random and drew the modified structures. The structures were single atoms, straight chains, branched chains, single rings, linked rings, spiro rings, fused rings, and a ring linked to fused rings. (This last example, a three ring system, was intended to be outside the capability of the program as written). The ring sizes varied from three to eight atoms. The molecular complexities considered had molecular masses ranging from sixteen to one thousand. The numerical order of coding the atoms was altered for the unmodified cases, above, and the structures were redrawn.
RESULTS The program successfully drew all the structures with the exception of the three ring system, in which case the third ring was mutilated only in shape. Total calculation time ranged from three to six seconds on a Control Data 3200 computer with 1000 1.p.m. printer. The coordinate positions (not the relative positions) of substituents and direction of branching altered with the coding order. DISCUSSION
sufficient to produce a two-dimensional diagram of the compound. Because the code used was not canonicalized, and the program produces diagrams oriented to some extent according to the order of numbering, the diagram can be rotated by manipulating the code order, perhaps a useful feature if the output is on a cathode ray tube device and code re-ordering routines are written. It may be a disadvantage when comparing substructures. Published flowcharts (12) for mass spectral analyses have been coded and modified to provide their identifications in the form of atom connection tables, and other routines are being developed which use the atom connection table for storage of structures during the investigation (13). The capability of the structure drawing program is illustrated in Figures 5 , 6 , and 7 where the nearest neighbor tables and printouts obtained for two types of molecular structure are given. RECEIVED for review September 16, 1968. Accepted March 7, 1969. ~
The atom connection table was found to be adequate for storing structural information about a chemical compound
(12) B. Pettersson and R. Ryhage, Arkiu Kemi, 26,293 (1967). (13) L. R. Cawford and J. D. Morrison, unpublished data, 1968.
Ultra-Trace Mass Spectrometric Metal Analysis Using Heptafluorodimethyloctanedione Chelates B. R. Kowalski and T. L. Isenhour Department of Chemistry, Unioersity of Washington, Seattle, Wash. 98105
R. E. Sievers Aerospace Research Laboratories, A R C , Wright-Patterson Air Force Base, Ohio 45433
A rapid, accurate ultra-trace mass spectrometric metal analysis using chelates of 1,1,1,2,2,3,3-heptafluoro-7,7dimethyl-4,6-octanedione has been developed. The analysis of fourteen metals (AI, Cr, Fe, Ni, Cu, Y, Pd,
Nd, Sm, Dy, Ho, Tm, Yb, Pb) has been accomplished using direct insertion to the ionizing source. Quantitative results have been obtained on the order of 10-12 g of the metal and sensitivities as low as 10-149. The fragmentation patterns are generally simple allowing analysis of mixtures without preconcentration or chemical separation. Sample preparation and introduction are discussed and mass spectra of pure compounds and mixtures are presented.
TRACEANALYSIS of metals by conventional mass spectrometry has been severely limited by the volatility of metal compounds which may be formed quantitatively. While radio frequency spark sources will vaporize the most refractory compounds, they are difficult to reproduce and produce ions with a wide range of kinetic energies, thereby limiting accuracy. Recently, a number of fluorinated P-diketones have been studied, many of which react directly with metals and metal compounds quantitatively forming volatile metal chelates (1-5). Gas (1) R. E. Sievers, J. W. Connolly, and W. D. Ross, J. Gas. Chromatogr., 5 , 241 (1967). ( 2 ) C . S . Springer, D. W. Meek, and R. E. Sievers, Znorg. Chem., 6, 1105 (1967). (3) W. D. Ross and R. E. Sievers, Talanfa, 15, 87 (1968). 14) M. L. Taylor, E. L. Arnold, and R. E. Sievers, Anal. Lett., 1, 735 (1968).(5) R. W. Moshier and R. E. Sievers, “Gas Chromatography of Metal Chelates,” Pergamon Press, Oxford, 1965. \
.I
998
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ANALYTICAL CHEMISTRY
chromatographic analyses using such compounds have been accomplished with excellent results at trace levels (1, 3-5). Mass spectrometry offers a competitively sensitive technique which is capable of identifying the species present and simultaneously analyzing multicomponent samples. Mass spectra of a number of volatile metal compounds have been reported in recent years (6-12). Majer and coworkers have studied several metal chelates of dimethylglyoxime, benzildioxime, and oxine as well as several Pdiketone complexes of holmium by mass spectrometry (13-16). Introducing samples by direct insertion probe and manually integrating the time resolved recorder trace, they obtained quantitative results for holmium P-diketones on the order of g and estimated extension of the method to as (6) M. J. Lacey, C. G. MacDonald, and J. S. Shannon, Org. Mass Spectrom., 1, 115 (1968). (7) R. B. King, J. Amer. Chem. Soc., 90, 1412 (1968). (8) Zbid.,p 1417. (9) Zbid., p 1429. (IO) C. G. MacDonald and J. S. Shannon, Aust. J. Chem., 19, 1545 (1966). (11) S. Sasaki, Y. Itagaki, T. Kurokawa, and K. Nakanishi, BUN. Chem. SOC.Japan, 40,76 (1967). (12) G. M. Bancroft, C . Reichert, and J. B. Westmore, Inorg. Chem., 7 , 870 (1968). (13) A. E. Jenkins and J. R. Majer, Talanra, 14, 777 (1967). (14) A. E. Jenkins, J. R. Majer, and M. J. A. Reade, ibid., p 1213. ibid... 15., (151 J. R. Maier. M. J. A. Reade. and W. I. SteDhen. ~, . 373 (1968). (16) R. Belcher, J. R. Majer, R. Perry, and W. I. Stephen, Anal. Chim. Acta, 43, 451 (1968). “
I
[DY ( l o d),-C
D y ( f od),
Fs]*
Dy (f o dI3
+
>.
-I-
Dy(todi
Figure 1. Mass spectra ' of N d ( f ~ d ) ~Sm(fod)p, , w D y ( f ~ d ) ~H, o ( f ~ d ) ~ , Tmz, (fodh, and Yb(fodh
Jl
L
11
Ili
Ho ( f 0 d 1;
Ho(f o d
CFA*
[no(fod),-
1
H o ( t od), Ho(fod7 i
1
2
I
I
L
L
m /e
low as g. We have used 1,1,1,2,2,3,3-heptafluoro-7,7dimethyl-4.6-octanedione m(fod)] for ultra-trace mass spec. . trometric analysis of fourteen metals (Al, Cr, Fe, Ni, Cu, Y ,Pd, Nd, Sm, Dy, Ho, Tm, Yb, Pb) and have obtained quantitative results on the order of IO-'* g and sensitivities as low as I O - l 4 g.
EXPERIMENTAL
Spectra were run on an Associated Electronic Industries MS-9 double focusing mass spectrometer operating at a resolution of one thousand (collector slit = 0.01 in., source slit = 0.004 in.), an ionizing voltage of 70 V, and an accelerating VOL. 41, NO. 8, JULY 1969
999
Al (f o dI3
C r ( f odl,
I
4 00
Z
I
so0
w
a
L
600
I
roo
m /e
L
,
8 00
1 900
Figure 2. Mass spectra of AKfodh, Cr(fod13, Fe(fodh, and Y ( f ~ d ) ~
m /e
potential of either 6 KV or 8 KV depending upon the molecular weight of the compound. The metal chelates were prepared as in References 1 and 2. Solutions were made by dissolving the metal chelates in pentane (or acetone) and performing the necessary dilutions. For reasons discussed below, pentane is preferable. The desired amount of solution (from 1-10 pl) was delivered to the retractable ceramic tip of the direct insertion probe using a Hamilton microsyringe. The probe was inserted into the instrument with the filament and accelerating voltages turned off, With the ceramic tip at room temperature, either solvent could be pumped away in the vacuum lock without noticeable loss of any metal chelate studied. After solvent removal, the probe was completely inserted and, with the tip still withdrawn, the instrument was brought to operating condition. With the source at 250 f 10 "C, the ceramic tip was extended and the chelate spectrum recorded as the sample vaporized into the source. About 1 pg of chelate was used to obtain each complete spectrum. For sensitivity measurements, a small amount of perfluorotributylamine (PFTBA) was introduced uia the gas inlet system and one of its standard masses monitored on the low mass setting. The necessary decade (which very accurately changes the accelerating potential) was set to produce the single mass to be used for analysis (usually the largest peak in the spectrum) on the high mass position of the instrument. A few seconds before the probe tip was extended, the recorder was 1000
e
ANALYTICAL CHEMISTRY
started and the detector allowed to scan only the high mass peak. The result was a series of lines, each produced by a 1-sec scan over the desired range, that formed a plot closely approximating a binomial distribution as the sample vaporized and was pumped away. Depending on the metal, a sample size of 1 pg requires from 20 to 100 sec to completely vaporize (at 250 "C). During this time the standard mass peak can be checked and the magnet current adjusted to correct for hysteresis. RESULTS AND DISCUSSION
Figure 1 shows the mass spectra of six rare earth fod complexes. All of these compounds gave clean spectra containing molecular ion peaks at masses above 1000 amu and were easily removed from the instrument as determined by comparison of blanks run before and after. No particular attention should be paid to exact ratios of one intensity to another in a single spectrum because the spectra were obtained as the compound vaporized from the probe tip and the ion current was constantly changing. Only peaks within two orders of magnitude in intensity of the largest peak in the spectrum are shown. In all of the spectra reported here, only a few of the major peaks were determined precisely by peak matching. Since
+ ["I ( f o d )rC
J
N l l f o d)
Ni( f od),
I
1
L
Cut f o d l2
>
Cdtod)'
1 400
Cult od),
u ( f od ).$ FA
t
07
Figure 3. Mass spectra of Ni(fodh, Cu(fod)n,Pd(fodh, and Pb(fod)* -z
+
Nl(fod),
500
I, 11 600
700
P d I f o d ,)
Pd(fod), Pd(fodi
[p b It od $- C 51
the purpose of the study was to determine the analytical feasibility of the method, the point to establish was that reproducible, easily distinguishable spectra could be produced with trace quantities of metal. Hence, the use of rapid vaporization from the insertion probe causes the sample to flow quickly through the source, thereby allowing the detection of very small quantities but simultaneously making accurate peak matching difficult. Figure 2 shows the spectrum of the tris chelates of Al, Cr, Fe, and Y . While most of the compounds were easily pumped out of the instrument, large quantities of Cr(fod)r and A l ( f ~ d (more )~ than 100 pg of metal) were difficult to remove
Pb(fod\
and required as much as 2 hours of pumping to be removed completely. Figure 3 shows the mass spectra of the bis chelates of Ni, Cu, Pd and Pb. Figure 4 is the spectrum produced from a mixture of Al(fod),, F e ( f ~ d ) ~H, o ( f ~ d ) ~and , Tm(fod),. The mixture was composed of enough of each chelate to give 100 pg of each metal. (The spectrum was recorded with a low multiplier setting because of the great sensitivity for these compounds.) The major fragments of each individual compound are easily distinguishable. The peaks due to aluminum and iron are readily separated because of the relatively
>
Figure 4. Mass spectrum of a mixture con- v, taining 100 pg of the metal each of Al(fod),, + Fe(fodh, Ho(fodh, and 5 Tm(fod)s
E
VOL. 41, NO. 8,JULY 1969
1001
XI
x IO I
I
I
2
I
3
4
5
I
6
AI (picograms)
x 100 I
0
I
IO
20
30
1
I
I
40
50
60
T I M E (sec.) Figure 5. Time resolution scan of the mass 617 peak [Al(fod) +2] produced by l pg of A1 in the form of Al(fod), large difference in atomic weight. Since all of the compounds tend to produce roughly the same fragmentation pattern, all of the aluminum peaks are below the corresponding iron peaks by the same amount. Among several solvents studied, pentane and acetone had the most desirable properties. Both solvents are easily obtained in high purity, dissolve all of the metal chelates rapidly, and are suitable for mass spectrometric work. Furthermore, both acetone and pentane are pumped off in a few seconds in the vacuum insertion lock. Although no comprehensive study was made of the solvent system involved, compounds dissolved in acetone tended to decompose when allowed to stand for more than a day. On the other hand, pentane solutions of Al(fod),, Tm(fod),, Fe(fod),, and Ho(fod), showed no signs of decomposition over a period of 1 week. It appears, therefore, that the best solvent for this system is pentane. Sensitivity. The absolute detectability limit by this method was determined for Al, Tm, and Fe as the fod complexes in pentane solution. After stock solutions were prepared and dilutions made, the solutions used contained :
(1)
1.00 X
(2)
1.14 X lo-'* g Tm/p1
(3)
1.04 X
g Al/pI
g Fe/pl
The M(fod)nTpeak which is normally the most intense for the tris complexes was observed by reference to PFTBA as described above. Figure 5 shows a scan of the Al(fod)2+ peak us. time of 1.0 pg of A1 with the probe inserted at 0 seconds. The small signal seen before 0 seconds on the X1 galvanometer is actually aluminum which is slowly vaporized from the probe even while retracted. The actual background of the instrument in this mass range gives no measurable 1002
ANALYTICAL CHEMISTRY
Figure 6. Absolute amount of aluminum introduced as Al(fod)s 1;s. area of Al(fod)+, peak in time resolved scan signal on the X1 scale with the multiplier voltage set at maximum. From the areas of the traces of the X1 and XlOO galvanometer, it is apparent that aluminum would be detectable on the order of g by this method. Sensitivity measurements were also made for thulium and iron. Amounts of these metals down to 0.1 pg were easily detectable over the background runs made before and after each run. As may be expected, the metals do not all volatilize at the same temperature and rate, suggesting temperature programming as a possible aid in the analysis of extremely complex sample matrices. This could, in particular cases, eliminate the requirement for increased resolution which results in decreased sensitivity. Quantitative Measurement in the Picogram Region. Figure 6 shows a plot of the absolute amount of aluminum OS. the integrated area of the time scan produced. As can be seen quantitative results may be obtained in the picogram region. This measurement is limited by the accuracy at which solution can be delivered from the microsyringe (around ~ 5 % and ) the reproducibility of the vaporization process. The reproducibility appears to be much superior to that with spark source mass spectrometric techniques. Because the sample is converted to a mixture of volatile metal chelates prior to analysis, matrix effects are greatly reduced. Furthermore, this approach allows conventional multi-purpose mass spectrometers to be employed for metal analysis, thereby making it possible in some instances to avoid acquisition of costly spark source instrumentation. The same simple and rapid techniques for sample preparation which have already been successfully employed for metal analysis by gas chromatography can be used in analysis by mass spectrometry. The properties which make the complexes so suitable for one technique are taken advantage of in the other. The preparation techniques are based either on direct reaction and dissolution of the sample by simply heating it in contact with the liquid--e.g., Cr, Fe, Be, or A1 in ferrous alloys, ore, blood, urine, and other biological on solvent extraction of aqueous samples (I, 4, 17)-0r (17) W. D. Ross and R. E. Severs, 156th National Meeting, ACS, Atlantic City, N. J., September 1968.
samples-e.g., A1 and Cr in high purity uranium, Al, Cr, and F e in nonferrous alloys, Be, Al, Ga, In in aqueous solutions, A1 and Cr in steel, etc. (3, 18-23). Mass spectrometric studies of several other fluorocarbon fl-diketone complexes are presently in progress. Several other studies of the application of &diketone complexes to ultra-trace quantitative analysis are presently under way. One study of particular interest is the possible analysis of complex samples. The combined resolution of mass spectrometry with the quantitative reactions of such chelating agents should permit rapid, accurate analysis of many types of samples having elements varying over several orders of magnitude concentration without separation or preconcentration steps.
__ (18) C. Genty, C. Houin, and R. Schott, 7th Intl. Symp. on Gas
Chromatography, Copenhagen, June 1968. (19) J. Savory, P. Musak, N. 0. Roszel, and F. W. Sunderman, Jr., Federation Proceedings (Biochem.) Abstracts 52nd. Mtg., Atlantic City, N. J., April 1968,p 777. (20)R. W.Moshier and J. E. Schwarberg, Tulunru, 13,445 (1966). (21) G. P. Morie and T. R. Sweet, Anal. Chim. A m . , 34, 314 (1966). 37,1552 (1965). (22) G.P.Morie and T. R. Sweet, ANAL.CHEM., (23)W. G. Scribner, M. T. Borchers, and W. J. Treat, ibid., 38, 1779 (1966),and references therein.
It should also be emphasized that metal isotope analyses can be conducted with conventional instrumentation by using volatile chelates. It is expected that this will be particularly helpful in studies of the origin and history of samples obtained from the surface of the moon and other extraterrestrial sources. This new method should also facilitate investigations of the introduction, function, transport, and excretion of biologically important metal ions. By intxoducing either a stable or radioactive tracer of a given metal isotope and analyzing minute samples of fluids or tissues to determine isotope dilution, the distribution can be easily quantitated and followed. ACKNOWLEDGMENT The authors gratefully acknowledge the advice and suggestions of A. L. Crittenden. We are also grateful for samples provided by C. S. Springer, Jr., J. W. Connolly, and W. G. Scribner. D. C. Eckert assisted in the experimental work. RECEIVED for review January 10, 1969. Accepted April 29, 1969.
Metal Complexing Properties and Proton Magnetic Resonance Spectra of 5-Halo-8-Quin01 inoIs R. G . Beimer and Quintus Fernando Department of Chemistry, University of Arizona, Tucson, Ariz.
A series of 5-halo-8-quinolinols and 5-halo-2-methyl-8quinolinols have been synthesized from the corresponding 5-nitroso and 5-amino compounds. The proton magnetic resonance spectra of these compounds have been obtained in dimethyl sulfoxide (DE) and the proton chemical shifts have been measured. The acid dissociation constants of these ligands and their chelate formation constants with several transition metal ions have been measured in 75% v/v dioxane-water. The electronic effects caused by the introduction of halogen substituents in the 5-position of the 8-quinolinol ring system have been eva Iuated. THEINTRODUCTION of a halogen substituent in the 5-position in the 8-quinolinol molecule will result in a redistribution of electron density in the molecule and will influence the availability of electrons at the oxygen and nitrogen donor atoms for metal chelate formation. This electron redistribution results in the shielding or deshielding of the protons in the quinoline ring system. It should be possible, therefore, to evaluate these electronic effects from a measurement of the proton chemical shifts in the ligands. The enthalpies of formation of the metal chelates of the 5-substituted 8-quinolinols will also be influenced by an electron redistribution in the ligand. In the absence of steric effects, the entropies involved when chelate formation occurs between a given metal ion and a series of 5-halogen substituted ligands can be assumed to be constant. Consequently, the free energies of chelate formation or the values of the metal chelate formation constants can be used as an index of the availability of electrons on the bonding atoms in the ligands. Although it is well known that the thiocyano group is a
pseudo halogen, there is little quantitative information on the electronic effects of the thiocyano group, especially in ligands that participate in metal complex formation. For this reason the ligands, 5-thiocyano-8-quinolinoland 5-thiocyano-2-methyl-8-quinolinolhave been included in this study of 5-halo-8-quinolinols. EXPERIMENTAL Synthesis of 5-Substituted Derivatives of 8-Quinolinol and 2-Methyl-8-QuinolinoI. ~-FLUORO-~-QUINOLINOL. 8-Quinolinol was first converted into the 5-nitroso derivative, reduced to the 5-amino-8-quinolino1, and finally converted into the 5-fluor0 compound by the Schiemann reaction. The method described by Urbanski ( I ) was used in the synthesis of the 5-nitroso derivative and its reduction to the 5-amino8-quinolinol. The Schiemann reaction as described by Hollingshead ( 2 ) was used to convert the 5-amino-8-quinolinol sulfate into the 5-fluoro derivative which was recrystallized from ethanol and purified further by a vacuum sublimation. Found C, 65.61; H,3.61; F, 11.55; C a l c d ( z ) : C, 66.26; H, 3.71; F, 11.64; (mp 111-112 "C). ~ - B R ~ M ~ - ~ - Q u I NA~ L Sandmeyer ~ N ~ L . reaction was used to convert the 5-amino-8-quinolinol sulfate into the 5-bromo derivative. The method used was an adaptation of the method described by Vogt and Jeske (3). The compound was purified by vacuum sublimation. Found C, 47.28; H,2.72; Br, 35.31; Calcd C,48.24; H, 2.70; Br, 35.66; (mp 124.5 "C).
(z):
(z):
(z):
(1) T. Urbanski, Rocz. Chem., 25,297(1951). (2) R.G. W.Hollingshead, Chem. bid. (London), 344(1954). (3) H.Vogt and P. Jeske, Arch. Phur., 291,168 (1958). VOL. 41,
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