Infrared estimation of oil content in sediments in presence of biological matter

Abstract

~~~~ 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 -NH- band 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. n a recent study of the effects of the winter 1969 oil blowI out 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 wdS 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.