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Infrared Estimation of Oil Content in Sediments in Presence of Biological Matter Harry B. Mark, Jr.,I and Ta-Ching Yu Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221
James S. Mattson2 Ouachita Industries, Inc., Monroe, La. 71201
Ronald L. Kolpack Department of Geological Sciences, University of Southern California, Los Angeles, Calif. 90007 ~~~~
The crude oil content of marine sediments was determined by ir spectrometry from the magnitude of 2925 cm-1 (-CHzstretching band) absorbance. Biological materials also absorb at 2925 cm-I and have a well-defined absorbance band at 1650 cm-1 (the -NHband characteristic of proteins) whereas, crude oils do not exhibit an amide band. The relative contributions of oil and organic material of recent biological origin in marine sediments were determined from measurements of these two absorbance bands, and a correction applied which enables the calculation of the oil content in the presence of these biological materials.
I
n a recent study of the effects of the winter 1969 oil blowout at Platform A in the Santa Barbara Channel, analytical procedures for the rapid determination of the oil content of the channel bottom sediments using both transmission and internal reflectance ir spectrometry were reported (Mattson et al., 1970b; Kolpack et al., 1971; Yu et al., 1971). In these analyses, the oil content of the sediment w d S considered to be related to the magnitude of the 2925 cm-1 (-CHzstretching band) absorbance. Those analyses were made primarily on bottom sediments which were deposited following a major flood. The rate of sedimentation of this highly oxidized detrital flood material was very rapid and in most samples there were no significant amounts of organic material of recent biological origin present. However, some of the samples were obtained from the central part of the Santa Barbara Channel up to 18 months after the flood. The rate of detrital sedimentation in this area is much slower, and the surficial sediments often were mixed with organic debris of biological origin. The presence of biological material interfered with the determination of the oil content as the -CH*groups of such biological matter also absorb at 2925 cm-l. This ir band is identical for any -CHz--containing compound, and the relative contributions of oil and biological matter to the observed absorbance cannot be determined by a simple measurement of the 2925 cm-l band. This paper reports a simple extension of the above ir procedure which permits estimation of the concentration of biological materials. This provides a method for correcting the 2925 cm-1 absorbance band to enable the estimation of the oil contribution alone.
Experimental The experimental procedures and the instrumentation employed in this study are described in detail in previous publications (Mattson et al., 1970b; Kolpack et al., 1971; Yu and Mark, 1971; Mattson et al., 1970~).A Beckman IR-12 infrared spectrometer was employed for all measurements described in this paper. Results and Discussions
The complete ir spectrum of a large number of different crude oils (Mattson, 1971) and of different biological materials was examined. All materials of biological origin exhibited a large, well-defined absorbance band at 1650 cm-I (the -NHband characteristic of proteins) while crude oils and sediments had no observable 1650 cm-I band (Figure 1). The ir spectra of a variety of finely ground biological materials in sediment were measured in the region from 4000 to 1200 cm-1. Similar spectra results were obtained for both transmission and internal reflectance modes of measurement. In each sample the peak absorbances of the -CHzband at 2925 cm-l and of the secondary amide band at 1650 cm-1 were measured and the -CH2-/-NHratio calculated from the absorbance bands. It was found that this -CHz-/-NHband ratio was relatively constant (varying from 1.24 to 1.42 for transmission ir measurement) for all of the biological materials examined (see Table I) and also was independent of the concentration of
Table I. Comparison of the -CHz/--NHPeak Ratios for Various Biological Materials -NH(1650 cm-l)
-CHz-
(2925cm-l) (transmis(transmission, sion peak length) peak length)
Plankton Algae Seaweed Shrimp Kelp Equal mixture of plankton, algae, seaweed, shrimp, kelp
12 12 9.5 9.5 10 11
7 6 6 6 5
7
-CHz-/ -NH(transmission length ratiop ,b
1.26 1.39 1.26 1.26 1.43 1.24
Ratio values given here are those obtained for transmission mode ir measurement, Radio values obtained for internal reflectance mode are larger as expected (Mattson et al. 1970c) with a similar variation of values. 6. Peak lengths converted to absorbance before calculation of band ratio. Q
To whom correspondence should be addressed. Present address, School of Marine and Atmospheric Science, University of Miami, Miami, Fla. 33149.
Volume 6, Number 9, September 1972 833
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Table 11. Example Analyses of Sediment Samples Containing Oil and Biological Material C-H
I
2600
Sediment sample no.a 12,888 12,889 12,929 12,930 12,932 12,934 12,935 12,972 12,973 12,981 13,027
1 1200
FREQUENCY (cm-9
Figure 1. Typical transmission ir spectra A , Oil-containing sediment sample containing biological (protein) material; B , oil-containing sediment sample containing no biological material
the material in the sediment. Thus, it is possible to correct for the contribution of the biological materials to the 2925 cm-l band by measuring the 1650 cm-l transmission band, converting percent transmission to absorbance units (so that a linear correction can be made) multiplying the 1650-l band height by 1.3 (the average of all -CH*-/--NHband ratios which was arbitrarily chosen as the correction factor), and subtracting the resulting number from the total 2925 cm-I band height (also converted to absorbance). Results for a few examples of the determination of the oil content in some Santa Barbara Channel sediments which contain biological matter are shown in Table 11. It is apparent that the accuracy of the estimation of the oil content decreases as the concentration of the biological matter increases. This decrease in accuracy arises from the uncertainty or variations of the -CH2-/--NHband ratios for various biological materials. The precision of the measurements themselves were better than flo%, and, thus any correction of the -CH2absorbance which shows that the oil content is only 10% or less of the total -CH2---containing material is a meaningless number. For example, the value of 0.6 ppt oil content for sample 12973 in Table I1 should be considered to be zero detectable oil content. However, for most applications in ecological and/or geological studies, this sensitivity limitation should not present a significant problem. It should be pointed out that this method must be used with caution as it is absolutely necessary for the analyst to know the chemical nature of organic material present in the sediment samples. For example, an organic material which does not contain -NHgroups, such as cellulose, could be present in sediments from some areas. If the analyst were not aware of its presence, it would be analyzed as part of a fossil fuel hydrocarbon in the sediment. Thus, it is recommended that the total ir spectra of the sediment sample be examined for other organic functional group bands which would suggest other -CH2--containing species were also present in significant amounts to cause significant error in the hydrocarbon content estimate. It is further suggested that, as a precaution, random sediment samples from the series being studied be analyzed by a separate means which can qualitatively identify the various organic species present to determine if a potential source of error is common to the area. Extraction and gas
834 Environmental Science & Technology
(2925
N-H
(1650
cm-l) trans- cm-l) transmission peak mission peak Oil concnbafter length length correction, ppt 14 8 4.3 16 11 4.6 16 9 5.1 14 3 5.5 19 4 7.5 15 3 6.1 24 5 9.8 13 12 2.9 9 14 0.6 7 4 2.4 49 10 19.5
See Kolpack et al. (1971). b Resultant -CHzpeak length converted to concentration by means of a calibration curve (Mattson et al., 1970a). Q
chromatograph were actually used in the Santa Barbara Channel study to determine if other types of organics were generally present in the sediments of this area in sufficient concentration to cause interference in the ir estimation of the hydrocarbon content. In this particular study, no other measurable interferents were found. Literature Cited Kolpack, R. L., Mattson, J. S., Mark, H. B., Jr., Yu, TaChing, “Hydrocarbon Content of Santa Barbara Channel Sediments,” in “Biological and Oceanographical Survey of the Santa Barbara Oil Spill, 1969-1970,” R. L. Kolpack, Ed., Vol 2, p 216-95, Allan Hancock Foundation, University of Southern California, Los Angeles, Calif., 1971. Mattson, J. S., Anal. Chem., 43 (13), 1872 (1971). Mattson, J. S., Kennedy, F. W., Dixon, J. M., Mark, H. B., Jr., Yu, Ta-Ching, ‘Infrared Spectroscopic Analyses of the Hydrocarbon Content of Santa Barbara Channel Sediments,” Rept. No. GA-10270, Gulf General Atomic Co., San Diego, Calif., 1970a. Mattson, J. S., Mark, H. B., Jr., Kolpack, R. L., Schutt, C. E., Anal. Chem., 42,234-8 (1970b). Mattson. J. S.. Mark. H. B.. Jr.. Weber, W. J.., ‘Jr.,. Decelon ~ p p lSpectiosc., . 8,‘91-104 (igjoc). Yu, Ta-Ching, Mark, H. B., Jr., Environ. Lett., 1, 55-9 ’
-,.
I1 071) \A,
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Yu, Ta-Ching, Mattson, J. S., Mark, H. B., Jr., unpublished results, 1971. Received for review January 28, 1972. Accepted June 21, 1972. This study was supported by the Environmental Protection Agency, Grant Number l60IO EHL and the Western Oil & Gas Ass., National Science Foundation Grant GB-8206 and National Sea Grant Program, US. Department of Commerce Grant GH-89. One of us ( H B.M. Jr.) would like to thank specifically the Office of Research, University of Cincinnati, for special travel support without which this joint research effort could not have been carried out.
