Anal. Chem. 1984, 56, 1115-1121
1115
Cluster Ion Distributions and Correlation with Fragment Valence in Laser-Induced Mass Spectra of Oxides Eric Michiels and Renaat Gijbels* Department of Chemistry, University of Antwerp (U.I.A.),Universiteitsplein 1, B-2610 Wilrijk, Belgium
Laser microprobe mass analysis (LAMMA) spectra are described for binary oxides belonging to different groups in the periodic table. The positive and negative cluster ion distributions show a strong correlation wlth the valence electron configuration of the metal in the oxide. The bond dissociation energy of the MO’ ion also affects the intensity distributlons.
Laser microprobe mass analysis (LAMMA) is a very rapid technique that allows the characterization of inorganic as well as organic compounds in single particles of only micrometric size. It has a fairly high detection sensitivity and lateral resolution which makes it applicable to various fields such as biomedical work, general chemistry, environmental research, geology, mineralogy, criminology, and others (I). Still, quantification of the technique is difficult because of the lack of knowledge about the laser induced ion formation mechanisms. Up to now, no theoretical model exists for calculating ion yields as a function of target and laser parameters. Laser mass spectra show a relatively high proportion of polyatomic or cluster ions which complicate the analysis of trace elements; but on the other hand, they can be used to obtain analytical information: The mass spectra can be regarded as “fingerprints” of the analyzed samples and sometimes information can be deduced about the compound stoichiometry; e.g., see ref 2. A systematic study of the types of clusters generated and their relative abundances is useful for estimating the extent of mass spectral interferences of molecular ions on atomic ions of the same nominal mass. Furthermore, such knowledge yields more information about the stabilities of these ions and, perhaps, contributes to a better understanding on how they are produced. The results can also be used to test theoretical or empirical models on ion formation. Therefore, we made a rather systematic survey of a large number of inorganic binary oxides (covering most of the periodic table) and accumulated data on the occurrence of cluster ions using high-purity materials. In a previous paper (2)we discussed the influence of instrumental parameters such as the laser energy density and variation in ion lens potential setting, on the cluster ion distributions. Also, the oxygen/ metal ratio in the sample affects the ion intensity patterns of the clusters. In this work, we correlate the ion distributions with stability considerations and investigate the dependence on the bond dissociation energy of the MO+ ion.
EXPERIMENTAL SECTION All laser mass spectra were obtained by using commercially available instrumentation (LAMMA-500of Leybold-Heraeus). The interaction with the sample of a Q-switched, frequency quadrupled, Nd-YAG laser pulse (power density 108-1011 W/cm2, h = 265 nm, 15 ns pulse width) generates positive and negative ions. Either of these can be accelerated through an ion optical Einzel lens into the drift tube of a time-of-flightmass spectrometer, including an ion reflector for focusing ions of the same mass but slightly divergent energy. The ion detector is an open Cu-Be secondary electron multiplier. The signals are stored in a 100-MHz transient recorder (Biomation 8100) and fed into a Digital 0003-2700/84/0356-1115$01.50/0
MINC-11 microcomputer for mass calibration and integration. The 32X objective of the optical microscope was used throughout and the energy delivered to the sample can be attenuated by inserting a 25-step UV absorbing filter sequence. A more detailed description of the equipment and of the performances of the LAMMA technique can be found in the literature (I, 3, 4). Oxide compounds were obtained commercially (most of them from Johnson and Matthey). If necessary,they were ground with an agate mortar and pestle to particles of micrometricdimensions. The powders were mounted on a very thin Formvar foil (less than 0.1 pm) supported by a copper TEM grid and particles of approximately equal diameters (about 1 wm) were selected for analysis. The energy delivered to the samples was about three to five times the threshold energy needed for perforation of the Formvar foil and for obtaining ion signals. Since the energy meter was not fully calibrated, this threshold energy is estimated to be ca. loQW/cm2 when assuming an irradiation area of 1 km2during 15 ns (32X lens). The threshold energy also depends on the oxide matrix (see Results and Discussion). All mass spectra were recorded with a samplinginterval of 20 ns, and the ion lens potential was fixed at 1150 V. Ion intensities were related to the M+ ion intensity. Due to the limited dynamic range of the Biomation recorder (5), spectra obtained for a different but overlapping mass range and under different instrumental conditions of sensitivity and laser energy density had to be combined properly. In the case of high ion intensities, the signal was sometimes picked up at the 12th instead of the 17th dynode. For each mass range, at least six representative mass spectra were averaged. Ions that can be detected with a relatively high intensity have a typical standard deviation of about 10%. A number of difficulties arise for the quantitativeinterpretation of the data, because of nonlinear detector response, ion lens effects, and laser energy effects. In particular, the combination of spectra taken under different experimental conditionsmay introduce systematic errors. Therefore no quantitative data are represented for the numerical values of the valence model parameters (see below), but only figures displaying general trends. The experimental errors are sufficiently small for these trends to be significant, however.
RESULTS AND DISCUSSION The positive and negative mode mass spectra of binary oxides (M,O,) are characterized by a number of polyatomic or cluster ions of the type M,O,’ in addition to the atomic ions M+ and sometimes M-. The number of metal atoms, m, and the number of oxygen atoms, n, can vary extensively depending on the analyzed compound. We use the “fragment valence” K as a uniform parameter to correlate the data of clusters of different atomic composition, M,On*. The fragment valence K, which is defiied as the formal valence number of the metal atom in an emitted cluster, was introduced by Plog et al. who developed an empirical model for describing secondary ion yields from oxidized metal surfaces and metal oxides in static secondary ion mass spectrometry (SIMS) (6). The fragment valence K of positively or negatively charged M,O,’ clusters is equal to K = ( q + 2n)/m,when ascribing the valence number -2 to oxygen and q to the total charge of the cluster ion (+1or -1). According to the valence model of Plog (6),positive or negative ion intensities of M,Onf clusters belonging to the same “group”,i.e. having the same number of metal atoms (m)and a different number of oxygen 0 1984 American Chemical Society
1116
ANALYTICAL CHEMISTRY, VOL. 56, NO. 7, JUNE 1984
t
I loo0
m
3MM Mass arnu
4MM
5000
*
Flgure 2. The fragment valence K o f the observed Ho,O,+ ions as a function of their mass (in amu). A solid circle represents the cluster with the highest intensity for a given m .
1
2
0
4 5 6 Fragment valence K
Flgure 1. Relative intensity of Sc,O,+ fragment valence K.
Ions
as
1
*
a function of the
atoms (n),are described by a Gaussian curve when plotted as a function of the fragment valence IC
I*(K) = Im,*
exp(-(K - G*)2/272)
(1)
with I-* the maximum intensity of the fitted curve, G’ the K value corresponding to I’, and y2 the variance of the distribution. The valence model, which was initially evaluated for results obtained with SIMS, was found to be also applicable to LAMMA data of silicon and titanium oxides (2, 7,8). The main conclusions of the results for positive ions can be summarized as follows: decreasing maximum intensity, I-+, with increasing number of metal atoms in a “group”; at the same time, shifting of G+ toward higher fragment valence values and decreasing values for y2. The higher clusters gradually approach a fragment valence of K equal to 4, which is chemically the most stable valency of Si and Ti in the oxide. In order to check whether this valence model is generally applicable, we made a systematic study of oxides having metal atoms belonging to different groups in the periodic table. Positive Ion Distributions. Group 4. For SO2,we could detect positive ion clusters containing up to 10 silicon atoms (8)and for Ti02up to 4 titanium atoms (2). Other group 4A element oxides (GeOz,Sn02,and PbO) and group 4B element oxides (Zr02 and Hf02) yielded clusters with maximum two metal atoms. This can be explained by the lower affinity for oxygen (Ge, Sn, Pb) and for the large number of isotopes resulting in too low ion intensities and unresolved ion peaks for the higher cluster ions (Zr, Hf, Sn). For the smaller cluster ions, similar distributions are obtained as in the case of Si02 and TiOz. Group 3 and the Lanthanides. The mass spectra of the sesquioxidesof the group 3B elements (Sc, Y, and La) are all similar. Figure 1shows the ion yields of Scz03as an example. They are plotted relative to Sc+ as a function of the fragment valence K. The f i s t number gives the number of metal atoms (m)and the second the number of oxygen atoms (n)in a cluster M,O,+. The distributions show predominantly ions of the type M2r+103,+1+: these are species having a fragment valence of exactly 3 corresponding to the most stable valency of the metal in the neutral compound. There are still four
ion clusters containing two scandium atoms, but further on clusters with the exact fragment valence become more abundant resulting in only two clusters (Sc304+,SC303’; ScbO,+, ScEO6+) and finally one cluster (Sc7010+)per group of ions with the same number of metal atoms. Clusters with an even number of metal atoms (Sc405+,Sc406+;Sc608+, ScsO,’) do not have a fragment valence of 3 and are indeed less abundant. This results in an odd-even effect for the relative intensities of the higher clusters: ions with an odd number of metal atoms have a higher intensity than adjacent clusters with an even number of metal atoms. Also the oxides of the lanthanides, which are chemically similar to the group 3B elements, display an odd-even effect with dominating odd metal ions of the type M&+103,+1+.X can range up to 13 in the case of HoZO3,for example (mass of Hoz,Om+ is 5095 amu, see Figure 2), which is probably due to the rather high bond dissociation energy of the MO+ ion (see also below). Mass spectra of oxides of group 3a elements (Al, Ga, In, and T1) show only clusters with a maximum of 3 metal atoms and these have a tendency for acquiring a lower fragment valence. This is probably correlated with their very low bond dissociation energy for the MO+ ion. Since the above ion distributions are characterized by clusters having a particular fragment valence K of 3, the valence model is not generally applicable; i.e., when plotting the ion intensities vs. the fragment valence K , one does not necessarily obtain Gaussian distributions. This is also the case for ion distributions of oxides having metal atoms belonging to other groups in the periodic table. Group 2. As it is not possible to generate clusters having a fragment valence of exactly 2, the spectra of group 2A element oxides are characterized by ions of the type M(MO),+ and (MO),+ as the nearest approach to a fragment valence of 2 (2+ is the usual oxidation state of an element in group 2). The intensity distribution of Be0 is shown in Figure 3. It should be noted that ions of the type (MO),+ are always accompanied by a significant (MO),H+ ion peak. Since the intensity of a cluster M,O,* is the sum of the peak areas corresponding with all the isotopic combinations of the M atoms, possible contributions of hydrogen are included. The cluster intensities having a hydrogen contribution are indicated by the figures in parentheses. The observation that clusters of the type (MO),H+ are especially stable is most probably correlated with their fragment valence K. The attachment of a proton results in a decrease of the K value of the corresponding cluster from more than 2 to exactly the “preferred”valence 2 of the metal in the resulting cluster. For MgO the attachment of hydrogen was even more pronounced resulting in clusters of the type M,0,+1H2’. Bruynseels et al. also found the same series M(MO),+ and (MO),’ for CaO with a significant intensity of (CaO),H’ clusters even in spectra of oven-dried samples (9).
ANALYTICAL CHEMISTRY, VOL. 50, NO. 7, JUNE 1984
1117
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K
Figure 3. Relative posltive ion distributions from Be0 and ZnO vs. the fragment valence K.
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Figure 4. Relative posltlve ion intensities from CuO and Ag,O as a functlon of the fragment valence K.
The transition element oxides of group 2B (ZnO, CdO, and HgO) have a tendency to form metallic clusters Mz+and M3+ (cf. Figure 3). Group 1. As for the group 1element oxides, we only analyzed CuO and AgzO (Figure 4). For CuO the intensities of clusters with the "preferred" fragment valence of 1are relatively high, while for Ag20 the metallic character of the element is more dominating, as is shown by the occurrence of Agz+, Ag3+, Ag*+,and even Ag5+ clusters. Group 5. The ion distributions of oxides of group 5A elements (As203,SbzO4, and BizO3) are predominantly charac-
terized by cluster ions with an exact fragment valence of 3 (Figure 5). The trioxides are indeed the most stable oxides of group 5A elements (10). Another interesting trend can be noticed in this group: the occurrence of M2+,and in the case of Biz03even M3+and M4+clusters, becomes more important with increasing metallic character of the elements (11). These clusters distort the distributions around ionic species with an appropriate fragment valence K equal to 3. Since the bond dissociation energy of the MO+ ion also decreases with increasing atomic number (from As toward Bi), this has also an important effect on the relative ion distributions; apparently,
1118
ANALYTICAL CHEMISTRY, VOL. 56, NO. 7, JUNE 1984
,4q-py=;oev I
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Flgure 5. Relative positive ion dlstributions from group 5A element oxides (As203, Sb20,, and Bi203) vs. the fragment valence K .
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Flgure 6. Relative positive ion intensities from Nb205 and Ta205as a function of the fragment valence K .
there is a combination of two distributions: one around the fragment valence 3 and one corresponding to the metallic ion clusters. The same phenomena can be seen in the mass spectra of the oxides of the group 5B transition elements, but in this case the ion distributions are much broader since the clusters apparently pursue a fragment valence K equal to 5. Figure 6 shows the positive ion distributions for Nb205and Ta205. SIMS spectra of an oxidized tantalum surface revealed the presence of Ta+, TaO+, Ta02+,and Ta03+ ions at relative intensities of 1, 1.6, 0.3, and 0.005 (12). Figure I discloses an interesting difference in intensity pattern between vanadium trioxide and vanadium pentaoxide. Neither clusters with an exact fragment valence of 3 nor those
with a K value of 5 are explicitly favored. The maxima of the distributions are situated between, but with the trioxide rather tending to 3 and with the pentaoxide to 5; V(1V) is known as the most stable oxidation state of vanadium (13). For vanadium trioxide, the valence model appears to be applicable, but in the case of vanadium pentaoxide the Gaussian distributions are distorted. The different ion distributions make a distinction possible between the stoichiometrically different vanadium oxides. Especially the larger clusters reflect the change in oxygen content in the sample. Also stoichiometrically different titanium oxides have been shown to give typical fingerprint spectra (2). Van Craen et al. studied the secondary ion emission (dynamic SIMS)of a number of metal oxide species from oxidized
ANALYTICAL CHEMISTRY, VOL. 56, NO. 7, JUNE 1984
1119
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metal surfaces under Ar+ bombardment (12). The secondary ion distributions including clusters with fragment valences 51 (e.g., V3+, V4+),could be described by the valence model, but for vanadium no definite information about the valence state of the metal could be obtained, probably because of preferential sputtering, leading to a modified surface composition. Wittmaack has also stated that high fluence SIMS studies of oxides will therefore not provide the correct fingerprint spectrum (14). He also notes that changes in secondary ion mass spectra, as a function of the average (surface) concentration of oxygen, are most pronounced for large clusters (m 2 3). This appears to be in line with our LAMMA observations of vanadium oxides. Group 6. The combination of ion distributions observed in Figure 5 is also seen in the mass spectra of oxides of group 6A elements (Se02and Te02)with TeOz shown as an example in Figure 8: on the one hand Te+, Te2+,Te3+,and Te4+in a relatively high intensity and on the other hand a distribution of cluster ions apparently approaching a K value 4. SeOa and TeOz are in fact more stable than the trioxides. For the oxides of the transition elements chromium, molybdenum, and tungsten (Cr03, Moo3, and W03) less information could be obtained, since Cr03 is deliquescent whereas Mo and W have too many isotopes resulting in unresolved ion peaks for the higher cluster ions. Group 7B. From the electronic configuration, elements of this group may be expected to form divalent compounds which are more stable than those from the preceding groups; the M2+ ion has a relatively stable electron configuration (10). This can be seen in the cluster ion distribution of MnOz whose clusters have a fragment valence close to 2 (Figure 9). Group 8. Of the group 8 element oxides, we only studied different iron oxides (Fe304,Fe2O3, and FeOOH), c0304, and NiO. The difference in O/M ratio between Fe304and Fe203 is too small to obtain significantly different cluster ion distributions. These are characterized by the ions Fe+, FeO+, Fez+,Fe20+,Fez02+,Fe30z+,Fe303+,and Fe404+.In the case of FeOOH, the relative Fez+intensity is much smaller. The Co304 and NiO samples generate only clusters with maximum three metal atoms (Co+, COO+;Cot+, CozO+, Co202+;Co30+,
I
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6
7
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Flgure 8. Relative intensity of Te,,,O,,+ fragment valence K .
ions as a function of the
Co302+,Co303+and Ni+; Ni2+,Ni20+;Ni3+, Ni30+l. Since other group 8 element oxides were not available and since larger cluster ions could not be detected with our instrument, the obtained data do not allow observance of significant regularities in this group: it is even hardly possible to conclude whether or not the valence model is valid. Actinide Oxides: Tho2 and U308. The positive mode spectra of T h o 2 are characterized by ions of the type Th+, Th,Ozm-l+ and Th,02,+ ( m = 1, 2, or 3), approaching a fragment valence of 4 with increasing m. The cluster ion distribution of U308appears to be very energy dependent and is dominated by the UO+ and U02+intensity (see also below).
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1120
ANALYTICAL CHEMISTRY, VOL. 56, NO. 7, JUNE 1984
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,
9
,
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Figure 10. Semilog plot of MO+/M+ intensity ratio as a function of the bond dissociation energy D(MO+) of the MO+ ion.
r(
Figure 9. Relative positive ion distributlon from MnO, vs. the fragment valence K .
In a group of clusters with the same number of uranium atoms, clusters of type Un03m-l+(m = 1, 2, or 3) have the highest intensity, indicating a preferred fragment valence approaching 6. The above examples clearly demonstrate the strong correlation between the cluster ion distributions and the group in the periodic table where the metal in the oxide belongs. The valence electron configuration of the metal determines the intensity distributions which are usually characterized by ions having a particular fragment valence K. The chemically most stable ions dominate the distributions of clusters containing at least two metal atoms. Negative Ion Distributions. In general, the negative mode mass spectra exhibit much less ion clusters. Frequently, only clusters with one M atom are observed. When more M,O,- ions (with m 2 1)are present, similar trends are observed as in the positive mode spectra, but this time the cluster ions approach the “preferred” fragment valence starting with larger K values (2, 7). The Bond Dissociation Energy. When plotting the MO+/M+ intensity ratio vs. the bond dissociation energy D(MO+)of the MO+ ion, there appears to exist an exponential correlation as can be seen in Figure 10. The ratio spans a range of 4 orders of magnitude depending on the element and its corresponding bond dissociation energy. Most of the D(MO+)values were taken from a compilation by Morgan and Werner (15). The values for Mg, Sc, V, Mn, Co, Cu, Zn, Nb, Sb, and Bi are deduced from SIMS experiments and are to be used with caution. Also the values for As and Mo have a rather high uncertainty (fleV). Reference 16 was consulted for the value of Ho and ref 17 for Te. The value of Sn was derived by using the thermodynamic cycle D(SnO+) = D(Sn0) + IP(Sn) - IP(Sn0) (2) with D(Sn0) = 5.49 eV (18), ionization potential (IP) of Sn = 7.344 eV (19) and IP(Sn0) = 10.5 eV (ZO),this results in D(SnO+) = 2.33 eV. In the same manner, the value D(GeO+) = 3.58 eV was obtained for Ge using D(Ge0) = 6.78 eV (13, IP(Ge) = 7.899 eV (19), and IP(Ge0) = 11.1eV (17). As could be expected, oxides having an O/M ratio of two or more tend to be situated at the upper side (e.g., SnOz,TeOP,
Moos, Sbz04, CeO,). Some oxides, for instance, MOO, and U308 which prefer a high fragment valence, have a considerable contribution of the M02+ion intensity. The amount of laser energy absorbed by the sample obviously affects the MO+/M+ ratio. The ratios displayed were obtained at an energy that was about 3 to 5 times the threshold energy for perforation of the Formvar foil and for observing ion signals. In Figure 10 the upper point for U308was obtained at about threshold energy (E,)while the lower point was measured at an energy El 2Ez. For TiO,, the influence was less drastic: the figure shows the range from about 2 times to about 5 to 6 times the threshold energy. This threshold energy depends on the oxide matrix. It would have been of interest to classify the investigated oxides according to their threshold energy; however, all samples should then preferably be mounted on the same Formvar foil and laser irradiated in a relatively short time interval with reproducible experimental conditions, in order to be able to observe significant differences. This has, however, not been done.
-
CONCLUSIONS Laser induced mass spectra of binary oxides (M,O,) are characterized by ions of the type M,O,*. The m / n ratio is high in the positive mode spectra and low in the negative mode spectra. The cluster ion distributions depend on the valence electron configuration of the metal in the oxide, i.e. there exists a correlation with the group in the periodic table the metal belongs to: ions having a particular fragment valence K dominate the distributions since they are chemically more stable. Moreover, some cluster ion distributions are characterized by ions of the type M,+ ( m can range up to 5), which is typical for M atoms with a pronounced metallic character. The valence model (6) appears to be not generally valid for all oxides. In general, cluster ion intensities decrease with increasing cluster size. However, in certain cases (when clusters with a particular fragment valence can be formed) an odd-even intensity effect appears: ions with an odd number of metal atoms and with the exact fragment valence are more abundant than adjacent clusters with an even number of metal atoms. Furthermore, there exists a correlation between the observed MO+/M+ratio and the bond dissociation energy of the MO+ ion, Also, oxides with a high bond dissociation energy
Anal, Chem. 1904, 56, 1121-1127
1121
(8) Michiels, E.; Celis, A,; Gijbels, R. { n t . J. Mass Spectrom. Ion Phys.
usually generate more complex clusters. Registry No. A1203,1344-28-1;MgO, 1309-48-4;CuO, 131738-0; Co304,1308-06-1;PbO, 1317-36-8;ZnO, 1314-13-2;BizO3, 1304-76-3;Fe203,1309-37-1;Ge02, 1310-53-8;BeO, 1304-56-9; Cr03, 1333-82-0; Mn02, 1313-13-9; Eu& 1308-96-9; SnOz, 18282-10-5; Tm203, 12036-44-1; Luz03, 12032-20-1; HozO3, 12055-62-8;Scz03,12060-08-1;TeOz,7446-07-3;Moo3,1313-27-5; VzO5, 1314-62-1; Ti02, 13463-67-7; Tb407, 12037-01-3; Yz03, 1314-36-9;Taz05,1314-61-0;Zr02, 1314-23-4;U308, 1344-59-8; Laz03, 1312-81-8; UO', 12509-76-1;UOz+, 21294-41-7; ThOz, 1314-20-1;Sbz04,1332-81-6;Nbz05,1313-96-8;PrsOll, 12037-29-5; CeOz, 1306-38-3;Asz03, 1327-53-3;Si02,7631-86-9.
1983, 47, 23-26. (9) Bruynseels, F. J.; Van Grieken, R. E. Anal. Chem. 1984, 56, 871-873.
(10) Sanderson, R. T. "Inorganic Chemistry"; Reinhold: New York, 1967; Chapter 12. (11) Cotton, F. A,; Wilkinson, G. "Advanced Inorganic Chemistry", 3rd ed.; Interscience: New York, 1972; p 384. (12) Van Craen, M. J.; Adams, F. C. Surf. Interface Sci. 1983, 5 , 239-246. (13) Cotton, F. A,; Wilklnson, G. "Advanced Inorganic Chemistry", 3rd ed.; Interscience: New York, 1972; p 825. (14) Wittmaack, K. Surf. Sci. 1979, 89, 668-700. (15) Morgan, A. E.; Werner, H. W. J. Chem. Phys. 1978, 68 (E), 3900-3909. (16) Ackermann, R. J.; Rauh, E. G.; Thorn, R. J. J. Chem. Phys. 1978, 65 (3), 1027-1031. (17) Huber, K. P.; Herzberg, G. "Molecular Spectra and Molecular Structure. vol. 4 Constants of Diatomic Molecules"; Van Nostrand-Reinhold: New York, 1979. (18) Rosen, B. "Donn6es Spectroscopiques relatives aux Mol6cules Diatomiques"; Pergamon Press: Oxford, 1970. (19) "CRC Handbook of Chemistry and Physics", 60th ed.; Chemical Rubber Publishing Company: Boca Raton, FL, 1981. (20) Colin, R.; Drowart, J.; Verhaegen, G. Trans. Faraday Soc. 1965, 67 (7), 1364-1371.
LITERATURE CITED (1) Proceedings of the LAMMA Symposium held in DUsseldorf, Federal Republic of Germany, 6-10 Oct 1980, Fresenius' 2. Anal. Chem. 1981, 308, 193-320. (2) Mlchiels, E.; Gijbels, R. Spectrochlm. Acta, Part 8 1983, 388 (lo), 1347-1 354. (3) Denoyer, E.; Van Grieken, R. E.; Adams, F.; Natusch, D. F. S. Anal. Chem. 1982, 54, 28A-41A. Hercules, D. M.; Day, R. J.; Balasanmugam, K.; Dang, T. A,; Li, C. P. Anal. Chem. 1982, 54, 280A-305A. Simons, D. S. I n "Microbeam Analysis-1982"; San Francisco Press: San Francisco, CA, 1982; pp 390-392. Plog, C.; Wiedmann, L.; Bennlnghoven, A. Surf. Scl. 1977, 67, 565-580. Michlels, E.; Celis, A.; Gijbels, R. I n "Microbeam Analysls-1982"; San Francisco Press: San Franclsco, CA, 1982; pp 383-388.
RECEIVED for review November 28,1983. Accepted February 3, 1984. This work was carried out under research Grant 80-85/ 10 from the Interministrial Commission for Science Policy, Belgium.
Instrument Database System and Application to Mass SpectrometryIMass Spectrometry Richard W. Crawford,* Hal R. Brand, and Carla M. Wong Lawrence Livermore National Laboratory, Box 808, L-310, Livermore, California 94550
Hugh R. Gregg, Phillip A. Hoffman, and Christie G . Enke Michigan State University, Chemistry Department, East Lansing, Michigan 48824
An Instrument database system first used for mass spectrometry/mass spectrometry but applicable to other lnstruments Is described. Thls software system allows real-tlme storage and rapid retrleval of all fixed instrument parameters, any varlables chosen to be stored by the user, and X-Y data of any type from a computer-Interfaced source. Timing data from three dlfferent minicomputer and dlsk systems are provided to show speeds for typlcal data extractlon. This instrument database system allows the storage and ready retrleval of data from many dlmenslons. All possible data surfaces avallable from a particular database can be reconstructed. Plotting and tabulating routlnes are also discussed. I t Is written primarily In FORTRAN I V and Is designed to operate efficiently on a mlnlcomputer. Thls software has been submitted to DECUS for general availablllty.
Many modern analytical instrumentation systems are capable of creating vast amounts of data in a very short period of time. The advent of computer-controlled instruments allows the routine variation of a number of measurement parameters, each of which can provide another dimension of information. In addition, multiple instruments can be coupled to simultaneously probe multiple characteristics of a sample. Among the first of such instruments was GC/MS (gas chro0003-2700/84/0356-1121$01.50/0
matography/mass spectrometry). Many other examples have appeared in recent years, including GC/FTIR (gas chromatography/Fourier transform infrared spectrometry) and GC/MS/FTIR. The advent of MS/MS (mass spectrometry/mass spectrometry) created multidimensional data on an even larger scale. Each of these instrument systems is capable of creating hundreds of data points per second for hours. Without computer storage and retrieval of data, these techniques would not be practical. The ability of these instruments to record rapidly and store efficiently has modified to some degree the classical approach to experimental design, especially in nonacademic laboratories. It is no longer cost-efficient to carry out a large number of exploratory experiments to get only the data necessary for the analysis. It is far more efficient to use a small amount of additional time recording unused data than to have to repeat an analysis because of missing data. Naturally, some care must be exercised in selecting reasonable parameters for storage. The evolution of GC/MS brought with it the development of computer data systems designed to handle the dimension of time in addition to mass and intensity. However, even three dimensions are inadequate to cope with the measurement capabilities of MS/MS instruments and many other modern computer-controlled systems. In the case of a totally computer-controlled MS/MS, a large number of variables can be scanned, either singly or jointly. Each such scan will produce 0 1984 American Chemical Society
