Application of stable isotopes and AF4/ICP-SFMS for simultaneous tracing and quantification of iron oxide nanoparticles in a sediment–slurry matrix

Abstract

One major challenge in nanomaterial analysis, especially in complex environmental matrices, is the unambiguous differentiation between natural and engineered nanomaterials (ENMs). Particularly with regard to the investigation of ENM's/engineered nanoparticle's (ENPs) fate, analytical methods are needed allowing for tracing and sensitive quantification. Several ENPs are metal-based and contain elements being omnipresent in environmental matrices (e.g., Al, Ti, Zn, Fe and non-metal Si) - hence, high background levels of these elements are expected, compromising sensitive detection. In this work we developed successfully a combined approach of stable isotope labeling (tracing) and reverse postchannel species-unspecific on-line isotope dilution (quantification) in combination with AF4/sector-field ICP-MS (AF4/ICP-SFMS). The approach was successfully applied to iron oxide nanoparticles isotopically enriched in Fe-57 coated with a SiO2 shell (Fe-57@SiO2 ENPs). Upon method development and validation the Fe-57@SiO2 ENPs were spiked into a filtered re-suspended river sediment-slurry matrix for proof-of-concept. Our approach allowed for unambiguous tracing of the Fe-57@SiO2 ENPs among natural iron colloid fractions as well as simultaneous sensitive quantification via reverse on-line ID despite high "natural" iron background. A limit of detection of 2.4 mu g Fe L-1 and a limit of quantification of 7.8 mu g Fe L-1 in real matrix was achieved. Furthermore, a good reproducibility in terms of peak areas was obtained (0.4-3.0%); the RSDs for elution times vary between 0.1 and 0.7%. To the best of the authors' knowledge, for the first time a reverse post-channel on-line isotope dilution AF4/ICP-SFMS approach in combination with isotopically labeled Fe-57@SiO2 ENPs was developed, allowing for (i) unambiguous tracing, and simultaneous (ii) sensitive quantification of the Fe-57@SiO2 ENPs within a sediment slurry matrix in the presence of natural iron colloid fractions. Based on the experience gained in this work, we feel certain that the approach is deployable to further stable isotope labeled metal-and nonmetal-based ENMs and shows great potential in ENMs studies

Atomic spectrometry update – a review of advances in environmental analysis

“…SSB procedure with inhouse Th standard solution to correct for mass bias. Intermediate precisions for 230 Th/ 232 Th in rock samples (0.24-0.49%, 2RSD) were similar to those achieved for synthetic solutions.…”

“…Two-step wash procedure after every sample to reduce Th backgrounds to acceptable levels. Measurement of 232 Th tail and its contribution at mass 230 subtracted. SSB procedure with inhouse Th standard solution to correct for mass bias.…”

ICP-MS for the analysis at the nanoscale – a tutorial review

“…55 No systematic differences were observed for the example of 107 Ag versus natural Ag. Apart from 107 Ag nanoparticles some further synthesis protocols from the literature are summarised in the following: Synthesis of 29 Si enriched nanoparticles starting from 29 Si elemental pellets (99.73% enrichment in 29 Si) 58 , synthesis of 67 ZnO nanoparticles starting from 67 Zn metal powder (89.6% enrichment in 67 Zn) 59 , 57 Fe nanoparticles starting from 57 Fe metal powder (95.06% enrichment in 57 Fe) 60 and 65 Cu nanoparticles starting from 65 CuCl 2 •2H 2 O (99% enrichment in 65 Cu) 61 . So far, stable isotope labelled ENPs have been applied in studies focussing on consumer product safety and on environmental transport and bioaccumulation.…”

“…The combined approach allowed for an unambiguous tracing as well as sensitive mass-based quantification of the 57 Fe-oxide nanoparticles next to natural iron containing colloids. 60 A smart application alienating the Fl-FFF/ICP-MS system as an "on-line filtration unit" for sample preconcentration and matrix removal was introduced by Al-Ammar et al. 177 Thereby a commercial FFF system was modified enabling large volume injections (up to 50 mL).…”

Stable isotope labeling of metal/metal oxide nanomaterials for environmental and biological tracing

“…The authors, along with collaborators, have made major advances in the labelling approaches of several particularly relevant nanomaterials, e.g., ZnO, 4,31,32 CuO, 33,34 and Ag 35,36 nanomaterials. In addition, TiO 2 nanomaterials labelled with 47 Ti and core/shell structured iron oxide@SiO 2 labelled with 57 Fe were also developed recently 37,38 . The labelling approaches were shown to be efficient and highly sensitive for detecting the nanomaterials in diverse environmental matrices and biological tissues at low concentrations, similar to the PECs of the nanomaterials.…”