1314
Anal. Chem. 1988, 60, 1314-1318
Comparison of Electron Impact, Desorption Chemical Ionization, Field Desorption, and Fast Atom Bombardment Mass Spectra of Nine Monosubstituted Group V I Metal Carbonyls Richard B. van Breemen,* LeRoy B. Martin, and Anton F. Schreiner Department of Chemistry, Box 8204, North Carolina State University, Raleigh, North Carolina 27695
Nlne monosubstituted group V I metal pentacarbonyls of the type M(CO),L (where M = Cr, Mo, or W and L = P(C6H5)3, AS( C,H,),, or Sb(C&),) were synthesized and purified by recrystalllratlon so that they contalned no unbound ligands, excess reagents, or other contamlnants as measured by hlgh-performance Hquld chromatography. Posltlve Ion mass spectra were obtained by electron Impact (E1 ), desorption chemical lonlratlon (DCI), field desorption (FD), and fast atom bombardment (FAB) mass spectrometry. B/E llnked scanning was used to conflrm the fragmentatlon pathway In FAB mass spectra. While all four Ionization methods formed molecular Ions,M", the desorptlon lonlzation methods tended to produce more abundant molecular Ions than EI. FD, for instance, formed molecular Ions wlthout any fragmentation. The most abundant fragment Ions of the ligand (L) were observed with DCI. FAB spectra contalned abundant molecular ions and extenslve structural informatlon in Ion fragments.
Group VI (group 6 in 1985 notation) transition-metal carbonyls are used as catalysts in organic synthesis (1,2) and as precursors in the preparation of other organometallic compounds ( 3 , 4 ) . Substituted carbonyl complexes of tungsten, chromium, and molybdenum have been shown to be catalysts for cis-trans isomerization and metathesis of acyclic olefins (1) and cocatalysts for the metathesis of internal olefins (2). Positive ion electron impact (EI) (5-10) and chemical ionization (CI) mass spectrometry (11-14) have been used to analyze several monosubstituted group VI carbonyls. Because these techniques required that samples be heated and vaporized prior to ionization, pyrolysis and ligand exchange were observed for some compounds, particularly the less volatile molybdenum complexes (9). In this investigation, monosubstituted transition-metal carbonyls of the type M(CO),L (where M = Cr, Mo, or Wand L = P(C6H5I3,AS(C~H,)~, or Sb(C6H5)3)were characterized by mass spectrometry. The in-beam method of desorption chemical ionization (DCI) is a promising technique for the ionization of compounds of low volatility (1516) and was used instead of CI in this investigation. Another desorption ionization technique, field desorption (FD), has been a valuable mass spectrometric method for ionization of various nonvolatile transition-metal complexes such as substituted platinum carbonyls (17). Like FD, fast atom bombardment (FAB) (18) is a useful ionization method for the analysis of nonvolatile and thermally labile compounds. Minard and Geoffroy (19) reported the first FAB mass spectra of a transition-metal carbonyl (a trimetallic cluster of cobalt). Since then, relatively few transition-metal carbonyls have been analyzed by FAB mass spectrometry. Nine menosubstituted group VI metal pentacarbonyls were analyzed in the present study by positive ion mass spec0003-2700/88/0360-13 14$01.50/0
trometry using four different ionization methods, EI, DCI, FD and FAB, and the spectra obtained by using DCI, FD, and FAB are reported here for the first time. This investigation provided an opportunity to compare the utility of a wide variety of ionization techniques for analysis of a related series of organometallic compounds. Results could be compared directly because all analyses were carried out with the same mass spectrometer.
EXPERIMENTAL SECTION Nine monosubstituted transition-metal pentacarbonyls were synthesized by standard methods based on previously described procedures (3, 20) and were purified at least twice by recrystallization. Purity exceeded 99% by HPLC analysis with UV detection at 254 nm where each compound absorbs very strongly (e 10000, cm-' M-l). Samples were stored desiccated in the dark until analysis by mass spectrometry. Positive ion mass spectra were obtained by using a JEOL (Tokyo, Japan) JMS-HX11OHF double focusing mass spectrometer of EB geometry, equipped with EI, DCI, FD, and FAB ionization sources, collision chamber in the first field-free region, and postacceleration detection. The accelerating voltage was 10 keV, and the resolving power was 1000 for all measurements. Spectra were recorded with a JMA-DA5000 data system, which had been calibrated by using either perfluorokerosine or sodium iodide and potassium iodide in glycerol. Samples were dissolved in HPLC grade methylene chloride (J. T. Baker Chemical Co., Phillipsburg, NJ) and introduced into the ionization source by direct insertion probe. For EI, DCI, and FD, approximately 1-2 Kg of each substituted carbonyl was used g was used for FAB. E1 mass spectra per analysis, while 3-5 W were obtained with an ion source temperature of 180 "C and an electron energy of 70 eV. The E1 direct insertion probe was heated from room temperature to 150 "c in approximately 1 min. For DCI analyses, samples were loaded onto a 100-Kmplatinum wire, which was heated in the CI ionization source by a current increasing at A/min. Isobutane or xenon was used as the reagent gas, and the electron energy was 100 eV. FD mass spectra were obtained at a cathode potential of 1.2 keV. Samples were loaded onto either carbon or silicon emitters, and ions were typically observed at emitter currents of approximately 10 mA. In FAB measurements, the carbonyls were analyzed in a matrix of 18-crown-6ether dissolved in tetraethylene glycol dimethyl ether (Aldrich Chemical Co., Milwaukee, WI) as reported by Minard and Geoffrey (19). Xenon gas at 3 keV was used for FAB ionization. For B/E linked scans, precursor ions were formed by FAB, and fragmentation was enhanced by collisional activation. The helium gas pressure in the collision cell in the first field-free region was increased until the precursor ion abundance was attenuated 70%. Mass spectra were recorded at constant B/E by the DA-5000 data system.
-
RESULTS AND DISCUSSION Each of the four ionization methods, EI, DCI, FD, and FAB, produced molecular ion radicals for all nine monosubstituted transition-metal carbonyls (Tables I-IV). This is the first report of DCI, FD, and FAB mass spectra for these com0 1988 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 60, NO. 13, JULY 1, 1988
1315
Table I. Positive Ion Electron Impact (EI) Mass Spectra molecular formula
M'+
[M - CO]"
454 (23)" 498 (9.8) 544 (14) 500 (14) 544 (16) 590 (16) 586 (32) 630 (45) 678 (100)
426 (11) 470 (1.5) 516 472 (19) 516 562 558 (33) 602 (1.2) 650
[M - 2CO]'+ 398 442 448 444 488 534 530 574 622
[M - 3CO]'+
(23) (12) (14) (2.9) (30) (37) (3.6) (77) (81)
370 (10) 414 (1.5) 460 (2.3) 416 (34) 460 506 502 (99) 546 (1.9) 594
[M - 4CO]'+ 342 386 432 388 432 478 474 518 566
[M - 5CO]'+
(20) (5.3) (2.3)
[L]'+
314 (100) 358 (100) 404 (100) 360 (100) 404 (100) 450 (100) 446 (100) 490 (100) 538 (99)
(1.9) (1.0) (2.2)
262 306 352 262 306 352 262 306 352
(22) (5.3) (1.7) (31) (31) (6.6) (15) (11) (4.7)
"Relative intensities for each m/z value appear in parentheses and are expressed as a percentage of the base peak within each set.
Table 11. Positive Ion Desorption Chemical Ionization (DCI) Mass Spectra molecular formula
M+ 454 498 544 500 544 590 586 630 678
(9.8) (9.8) (21) (15) (30) (83) (6.0) (69) (100)
[M - CO]'+ 426 470 516 472 516 562 558 602 650
(3.9) (16) (2.2) (3.7)
[M - 2CO]*+ 398 442 448 444 488 534 530 574 622
[M - 3CO]'+
(2.4) (7.4) (8.4) (6.8) (48) (57) (1.9) (100) (93)
370 414 460 416 460 506 502 546 594
(23) (3.6) (14) (12)
[M - 4CO]'+ 342 386 432 388 432 478 474 518 566
[L + H]+
[M - 5CO]'+
(9.3) (3.9) (1.3)
314 (100)
358 404 360 404 450 446 490 538
(1.2)
(16) (100) (45) (100) (100) (6.7) (44) (43)
263 307 353 263 307 353 263 307 353
(31) (100) (4.9) (100) (57) (98) (100) (62) (19)
Table IV. Positive Ion Fast Atom Bombardment (FAB) Mass Spectra molecular formula
M'+ 454 498 544 500 544 590 586 630 678
(40) (75) (100) (36) (37) (64) (100) (100) (100)
[M - CO]'+ 426 470 516 472 516 562 558 602 650
(27) (8.0) (46) (5.7) (59) (6.7)
[M - 2CO]'+ 398 442 448 444 488 534 530 574 622
(19) (30) (7.2) (20) (57) (65) (6.2) (69) (44)
pounds. Characteristic fragment ions, corresponding to losses of carbonyl groups or ligand (L) from the molecular ion, were observed in all spectra except FD and are discussed in detail below (Tables I-IV). Loss of carbonyl groups usually occurred in preference to cleavage of other metal-ligand bonds, except in DCI where loss of protonated ligand (L) was the predominant fragmentation pathway. Two aspects of the data are consistent with knowledge from other carbonyl studies. First, the observation of complex ions with less than five carbonyls as in M(C0)4Lis consistent with the ground-state knowledge for M(CO),L, molecules, such that the carbonyl fragment ions which have eliminated CO groups contain more stable M-CO bonds than their precursors (21-23). The reason for this is that Mo-CO da-a* back bonding from the soft metal center increases with the loss of some of these strongly a-accepting CO ligands. Second, the dominance of four-coordinate species, [M(C0)3PPh3]'+,is consistent with the fact that the ligand
[M - 3CO]'+ 370 414 460 416 460 506 502 546 594
(10) (6.3) (52) (7.7) (5.0) (65) (12)
[M - 4CO]'+ 342 386 432 388 432 478 474 518 566
[M - 5CO]'+
(24) (17)
314 358 404 360 404 450 446 490 538
(8.0) (5.7) (9.2) (7.0) (7.2) (6.7)
(93) (100) (98) (100) (100) (100) (71) (68) (29)
[LIS+ 262 306 352 262 306 352 262 306 352
(100) (14) (15) (19) (34) (36) (10) (68) (19)
I
ll
350
50
I Il
Il 474
I,
,
400
k58
130
Figure 1. Positive ion E1 mass spectrum of W(CO),P(C,H,),
K80
1318
ANALYTICAL CHEMISTRY, VOL. 60, NO. 13, JULY 1, 1988 203
A
R
I
I
1
p. b
t
I
b
,
,11111, 260
,
, ,,,
I
,,
288
328
388
348
368
388
188
428
408
T I
I
Ill 58-
118 E
t5.0
I,,,
11,//
1111.
558
508
450
440
11111.
sse I
Figure 2. Positive ion DCI mass spectrum of W(CO)5P(CeH,)3using (A) isobutane and (B) xenon as the reagent gas. The isobutane DCI mass spectrum (A) was obtained during a single scan, whereas the xenon DCI data (B) was acquired by using the multichannel analyzer of the data system and represents the sum of three successive scans. 188 R 100,
488
588
528
548
568
588
688
n/z
Figure 3. PosWe ion FD mass spectrum of W(CO)5P(C,H5h. Because no fragmentation was observed, the molecular ion region has been expanded for clarity. The theoretical molecular ion isotope distribution is shown for comparison.
field stabilization energy of such structurally predicted square planar species (LFSE (spl)) would be nearly as large as the octahedral (LSE(o)) for these high-field ligands in the stable parent molecule, M(CO)5PPH3(24). The appearance of the molecular ions and fragment ions containing multiisotopic metal atoms was characterized by the isotope pattern of the metal atoms, which facilitated the interpretation of the mass spectra (Figures 1-4). Except for the expected variation from scan to scan caused by noise or other experimental factors, isotope patterns were identical with the theoretical values with respect to mass-to-charge and relative abundance. For il-
lll.1.
I,I,.,..
,I/,/,
588
520
540
568
588
688 W Z
Flgure 4. Positive ion FAB mass spectrum of W(CO)5P(CeH5)3. Matrix ions are indicated by an asterisk.
lustration, mass spectra of one compound, W(CO)5P(C6H5)3, are presented in Figures 1-4. All other mass spectrometric data are presented in Tables I-IV. E1 Mass Spectra. As summarized in Table I, E1 mass spectra of monosubstituted transition-metal carbonyls were characterized by molecular ion radicals and a series of fragment ions due to the loss of neutral carbon monoxide molecules. Molecular ions, M + , were detected for all nine carbonyls ranging from a relative intensity of 10% in the E1 mass spectrum of Cr(CO)5As(C6H5)3 to the base peak in the spectrum of W(CO)5Sb(C6H5)3.Loss of all five carbon monoxide groups, [M - 5CO]'+, usually resulted in the base peak of the mass spectrum. Also prominent were the [M - 2CO]'+ ions, but losses of one and three carbon monoxide neutrals, [M CO]'+ and [M - 3CO]'+, were not favored. In general, the extent of fragmentation tended to decrease with increasing molecular weight, and the molecular ions were more abundant for the heavier compounds (Table I). The relative intensity of the ligand fragment ion, [L]'+, also tended to decrease with the mass of the ligand, [P(C,H,),]'+ > [As(C6H&]*+> [Sb(C,H,),]'+ and is consistent with the R acidity order PR3 < AsR3 SbR3. Other fragment ions pertaining to the ligand were formed by loss of one or more phenyl groups from the ligand, L, or loss of the ligand along with carbonyls from the molecular ion (not shown in Table I). Doubly charged molecular ions were sometimes observed but, relative to the singly charged molecular ion, were less than 20% as abundant. [M - L]" ions were not detected. DCI Mass Spectra. Like E1 mass spectra, DCI spectra contained molecular ion radicals, Ma+,and fragment ions corresponding to elimination of neutral CO molecules (Table 11). However, DCI mass spectra were distinguished by prominent protonated ligand ions, [L + HI+, which were sometimes the base peaks of the spectra. Only these ligand ions showed protonation by the isobutane reagent gas. The heavier carbonyls produced more abundant molecular ions and less fragmentation than the lower mass compounds (Table 11), which was also the trend observed in EI. The relative abundances of fragment ions resulting from neutral losses of CO from the molecular ion tended to be smaller in DCI than in EI, probably because of the dominance of the protonated ligand ions. However, molecular ions were as abundant relative to the base peak in DCI as in E1 (Tables I and 11). Although protonated molecular ions were not observed, the initial step in the formation of the abundant [L + H]+ fragment ions was probably protonation of the ligand (L) group as part of the intact molecule, M(CO)5L. This should have occurred on either the ligand group L or CO instead of the metal atom because of the higher affmity of these ligands. The protonated substituted metal carbonyl complex apparently
* 468
488
680
M/Z
11.
468
-
ANALYTICAL CHEMISTRY, VOL. 60, NO. 13, JULY 1, 1988
decomposed immediately to form [L + HI+ or [CO + HI+ and a neutral fragment containing the transition metal. Ions appearing below m / z 100, such as [CO + HI+, were not recorded because of the overwhelming abundance of reagent gas ions in this mass range. Therefore, [L + H]+ was detected as the base peak in many of the DCI mass spectra. The origin of the molecular ion radicals (M'+) and their daughter ions formed by elimination of neutral molecules was probably charge-exchangereactions within the DCI ion source. The isobutane reagent gas contained proton-donating species, predominantly [C4H9]+,responsible for the formation of the protonated ligand species described above (25). However, charge-exchange reactions between radical cations like [C4H,,]'+ and the neutral metal complex, M(CO)&, could have formed molecular ions [M(CO),]'+. In order to further investigate this ionization process, xenon was substituted for isobutane as the reagent gas, and DCI mass spectra were acquired as before. Because xenon is aprotic, the reagent gas species were Xe'+ and Xe2+instead of protonated ions. If ionization were to occur under these conditions, then charge exchange was expected to be the primary mechanism. The results, shown in Figure 2B, support ionization by charge exchange because the molecular ion radical cation, M'+, and the fragment ions formed by elimination of neutral CO groups dominated the spectra. Protonated ions corresponding to the ligand, L, including [L + H]+ were greatly diminished in abundance relative to the molecular ion. FD Mass Spectra. Field desorption (FD) mass spectra were unique, because only the molecular ions, Me+,were detected for all nine carbonyls. (See Table 111.) There was no fragmentation. (See Figure 3 for comparison of the theoretical and measured molecular ion distributions for W(C0)5P(C6H6)3 using FD.) In FD, ionization occurs by removal of an electron from the sample molecule in a high electric field, so that only sufficient thermal energy must be added to cause surface mobility of the sample. Therefore the excess thermal energy which led to fragmentation in EI, DCI, and FAB was absent from molecular ions formed by this soft ionization process, and no fragmentation was observed. Furthermore, the absence of matrix ions, adducts, or other matrix effects in this matrix-free system simplified these mass spectra compared to those obtained by FAB ionization, which are discussed in the next section. FAB Mass Spectra. Because FAB is a matrix-mediated ionization technique, preliminary experiments were carried out to determine a suitable FAB matrix for the analysis of the carbonyls used in this investigation. No sample ions were detected when using matrices of glycerol, thioglycerol, or 3-nitrobenzyl alcohol, presumably because of the instability of the sample in protic solvents, which led to decomposition prior to ionization. When 18-crown-6ether in tetraethylene glycol dimethyl ether was used as the matrix (19),both molecular ions and numerous fragment ions were formed in abundance for all nine carbonyls. Molecular ion radicals, M + , were detected instead of protonated species and accounted for the base peaks in the spectra of the three tungsten derivatives and pentacarbonyl(tripheny1phosphine)chromium (Table IV and Figure 4). Fragmentation in FAB was surprisingly extensive considering that no fragment ions were formed in FD (Tables I11 and IV). Compared to EI, the relative abundances of fragment ions were greater, and the same types of fragmentation occurred (Tables I and IV). Ions corresponding to loss of one, two, three, or four carbon monoxide neutrals from the molecular ion were more abundant in FAB than in E1 or DCI mass spectra. Loss of all five carbonyls, [M - 5CO]'+, generally remained the predominant fragmentation pathway, but it was less extensive. Ligand fragment ions, [LIB+instead of [L +
1317
ass t ~ - f f i ~ - ~ , n , ~ +
?3a
I
I
1
UTI!
-17.
Figure 5. B/E linked scan of W(CO)5P(C,H5), using positive ion FAB. The mass spectrum represents the sum of nine scans accumulated with a multichannel analyzer on the DA5000 data system.
HI+, were detected but were lower in abundance relative to the base peak compared to E1 mass spectra. Like E1 and DCI, FAB produced more extensive fragmentation for the lower mass compounds. For example, the FAB mass spectrum of Cr(C0)~(C6H5)3 (molecular weight 454) showed fragment ions corresponding to loss of one, two, three, four, and five carbon monoxide neutrals from the molecular ions with [M - 5CO]'+ as the base peak, while the spectrum of W(C0)5Sb(C6H5)3 (molecular weight 678) contained the fragment ions [M 2CO]'+ and [M - 5CO]'+, corresponding to loss of only two and five carbonyl groups with the molecular ion as the base peak (Table IV). Matrix ions were observed in all FAB spectra with the largest peaks occurring at mlz 529, 527, 485, 265, and 263 (Figure 4). Because some overlap of matrix and sample ions occurred in the low mass region of the spectrum (primarily in the region containing the ligand fragment ions), the matrix background contribution was subtracted and yielded the mass spectra summarzied in Table IV. The matrix spectrum used for background subtraction was obtained immediately preceding each sample analysis and under identical measurement conditions. B/E Linked Scans. Because FAB mass spectra of monosubstituted transition-metal pentacarbonyls have not been previously reported, metastable analyses were carried out by using B / E linked scanning with collisional activation to confirm the fragmentation pathways discussed above. The B/E linked scan of W(CO)6P(C,&)3 is presented in Figure 5. Fragmentation of the molecular (or parent) ion at m/z 586 in the first field-free region of the mass spectrometer produced daughter ions at m / z 558, 530, 502,474, and 446 corresponding to loss of one, two, three, four, and five carbon monoxide neutrals. This confirms that these fragment ions were formed from the molecular ion and were not contaminants such as matrix ions. Matrix ion peaks were eliminated by use of the B/E linked scan. The daughter ion at m/z 369 resulted from loss of five carbon monoxide neutrals plus a phenyl radical, [M - 5CO - C6H6]+. The ion corresponding to the triphenylphosphine ligand was present at m/z 262 but at very low relative abundance. Multistep fragmentation might contribute to the greater abundance of this ion in conventional FAB mass spectra.
CONCLUSIONS The comparison of four ionization techniques for the analysis of monosubstituted Cr, Mo, and W metal pentacarbonyls by mass spectrometry has indicated strengths and weaknesses of each method for particular applications. Because FD formed molecular ions without fragmentation, this
Anal. Chem. 1988, 60, 1318-1323
1318
would be the method of choice for molecular weight confirmation. DCI with isobutane produced the most abundant ligand (L) fragment ions and the most structural information for this substituent. E1 and FAB spectra contained both molecular and fragment ions and the most complete structural data. Although E1 was more sensitive than FAB, FAB formed more abundant molecular ions and fragment ions such as [M - 3COj'+ and [M - 4CO]'+, which were often not observed in E1 spectra. Therefore FAB would be the best single ionization technique for the analysis of substituted transition-metal carbonyls by positive ion mass spectrometry. These results for nine complexes might be indicators for the mass spectrometric behavior of the very large class of neutral transition-metal carbonyls. We are expanding this investigation to include mixed ligand complexes (CS in place of a CO) and multiply substituted carbonyls. Investigations are also in progress to evaluate negative ion formation by these ionization methods.
ACKNOWLEDGMENT The authors thank Tetsuo Higuchi of JEOL, USA, Inc., for his technical assistance with the FD measurements. Registry NO. Cr(CO)5P(C6H5)3, 14917-12-5;Cr(CO)&(C6H5)3, C6H5)3, 29742-98-1; Cr (CO),Sb( C6H5)3,29985-15-7; Mo(co)5P( 14971-42-7;Mo(CO)&(C,H5),, 19212-22-7;Mo(CO)~S~(C~H,)~, 19212-21-6; W(CO)5P(CsH5)3, 15444-65-2; W(CO)~AS(C~H~),, 29743-02-0; W(CO)5Sb(CsH5)3, 29743-03-1; Xe, 7440-63-3; isobutane, 75-28-5. LITERATURE CITED (1) Leconte, M.; Basset, J. M. J. Am. Chem. SOC. 1979, 101, 7296-7302. (2) Tamagaki. S.;Card, R. J.; Neckers, D. C. J. Am. Chem. Soc. 1978, 100, 6635-6639. (3) Magee, T. A.; Matthews, C. N.; Wang. T. S.; Wotiz, J. H. J. Am. Chem. SOC.1981, 8 3 , 3200-3203.
(4) Hyde, C.L.; Darensbourg, D. J. Inorg. Chim. Acta 1973, 7 , 145-149. (5) Lewis, J. Manning, A. R.; Miller, J. R.; Wilson, J. M. J. Chem. SOC.A 1986. 1663-1670. (6) Pignataro, S.; Foffani, A.; Innorta, G.; Dlstefano, G. Adv. Mass. Spectrom. 1968, 4 , 323-332. (7) Distefano, G.; Innorta, S.; Pignataro, S.; Foffani. A. J. Organomet. Chem. 1988, 1 4 , 165-172. (8) Innorta, G.; Distefano, G.; Pignataro, S. Int. J . Mass Spectrom. Ion. Phys. 1968, I , 435-442. (9) Bond, S. T.; Duffy, N. V. J. Inorg. Nucl. Chem. 1973, 3 5 , 3241-3247. .._ (10) Torroni, S.; Innorta, G.; Foffani, A,; Distefano, G. J. Organomet. Chem. 1974. 65. 209-213. (11) Operti, L.; Vagiio, G. A.; Volpe. P.; Giancaspro. C.; Margonelii. A,; Speranza, M. Ann. Chim. (Rome) 1984, 7 4 , 687-698. (12) Gambino, 0.; Michelin-Lausarot, P.; Vaglio, G. A,; Vaile, M.; Volpe, P.; Operti, L. Transition Met. Chem. (Weinheim, Ger.) 1982, 7 , 330-332. (13) Cetini, G.; Michelin-Lausarot, P.; Operti, L.; Vaglio, G. A,; Valle, M.; Volpe, P. Int. J. Mass Spectrom. Ion. Processes 1985, 6 4 , 25-31. (14) Cetini, G.;Michelin-Lausarot, P.; Operti, L.; Vaglio, G. A,; Vaiie, M.; Volpe, P. Transition Met. Chem. (Weinheim, Ger .) 1983, 8 , 380-382. (15) Bruins, A. P. Anal. Chem. 1980, 52, 605-607. (16) Cotter, R. J. Anal. Chem. 1980, 52, 1589A-1602A. (17) Wuerminghausen, T.; Reinecke, H. J.; Braunstein, P. Org. Mass Spectrom. 1980, 15, 38-40. (18) Barber, M.; Bordoii, R . S.;Sedgwick, R. D.; Tyler, A. N. J. Chem. SOC Chem. Commun. 1961, 325-327. (19) Minard, R. D.; Geoffroy, G. L. Paper presented at the 30th Annual Conference on Mass Spectrometry and Allied Topics, Honolulu, HI, June 6-11, 1982. (20) Poilblanc, R.; Bigorgne, M. Bull. SOC. Chim. F r . 1962, 1301-1325. (21) Cotton, F. A.; Kraihanzei, C. S. J. Am. Chem. SOC. 1962, 8 4 , 4432-4438. (22) Kraihanzei, C. S.;Cotton, F. A. Inorg. Chem. 1983, 2 , 533-540. (23) Cotton, F. A. Inorg. Chem. 1964, 3 , 702-711. (24) Basolo, F.; Pearson, R. G. Mechanisms of Inorganic Reactions: a Study of Metal Complexes in Solution; Wiley: New York, 1988. (25) Field, F. H. J. Am. Chem. SOC. 1989, 91, 2827-2839. .1
RECEIVED for review August 27,1987. Accepted February 21, 1988. This investigation was supported by Grant 86-U-00790 from the North Carolina Biotechnology Center and was presented at the 35th ASMS Conference on Mass Spectrometry and Allied Topics, May 24-29, 1987, in Denver, CO.
Determination of Naphthenic Acids in California Crudes and Refinery Wastewaters by Fluoride Ion Chemical Ionization Mass Spectrometry Ismet Dzidic,* A. C. Somerville, J. C. Raia, and H. V. Hart Shell Development Company, Westhollow Research Center, P.O. Box 1380, Houston, Texas 77251
A method based on negative ion chemlcal ionization mass spectrometry udng fluorlde (F-) ions produced from NF, reagent gas has been applied to the analysis of naphthenlc aclds In Caltfornla crude olls and refinery wastewaters. Slnce complex mixtures of naphthenic aclds cannot be separated Into indlvkluai components, only the determination of relative distribution of aclds classified by the hydrogen deficiency was possible. The identities and relative distribution of paraffinic and mono-, dC, tri-, and hlgher polycyclic acids were obtained from the intensities of the carboxylate (RCOO-) ions.
Crude oils are known to contain carboxylic acids that are often called naphthenic or petroleum acids. The acid content of crudes varies from 0% to 4% and is particularly high in California San Joaquin Valley crudes. Seifert and Teeter ( I )
found that these crudes contain a complex mixture of acids, the predominant types being mono-, di-, tri-, and polycyclic structures. Their analyses were very elaborate and involved exhaustive extraction, separation, and chemical reaction steps prior to the characterization by various spectroscopic techniques. The analysis of naphthenic acids is of major importance for the studies of geochemical correlations, biodegradation mechanisms (2)) and corrosion problems at refineries. Also, the fate of the acidic compounds throughout the refining process must be known in order to develop appropriate source control measures and wastewater treatment methods that will ensure compliance with environmental permit requirements. Therefore, there is a continuing demand for improved methods for the analysis of acids in petroleum-related samples. Some of the published work has relied on the use of the gas chromatography/mass spectroscopy (GC/MS) technique with
0003-2700/88/0360-1318$01.50/00 1988 American Chemical Society
