Inverse supercritical fluid extraction as a sample preparation method for the analysis of the nanoparticle content in sunscreen agents

Separation and size characterization of highly polydisperse titanium dioxide nanoparticles (E171) in powdered beverages by using Asymmetric Flow Field-Flow Fractionation hyphenated with Multi-Angle Light Scattering and Inductively Coupled Plasma Mass Spectrometry

The application of titanium dioxide as E171 food additive has become an issue of debate due to numerous reports that titanium dioxide nanoparticles (TiO₂ NPs) inside the products may pose risks to human health. However, there is still a lack of an official standardized methodology for the detection and size characterization of TiO₂ particles in foods containing E171. In this study, a method was presented for size characterization of TiO₂ particles with various independent verifications in coffee creamer and instant drink powders, using Asymmetric Flow Field-Flow Fractionation hyphenated with Multi-Angle Light Scattering and Inductively Coupled Plasma Mass Spectrometry (AF4-MALS-ICP-MS). TiO₂ particles from these products were well extracted, followed by their optimized AF4 separation using anionic surfactant Sodium Dodecyl Sulfate (SDS) (0.05%, pH 9) and mixed surfactant NovaChem (0.2%), respectively. Size determination of TiO₂ NPs was conducted based on AF4 calibration with polystyrene nanospheres and verification with TiO₂ NPs standard suspension of 100 nm under two different AF4 conditions. The TiO₂ particle sizes detected ranged from 24.4 - 544.3 nm for coffee creamer and 27.7 - 574.3 nm for instant drink powders, with the TiO₂ NPs detection recoveries of 75% and 92%, respectively. Hydrodynamic diameters from AF4 size calibration could be independently validated by the gyration diameters from online MALS measurement. The established approach was demonstrated to be reliable and pragmatic for size profiling of highly polydisperse TiO₂ particles and thus useful for monitoring E171 in similar foodstuffs.

Challenges in Determining the Size Distribution of Nanoparticles in Consumer Products by Asymmetric Flow Field-Flow Fractionation Coupled to Inductively Coupled Plasma-Mass Spectrometry: The Example of Al2O3, TiO2, and SiO2 Nanoparticles in Toothpaste

According to the current European regulation on cosmetics, any ingredient present as a nanomaterial should be indicated in the ingredient list. There is a need for analytical methods capable of determining the size of the relevant ingredients and thus assessing if these are nanomaterials or not. An analytical method based on asymmetric flow field-flow fractionation (AF4) and inductively coupled plasma-mass spectrometry (ICP-MS) was developed to determine the size of particles present in a commercial toothpaste. Multi-angle light scattering (MALS) was used for on-line size determination. The number-based particle size distributions (PSDs) of the particles were retrieved upon mathematical conversion of the mass-based PSDs recovered from the AF4-ICP-MS fractograms. AF4-ICP-MS allowed to separate and detect Al2O3 and TiO2 particles in the toothpaste and to retrieve a correct TiO2 number-based PSD. The potential presence of particles in the lower size range of the Al2O3 mass-based PSD had a strong impact on sizing and nanomaterial classification upon conversion. AF4 coupled with ICP-MS and MALS was found to be a powerful approach for characterization of different particles in a multiple-particle system such as toothpaste. Confirmation of particle size by a secondary method such as single particle ICP-MS or hydrodynamic chromatography was crucial.

Continuous Hydrothermal Synthesis of Inorganic Nanoparticles: Applications and Future Directions

Nanomaterials are at the leading edge of the emerging field of nanotechnology. Their unique and tunable size-dependent properties (in the range 1-100 nm) make these materials indispensable in many modern technological applications. In this Review, we summarize the state-of-art in the manufacture and applications of inorganic nanoparticles made using continuous hydrothermal flow synthesis (CHFS) processes. First, we introduce ideal requirements of any flow process for nanoceramics production, outline different approaches to CHFS, and introduce the pertinent properties of supercritical water and issues around mixing in flow, to generate nanoparticles. This Review then gives comprehensive coverage of the current application space for CHFS-made nanomaterials including optical, healthcare, electronics (including sensors, information, and communication technologies), catalysis, devices (including energy harvesting/conversion/fuels), and energy storage applications. Thereafter, topics of precursor chemistry and products, as well as materials or structures, are discussed (surface-functionalized hybrids, nanocomposites, nanograined coatings and monoliths, and metal-organic frameworks). Later, this Review focuses on some of the key apparatus innovations in the field, such as in situ flow/rapid heating systems (to investigate kinetics and mechanisms), approaches to high throughput flow syntheses (for nanomaterials discovery), as well as recent developments in scale-up of hydrothermal flow processes. Finally, this Review covers environmental considerations, future directions and capabilities, along with the conclusions and outlook.