Low extraction recovery of fullerene from carbonaceous geological materials spiked with C60

Soxhlet extraction, sonication, and ultracritical extraction were tested with respect to their capacity to extract fullerenes from natural carbonaceous materials. Toluene solutions with various contents of synthetic C(60) were added to powdered graphite, shungite, bituminous coal, and quartz, with final C(60) concentration 0.1-100 ppm. The C(60)-doped materials were leached in three kinds of extraction apparatus. High-performance liquid chromatography (HPLC) was used to analyse the fullerene content in the obtained toluene extracts. Surprisingly low yields of the C(60) extraction (most of them well below 5%) were determined for all the carbonaceous matrices and all the extraction techniques employed in the fullerene isolation. This finding has serious consequences for better understanding of the reported fullerene occurrence in the geological environment, because a greatly limited extraction yield can be responsible for some negative results of fullerene analyses in various geological samples. Both fullerene stability in solvents and fullerene interaction with the surfaces of geological carbonaceous matrices are discussed to explain the obtained results. (C) 2005 Elsevier Ltd. All rights reserved.