Thermogravimetry–Mass Spectrometry for Carbon Nanotube Detection in Complex Mixtures

Abstract

In spite of the growth of the carbon nanotube (CNT) industry, there are no established analytical methods with which to detect or quantify CNTs in environmental matrices. Given that CNTs have relatively high thermal stabilities, we investigated the use of thermal techniques to isolate and quantify single wall carbon nanotubes (SWCNTs). Test materials included ten types of commercial SWCNTs, representative biological macromolecules (bovine serum albumin and methylcellulose), soot, natural coastal sediments, and SWCNT-amended sediments. Different SWCNTs exhibited widely diverse degradation temperatures, and thermal analytical methods may require SWCNT-type specific parameters. To improve quantification capabilities, evolved gases were monitored by mass spectrometry. SWCNTs produced diagnostic ion ratios reflective of their high carbon and low hydrogen and oxygen contents. Current detection limits are roughly 4 μg(SWCNT) per sample (e.g., 100 μg(SWCNT) g(-1)(sediment) and 40 mg sample), controlled by interfering ions associated with the instrument's non-airtight design. Although future modifications could improve this limitation, the current method is sufficient for quantifying SWCNTs in laboratories and industrial sites where SWCNTs are handled. Furthermore, the method shows promise to distinguish between incidental (e.g., soot) and engineered (e.g., SWCNTs) nanoparticles, which is not possible with current state-of-the-art techniques.