Evaluation of carbon disulfide as an alternative to carbon tetrachloride for the determination of hydrocarbon oils in water by infra-red spectrophotometry

The replacement of carbon tetrachloride as an extraction solvent for the determination of hydrocarbon oils has been investigated. A detailed comparison of the performance of carbon tetrachloride and carbon disulfide has been undertaken using sets of homogeneous artificial seawater samples spiked with three different oils (gas oil,medium fuel oil and Forties field crude oil) at varying levels. An initial study of two sets of samples spiked with gas oil at different concentrations indicated problems with the homogeneity of the samples. A multiple interleaved run-off technique for sample preparation was therefore developed and this was found to significantly improve the sample homogeneity. A further three sets of samples spiked with gas, fuel and crude oil were prepared using this technique. In total, five sets of samples were analysed. In all cases, there was no significant difference between the variation in the results obtained for each solvent. In three cases the means of the results obtained using the two solvents were found to be significantly different. For the samples spiked with fuel oil and the lowest level of gas oil, the results obtained using carbon disulfide were significantly higher than those obtained using carbon tetrachloride. For the samples spiked with crude oil the carbon tetrachloride results were significantly higher, however the difference was not as great as in the other cases. It is concluded that carbon disulfide could be used as a replacement for carbon tetrachloride in the analysis of hydrocarbon oils in water by infra red spectrophotometry. However, there is some evidence that current regulatory limits based on carbon tetrachloride extraction may require re-evaluation, especially for specific oil types, if identical rather than similar overall effects in enforcement are to be achieved.