substituted with two alkyl chains each containing a methylthio group CY to the ring (Scheme I). It is remarkable that only the internal carbons of the double bonds are contained within the ring in the derivative. Moreover, compounds containing conjugated double bonds form five-membered cyclic thioethers in which the tetrahydrothiophene ring is substituted with two methylthio groups and the two respective alkyl chain. In this case all the carbons of the double bonds are contained within the ring. The mass spectra of the DMDS derivatives show a general and meaningful pathway of fragmentation. The characteristic (16-19) cleavage of the bonds between the two carbon atoms linked to sulfur (Scheme I) indicates the original position of the double bonds and at the same time allows an unequivocal identification of the derivative. However, the E,Z isomers studied all underwent derivatization to a similar extent, showing identical mass spectra of the derivatives. The mass spectrum of all the tetrasubstituted linear derivatives of octadecadien-1-01acetates shows a well detectable molecular ion a t mlz 496 (2-4%) and fragment ions corresponding to even sequential losses of CH3S or CH3SH and
SCH3 CH3- (CH21y-CH-CH-(CH2),-CH i
[BC]*=
I
=8 S-CH3
SCHj
CH3COO SCH3
SCH3
4I i I
Figure 1. Mass spectrum of DMDS derivative of Z,Z-d,g-octadecadien-1-01 acetate.
"I'
100
]1
80
43
I
CHSOO 95
I
kH3
4CH3
60
LO
20
0 50
1W
150
200
250
300
350
LOO
450
500
Mass spectrum of DMDS derivative of Z,Z-7,13-octadecadien-1-01 acetate. Figure 2.
CH3COOH (ions at m / z 448,449 (0-170); 401,402 (0.2-2%); 388, 389 (O-l.l%); 353, 355 (0.7-2%)). The cleavage of the carbon-carbon bond between the two methylthio groups provides a fundamental fragmentation step, as shown in Scheme 11. Each of the key fragments can lose molecules of CH3SH or CH,COOH, leading to secondary fragments which confirm the original location of the double bonds in the octadecadien-1-01 acetate. Peak A (Scheme 11) is not present when a loss of acetic acid strongly enhances the stability of the ion as is evident in compounds containing a double bond in position 3 (Table 11,Figure 1). I n such cases the peak a t mlz 147 has a negligible intensity while the peak at mlz 87 (CHz=CHCH=SCH3)+ shows a relative intensity of 5+80%. The low mass range of the spectra is dominated by the saturated and unsaturated hydrocarbon fragments. The ion a t mlz 61 is the base peak in all the linear derivatives studied, even though the ions [CH2=SCH3]+ and [CH3COOHz]+both have the same nominal mass, mainly the first structure con-
696
ANALYTICAL CHEMISTRY, VOL. 59, NO. 5, MARCH 1, 1987
Scheme 111 1 80 °1
T 1 IK97
i
239
'1"
281
20
,/,y 387
0
50
100
150
200
250
4?4
0-
Figure 4. Mass spectrum of DMDS derivative of Z,Z-3,8-octadecadien-1-01 acetate.
2jl
1007
]ol 80
386
259
50
100
150
200
2$0
360
340
4bO
490
Figure 3. Mass spectrum of DMDS derivative of Z,Z-B,Osctadecadien-1-01 acetate.
tributes to the peak abundance. Figures 1 and 2 show examples of mass spectra of linear derivatives and Table I1 lists the key fragments for all the studied compounds. A similar and significant fragmentation is observed for four-, five-, and six-membered cyclic thioethers produced by reaction of DMDS and iodine with those dienyl acetates in which the two double bonds are separated by one, two, or three -CH2groups (Scheme I). The fragmentation pattern is summarized in Scheme 111. On comparison of the linear and cyclic derivative fragmentation schemes (Schemes I1 and 111),i t is evident that the fragment ions A and C are analogues, whereas the fragment ions AB and BC are different. The cyclic ion structure is rather stable and the number of leaving groups within the ion is reduced (Scheme 111). Therefore the mass spectra of these derivatives show higher abundances of ions in the high mass range and key fragments display considerable intensities. Losses of methanethiol and acetic acid from key fragments of acetates also occur. As an example, Figures 3 and 4 show the mass spectrum acetate and the Z,Z-3,8-ocof the Z,Z-5,9-octadecadien-l-ol tadecadien-1-01 acetate derivatives. The key fragments of all the cyclic derivatives and their relative intensities are reported in Table 111. The ranges of abundance in Table I11 are due to the presence of chromatographically separated isomers with slight differences in their mass spectra. It is understandable that the reduced intensity of the fragment at mlz 61 is in agreement with the reduced number of methylthio leaving groups present in the molecule. The last class of derivatives (according to Scheme I) is the one obtained when conjugated double bonds are reacted with DMDS, forming a fully substituted tetrahydrothiophene carrying the methylthio groups in positions 3 and 4 of the ring.
50
100
150
I
200
250
300
350
400
450
Figure 5. Mass spectrum of DMDS derivative of E,Z-3,5-tetradecadien-1-01 acetate.
87
100
'
97
$' I1
CH3COO
I'
20
0
50 Figure 6.
100
150
200
250
300
350
400
450
Mass spectrum of DMDS derivative of €-9,1 ldodecadien-
1-01 acetate.
Since the carbon-carbon bond between the two sulfurated substituents is contained within the ring, no chain fragmentation is favorably activated. Thus, a double loss of methanethiol from the molecular ion to give a thiophene ring dominates the mass spectrum, and a simple and general fragmentation pathway cannot be drawn. Therefore, the double bonds are easily recognized as conjugated, but their location within the chain may be uncertain. In our case however, a thorough interpretation of the mass spectrum may provide the information required since the mass spectrum of the derivatized compound is a better fingerprint than that of the underivatized one (22). This is exemplified by the mass acetate spectra of the derivatized E,Z-3,5-tetradecadien-l-o1 and E-9,ll-dodecadien-1-01 acetate, which are shown in Figures 5 and 6.
ANALYTICAL CHEMISTRY, VOL.
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1987 697
Table 11. Linear Tetrasubstituted Derivatives, Mass Spectra of Key Fragments (Relative Abundance)
[AB [BC [AB]+ [BC]+ CH3SH]+ CH3SHI'
[AB CH3COOH]'
starting compds
[MI+
Z,Z-7,13-C18Ac Z,Z-3,9-C18Ac E,Z-2,9-C18Ac E$- JE,Z-JZ,E-JZ, Z-2,13-C18Ac Z,Z-3,13-C18Ac Z,Z-3,14-C18Ac Z,Z-3,12-C18Ac Z,Z-5,11-C16Alc E,Z-3,13-C18Al~ l,7-octadiene
496 (2) 496 (2) 496 (4) 496 (3)
379 (1) 323 (3) 323 (1) 379 (-)
293 (3) 349 (1) 363 (-) 363 (-1
331 (10) 275 (13) 275 (5) 331 (3)
245 (13) 301 (5) 315 (3) 315 (3)
496 (3) 496 (3) 496 (4) 426 (-) 454 (-1 298 (1)
379 (1) 393 (1) 365 (1) 309 (1) 337 (1) 237 (8)
349 (-) 349 (-) 349 (-) 293 (-) 349 (-) 237 (8)
331 (8) 345 (12) 317 (12) 261 (15) 289 (10) 189 (10)
[AB CH3SHCH3COOH]'-
[BC2CH3SH]'
[AB2CH3SH]'
271 (-) 197 (19) 215 (5) 253 (8) 215 (14) 267 (3) 271 (10) 267 (2)
283 (7) 227 (10) 227 (3) 285 (-)
255 (11) 255 (17) 255 (11) 197 (5) 253 (2) 141 (40)
285 (4) 299 (5) 271 (5) 213 (19) 241 (9) 141 (40)
[A]'
[Cl'
319 (-) 263 (1) 263 (11) 319 (6)
203 (12) 147 (-) 133 (11) 133 (5)
117 (40) 173 (32) 173 (45) 117 (50)
301 (5) 319 (3) 301 (6) 333 (3) 301 (5) 305 (3) 85 (100)' 245 (3) 301 (4) 88 189 (10)
147 (-) 147 (-) 147 (3) 133 (8) 105 (10) 61 (100)
117 (37) 271 (5) 103 (36) 285 (9) 131 (38) 257 (10) 117 (22) 69 (28)b 117 (35) 69 (20) 61 (100)
'Value for fragment [A - SCH3]'. bValuefor fragment [C - CH,SH]'.
CValuefor fragment [A - OH]'.
Table 111. Cyclic Derivatives, Mass Spectra of Key Fragments (Relative Abundance)
starting compds Z,Z-5,9C18Ac Z,Z-6,9C18Ac Z,Z-4,9C18Ac Z,Z-3,8C18Ac Z,E-/Z,Z7,11C16Ac Z,Z-5,9C18Alc Z,Z-8,12Cl8Est
[MI+
[M CH,SH]+
[AB]+
[BC]+
[AB CH,SH]+
[BC CH3SHI'
[A]' 175 (5)
[CI'
[ABCHSCOOH]'
[AB CH3SHCHSCOOHI'
434 (2-7) 386 (8-26) 261 (20-24) 259 (26-34) 213 (61)
211 (100)
173 (20-22) 201 (4-5)
153 (55-72)
434 (4-7) 386 (7-32) 261 (3)
245 (15-21) 213 (10)
197 (71-78) 189 (4-7) 173 (28-32) 201 (2-3)
153 (68-73)
434 (5)
387 (4)
261 (17)
273 (27)
213 (18)
225 (57)
161 (1)
173 (12)
201 (22)
153 (61)
434 (6)
387 (3)
247 (27)
287 (20)
199 (20)
239 (43)
147 (3)
187 (33)
187 (33)
139 (66)
406 (2-3) 358 (7-13) 289 (4-5)
203 (18)
241 (16-17) 155 (90)
203 (18) 117 (12-13) 229 (1)
392 (-)
344 (4)
219 (2)
259 (1)
171 (55)
211 (8)
133 (5)
173 (13)
420 (11) 372 (9)
289 (1)
217 (23)
241 (20)
169 (6)
203 (17)
131 (33)
181 (11-14)
85 (100)' 125 (3)* 209 (48)c 155
"Value for fragment [A - CH3S]'. bFragmentfor [C - CH3S]'. cFragmentfor [AB - CH3SH- CH30H]'. dFragmentfor [A - CH,SH]'. Scheme IV
Table IV. '% and *€I Chemical Shifts of the Z,Z-7,11-Hexadecadien-l-ol Acetate Derivative group
13C6 Jppm 20.7 170.8 64.3 26-35
CH3COO CH3COO C'H2 C2*Hz; C'"14H2 CH3S C7AllJ2H C9-loHz C"Hz Cl6H2
It is noteworthy that the nonsymmetrical cyclic derivatives, like those shown in Scheme IV,which contain one methylthio group on the ring and one on the chain were not observed in any case. In other words only the internal carbons of the diene system were used to form the ring structure. For example, Z,Z-6,9-octadecadien-l-ol acetate only yielded a four-membered symmetrical ring and Z,Z-4,9-octadecadien-l-ol acetate yielded a symmetrical six-membered ring. To confirm the fact that only symmetrical rings are present, a characterization of the cyclic structures of the Z,Z-7,11hexadecadien-1-01 acetate derivatives by 'H and 13C NMR
'H 6/ppm
4.00 1.2-2.0 i.9s/2.os 3.2-3.8 1.2-2.0
52-55 53.3/53.4 22.4 13.1
0.92
experiments was carried out. Because of the presence of several diastereomers (which are discussed below) a complete resonance assignment was not attempted; however, the chemical shift of the more significant carbon atoms was ascertained through completely decoupled and off-resonance NMR spectra. A further confirmation of the CH assignments was based on a spectrum obtained with a DEPT pulse sequence. The results for the depicted compound 910
C
H
$
O
O
M
s
W 14
SCH3
16
SCH3
are reported in Table IV. Isomers show some differences in the chemical shift of the chiral carbon atom and of the atoms adjoining them. The two peaks at 53.3 b/ppm and 53.4 b/ppm relative to the -CH2- groups on the ring distinguish the cyclic
698
ANALYTICAL CHEMISTRY, VOL.
59, NO. 5, MARCH 1, 1987
I!
0
5
10
15 ~
20
25
mln
30
CH3
Figure 7. Gas chromatogram of the DMDS derivatiration mixture of Z,Z-7,1l-hexadecadien-l-ol acetate on a SP2340 capillary column.
products from the linear ones and confirm the symmetrical structure of the derivatives. The addition of DMDS on one double bond catalyzed by iodine is described (17) as antistereospecific. We observed only a moderate stereoselectivity on the cyclic products, where the diastereomers are easily separated by gas chromatography. In fact, Figure 7 shows a gas chromatogram on a polar SP2340 column of the product mixture formed by reacting the Z,Z7,11-hexadecadien-1-01acetate with DMDS. Eight peaks with various intensities are detected, all corresponding to the same mass spectrum. Therefore, these peaks may represent the eight diastereomers associated with four asymmetrical carbon atoms and derived from two relatively unselective reaction steps. Two totally specific steps would have led to the formation of only two couples of enantiomers. Since two diastereomers are present in a noticeably higher amount, a reaction mechanism with a moderate selectivity can be invoked. The reaction mixture cannot be separated with the same efficiency if a nonpolar OV-1 column is used, and only four/five scarcely resolved peaks can be detected. When a linear derivative (Le., one of the 2,13-octadecadien-1-01 acetate isomers) was analyzed, only the nonpolar OV-1 column could be used since the derivative was not eluted on the polar SP2340 or Carbowax columns. The gas chromatogram of the reaction mixture showed a single peak in all cases. The retention times of the derivatives arising from the four different E,Z isomers of 2,13-octadecadien-l-o1 acetate were almost identical. Thus, the OV-1 column is unsuitable in separating the diastereomers of the linear derivatives that might be produced from the different E,Z isomers or even from a single isomer. Thus, it is not possible to make any conclusion on the stereochemistry of the derivatization leading to the linear polythioethers. Some mechanistic aspects of the derivatization reaction have been studied on the previously mentioned compound (Z,Z-7,11-hexadecadien-l-ol acetate). Some experiments performed with catalytic amounts of iodine showed that after a variable period of time, the solution became colorless and the reaction stopped. Therefore, the iodine was consumed during the reaction and had to be added in stoichiometric amount. By contrast, linear tetrasubstituted derivatives were formed without consumption of iodine. Thus, iodine acts as a catalyst in the simple addition of the DMDS on a double bond to form linear derivatives but as a reactant in the cyclization step of compounds leading to cyclic derivatives. The previous observation and the product analysis suggest the reaction mechanism depicted in Scheme V. In a recent paper (23), Caserio et al. proposed a similar intermediate ion to explain the stereospecific addition of DMDS to a double bond catalyzed by boron trifluoride. The highly deactivated positions of a double bond, i.e., the position 2 in diunsaturated acetates, react very slowly with DMDS. Thus, the reported experimental conditions can
always be used without product decomposition, although there are many substances that react faster or at a lower temperature. The only undesired effect of prolonged reaction time is the increased amount of sulfurated reaction byproducts originating from the DMDS. The use of carbon disulfide as the solvent instead of hexane (17) or heptane (19) increases the reaction rate at a given temperature. The same effect is observed when a strong excess of DMDS is used, without solvent. This treatment seems to be necessary when electron-withdrawing groups deactivate the double bond (Le., position 2 in diunsaturated acetates). In such cases variable amounts of disubstituted products were detected whereas no unreacted compound was ever found. Small quantities of disubstituted derivatives were also formed when acetates with conjugated double bonds were reacted. In all other cases the percentage of di- and tetrasubstitution can be modulated by changing the reaction conditions (time and temperature of reaction, concentration of iodine). Although the conversion yields were not always assessed, quantities of starting materials ranging from 200 to 500 ng always yielded amounts of derivatives which could easily be interpreted by their mass spectra. The present derivatization method was applied to a restricted number of diunsaturated compounds, and only a few examples for each class of derivatives are available. Therefore it is not yet possible to assess definitively the applicability of the method. Nevertheless, under the described conditions, none of the tested compounds failed to react and all of them gave a meaningful mass spectrum, allowing the position of the double bonds to be identified. A further demonstration of the feasibility of this method was the determination of the double bond positions of the diunsaturated main component of a pheromone extract. Approximately 500 ng of an unknown octadecadien-1-01 acetate, isolated from abdominal tip extracts of the female leopard moth, Zeuzera pyrina L., were reacted and analyzed by the methods described. The mass spectrum of the tetrasubstituted linear derivative allowed us to determine the position of the double bonds, while the gas chromatographic retention time of the underivatized acetate revealed the E.2 isomer by comparison with standard substances. Thus, the compound was identified as E,Z-2,13-octadecadien-1-01acetate. Further details of this application have been reported elsewhere ( 2 4 ) . ACKNOWLEDGMENT We wish to thank Luigi Abis and Mauro Botta for the interpretation of the NMR spectra and Fausto Elisei and
Anal. Chem. 1987, 59, 699-703
699
LITERATURE CITED Ettore Santoro for suggestions and helpful discussions. Leonhardt, 8. A.; De Viibiss, E. D.; Klun, J. A. Org. Mass Spectrom. Registry No. Z,Z-7,13-C18Ac, 105835-82-3;Z,Z-3,9-C18Ac, 1983, 78, 9-11. 105835-83-4; E,Z-2,9-C18Ac, 105835-84-5; Z,Z-2,13-C18A~, Lanne, B. S.;Appelgren, M.; Bergstrom, G.; Lofstedt, C. Anal. Chem. 86252-65-5; E,Z-2,13-C18Ac, 86252-74-6; Z,E-2,13-C18A~, 1985, 57, 1621-1625. Hogge, L. R.; Olson, D. J. H. J. Chromafcgr. Sci. 1983, 27,524-528. 102637-06-9; E,E-2,13-C18Ac, 105835-85-6; Z,Z-3,13-C18Ac, Peake. D. A.; Gross, M. L. Anal. Chem. 1985, 57, 115-120. 53120-27-7; Z,Z-3,14-C18Ac, 86252-66-6; Z,Z-3,12-C18Ac, Jensen, N. J. J.; Tomer, K. B.; Gross, M. L. Anal. Chem. 1985, 57, 105835-86-7; E,Z-3,13-C18Alc, 66410-28-4; Z,Z-5,11-C16Al~, 2016-2021. 105835-87-8; Z,Z-5,9-C18Ac, 105835-88-9; Z,Z-6,9-C18Ac, Ferrer-Correia, A. J. V.; Jennings, K. R.; Sen Sharma, D. K. Org. Mass Specfrom. 1976, 7 7 , 867-872. 105835-89-0; Z,Z-4,9-C18Ac, 105835-90-3; Z,Z-3,8-C18Ac, Chai, R.; Harrison, A. G. Anal. Chem. 1981, 53,34-37. 105835-91-4; Z,Z-7,11-C16A~,52207-99-5; Z,E-7,11-C16Ac, Ghaderi, S.;Kuikarni, P. S.; Ledford, E. B.; Wilkins, C. L.; Gross, M. L. 53042-79-8; Z,Z-5,9-C18Alc, 105835-92-5; Z,Z-8,12-C18Est, Anal. Chem. 1981, 53,428-437. Budzikiewicz, H.; Busker, E. Tetrahedron 1980, 36, 255-266. 26258-13-9;Z,Z7,9-C18Ac, 105835-93-6;E,Z3,5-€14Ac, 61360-85-8; Doolittle, R. E.: Tumlinson, J. H.; Proveaux, A. Anal. Chem. 1985, 57, E-9,11-C12Ac, 50767-78-7; 1,7-octadiene, 3710-30-3; dimethyl 1625- 1630. disulfide, 62492-0; 7,8,13,14tetramethylthi~decan-l-ol acetate, Brauner. A.; Budzikiewlcz, H.; Boland, W. Org . Mass Spectrom . 1982, 105835-94-7; 3,4,9,10-tetramethylthiooctadecan-l-olacetate, 77,161-164. Bambagiotti, M. A.; Coran, S. A.; Giannellini, V.; Vincieri, F. F.; Daoiio, 105835-95-8; 2,3,9,10-tetramethylthiooctadecan-l-olacetate, S.;Traldi, P. Org. hhss Specfrom. W83, 78, 133-134. 105835-96-9; 2,3,13,14-tetramethylthiooctadecan-l-ol acetate, Bambagiotti, M. A.; Coran, S. A,; Gianneliini, V.; Vincieri, F. F.; Daolio, 105835-97-0; 3,4,13,14-tetramethylthiooctadecan-l-ol acetate, S.;Traldi, P. Org. Chem. Spectrom. 1984, 79,577-580. 105835-98-1; 3,4,14,15-tetramethylthiooctadecan-l-olacetate, Kidweii, D. A.: Biemann, K. Anal. Chem. 1982, 54,2462-2465. Cervilla, M.; Puzo, G. Anal. Chem. 1983, 55,2100-2103. 105835-99-2; 3,4,12,13-tetramethylthiooctadecan-l-ol acetate, Francis, G. W.; Veiand, K. J. Chromatogr. 1961, 279, 379-384. 105836-00-8; 5,6,11,12-tetramethylthiohexadecan-l-o1, 105836-01-9; Buser, H. R.; Arn, H.; Guerin, P.; Rauscher, S.Anal. Chem. 1983, 55, 3,4,13,14-tetramethylthiooctadecan-l-ol, 105836-02-0; 1,2,7,8818-822. tetramethylthiooctadiene, 105836-03-1;2-(1-acetoxy-5-methylDunkelblum, E.; Tan, S. H.; Silk, P. J. J . Chem. Ecol. 1985, 7 7 , 265-277. thiopentan-5-y1)-5-(1-methylthiononan-1-yl)tetrahydrothiophene, Leonhardt, B. A.; De Vilbiss, E. D. J. Chromatogr. 1985, 322, 105836-04-2;2-(l-acetoxy-6-methylthiohexan-6-yl)-4-(l-methyl484-490. thiononan-1-yl)thietane,105836-05-3; 2-(1-acetoxy-4-methylNiehaus, W. G.,Jr.; Ryhage, R. Anal. Chem. 1968, 4 0 , 1840-1847. thiobutan-4-~1)-6-( l-methylthiononan-l-yl)-2H-tetrahydrothioHogge, L. R.; Underhiil, E. W.; Wong, J. W. J. Chromatogr. Sci. 1985, 23, 171-175. pyran, 105836-06-4; 2-(l-acetoxy-3-methylthioprop-3-yl)-6-(l413-421. Ando, T.; Katagiri, Y.; Uchiyama, M. Agric. Biol. Chem. 1985, 49, methylthiodecan-l-yl)-2H-tetrahydrothiopyran,105836-07-5; 2-(l-acetoxy-7-methylthioheptan-7-yl)-5-(l-methylthiopentan-lCaserio, M. C.; Fischer, C. L.; Kim, J. K. J. Org. Chem. 1985, 5 0 , 4390-4393. yl)tetrahydrothiophene, 105836-08-6; 2-(1-hydroxy-5-methylTonini, C.; Cassani, G.; Massardo, P.; Guglieimetti, G.; Casteiiari, P. L. thiopentan-5-~1)-5-( 1-methylthiononan-1-yl)tetrahydrothiophene, J . Chem. Ecol. 1986, 72,1545-1556. 105836-09-7; 2-(methyl-8-rnethylthiooctanoate-8-yl)-5-(1methylthiohexan-1-yl)tetrahydrothiophene,105836-10-0; 241for review May 29,1986. Accepted October 20,1986. acetoxyoctan-8-yl)-3,4-dimethylthiotetrahydrothiophene, RECEIVED 105836-11-1;2-(l-acetoxyethan-2-yl)-3,4-dimethylthio-5-(octan- Part of this work had been presented a t the A. J. P. Martin 1-yl)tetrahydrothiophene, 105836-12-2. Honorary Symposium (Urbino, Italy, May 27-31, 1985).
Stability of Hydrocarbon Samples on Solid-Phase Extraction Columns David R. Green*l and Donna Le Pape Seakem Oceanography Ltd., 2045 Mills Road, Sidney, British Columbia, Canada V8L 35'1
The stabillty of hydrocarbon samples sorbed from water onto two types of solid phases was examined. The two solid phases, X A P P macroreticular resln and octadecane bonded on silica gel, were found to have a preservative effect which prevented the breakdown of sorbed hydrocarbons by bacteria. Hydrocarbons stored on these solid phases for perlods of up to 100 days In the presence of an oieophllic bacterial population showed no evldence of biological degradation as lndlcated by changes in chromatographic pattern or degradation of a radiolabeled hydrocarbon. I n contrast, hydrocarbons stored in water samples containing the same bacteria showed pronounced degradation over much shorter storage periods. The macroreticular or pore structure of the solid phases is thought to be the mechanism by which the extracted hydrocarbons are preserved from bacterial attack. Present address: Seakem Oceanography Ltd., Argo Building, B e d f o r d Institute of Oceanography, P.O. B o x 696, Dartmouth, N o v a Scotia, Canada B 2 Y 3Y9.
Determination of trace organics in water has benefited from remarkable improvements in analytical methodology over the last decade. However, sampling methodology has progressed scarcely at all and the problems identified a decade ago (nonrepresentative samples, insufficient volumes, contamination, undocumented preservation techniques, labor intensive extraction procedures) remain largely unsolved ( I ) . The use of solid-phase extraction columns to concentrate trace organics from water presents solutions to some of these problems (2, 3). The technique is less labor intensive than solvent extraction and enables concentration of organics from larger volumes of water, permitting improvements in analytical precision and accuracy. However, the real advantages of the use of solid-phase sorbents become apparent when the extraction columns are deployed in the field by using newly available submersible instrumentation ( 4 , 5 ,6). With field deployment, extraction is done in situ and the collection of the water itself is avoided, thereby eliminating most contamination and handling problems.
0003-2700/87/0359-0699$01.50/00 1987 American Chemical Society
