FULLERENE MOLECULAR-WEIGHT DISTRIBUTIONS IN GRAPHITE SOOT EXTRACTIONS MEASURED BY LASER DESORPTION FOURIER-TRANSFORM MASS-SPECTROMETRY

Fullerenes were extracted from graphite soot produced by the Huffman-Kratschmer process by using a number of solvents, including refluxing in xylenes, 1,3,5-trimethylbenzene, 1,2,4-trichlorobenzene, alpha,alpha,alpha-trichlorotoluene, and 1-methylnaphthalene, and by using high-pressure, high-temperature o-xylene and supercritical carbon tetrachloride. The extract was dried and analyzed using laser desorption/Fourier transform mass spectrometry in order to measure fullerene molecular weight distributions. Positive and negative ion mass spectra were taken of all samples in order to compare the types of spectra. It is expected from mechanistic considerations and from past results that negative ion spectra should be less sensitive to growth or fragmentation of the fullerenes. The determination of the most reliable fullerene distributions requires a comparison of both positive and negative ion mass spectra, however. The highest mass distribution, with fullerenes to 2500 amu, was found for 1-methylnaphthalene extract, although there was evidence for dimers, trimers, and tetramers of the solvent in the extract. High-pressure o-xylene yielded fullerene distributions to 2000 amu. It was found that, for some solvents, residual solvent or solvent polymerization affected the reliable measurement of fullerene distributions by laser desorption. Extraction with supercritical carbon tetrachloride degraded the fullerenes or the soot into perchlorinated aromatic molecules.