Thermogravimetry and Mass Spectrometry of Extractable Organics from Manufactured Nanomaterials for Identification of Potential Coating Components.

Per Axel Clausen,Asger W Nørgaard,Keld Alstrup Jensen,Vivi Kofoed-Sørensen,Nicklas Mønster Sahlgren

doi:10.3390/ma12223657

Per Axel Clausen, Asger W Nørgaard + Show 3 more

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https://doi.org/10.3390/ma12223657

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Abstract

Manufactured nanomaterials (MNMs) often have a surface-chemical modification in order to tailor their physicochemical properties, including also powder properties and miscibility. Surface-chemical modifications may influence the toxicological properties of the MNM, but the specific chemistry and extent are rarely described in detail in suppliers’ technical data sheets. Chemical and quantitative information on any surface-chemical treatment, coating and functionalization are required for chemicals registration in Europe. Currently there is no globally accepted and documented approach to generate such data. Consequently, there is a continued research need to establish a structured approach to identify and quantify surface-chemical modifications. Here we present a tiered approach starting with screening for mass-loss during heating in a furnace or thermogravimetric analysis (TGA) followed by solvent extraction, and analysis by several mass spectrometry (MS) techniques depending on the target analytes. Thermal treatment was assumed to be able to quantify the amount of organic coating and MS was used to identify the extractable organic coatings after pressurized liquid extraction (PLE) using methanol at 200 °C. Volatile organic compounds in extracts were identified with gas chromatography and MS (GC-MS), non-volatile organic compounds with liquid chromatography MS (LC-MS), and polymeric compounds with matrix-assisted laser desorption ionization time-of-flight MS (MALDI-TOF-MS). The approach was demonstrated by analysis of 24 MNM, comprising titanium dioxide, synthetic amorphous silica, graphite, zinc oxide, silver, calcium carbonate, iron oxide, nickel-zinc-iron oxide, and organoclay. In extracts of 14 MNMs a range of organic compounds were identified and the main groups were silanes/siloxanes, fatty acids, fatty acid esters, quaternary ammonium compounds and polymeric compounds. In the remaining 10 MNMs no organic compounds were detected by MS, despite the fact an organic coating was indicated by TGA.

Highlights

Manufactured Nanomaterials (MNMs) may be chemically modified by surface coating or functionalization depending on their technical applications, see e.g., Baraton [1], Gref et al [2], Kinge et al [3], Basiruddin et al [4], and Sperling and Parak [5]
All MNM were analysed with thermogravimetric analysis (TGA) and when it indicated >1% mass-loss due to apparent organic coating, i.e., corrected for initial water loss, the MNM was selected for extraction and mass spectrometry (MS) analysis
Water loss was defined as mass loss in the interval 25–110 ◦ C and loss of associated organic material or coating as mass loss from 110 ◦ C to 800 ◦ C except for the graphite that decomposed at 450–600 ◦ C, the carbonates that decomposed at 700–800 ◦ C, and in cases where a weight gain is observed at the end of the TGA curve

Summary

Introduction

Manufactured Nanomaterials (MNMs) may be chemically modified by surface coating or functionalization depending on their technical applications, see e.g., Baraton [1], Gref et al [2], Kinge et al [3], Basiruddin et al [4], and Sperling and Parak [5]. Surface coatings may change the physical, chemical and toxicological properties of the MNM as compared to that of the core material and prevent them from agglomeration [6] before incorporation into intermediates and final products such. The strategy for coating or surface functionalization of core/shell MNMs [12], generally falls into four classes [5]: (1) ligand-like binding by chemisorption, (2) electrostatic adsorption, (3)

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