Carbon engineered nanomaterials (CENMs) are relativity new (Kroto, 1985;lijima, 1991), and despite the fast-advancing research that utilizes the unique properties of CENMs, understanding of their toxicology is only now developing. The characterization of nanoparticles to identify the causal properties for toxicology studies has been a source of controversy in the growing nanotechnology field, and a number of lists of the "minimum characterization data set" have been published (Oberdorster et al., 2005;Powers et al., 2006;NCI, 2009). An unrecognized and confounding problem discovered by RTI researchers is random endotoxin contamination in commercial CENMs (Esch et al., 2010). A second confounding problem is that the CENMs may retain solvents used during purification, which may influence ttie outcomes of toxicology studies (Spohn et al,, 2009), Therefore, the method of purification ofthe CENMs must be carefully selected and the volatile content ofthe test material determined. Since the graphene-derived CENMs are formed by the assembly of carbon atoms in the vapor state, methods such as plasma arc discharge, laser ablation, and chemical vapor deposition (CVD) are the main synthetic approaches. These procedures afford COO, as well as other polyhedral carbon moieties (e.g., fullerenes), polyaromafic compounds, amorphous carbon, and carbon (Hou, 2008). Isolation and characterization of COO as a well-defined organic molecule with some solubility in organic solvents is relatively simple (see Section 4, Preliminary Studies/Progress Report). MWCNTs derived from CVD, which involves catalyst-assisted decomposition of hydrocarbons and growth over metal catalysts, have a higher incidence of defects than those produced by arc discharge. Contaminants are metals, which may be within the MWCNTs or within polyhedral carbon byproducts, aromafic hydrocarbons, or amorphous carbon. On the other hand, MWCNTs obtained from arc discharge are considered to be relatively pure (Henstridge, 2008). RTI's approach is to use an in-house research-scale plasma arc discharge method (see Section 4, Preliminary Studies/Progress Report) that has been used for the past 4 years to provide well-characterized, pure carbon-14 uniformly labeled 060, MWCNT, and single-walled carbon nanotubes (SWCNT) to researchers in universities and government. This approach also eliminates any possibility of process or environmental contamination. It has been our experience that our synthetic procedure is reproducible and that the physical and chemical characterisfics are identical for the carbon-14 labeled and unlabeled materials. We have conducted characterization studies of commercial 060 and MWCNT (Esch et al., 2010;Levine et al., 2010) and found that our synthesized materials have comparable physical characteristics.
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