Characterisation of refractory wastes at hydrocarbon-contaminated sites-II. Screening of reference oils by stable carbon isotope fingerprinting.

The preliminary evaluation of stable carbon-isotope ratio mass spectrometry (IRMS) as a novel, alternative method for screening residual heavy or weathered petroleum wastes is presented. Seven well-characterised middle-to high-boiling range oils (predominant boiling range: 150-600 degrees C) and their isolated class fractions were analysed by IRMS. Whole oil delta13C values (which express the ratio of (13)C to (12)C within each sample) showed a small but significant decrease with decreasing oil asphaltene content, from -26.8% for heavier oils to -28.8% for lighter, predominantly paraffinic oils. In agreement with the conventionally observed trend, delta13C values of isolated class fractions were found to increase in the following order: delta13Csat (congruent with delta13Coil) < delta13Caro < delta13Cpol < delta13Casp, delta13Csat up to 2.5% more negative than delta13Cpol and delta13Casp. However, this variation was much less pronounced for the heavier oil samples. As a result, isotope type curves exhibited a clear distinction between heavier oils, which produced much flatter type curves, and lighter oils, for which type curves were characteristically sloping. From these preliminary results, IRMS would appear to have application as a potential method for identifying a predominance of asphaltene class fractions in residual hydrocarbon wastes and for distinguishing between heavy and light oily contaminants.