Detection of single walled carbon nanotubes by monitoring embedded metals

Abstract

Detection of single walled carbon nanotubes (CNTs) was performed using single particle-inductively coupled plasma-mass spectrometry (spICPMS). Due to the ambiguities inherent in detecting CNTs by carbon analysis, particularly in complex environmental matrices, this study focuses on using trace catalytic metals intercalated in the CNT structure as proxies for the nanotubes. Using a suite of commercially available CNTs, the monoisotopic elements Co and Y were found to be the most effective for differentiation of particulate pulses from background. The small, variable, amount of trace metal in each CNT makes separation from instrumental background challenging; multiple cut-offs for determining CNT number concentration were investigated to maximize the number of CNTs detected and minimize the number of false positives in the blanks. In simple solutions the number of CNT pulses detected increased linearly with concentration in the ng L−1 range. However, analysis of split samples by both spICPMS and Nanoparticle Tracking Analysis (NTA) showed the quantification of particle number concentration by spICPMS to be several orders of magnitude lower than by NTA. We postulate that this is a consequence of metal content and/or size, caused by the presence of many CNTs that do not contain enough metal to be above the instrument detection limit, resulting in undercounting CNTs by spICPMS. However, since the detection of CNTs at low ng L−1 concentrations is not possible by other techniques, spICPMS is still a more sensitive technique for detecting the presence of CNTs in environmental, materials, or biological applications. To highlight the potential of spICPMS in environmental studies the release of CNTs from polymer nanocomposites into solution was monitored, showcasing the technique's ability to detect changes in released CNT concentrations as a function of CNT loading.

Single Particle ICP-MS: Advances toward routine analysis of nanomaterials

“…This results in the apparent detection of fewer and larger particles, which both misrepresents the size distribution of the particle and underestimates the particle number concentration. In the early stages of single particle method development, when 3-20 ms dwell times were used, coincidence was prevented by working at low particle number concentration (i.e., 5 % of total readings are NPs) [39,[46][47][48].…”

Current status and future direction for examining engineered nanoparticles in natural systems

“…[81,92,93,95,97] Utilising millisecond to microsecond dwell times, the count intensity arising from a single particle ablation event can be detected. This count intensity can then be converted into a mass using a calibration curve of dissolved standards that relate elemental mass to count intensity.…”

“…[92][93][94][95][96] However, the size detection limit for this technique is dependent on the signal generated by the ablation of the nanoparticle, which may require a significant amount of ions to generate a recognisable intensity pulse. In addition, although its elemental specificity is a desirable attribute, it may be unable to differentiate between an engineered and naturally occurring nanomaterial of the same elemental composition.…”

“…In addition, although its elemental specificity is a desirable attribute, it may be unable to differentiate between an engineered and naturally occurring nanomaterial of the same elemental composition. [81,[92][93][94][95]97] Despite the limitations of FFF-ICP-MS and sp-ICP-MS, the use of these methods for ENP detection may be a significant step forward and will be elaborated upon in a subsequent discussion.…”

Exposure assessment method for products containing nanomaterials using a gas sample introduction system for ICP-MS

“…Another study quantified nanomaterials using contaminating metal catalysts in CNTs [6]. All of these examples evaluated CNT by weight concentration.…”