The potential of asymmetric flow field-flow fractionation hyphenated to multiple detectors for the quantification and size estimation of silica nanoparticles in a food matrix

This work represents a first systematic approach tothe size-based elemental quantification and size estimation ofmetal(loid) oxide nanoparticles such as silica (SiO2) in a realfood matrix using asymmetric flow field-flow fractionationcoupled online with inductively coupled plasma mass spectrometry(ICP-MS) and multi-angle light scattering (MALS)and offline with transmission electron microscopy (TEM)with energy-dispersive X-ray analysis (EDAX). Coffeecreamer was selected as the model sample since it is knownto contain silica as well as metal oxides such as titania at themilligramme per kilogramme levels. Optimisation of samplepreparation conditions such as matrix-to-solvent ratio,defatting with organic solvents and sonication time that mayaffect nanoparticle size and size distribution in suspensionswas investigated. Special attention was paid to the selection ofconditions that minimise particle transformation during samplepreparation and analysis. The coffee creamer matrix componentswere found to stabilise food grade SiO2 particles incomparison with water suspensions whilst no significant effectof defatting using hexane was found. The use of samplepreparation procedures that mimic food cooking in real lifewas also investigated regarding their effect on particle sizeand particle size distribution of silica nanoparticles in theinvestigated food matrix; no significant effect of the watertemperature ranging from ambient temperature to 60 °C wasobserved. Field-flow fractionation coupled to inductivelycoupled plasma-mass spectrometry (FFF-ICP-MS) analysisof extracts of both unspiked coffee creamer and coffee creamerspiked with food grade silicon dioxide, using differentapproaches for size estimation, enabled determination ofSiO2 size-based speciation. Element-specific detection byICP-MS and post-FFF calibration with elemental calibrationstandards was used to determine the elemental composition ofsize fractions separated online by FFF. Quantitative data onmass balance is provided for the size-based speciation ofthe investigated inorganic nano-objects in the complexmatrix. The combination of FFF with offline fractionationby filtration and with detection by ICP-MS and TEM/EDAXhas been proven essential to provide reliable information ofnanoparticle size in the complex food matrix