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(19) VanderHart, D. L.; Retkofsky, H. L. Fuel 1978, 55, 202-206. (20) Retkofsky, H. L. I n Coal Science; Gorbarty, M. L., Larsen, J. M., Wender, I., Eds.; Academic: New York, 1982; Voi. 1, pp 43-80. (21) Wilson, M. A.; Collin, P. J.; Pugmire. R. J.; Grant, D. M. Fuel 1982, 61, 959-967. (22) Botto, R. E.; Wilson, R.; Hayatsu, R. J.; McBeth, R. L.; Scott, R . G.; Winans. R. E. Prepr. Pap-Am. Chem. SOC.,Div. FuelChem. 1985, 30(4), 187-192. (23) Sullivan, M. J.; Maciel, G. E. Anal. Chem. 1982, 5 4 . 1606-1614. (24) Kaiman, J. R. I n Magnetic Resonance, Introduction, Advanced Topics and Applications to Fossil Energy; Petrakis, L., Fraissard, J. P., Eds.; D. Reidel: Dordrecht, 1984; pp 557-567. (25) Vassalio, A. M.; Wilson, M. A.; Collin, P. J.; Oades, J. M.; Waters, A. G.; Malcolm, R. J. Anal. Chem. 1987, 5 9 , 558-562. (26) Wemmer, D. E.; Pines, A.; Whitehurst, D. D. Phllos. Trans. R . SOC. London, A 1981, 300, 15-41. (27) Hagaman, E. W.; Chambers, R. R., Jr.; Woody, M. C. Anal. Chem. 1988. 58, 387-394. (28) Hatcher, P. G.; Breger, I.A.; Dennis, L. W.; Maciei, G. E. I n Aquatic and Terrestrial Humic Material; Christman, R. F.. Gjessing, E. T., Eds.; Ann Arbor Science: Ann Arbor, MI, 1983; pp 37-82. (29) Wilson, M. A.; Pugmire, R. J.; Grant, D. M. Org. Geochem. 1983. 5 , 121-129. (30) Pfeffer, P. E.; Gerasimowicz, W. V.; Piotrowski, E. G. Anal. Chem. 1984, 56. 734-741. (31) Preston, C. M.; Dudley, R. L.; Fyfe, C. A,; Mathur. S. P. Geoderma 1984, 33, 245-253. (32) Perdue, E. M. Geochim. Cosmochim. Acta 1984, 48, 1435-1442. (33) Wilson. M. A.; Philp, R . P.; Giilam, A. H.: Gilbert, T. D.; Tate, K. R. Geochim. Cosmochim. Acta 1983, 4 7 , 497-502. (34) Anderson, H. A.; Russell, J. D. Nature (London) 1978, 260, 597.
(35) Braceweli, J. M.; Robertson, G. W.; Welch. D. I.J. Anal. Appl. Pyro&SiS 1980, 1 , 239-248. (36) Reuter, J. H. Chemical and Spectroscopic Characterization of Humic Substances Derived from River Swamps In the Flood Plains of Southeastern Georgia; U S . Coastal Streams Technical Report USOI/OWRT Project No. B-132-GA; Georgia Institute of Technology, Atlanta, GA, 1980. (37) Opelia, S.J.; Frey, M. H. J. Am. Chem. SOC.1979, 101, 5854-5856. (38) Bayer, E.; Albert, K.; Bergmann, K. J.; Eusener, W.; Peters, H. K. Angew. Chem., Int. Ed. Engl. 1984, 23, 147-149. (39) Wershaw, R. L.; Miklta, M. A.; Steelink, C. Envlron. Sci. Techno;. 1981. 15. 1461-1463. (40) Simmonds, P.-G.; Schulman, G. P.; Stembridge, C. H. J . Chromatogr. Scl. 1989. 29. 36-41. (41) Wilson, M: A.; Vassallo, A. M.; Collin, P. J.: Rottendorf, H. Anal. Chem. 1984, 56, 433-436. (42) Perdue, E. M.; Reuter, J. H.; Ghosal, M. Geochim. Cosmochim. Acta 1980, 44, 1641-1851. (43) Perdue, E. M. I n Humic Substances in Soil, Sediment, and WaterGeochemistry, Isolation, and Characterization; Aiken, G., McKnight. D., Wershaw, R., MacCarthy, P., Eds.; Wiley-Interscience: New York, 1985; pp 493-526. (44) Hatcher, P. G.; Schnitzer, M.; Dennis, L. W.; Maciel, G. E. Soil Sci. S o c . A m . J . 1 9 8 1 ,45, 1089-1094. (45) Wilson. M. A.; Heng, S.; Goh, K. M.; Pugmire, R. J.; Grant, D. M. J. Soil Sci. 1983, 3 4 , 83-97.
RECEIVED for review June 30, 1986. Accepted October 20, 1986.
Structural Analysis of Geochemical Samples by Solid-state Nuclear Magnetic Resonance Spectrometry. Role of Paramagnetic Material Anthony M. Vassallo,* Michael A. Wilson, and Philip J. Collin CSIRO Division of Fossil Fuels, P.O. Box 136, North Ryde, New South Wales, Australia
J. Malcolm Oades and Angela G . Waters Department of Soil Science, Waite Agricultural Research Institute, University of Adelaide, Glen Osmond, South Australia, Australia
Ronald L. Malcolm U S . Geological Survey, Denver Federal Center, Denver, Colorado 80225
An examination of coals, coal tars, a fulvlc acid, and soli fractions by solid-state I3C NMR spectrometry has demonstrated widely dlffering behavlor regardlng quantltatlve representatlon In the spectrum. Spln counting experlments on coal tars and the fuivlc acid show that almost all the sample carbon Is observed In both solution and soild-state NMR spectra. Simliar experlments on two coals (a lignite and a bitumlnous coal) show that most ( 7 0 4 7 % ) of the carbon Is observed; however, when the lignite Is ion exchanged with 3 % (w/w) Fe3+, the fractlon of carbon observed drops to below 10 YO. I n addltlonai experlments slgnai IntensHy from sol1 samples Is enhanced by a slmple dithionite treatment. This is illustrated by "C, "AI, and 20Slsolld-state NMR experiments on soli fractions.
Over the last few years there has been extensive application of high-resolution solid-state, nuclear magnetic resonance (NMR) spectrometry in the study of fossil fuels, soils, and humic substances. This work has demonstrated the enormous
usefulness that solid-state NMR can have in such areas of structure elucidation, chemical reactivity, and biogenesis. One of the problems however in the interpretation of these data has been, and remains, the uncertainty of how much of the substance under investigation is represented in the final spectrum. For example, in 13C cross polarization with magic angle spinning (CP-MAS) it has been demonstrated that in some samples, proton spin-lattice relaxation times in the are reduced by paramagnetic material rotating frame ( T 1 8 (1,2). Relative signal intensity may also be not quantitatively represented in a single spectrum because of inhomogeneous T I H and Tl$Y's (3-7). Some of these latter problems can be overcome by a judicous choice of contact time or recycle delay or by curve fitting the relaxation behavior to obtain the signal intensity in the absence of relaxation effects. However, although this approach may produce the correct representation of observable carbons, it does not indicate how much carbon is actually being observed. There have been several reports concerning the estimation of how much carbon is represented in the spectra of problem materials, such as coal (5,8-11). The approach has generally
0003-2700/87/0359-0558$01.50/00 1987 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 59, NO. 4, FEBRUARY 15, 1987
Table I. Elemental Analysis of Samples Used in CP-MAS NMR Studies sample
%C
69.0 66.8 78.5 87.4 2 87.1 3 88.1 4 89.8 5 88.2 4.6 Soil PP012 3.94 Soil PP012c Suwannee fulvic acid 51.3
Morwell coal Morwell coalb Millmerran coal coal tar 1
% H
% ash
% Fen % Mnn
4.8 4.6 6.5 7.0 6.5 6.6 6.1 6.7 N.D.d N.D. 4.32
2.3 N.D. 15.1 > TIJI and S , in eq 1 tends to zero. It is also likely that the resonance frequency of the protons is now so broad that they cannot be adequately irradiated with a 5-ps pulse. Although different amounts of carbon are seen in the Fe3+-exchanged and natural coal, the aromaticity measurements are almost identical. This suggests that reasons other than paramagnetics must be sought to explain why some data on coals can be shown to be nonquantitative ( 3 , 4 ) . A probable explanation is found in the heterogeneity of coal. Minerals,
ANALYTICAL CHEMISTRY, VOL. 59, NO. 4, FEBRUARY 15, 1987
561
a) a)
i!
b)
*
-
0 -50 -100 -19 -200 Chemical shift, Bppm
Flgure 1. Solid-state 28Sidipolar decoupled MAS spectra of Urrbrae soil fraction
