1227
Anal. Chem. 1981, 53, 1227-1231
to both the iron borate and copper borate species. Their identical ligand environments should result in a similar elution volume. The other iron-containing peaks, in order of increasing retention volume and decreasing size, are diacetylferrocene and ferrocene. The bis(dihydrogen dipyrazolylborate)copper(II) elutes as a shoulder in the copper and boron channels at 8.23 mL retention volume. This is consistent with the smaller ligand system incorporated in the molecule. Quantitation. Although the C-21 standards were not composed of single species, they were produced to be quantitative in total metal content. A calibration of the LC-ICP system can be achieved by elimination the separation column and injecting known concentrations of standard. For this calibration, C-21 standards a t 6.25, 12.5, and 25 ppm were used. Calibration graphs of intensity minus background for several monodispersed metal species (Le., Al, Ca, V, and Cr) were linear. The data points corresponded to an average of two injections. The information for each metal was obtained simultaneously and plotted with aid of the software developed. The flow rates were reduced to 0.3 mL/min to ensure that there were sufficient number of data points obtained per peak. This was necessary because the peak spread sometimes resulted in the peak maxima being missed. In this case, the datum was not considered in the average. Overall, good linearity and background correction were achieved in the toluene matrix. In summary, the technique of LC-ICP has been illustrated employing size exclusion separation for organically bound metal species with toluene eluent. For elimination of carbon buildup and abnormally high nebulization efficiencies, a thermostated spray chamber was developed which yielded detection limits in toluene 10-100 times lower than measured
with conventional spray chambers. Extension of this work to the speciation of organometallics in nonaqueous solvents is under way.
ACKNOWLEDGMENT We thank Edwige Denyszyn for assistance in preparing this manuscript. Helpful discussions with R. Brown, H. McNair, and H. Dorn are appreciated.
LITERATURE CITED Van Loon, J. Anal. Chem. 1979, 57, 1139A-1150A. Feranandez, F. At. Abs. News/. 1977, 76, 33-36. Fraley, D. M.; Yates, D.; Manahen, S. E. Anal. Chem. 1979, 57,
2225-2229.
Uden, P. C.; Barnes, R. M.; Disanzo, F. Anal. Chem. 1978, 50,
852-855. Lloyd, R. J.; Barnes, R. M.; Uden, P. C.; Elliott, W. 0. Anal. Chem. 1978, 50, 2025-2029. Uden, P. C.; Quimby, 8. D.; Barnes, R. M.; Elliott, W. 0. Anal. Chlm. Acta 1978, 707, 99-109. Sommer, D.; Ohio, K. Fresenius' 2. Anal. Chem. 1879, 295,
337-341. Morlta, M.; Uehiro, T.; Fuwa, K. Anal. Chem. 1980, 52, 349-351. Gast, C. H.; Kraat, J. C.; Poppe, H.; Maessen, F. J. M. J. J. ChromatOgr. 1979, 785, 549-561. Windsor, D. L.; Denton, M. B. Anal. Chem. 1979, 57, 1116-1119. Orooves, R. L., Conoco Oil Co., personal communication, 1980. Barnes, R. M. Crn. Rev. Anal. Chem. 1978, 7, 203-296. Hausler, D. W.; Heligeth, J. W.; McNair, H. M.; Taylor, L. T. J. ChromatOgr. SCi. 1979, 77, 617-623. Coleman, W. M.; Wooton, D. L.; Dorn, H. C.; Taylor, L. T. Anal. Chem. 1977, 49, 533-537. Jesson, J. P.; Trofimenoko. S.; Easton, D. R. J. Am. Chem. Soc. 1987, 89, 3158-3164.
RECEIVED for review September 16,1980. Accepted April 2, 1981. The generous financial assistance provided by Department of Energy Grant DE-AC22-80PC30041 and the Commonwealth of Virginia is acknowledged.
Size Exclusion Chromatography of Organically Bound Metals and Coal-Derived Materials with Inductively Coupled Plasma Atomic Emission Spectrometric Detection D. W. Hausler and L. T. Taylor" Department of Chemistty, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 2406 1
Organometallic and metalloorganlc compounds have been separated by slze exclusion chromatography using pyrldlne eluent. A dlrectly Interfaced inductively coupled plasma atomlc emlsslon spectrometer was used for detectlon of these metal-contalnlng specles. Problems relating to the use of pyridine In the chromatography of these species are discussed. Most problems appear to be related to non-carbonbound metal systems. The application of this technlque to solvent-refined coal fractions and process solvent Is presented. Evldence of solvent selectivity for some of the organlcally bound metals In the solvent refined coal is given.
In the preceding paper (I),we demonstrated the feasibility of interfacing a liquid chromatography to an inductively coupled plasma atomic emission spectrometer (ICP-AES) for simultaneous multielement detection. Size exclusion separations of several metal-containing compounds with toluene as the mobile phase were illustrated. Peak broadening by the
ICP detector was comparable to that observed with the more commonly used differential refractive index detector. Previously, ICP-AES had been primarily limited to aqueous based solvents (2) and chromatographic applications had been restricted to the sequential, single element mode ( 3 , 4 ) . Very little work in an organic matrix has appeared in the open literature. The simultaneous determination of 15 different wear metals in lubricating oils dissolved in 4-methyl-2-pentanone has been reported (5). Detection limits range from 0.0004 to 0.3 ppm. One chromatographic separation of a mixture of ferrocene compounds with ICP-AES as a singleelement detector and toluene eluent has appeared (6). The particular difficulties of hydrocarbon solvents in plasma analysis have been discussed by Uden et al. (7).Mixtures of Skellysolve B and either methylene chloride or acetonitrilediethyl ether have been investigated albeit with a DC plasma rather than an ICP. Trace metal analyses and detection in an organic phase offer several advantages: (1)fewer sample handling techniques, (2) no opportunity for the introduction of trace metal impurities in an ashing step, (3) direct analysis
0003-2700/81/0353-1227$01.25/00 1981 Amerlcan Chemical Society
1228
ANALYTICAL CHEMISTRY, VOL. 53, NO. 8, JULY 1981
Table I. Detection LimitsQin Organic Solvents element pyridine tolueneC MIBKd aqueouse Ag A1 Ba Cd Cu Fe Mg Mn Ni
0.037 0.023 0.004 0.005 0.02 0.02 0.003 0.005 0.061 0.48 0.53 0.22
Pb Si Sn Ti
0.01
V Zn
0.05 0.008
0.0246 0.0137 0.0029 0.0050 0.0165 0.0695 0.0005 0.0018 0.0345 0.0905 0.197 0.0414 0.0033 0.0395 0.00475
0.02 0.09 0.006 0.04 0.007 0.01 0.1 0.3 0.07 0.03 0.03 0.03 0.04
0.007
0.045 0.0013 0.0034 0.0054 0.0062 0.00015 0.0014 0.015 0.042 0.027 0.025 0.0038 0.0075 0.0040
a Results reported in ppm. Detection limits = 2 x background e uivalent concentration. This work. Reference 1. $ Reference 2. e Reference 11.
of organically bound metals, and (4) possible metal speciation data when coupled with high-performance liquid chromatography (HPLC). Pyridine is a particularly good solvent for most synfuel materials (8). In addition, we (9) have shown pyridine to be an acceptable mobile phase for size exclusion chromatography (SEC) of synfuels. Its use as a mobile phase for the separation of organically bound metals has not been examined. An evaluation of pyridine as the mobile phase for the SEC separation of several coal-derived materials and simpler metal-containing compounds utilizing ICP detection is presented. EXPERIMENTAL SECTION The basic LC-ICP system employed in this study has been described previously ( I ) . An ARL (Applied Research Laboratory, Sunland, CA) ICP-AES Model 137000 was used for metal detection. Chromatographic grade pyridine (Fisher Scientific Co.) was used as received. The pumping system for the chromatographic separations was a Waters 6000A (Milford, MA). Separations were achieved by using a 100-AWStyragel column (Waters, Milford, MA) at a flow rate of either 1.0 or 0.5 mL/min. Elemental standards (Conoco C-21, Pomoco, OK) in a petroleum-based organic matrix were obtained and appropriately diluted. Other compounds employed were commercially available or were synthesized by established procedures. Samples for chromatography were dissolved in pyridine at a concentration of approximately 0.1 mmol/lO mL of solvent. The plasma was maintained at 1400 W incident power and 0 W reflected power. Detection limits were ascertained on aspirated pyridine solutions of Conoco C-21 standards. The detection limits were based on twice the background noise. Integration times for static and chromatographic conditions were 10 and 5 s, respectively. The spray chamber reported previously ( I ) was thermostated at room temperature (20 "C) with a water circulation bath. The coal-derived material investigated here is Amax solventrefined coal (SRC) and process solvent developed from a Southern Services Inc. pilot plant (Wilsonville,AL) funded by the Electric Power Research Institute and operated by Catalytic Inc. The SRC was initially separated into chloroform, tetrahydrofuran, and pyridine soluble fractions using a solvent to sample ratio of 40:l followed by filtration of the material through a 1-pM filter. The soluble portion was then rotary evaporated under vacuum to remove the solvent. The solid samples were then dried in vacuo at 100 "C and stored under an argon atmosphere. Approximately 0.5 g of each fraction was subsequently redissolved in 4 mL of pyridine. Two hundred microliters of each fraction was then injected onto a 100-A p-Styragel size exclusion column and eluted with pyridine at 0.5 mL/min. RESULTS AND DISCUSSION Table I lists the detection limits for 15 metals in pyridine. Nearly all of the metals have detection limits within a factor
'50m*
RETENTION
j\
VOLUME
C"
(mll
Figure 1. Elution of Conoco C-21 organometallic standard on a 100-A p-Styragel size exclusion column with specific metal detection by, ICP-AES: flow rate, 0.5 mL/min; solvent, pyridine; injection, 50 pL of 60 ppm standard.
of 5 of the detection limits in methyl isobutyl ketone (2) and water (11)published by Fassel. Also listed are detection limits for selected metals in toluene (1). Detection limits in an organic phase are slightly greater than those obtainable in water because the background continuum for the organic phase and recombinant molecular emissions should be higher. Although a stable plasma in toluene required thermoetating the spray chamber a t 0 "C, pyridine was found to produce a similar plasma with the spray chamber thermostated a t 20 "C. The size exclusion chromatographic behavior of several synthetic and commercial mixtures of metal-containing compounds with pyridine as the mobile phase was studied. With an element-specific detector, metal-specific fractions were readily identified. A 21-element quantitative standard (Conoco C-21) provided a complicated metal-containing mixture for chromatographic p-Styragel separation. The upper molecular weight limit of this column was found to be approximately 750 amu based on elution of hydrocarbon standards in tetrahydrofuran solvent. Since all metal compounds should be electrically neutral by virtue of their organic solubility, we have assumed that the highest oxidation state should yield the largest size complex. Each elemental standard is believed to be a dialkylbenzenesulfonate with an approximate molecular weight of 1500 amu exclusive of metal (12). Clearly, this should be beyond the totally excluded molecular weight capability of a 100-A p-Styragel column. Nevertheless, some of the C-21 standards exhibited selective permeation with pyridine elution as shown in Figure 1. Three characteristic peak shapes are evidenced in this separation. Simple monotonic peaks (Ti, Cr, V, Mn, Cu, Ni, Cd, and Al) appear; peaks with shoulders are evident (Mg and Ca); and multiple peaks are indicated for Fe and Zn. The four metal complexes that elute at 5.32 mL (Al, Cr, Ti, and V) show reasonable symmetry due to the fact that the peak fronts are eluting near the totally excluded volume of 4.75 mL. Again, this is anticipated because these metal species should be a t least trivalent and their complexes with dialkylbenzenesulfonates would have molecular weights in excess of 1000 amu. Nickel, copper, manganese, and cadmium elute in the permeated region and have simple monotonic approximately Gaussian shaped peaks. As these standards are produced from a reaction of dialkylbenzenesulfonic acid and the basic metal oxide ( I 2 ) , it is tempting to try to correlate the retention
ANALYTICAL CHEMISTRY, VOL. 53, NO. 8, JULY 1981
1229
Table 11. Size Exclusion Chromatographic Retention Volumes of (2-21 Standards Using Specific Metal Detection retention retention metal volume, mL metal volume, mL A1
5.32 5.32 5.32 5.32 5.66 5.74
Cr Ti V
cu Ca
Mt3
Mn Cd Ni
Fe Zn
5.74 5.91 6.00 6.00 5.32, 6.00 5.66, 6.00 7.00-8.20
I\
A
9E-*, d5 B
”
L
615
C
OH2
E
”
D
F
Flgwe 2. Structural formula of compounds separated by size exclusion chromatography: (A) bis(tetrapyrazolylborate)iron(II), (6) 1,l’-diacetylferrocene, (C) acetylferrocene, (D) ferrocene, (E) copper(I1) acetate 1-hydrate, and (F) bis(o-amlnobenzaldehyde)ethylenedllmlnecopper(I1).
volume with the expected oxidation state of the metallic species. The permeation of Mn, Ni, Cu, and Cd species which are believed to contain divalent metal suggests an apparent smaller size even though molecular weights in excess of 700 amu are probable (Table 11). This observation is in contrast to the results on C-21 standards obtained in toluene; where, these divalent metal species were totally excluded (I). One explanation of this observation could be differing solvolysis whereby the pendant alkyl chains are more tightly “kinked” in pyridine than that observed using toluene eluent. Support for this argument comes from the fact that apparent exclusion limits in pyridine for hydrocarbon injections have been found to double the exclusion limits in toluene for the same hydrocarbons (9). The multiplet peak of iron and zinc is more difficult to explain. The earlier eluting iron peak is coincident with the elution of higher oxidation state species (e.g., V, Al, Cr, and Ti). This peak may be due to an iron(II1) species. The second peak elutes at a much smaller size and may be due to iron(I1). The multiplet for zinc is equally difficult to explain. The first peak may be the expected zinc bis(dialkylbenzenesulfonate). The remaining peaks could arise from the presence of pyridine adducts, or mixed ligand-metal complexes such as [M(OH)L]. A simpler mixture composed of ferrocene 1,l’-diacetylferrocene, acetylferrocene and bis(tetrapyrazolylborate)iron(II) has been studied (Figure 2). The four compounds are clearly
l
N
658 702
1
1
754 7 9 9
1
1
8
853
907 951
RETENTION
VOLUME
8
1
1005 1018
I
1102
(mll
Figure 3. Separation of bls(tetrapyrazolylborate)iron(II), 1 , l ‘aiacetylferrocene, acetylferrocene, and ferrocene with Fe and B detection: flow rate, 0.5 mL/min; injection, 50 pL of 0.01 M solution; solvent, pyridine.
resolved (Figure 3) via SEC with pyridine elution. Since the boron response shows a peak at the same elution volume as the first iron peak, peak no. 1is assigned to the iron borate. Elution in the order of decreasing molecular size was observed for the other three complexes as expected. All four peaks were independently identified by comparison of single compound injections and by spiking the mixture with each compound. No nonsize exclusion effects were noted. Comparison of the separation of the same mixture in pyridine and in toluene reveals interesting solvent interactions. The separation (with Fe detection) of ferrocene, 1,l’-diacetylferrocene, and bis(tetrapyrazolylborate)iron(II) with toluene and pyridine elution is shown in Figure 4. The same 100-A 1-Styragel column was employed and equilibrated in the solvent of choice. In the first case (Figure 4) the mixture was made up in toluene, injected (50 pL), and eluted with toluene. The resolution between 1,l’-diacetylferrocene (peak 2) and ferrocene (peak 4) has decreased markedly from that shown in Figure 3. Equilibration of the same column in pyridine and injection of the same mixture (made up in toluene) yielded different retention volumes (Figure 4) for all components. Bis(tetrapyrazolylborate)iron(II) (peak 1)and ferrocene (peak 4)have retention volumes identical with those experienced in Figure 3 (i-e.,sample made up in pyridine and eluted with pyridine). The 1,l’-diacetylferrocenepeak is now a partially resolved doublet, considerably shifted from the retention volume measured with toluene elution. Clearly, there are interactions at work in this sequence of separations that are not fully understood. It is possible that the changing retention volumes are due to associations of the ligand and/or iron center with pyridine which do not exist in toluene. In the case of the 1,l’-diacetylferrocene,the double peak could represent a nonequilibrium mixture of compounds where one and two pyridine molecules are associated with the organometallic possibly through the carbonyl moiety. The
1230
ANALYTICAL CHEMISTRY, VOL. 53, NO. 8, JULY 1981
r
H 2599.4 A
A ~P~ACETATE),
0
A
2 4 6 8 RETENTION VOLUME (ml)
Flgure 6. Separation of (A) dimeric copper(I1) acetate and (B)bis(oaminobenzaidehyde)ethyienediiminecopper(II). Conditions are same as in Figure 3.
RETENTION VOLUME (ml)
Separation of bis(tetrapyrazoiyiborate)iron(II), 1,l’-diacetylferrocene, and ferrocene: flow rate, 0.5 mL/min; inlection, 50 fiL of 0.01 M solution sample dissolved in toluene; eluting solvent, toluene and pyridine. Figure 4.
C d a c a c l2
A
0
2 4 6 8 1 RETENTION VOLUME (rnl)
0
Figure 7. Separation of (A) tris(acetyiacetonato)cobaR(III), (B) bis-
(acetyiacetonato)cobait(II),and (C) the mixture of (A) and (B). Con-
i\ I
0
I
I
2
I
4
I
6
I
I
6
I
1
I
ditions are same as in Figure 3.
~
0
I
1
I
I
2
RETENTION VOLUME (ml)
Figure 5. (A) Separation of bis(acetylacetonato)opper(II), conditions same as in Figure 3. (B)Same sample as (A) but injected immediately after elution of (A), conditions same as in Figure 3.
other models contain no carbonyl group and do not yield multiple peaks. Interaction of pyridine with eluting molecules was even more serious with other systems. Many oxygen and nitrogen ligand systems in combination with more labile metals interact strongly with pyridine. Nonreproducible retention volumes were characteristic of this group of models upon successive injections. The copper metallograms produced during the separation of bis(acetylacetonato)copper(II) serve as an example of these changes. A different multicomponent peak (Figure 5) is produced after equilibration relative to before equilibration of the pyridine solution. Furthermore, the ratio of each peak component changes with time. This behavior is suggestive of the presence of several species which may or may not be in equilibrium with each other. The separation of dimeric copper(I1) acetate (Figure 2E) provides another example of anomalous retention/solvent interaction characteristics. Two peaks are evident in the copper metallogram (Figure 6) suggestive of dimeric and monomeric copper. A similar situation developed in the separation of bis(oaminobenzaldehyde)ethylenediiminecopper(II) (Figure 2F). Three resolved peaks appear in the copper metallogram
(Figure 6B). In each of these examples, we believe that solvent-solute interactions are evident. Either successive replacement of coordinated water molecules, disruption of the dimer structure, or production of a higher coordinate copper(I1) species can be envisioned. A dramatic demonstration of what may be generally the case regarding labile and kinetically inert metal species in a good donor solvent is afforded by bis(acety1acetonato)cobalt(I1) and tris(acetylacetonato)cobalt(III). C o ( a ~ a c )is~ monomeric and inert to substitution, whereas Co(acac)z is tetrameric and labile to substitution (13). Separation of Co(acac)3reveals a symmetrical peak (Figure 7) which we believe is evidence of minimal solvent interaction and a montonic species. The retention volume and peak shape (Figure 7B) for the separation of [ C o ( a c a ~ ) is ~ ]markedly ~ different. The tailing that is present is evidence of solventsolute interaction. A mixture of [Co(acac)2]4 and Co(acac)3 in pyridine when separated (Figure 7C) yields two characteristic peaks (e.g., broad peak, lower retention volume-labile Co(11); narrow peak, larger retention volume-inert Co(II1)). It is thought that these solvent interactions resulting in anomalous behavior could be beneficial for speculation even though the results, at first glance, might appear to the contrary. Coal-Derived Materials. Size exclusion chromatograms of chloroform, tetrahydrofuran, and pyridine soluble fractions with specific metal detection are shown in Figures 8 and 9. The quantity of metals eluting with pyridine increases in the order CHC1, < THF < Py. For example, Al, Ca, and Ti show no detectable quantities in THF- and CHC13-solublefractions, but each have well-developed peaks at the totally excluded volume for pyridine soluble SRC. Cu and Fe are totally
ANALYTICAL CHEMISTRY, VOL. 53, NO. 8, JULY 1981
n
R . .
1231
Pyridine Soluble
Separation of CHCI,-, tetrahydrofuran-,and pyridinasolubie fractions of A m SRC eluted with pyridine on 100-A p-styragel column with Mg, Ca, and AI detection: flow rate, 0.5 mL/min; injection, 200 Figure 8.
;=-.,
CLL.
Cd
Ismr
NcL.h.c.I*
.:;=gIPgF:
z g g : g $ g Q
n m ~ f o a h m m
Ism?
Hg
;..$?. =gp:z$gQ ; & . . I
m n v n i ~ ~ m mn n v o l o c m m RETENTION
VOLUME
(mll
Separation of an SRC process solvent diluted 1:l with pyridine with specific metal detection. Conditions are same as in Figure Flgure 10.
a.
RETENTION
Flgure 9.
VOLUME
lmll
Same as Figure 8 but with Ti, Fe, and Cu detection.
different. Multiple peaks associated with Fe suggest a rich variety of iron-containing species. The chloroform soluble fraction has a good percentage of material eluting in the permeated region, whereas the pyridine fraction appears to elute near the high molecular size limit for this column. The situation regarding Cu is also interesting. Cu elutes completely within the molecular size range of the column to yield rather narrow peaks. Peak maxima for CHCl,-soluble and THFsoluble SRC are significantly different. This indicates different Cu species have been solubilized by the two solvents, or interaction of the same Cu species with the two solvents is different. It is also interesting to note that the copper peak obtained with pyridine-soluble SRC appears to be a composite of the copper metallograms obtained with CHC13- and THFsoluble SRC. Quite possibly the differing Cu species are both soluble only in pyridine. Of the remaining metals monitored, only Mn showed a significant concentration qf metal. This material appeared in pyridine-soluble SRC and eluted near the totally excluded volume. A coal liquefaction process solvent was also examined for organically bound trace metals (Figure 10). Mg which obviously is of low concentration, shows a wide molecular weight distribution. T i is also low in concentration but appears to have a more monodispersed distribution. Mn has a very distinct bimodal distribution. Although not present in a large number of other coal-derived materials, Cr shows a concentrated high molecular weight distribution as does Fe albeit less concentrated. There has been evidence of erosion/cor-
rosion of some of the alloys used at the Wilsonville plant and this may account for the high Cr concentration. Cu and Zn show low molecular weight distributions with the Cu again exhibiting multiple species. Hg shows small amounts of relatively high molecular weight material. The implications of detecting organically bound metals in coal-derived materials are clear. Hopefully, specific speciation techniques for several elements can be developed. We believe the simultaneous multielement detection afforded by "on-line" LC-ICP is a viable pathway toward the speciation.
ACKNOWLEDGMENT We thank E. Denyszyn and D. Perdue for assistance in preparing this manuscript. Helpful discussions with R. Brown and H. Dorn are appreciated. LITERATURE CITED Hausler, D. W.; Taylor, L. T. Anal. Cbem. 1981, 5 3 , 1223-1227. Fassel, V. A.; Kniseley, R. N Anal. Cbem. 1974, 46, llOA-120A. Morita, M.; Uehiro, T.; Fuwa, K. Anal. Cbem. 1080, 52, 349-351. Sommer, D.; Ohlo, K. Fresenius' Z . Anal. Cbem. 1979, 295, 337-341. (5) Fassel, V. A.; Peterson, C. A.; Abercrombie, F. N.; Kniseley, R. N. Anal. Cbem. 1976, 48, 516-519. (6) Gast, C. H.; Kraak, J. C.; Poppe, H.; Maessen, F. J. M. J. J. Cbromatogr. 1979, 185, 549-561. (7) Uden, P. C.: Quimbv, B. D.: Barnes. R. M.: Elliott. W. G. Anal. Cbim. Acta 1978, 701, 99-109. Mayo, F. R.; Kirshen, N. A. Fuel1978, 5 7 , 405-408. Hausler, D. W.; Heiigeth, J. W.; McNair, H. M.; Taylor, L. T. J. Chromafogr. S o . 1979, 17, 617-623. Cassity, R. P.; Taylor, L. T. J. Coord. Cbem. 1979, 9 , 71-77. Winge, R. K.; Peterson, V. J.; Fassel, V. A. EPA Report 600/679-017. March 1979, "Inductively Coupled Plasma-Atomic Emission Spectroscopy: Prominent Llnes". Groves, P. L., Conoco Oil Co., Pomoco, OK, private communication, 1980. Cotton, F. A.; Elder, R. C. Inorg. Chem. 1965, 4 , 1145-1151. (1) (2) (3) (4)
RECEIVED for review October 3, 1980. Accepted April 2,1981. The generous financial assistance provided by Department of Energy Grant DE-AC22-80PC30041 and the Commonwealth of Virginia and Department of Interior Virginia Mining and Mineral Resources and Research Institute is acknowledged.
