Anal. Chem. 1982, 5 4 , 1108-1113
1108
selected. In the present case, the monitoring of the molecular anion was possible only when a relatively large amount of Firemaster BP-6 was present. To achieve the goal of low detection limits, we monitored the bromine fragment anions. This provided significantly lower detection limits and, a t the same time, considerably increased specificity with respect to electron capture gas chromatography. In addition to the chromatographic retention times, which are common to both techniques, the present method increases specificity because only one particular mass, that of the bromine anion, is monitored. Thus, only compounds yielding a contribution to the m l e = 79 mass may interfere. In addition, the mle = 81 peak may also be monitored for proper isotopic ratio, thus, in fact, only bromine-yielding compounds may conceivably interfere. Areas of Application. The technique reported here provides an approximately 20-fold decrease in detection limits and increased specificity over electron capture gas chromatography. The method is thus well suited to the analysis of serum samples containing low levels of PBB such as in the borderline cases that occur in the general population, and also for the study of changes in the relative quantities of individual brominated biphenyls in samples from directly exposed individuals (such as chemical workers) and also those indirectly exposed through the food chain. In addition, the low detection limits allow for the search for PBBs in separated blood compartments and other tissues. Such studies are now in progress in this laboratory.
Matthews, H.; Kato, S.; Morales, N.; Tuey, D. J. Toxicol. Environ. Health 1977, 3 , 599. Ballschmiten, K.; Zell, M.; Neu, M. Chemosphere 1878, 7 ,173. Wlllett, L.; Brumm, C.; Williams, C. J. Agric. Food Chem. 1978, 26, 122. Domino, E.; Domlno, S. J. Chromatogr. 1980, 197,258. Farrell, T. J. Chromatogr. Sci. 1880, 16, 10. Burse, W.; Needham, L.; Liddle, J.; Bayse, D.; Price, H. J. Anal. ToxiCOl. 1980, 4, 22. Wolff, M.; Haymes, N.; Anderson, H.; Selikoff, I. EHP, Envlron. Health ferspect. 1878, 23, 315. Dannan, G.; Moore, R.; Aust, S. EHP, Envlron. Health Perspect. 1978, 23, 51. Robertson, L.; Parkinson, A.; Safe, S. Toxicol. Appl. fharmacol. 1981, 57,254. Patterson, D.; Hill, R.; Needham, L.; Orti, D.; Kimbrough, R.; Liddle, J. Science 1981, 213, 901. Wolff, M.; Anderson, H.; Camper, F.; Nikaido, M.; Daum, S.; Haymes, N.; Selikoff, I. J. Envlron. fathol. Toxicol. 1879, 2 , 1397. Wolff, M.; Anderson, H.; Rosenman, K.; Selikoff, I. Bull. Envlron. Contam. Toxicol. 1978, 2 1 , 775. Domino, E.; Flvenson, D.; Domino, S. Drug Metab. Dispos. 1980, 8 , 332. Bekesi, J.; Holland, J.; Anderson, H.; Fishbein, A,; Rom, W.; Wolff, M.; Selikoff, I. Science 1978, 199, 1207. Roboz, J.; Suzuki, R.; Bekesi, J.; Holland, J.; Rosenman, K.; Sellkoff, I. J. Environ. fathol. Toxicol. 1980, 3 , 363. Hass, J.; Frlesen, M.; Harvan, D.; Parker, C. Anal. Chem. 1978, 50, 1474. Crow, F.; Bjorseth, A,; Knapp, K.; Bennett, R. Anal. Chem. 1881, 53, 619. Greaves, J.; Bekesi, G.; Roboz, J. Biomed. Mass Spectrom., in press. Dougherty, R., personal communication. Jacobs, L.; Chou, S.; Tiedje, J. J. Agric. Food Chem. 1976, 24, 1198. Hass, J.; McConnel, E.; Harvan, K. J. Agric. Food Chem. 1878, 26, 94. Domlno, E.; Wright, D.; Domino, S. J. Anal. Toxicol. 1980, 4 , 299.
LITERATURE CITED (1) Anderson, H.; Wolff, M.; Lilis, R.; Holstein, E.: Valciukas, J.; Anderson, K.; Petroccl, M.; Sarkozi, L.; Sellkoff, I. Ann. N .Y . Acad. Sci. 1878, 320, 664. (2) Gupta, B.; McConnell, E.; Harris, M.; Moore, J. Toxlcol.Appl. fharmacol. 1981, 57,99.
RECEIVED for review October 8, 1981. Accepted March 19, 1982. This research was supported by the National Institute of Environmental Health Sciences (Contract NO-1-ES-9-0004) and by the National Cancer Institute (Grant 5Pll-CA-15936).
Evaluation of Fast Atom Bombardment Mass Spectrometry for Identification of Nitrogen-Containing Compounds in Fossil Fuels R. D. Grlgsby," S. E. Scheppele," Q. G. Grlndstaff, and G. P. Sturm, Jr. U.S. Department of Energy, Bartlesville Energy Technology Center, Bartlesville, Oklahoma 74003
L. C. E. Taylor, H. Tudge, C. Wakefield, and S. Evans Kratos Scientific Instruments, Ltd., Manchester, England
The appllcablllty of fast atom bombardment mass spectrometry (FAB/MS) to the analysis of fossil fuel materials has been explored hy acquiring FAB mass spectra of 20 nitrogenous bases and a base fraction from anthracene oil. The spectra are characterized by slgnlflcant M+-, (M H)', and (M - H)+ Ions. Fragmentation parallels that expected for electron impact (EI)and chemlcal Ionization and several fragmentation pathways are proposed from the observatlon of peaks corresoondlng to metastable-Ion decomposltlons. Comparlson of the FAB spectrum of the base fractlon with a fleld lonlzatlon ( F I ) spectrum recorded earller reveals that many of the molecular Ions appearlng In the F I spectrum are shlfted to (M H)' Ions in the FAB spectrum. The M+. and (M -k H)+ Ions In the FAB spectrum of the base fraction are used to classify Its components by nomlnal-mass 2 serles. Thls classlflcatlon Is in agreement with one deduced from hlgh-resolution mass spectral data recorded earller.
+
+
0003-2700/82/0354-1108$01.25/0
Fast atom bombardment mass spectrometry is a new technique that has been developed to provide spectra of underivatized polar molecules. To date, almost all reported applications have been made on compounds having biological significance (1-6). Because of the interest in the structures of polar molecules existing in coal and petroleum, we decided to apply FAB/MS to a number of nitrogenous bases representative of those found in fossil fuels and to a base fraction separated from anthracene oil to determine whether the technique has potential for analyzing nitrogenous samples of interest to the energy industry. EXPERIMENTAL SECTION Instrumentation. The FAB ion source was a prototype developed by Kratos Scientific Instruments, Ltd., and was fitted to an MS-80 mass spectrometer. All spectra were recorded oscillographically at low resolution with an accelerating potential of 4 kV and a scan rate of 100 sldecade. The pressure in the 0 1982 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 10:
93
1
OH
OH
54,NO. 7, JUNE 1982
*
(M*i)'
C3H803
4
I
m / Z 93 (100%)
A
OH
OH
+
m / Z 185 (29%)
m / Z 75 ( 2 4 % )
0
1109
20
40
EO
I00
80
120
140
1EO
180
m / Z 75(24%)
200
a/2
Ho
Figure 1. Partial FAB spectrum of glycerol. Asterisks indlcate that
peaks corresponding to metastablaion decompositions were observed. ion-source housing was maintained within the lo4 torr region. Method. A copper target on the end of a direct-introduction probe was cleaned with nitric acid, rinsed with distilled water, and dried with a paper towel. One drop of glycerol was placed on the target and -1 mg of sample was added from the end of a 1 mm 0.d. capillary tube. The mixture was then stirred with the tube to form ai film of solution over the face of the target. After the sample was degassed for 1min in the vacuum lock of the mass spectrometer, the probe was inserted into the ion source, the high voltage was turned on, and the spectral recording was started. Samples. All model compounds (Aldrich Chemical Co., Inc., Milwaukee, WI) were of reagent grade purity. The base fraction was separated from anthracene oil in a procedure described in the literature (7).
=L .+ L-
m / Z 5 7 (19 % )
Figure 2. Partial fragmentation of glycerol. Relative intensities are
shown In parentheses,
CH3
CH3
m / Z 98 (100%)
m / Z 99 ( 9 0 % )
N
RESULTS AND DISCUSSION The ion source consists of a fast-atom gun, a copper target on which the sample is deposited in glycerol or some other low-volatility solvent such as a polyglycol ether, and conventional focusing plates for accelerating the ions toward the analyzer region of the instrument. Argon ions with controlled energies between 4 and 6 keV are produced by a cold-cathode discharge (8, 9) or by other means (IO). These ions collide with Ar atoms a t a pressure of to torr. Resonant charge exchange occurs, resulting in an Ar-atom beam in which the atoms have virtually the same kinetic energy as the Ar ions. These fast atoms are then ejected from the gun to bombard the target. The technique, which is related to secondary ion mass spectrometry, requires that a new surface be continually exposed to the bombarding atoms. With the sample dissolved in a low-volatility solvent, molecules can diffuse to the surface continuously, replacing those that have been ionized. In a typical experiment, spectra can be recorded for 20 min or longer before the sample is gone. The spectrum of the solvent appears along with that of the sample and must be taken into consideration when a spectral interpretation is made. Figure 1 shows the partial FAB spectrum of glycerol and exemplifies the cluster ion formation which occurs during the sputtering process. Peaks at m / z 93, 185, ...,correspond to n(M + H)' where n = 1, 2, ..., and M is the molecular mass of glycerol. These peaks are observable a t least to mlz 829, and metastable-ion decompositions show that the lower mass species are formecl from those of higher mass by loss of glycerol molecules. The spectrum also shows that ions are formed by loss of H20from other ions. For example, mlz 75 arises from rnlz 93 by loss of water. The partial fragmentation of glycerol as supported by the observation of peaks from metastable ion decompositions is
CH3
CH3
m / Z 84 (34%)
m / Z 99 ( 9 0 % )
Figure 3. Partlal fragmentation of 1,2-dimethyIpyrrolidine.
shown in Figure 2. Two glycerol molecules held together by a proton bridge between two oxygens lose one glycerol to form the (M H)+ion at mlz 93. For convenience, the bridge is shown between oxygens in the 2-position although no evidence exists to rule out other possibilities. By a two-electron shift mechanism, water is ejected from mlz 93 to give m/z 75. This ion then undergoes hydrogen rearrangement before losing water to give the ian a mlz 57. Whether the rearranged hydrogen is originally located in the 3-position, as shown in the figure, depends on the charge location and on other factors. The possibility of hydrogen scrambling before water loss cannot be ruled out from existing evidence. Table I shows the samples run by FAB/MS together with the masses and intensities of major ions in the spectra. Most of the model compounds give spectra that are characterized by significant M+., (M H)+, and (M - H)+ ions. Fragmentation generally parallels that expected for electron-impact and chemical ionization, and the existence of many of the ions is explained by unimolecular decomposition in the gas phase. Proton transfer to M from the mlz 93 ion of glycerol or from other protonated species accounts for the formation of the (M H)+ions. This reaction probably takes place on the surface of the liquid. The generation of molecular ions is not explained as easily. If these are formed in the gas phase from (M H)+, odd-electron ions and hydrogen radicals would appear as products of the reaction. Because this is not a favorable process (11),it is more probable that the reaction takes place on the liquid surface where OHcan be removed rapidly by reaction with other species. The spectrum of sample I (1,2-dimethylpyrrolidine) shows strong (M - H)+ and (M - CH3)+ions at m/z 98 and 84, respectively. The origin of these ions is explained by gas-phase a-cleavage mechanisms as seen in Figure 3. The presence of six hydrogens on carbons adjacent to the nitrogen probably
+
+
+
+
ANALYTICAL CHEMISTRY, VOL. 54, NO. 7, JUNE 1982
1110
Table I. Samples Run by Fast Atom Bombardment Mass Spectrometry sample no
structure
M'.
I
99 ( 9 )
I1
85 (64)
(M
+ H)'
100 ( 2 )
86 (100)
mass (re1 intens) (M - H)'
other
98 (100)
97 (10); 96 (16); 9 1 ( 7 ) ; 84 (34); 82 (16); 70 (20)
84 (28)
87 (160); 70 (49); 6 8 (40)
I11
1 1 3 (24)
114 (68)
1 1 2 (100)
98 (104); 94 (28); 69 (27); 6 8 (15); 56 (44); 55 (40)
IV
1 2 1 (62)
1 2 2 (100)
120 (15)
106 ( 7 )
K
80 (91)
VI
136 (100)
137 (70)
1 3 5 (23)
1 3 8 (55); 131 (25); 119 (43); 100 (72); 97 (22)
VI1
1 2 9 (100)
130 (69)
128 (30)
103 (9); 1 0 2 (13); 101 ( 9 )
1 2 9 (78)
130 (100)
1 2 8 (34)
103 (19); lOZ(18); 101 (12)
1 4 5 (100)
146 (42)
144 (11)
128 ( 4 ) ; 117 (38); 116 (17); 90 (15); 89 (23)
1 5 9 (95)
160 (100)
1 5 8 (18)
1 4 5 (5); 144 (7); 130 (16); 1 2 9 (13);1 2 8 (21); 117 (33); 116 (28)
174 ( 2 0 )
1 7 5 (100)
173 (-)
1 6 1 (12); 160 (17); 159 (20); 1 2 8 (38); 115 (25); 101 (18)
159 (10)
1 6 0 (100)
158 (-)
133 (76)
134 (73)
132 (100)
1 3 1 (20); 1 3 0 (53); 1 1 8 (28); 117 (42); 1 0 6 (27); 1 0 5 (29); 104 (17); 91 (38)
119 (100)
1 2 0 (41)
118 (100)
117 (2G); 91 (19); 77 (12)
1 4 5 (100)
146 (18)
144 (52)
1 3 0 (8); 1 6 5 (13)
1 7 3 (22)
174 (100)
172 (4)
1 5 8 (25); 132 (18); 1 3 0 (10)
1 7 9 (15)
180 (100)
1 7 8 (5)
152 ( 4 )
XVIII
1 9 3 (15)
194 (100)
1 9 2 (11)
XIX
1 7 9 (40)
180 (100)
178 (13)
VI11
IX
m N
($Q
81 (100)
79 (21)
OH
X
cH3y33
XI OH
XI
XI11
XIV
xv
QxCH3 CH3
e XVI H
XVII
m
152 (15); 147 (17); 1 3 3 (12)
ANALYTICAL CHEMISTRY. VOL. 54, NO. 7, JUNE
1982 1111
Table I (Continued) mass (re1 intens) sample no.
structure
M'.
xx
167 (45)
XXI
+
H)'
other
(M - H)+
168 (100)
166 (13)
base fraction from anthracene oil
m/z
Flgura 4.
(M
91 119%)
Partial fragmentation of 2.3-cyclopentenopyrMine
accounts for the strong intensity of the (M - H)+ ion as compared to the intensities of the other ions in the spectrum. Similar reasoning explains the presence of intense (M- H)+ ions in the spectra of samples I11 and XV and the intense (M - CH3)+ion in the spectrum of 111. Two peaks corresponding to metastableion decompositions were observed in the spectrum of XIV (2,3-cyclopentenopyridine). One of these shows that the m / z 118ion arises from m / z 119 by loss of .H.See Figure 4. The ion could be formed by loss of H, from the (M+ H)+ion at m / z 120 although loss of H, from molecular ions formed by electron impact is not a common occurrence (Z2,13). A metastable-ion decomposition was observed for the loss of 27 mass units from m / z 118 to give m / z 91. Presumably, the neutral species is HCN and m / z 91 is the tropylium ion (14). A second possibility is that CzH3.is last from m / z 118, giving an ion of cumpition C,H,N*. for m / z 91. This reaction is energetically unfavorable, however, for the reason cited above (ZZ). Although peaks from metastableion decompositions were not observed in the spectrum of XI11 (2,3-cyclohexenopyridine),the similarities of its structural and spectral features with those of XIV suggest that the mechanisms shown in Figure 4 explain the formation of m / z 132 and m / z 105 in the spectrum of XIII. The presence of some of the ions in the spectra of the compounds listed in the table is not readily explained. The strong '(M + 2)" ions in the spectra of I1 (2-methyl-2-oxazoline) and VI (tetramethylpyrazine) may be molecular ions of the saturated analogues present as impurities. Significant ions a t m / z 100 and 119 in the spectrum of VI cannot occur by loss of one or more common neutrals from the M+. or (M + H)+ ions. Therefore, they probably originate from impurities. Also, the presence of impurities may explain the ions at m / z 133 and 147 in the spectrum of XIX (I&henzoquinoline). One or more ions in the spectra of the quinolines are explained by the loss of HCN from M+., (M+ H)+, or (M - H)+.This loss is known to occur from M+.in the electron-impact fragmentation of heterocyclic compounds containing nitrogen (14). Another possible explanation for the presence of some of the anomalous ions is a reaction between sample and solvent in a manner not presently understood. Further experimentation would be required to establish the origin of these ions. The FAB spectrum of the base fraction separated from anthracene oil is shown in Figure 5. By comparison with the
.
D
I P ,.
~
.
. ~. , , I
j
. I
I' I
.
.
, t.
T
-
,.
~
.
~
,
: a
,,
spectrum of a base fraction separated from anthracene oil. Resolution -1100. Peaks at m l z 185 and 186 (glycerol background) have been omitted.
Figure 5. FA0 mass
I
Ii'
~-uno. I
Figure 6. F I mass spectrum of a base fraction separated from anthracene ou. resolution -2200.
FI spectrum of the sample (15) seen in Figure 6, it is apparent that the two spectra are similar except that many of the molecular ions observed in the latter spectrum are shifted to (M + H)+ ions in the FAB spectrum. Therefore, FAB mass spectra contain much of the same information about complex mixtures as that present in the mass spectra from more conventional ionization methods. Figures 5 and 6 are diseuased in terms of the specific Z series and nominal-mass Z series concepts which were utilked in the development of mass spectrometric group-type met$ods for petroleum analysis (16-24). It is convenient to group the species encountered in fossil-fuel mass speccrometry 'into homologous series. Successive members of each homologous series differ in composition hy CH,. Therefore, these Z-series concepts are defined helow for the homologous entity CH, because the terminology is neither common to the various mass spectrometric disciplines nor defmed explicitly elsewhere. I t should be noted that these definitions are based upon the generalized defmitions given in ref 25. Let the general formula for species of present interest he
1112
ANALYTICAL CHEMISTRY, VOL. 54, NO. 7, JUNE 1982
1 2 C , 1 3 C , H , 2 H , ’ 4 N b 1 5 N c 1 6 0 d 1h....~ ~ ~The 2 ~ ~elements 3~~4~ carbon and hydrogen define the homologous unit of present interest. Thus, the specific 2 value for each series of homologous species, Z(H;Nb+cOd+eSf+g+h...), is by definition
Z ( H ; N ~ + ~ O ~ ~ e S ~E+xg + + ~u .-. .2(n ) + W)
(1) The specific 2 value for a species is independent of isotopic substitution. Consequently, a value of 2(H;Nb+cOd+eSf+g+h...) uniquely classifies all isomeric and homologous species and, hence, defines a group-type classification. For example, pyridine (C5H5N) and the three isomeric methylpyridines (CH3C5H4N)belong to the -5(H;N) specific 2 series independent of their isotopic substitution. The nominal mass or mass number of a species, NM, is the sum of its constituent protons and neutrons (25). Thus, the nominal masses for all species are members of the set of positive integers. A nominal-mass 2 series, NMZ:I;H), contains those species whose mass numbers satisfy eq 2 NMZ(1;H) = NM - 14ki (2) where 14 is the mass number of CH2 and ki is 0, 1, 2, 3, ..., such that -11 5 1 5 2. Since eq 2 is a modulo function, I is the remainder obtained from dividing NM by 14, where the set of all remainders for the homologous entity CH2 is chosen as -11 5 1 5 2 in order to adhere to conventional practice in fossil-fuel mass spectrometry (16-24). Thus, a nominal-mass Z series will contain species having the same nominal mass but differing in composition. For example, 4-butylpyridine (C9H13N) and 4-hydroxy-2,3-dihydroindole(C8HgNO) are compounds in the -5(H;N) and -7(H;N,0) specific 2 series, i.e., homologous series. Since the nominal mass for both compounds is 135, they are in the (-5;H) nominal mass 2 series; the notation is NMZ(-5;H). In order to uniquely classify the ions observed in a mass spectrum and, hence, the precursor neutral species according to homologous series requires that the ion masses be acquired at a resolution sufficient to separate ions having the same nominal mass but different carbon-12 masses. In contrast, the use of the nominal-mass 2 series concept requires a resolution of only one part in the ion’s nominal mass. Thus, both the nominal-mass and specific 2 series concepts are applicable to the interpretation of “high-resolution” mass spectral data. However, the former but not the latter concept is uniquely applicable to the interpretation of “low-resolution” mass spectral data. Although not apparent in the low-resolution spectra shown in Figures 5 and 6, many of the peaks represent multiplets. These were identified during earlier analyses on the base fraction by high-resolution mass spectrometry with ion formation by E1 and FI (7, 15). The results of these measurements are given in Table I1 which lists, as a function of seven odd-numbered nominal-mass 2 series, the dominant aromatic compounds containing nitrogen and nitrogen plus oxygen. The first mass in each series is given in the second column of the table, and subsequent masses are generated by adding 14n to the first mass where n = 1,2, -.. Thus, the odd-mass peaks in Figure 6 belong to one of the series listed in the first column and represent, in general, the presence of molecular ions having the elemental compositions given in the third column. The base fraction was analyzed twice by FI experiments performed at different times (7, 15). The results from both analyses are in good agreement if allowance is provided for enhanced sensitivity realized by improvements in instrumentation made before the second analysis was conducted (7). Quantitatively, both analyses agree w*ll on all but the minor components. In the first analysis, compounds belonging to the following Z series were identified: -5(H;N) through -23 (H;N); -27 (H;N); -1 5(H;N,O) ; -19 (H;N,O); a n d -2l(H;N,O). Although C8 and Cg homologues in the -5(H;N)
Table 11. Compound Types Identified in an Anthracene Oil Base Fraction as a Function of Odd-Numbered Nominal-Mass Z Series first mass in NMZ(1;H) series compound type +1
155
-1
153
-3
179
-5
121
-7
119
-9
117
-1 1
129 ..
-. .
.
series were identified in the first analysis, they could not be detected conclusively from the data acquired during the second analysis. On the other hand, data from the second analysis showed the presence of compounds in all Z(H;N) series from -7 through -39 and in all Z(H;N,O) series from -7 through -33. The results obtained in this study lead to several preliminary conclusions concerning FAB/MS as an analytical technique for liquid fossil fuels. The identification and quantification of the homologues of the various compound types comprising these materials are accomplished principally by mass spectrometry (26). The analytical methods require ionization techniques which produce ions uniquely attributable to the homologues of the various compound types and whose intensities can be quantitatively related to the amounts of each of these homologues. In this regard, either low-voltage electrons (27) or high-electric fields (28) are ideal for ionization because they produce essentially fragment-free mass spectra and molecular-ion intensities permitting the calculation of valid quantitative distributions. The data in Table I show that FAB, in general, produces mass spectra characterized by the presence of molecular, pseudomolecular, and fragment ions having relative intensities dependent upon the structure of the neutral precursor. Furthermore, FAB mass spectra contain ions derived from the compound used to dissolve/suspend the sample under analysis with the intensities of these ions being either enhanced or diminished in a rhanner which is not presently understood. Thus, as demonstrated by Figures 5 and 6, the result of these facts will be to increase the complexity of the FAB mass spectra of fossil energy-derived materials compared to the corresponding FI and low-voltage E1 mass spectra. The use of FAB/MS in detailed qualitative analysis will require resolution and mass measurement capabilities at least equal to those required in FI/MS and low-voltage EI/MS. With respect to the latter two techniques, the requirements often tax the capabilities of medium-resolution mass spectrometers, and hence the analyses benefit from state-of-the-art ultra-high-resolution mass spectrometers even if sophisticated methods are used to separate the material prior to mass spectrometric analysis. Thus, it appears that FAB/MS enjoys no particular advantage over either FI/MS or low-voltage EI/MS for the identification of compound types possessing masses up to ca. 600 amu. On the other hand, identification of higher-molecular-weightcompounds by either of the latter two techniques or field-desorption mass spectrometry suffers from major problems associated with sample
Anal. Chem. lQ82, 5 4 , 1113-1118
volatilization and technique implementation, respectively. Therefore, FAB/MS has considerable potential at least as a qualitative analytical technique in the higher mass range provided that sample siispension/dissolution techniques are developed which afford adequately intense ion beams. In this regard, i t should be noted that this exploratory research achieved no real success in producing FAB mass spectra of nitrogenous materials from heavy petroleum and coal liquids boiling in excesii of 500° C. Finally, conclusions concerning the use of FABIMS in quantitative analysis require detailed studies of the ionization/fragmentation mechanisms and of the intensities of significant ions per mole of neutral precursor as a function of molecular structure. However, the potential significance of F‘AB/MS to the emerging, significant field of high-mass/mass spectrometry applied to the analysis of liquid fossil fuels provides cogent justification for conducting basic research to determine its qualitative and quantitative capabilities. ACKNOWLEDGMENT We thank P. E. Pulley and D. N. Pope, Data Processing Center, Texas h&M TJniversity, College Station, TX, for providing the program used to process the bar-graph spectra. LITERATURE CITED (1) Surman. D. J.: Vlckertnan, J. C. J. Chem. SOC., Chem. Commun. 1981, 324-325. Barber, M.; Bordoll, R. S.; Sedgwick, R. D.; Tyler, A. N. J. Chem. SOC., Chem. Commun. 1981, 325-327. Barber, M.; Bordoll, R. S.; Sedgwlck, R. D.; Tetler, L. W. Org. Mass Spectrom. 1981, 16, 256-260. Barber, M.; Bnrdoli, R. S.;Sedgwick, R. D.: Tyler, A. N. Nature (London) 1981. 293. 270-275. (5) Taylbr, L. C. E:. ind. ResJDev. 1981, 23, 124-128. (6) Wllllams, D. H.; Bradley, C.; Bolesen, G.; Santlkarn, S.;Taylor, L. C. E. J. Am. Chem. SOC. 1981, 103, 5700-5704. (7) Scheppele, S.E.; Greenwood, G. J.; Panclrov, R. J.; Ashe, T. R. ACS Symp. Ser. 1981, No. 156, 39-73.
1113
(8) Beeck, 0. Ann. Phys. (Le@@) 1934, 19, 121-128. (9) Berry, H. W. Phys. Rev. 1949, 75, 913-916. (10) McDowell, R. A.; Dell, A.; Morris, H. R. Presented at the 29th Annual Conference on Mass Spectrometry and Allied Topics, Minneapolis, MN, May 24-29, 1981; Paper No. WAMOA3. II) McLafferty, F. W. “‘Interpretation of Mass Spectra”, 3rd ed.; University Science Books: Mlll Valley, CA, 1980; pp 48-50. 12) McLafferty, F. W. “‘Interpretation of Mass Spectra”, 3rd ed.; University Science Books: Mill Valley, CA, 1980; p 35. 13) Budziklewlcz, H.; Djerassi, C.; Williams, D. H. “Mass Spectrometry of Organic Compounds”; Holden-Day: Can Francisco, CA, 1967; p 23. 14) Budzikiewicz, H.; Djerassi, C.; Williams, D. H. “Mass Spectrometry of Organic Compounds”; Holden-Day: San Franclsco, CA, 1967; Chapter 20. (15) Grigsby, R. D.; Schronk, L. R.; Grindstaff, Q. G.; Scheppele, S. E.; Aczel, T. Presented at the 27th Annual Conference on Mass Spectrometry and Allied Topics, Seattle, WA, June 3-8, 1979; Paper No. MAMOA3. (16) Brown, R. A. Anal. Chem. 1951, 2 3 , 430-437. (17) Lumpkin, H. E.; Thomas, B. W.; Elllott. A. Anal. Chem. 1952, 24, 1389-1391. (18) Lumpkin, H. E.; Johnson, B. H. Anal. Chem. 1954, 26, 1719-1722. (19) Clerc, R. J.; Hood, A.; O’Neal, M. J. Anal. Chem. 1955, 27, 868-875. (20) Lumpkin, H. E. Anal. Chem. 1956, 28, 1946-1948. (21) Hood, A.; O’Neal, M. J. Adv. Mass Spectrom. 1959, 1 , 175-192. (22) Carlson, E. G.; Paullssen, G. T.; Hunt, R. H.; O’Neai, M. J. M a l . Chsm. 1960, 32, 1489-1494. (23) Galiegos, E. J.; Green, J. W.; Lindeman, L. P.; Le Tourneau, R. L.; Teeter, R. M. Anal. Chem. 1967, 39, 1833-1838. (24) Aczel. T.; Allan, D. E.; Hardlng, J. H.; Knlpp, E. A. Anal. Chem. 1970, 42, 341-347. (25) Scheppele, S. E.; Chung, K. C.; Hwang, C. S. submitted to Int. J. Mass Spectrom. Ion Phys. (26) Scheppeie, S. E. ’ Mass Spectrometry and Fossil-Energy Conversion Technology--A Review;” US. Department of Energy, FE 2537-7, Distribution Category UC-Sod, June 1978. (27) Lumpkin, H. E.; Aczel, T. Anal. Chem. 1964, 36, 181-184. (28) Scheppele, S. E.; Grlzzle, P. L.; Greenwood, G. J.; Marriott, T. 0.;Perrelra, N. B. Anal. Chem. 1978, 48, 2105-2113.
RECEIVED for review December 18,1981. Accepted February 17,1982. Presented in part at the 8th Annual Meeting of the Federation of Analytical Chemistry and Spectroscopy Societies, Philadelphia, PA, September 20-25, 1981.
Electronic Bubble Gate for Colorimetric, Air-Segmented, Continuous Flow Analyzers Chas. J. Patton, Martln Rabb, and S. R. Crouch* Department of Chemistry, Michigan State University, East Lansing, Michigan 48824
The electronlc bubble gate described permlts the use of low volume bubble-through flow cells wlth the photometrlc detectors of air-segmented continuous flow (CF) analyzers. Experlmental data on the performance of CF analyzers with 2 mm 1.d. and 1 mm 1.d. manifold components and debubbllng or bubble-through flow cells are reported. The wash of CF analyzers wlth bubble-through flow cells Is improved relatlve to those with dehubbling flow cells but Is somewhat poorer than predicted by theory because of mlxlng between unsegmented sample and wash slugs as they pass through the pump Into the manifold. A mlnlature CF analyzer Is described and used to determine micromolar concentrations of nltrlte In aqueous solution at an analysis rate of 360 h-’ wlth a preclslon of 0.7% relatlve standard deviation and 1.0% Interaction. The analytlcal performance reported for a flow-lnJectlonanalyzer used to assay nltrlte In the same concentration range Is compared with that of the mlnlature CF analyzer.
Most commercially available colorimetric air-segmented continuous flow (CF) analyzers are equipped with debubbling 0003-2700/82/0354-1113$01.25/0
flow cells to eliminate the erratic detector signal that would result from the repetitive passage of highly reflective air segments across the colorimeter’s light path. Unfortunately, this expedient contributes significantly to loss of wash in CF analyzers and thus reduces the rate at which analyses can be performed (1). Loss of wash due to flow cell debubblers can be eliminated by several techniques. Analog (2) or digital (3) curve regeneration of the detector signal can provide mathematical compensation for loss of wash due to flow cell debubblers and other unsegmented zones within the CF analyzer without physical modification of the apparatus. Alternatively, loss of wash can be eliminated by a technique known as “bubble gating”. Here, the segmented stream is passed directly into the flow cell and the detector signal is sampled only when the flow cell is completely filled by a liquid segment. Flow cells with volumes less than that of a single liquid segment are required in this technique. One major advantage of bubble gating is that the analytical stream remains segmented and thus maintains its integrity at the detector so that multiple detectors can be used with minimal loss of wash. Habig and co-workers (4) appear to have developed the first bubble gate, which was activated by conductance changes within a specially designed flow cell. They concluded, however, 0 1982 American Chemical Society
