Determination of the Nanoscale Silica Mass Fraction by AF4/ICP-MS with Isotope Dilution Analysis Using Si-Enriched Silica Nanoparticles.

A methodology based on the use of asymmetrical flow field-flow fractionation (AF4) coupled to ICP-MS with size fraction-targeted isotope dilution analysis (IDA) has been developed, validated, and applied for the first time to determine the mass fraction of nanoscale silica (SiO). For this purpose, Si-enriched SiO nanoparticles, to be used as an IDA spike/internal standard, were synthesized and characterized . Double IDA was used to quantify an aqueous suspension of Stöber silica particles of similar characteristics to those of the SiO nanoparticle (NP) spike using a representative test material of natural Si isotopic composition as the calibrant. For fumed SiO NP in a highly complex food matrix, a methodology based on single IDA with AF4/ICP-MS using the same SiO NP spike was developed and validated. Relative expanded measurement uncertainties ( = 2) of 4% (double IDA) and 8% (single IDA) were achieved for nanoscale silica mass fractions of 5143 and 107 mg kg in water suspension and food matrix, respectively. To assess the accuracy of AF4/ICP-IDMS for the characterization of SiO NP in a food matrix, standard addition measurements on samples spiked with Aerosil AF200, also characterized for Si mass fraction, were undertaken, with an average recovery of 95.6 ± 4.1% (RSD, = 3) obtained. The particle-specific IDA data obtained for both SiO NP-containing samples were also compared with that of post-AF4 channel external calibration using inorganic Si standards. The mass fractions obtained by IDA agreed well with those obtained by external calibration within their associated measurement uncertainties.