Analysis of single-walled carbon nanotubes using spICP-MS with microsecond dwell time

Abstract

8Although catalytic metal nanoparticle (NP) impurities in carbon nanotube (CNT) structures are undesirable 9 in a manufacturing context, they can be used as proxies to detect CNTs by single particle inductively 10 coupled plasmamass spectrometry (spICP-MS). The use of 100 microsecond dwell times, a recent 11 advancement for spICP-MS, increases resolution between pulse events and reduces background signal, 12 improving the detection of low metal-content CNTs. Serial filtration supports the assertion that metal NPs, 13 containing yttrium in this study, are primarily incorporated in CNT structures and remain bound to the tubes 14 throughout analysis. Analysis of both acid-digested and suspended CNTs confirmed that CNTs are fully 15 ablated in the plasma and that all residual metals are ionized. This result, combined with good agreement 16 with UV-Vis spectroscopy analysis, indicates that spICP-MS can provide quantitative CNT mass analysis.17 Though Nanoparticle Tracking Analysis (NTA) was less accurate than spICP-MS when counting Au-PVP 18 NPs, it gave higher particle number concentrations than spICP-MS for CNTs. The likely undercounting of 19 CNTs by sp-ICPMS is ascribed to the heterogeneous distribution of yttrium NPs among CNTs, and the small 20 diameter of many yttrium NPs (~15 nm), nearing their detection limit. Despite this limitation, its sensitivity 21 and elemental specificity make spICP-MS a powerful nanometrology method for environmental exposure 22 assessment of CNTs. To illustrate this capability, CNT association with Daphnia magna was measured at 23 μg/L CNT concentrations. After 48 hours of exposure to a CNT suspension, 3.48 ± 0.32% of CNTs were 24 taken up by D. magna adults. This simple and direct application of spICP-MS to detect CNTs in organisms 25 can be applied to toxicological investigations to help understand potential bioaccumulation of CNTs in 26 aquatic ecosystems. 27 28

Yttrium Residues in MWCNT Enable Assessment of MWCNT Removal during Wastewater Treatment

“…We presume these residuals are catalyst impurities in the metals used in MWCNT synthesis rather than intentionally added by manufacturers. These results align well with reports of Y and Co in SWCNTs [15,17] Figure 1 shows the sensitivity of these three metal residuals by ICP-MS after microwave digestion of the CNT.…”

“…We operated ICP-MS in single particle mode following methods published previously [23,31,32,33] and followed the approach of analyzing for trace metals in MWCNTs as demonstrated for SWCNTs [15,23]. For samples analyzed with spICP-MS, if the sample contains dissolved metals, the ions will be distributed homogenously within the solution, producing a consistent intensity signal vs. time across readings.…”

“…Current analytical techniques to detect and quantify carbon nanoparticles include programmed thermal analysis (PTA), Raman spectroscopy, UV-visible spectrophotometry, and microwave treatment with thermal analysis, but most available techniques have detection limits in solid matrices and water on the order of 10–100 mg kg −1 or 0.1–10 mg L −1 , respectively [14]. Recent studies evaluated the ability of single particle inductively coupled plasma-mass spectrometry (spICP-MS) to detect residual trace catalytic metals (e.g., Fe, Y, Ni, Co, Mo) that persisted in single- or multi-walled carbon nanotubes (SWCNTs) at ng L −1 levels in an aqueous matrix [15,16,17,18,19,20,21,22,23,24]. Therefore, we explored spICP-MS and ICP-MS directly for the detection of known specific commercial MWCNTs in complex wastewater matrices.…”

Polypropylene–MWCNT composite degradation, and release, detection and toxicity of MWCNTs during accelerated environmental aging

“…The purpose of SP-ICP-MS was reported for detecting metal-containing nanoparticles in different matrices [34,35]. The system can differentiate the particulate forms from the dissolved ion form of the elements that makes the technique a useful method for studying transformation on nanomaterials.…”

Bioaccumulation of Multiwall Carbon Nanotubes in Tetrahymena thermophila by Direct Feeding or Trophic Transfer

“…The use of a sensitive detection method – accelerator mass spectrometry (AMS) - allowed for tracing 14 C-MWCNTs in the biological matrices at low (sub µg/kg) levels; this is the lowest detection level obtained to date for CNT quantification in tissues to our knowledge. 19, 20 Since MWCNTs were not expected to biodegrade under the experimental laboratory conditions of this study, quantification of 14 C could be used to trace MWCNTs in biota. Two environmentally relevant scenarios of CNT transfer to ciliates were compared at the same MWCNT doses: (i) MWCNT uptake via bactivory of MWCNT-encrusted bacteria, and (ii) grazing on medium-dispersed MWCNTs.…”