Performance Evaluation of Analytical Method for Nanoparticles using a Single Particle Inductively Coupled Plasma and Application to Nanoparticle-containing Consumer Products

Abstract

Objective: Single particle inductively coupled plasma (SP-ICP-MS) is a promising technique to detect nanosized inorganic particles at very low concentrations. The purpose of this study was to validate analytical procedures for detecting nanoparticles (NPs) in solution using SP-ICP-MS and to apply these procedures for the analysis of Ag and TiO2 NPs in a consumer spray product. Methods: The performance evaluation experiment tested the accuracy, precision, and stability of analytical procedures using three sizes of Ag and TiO2 reagents. Accuracy was evaluated with regards to both size accuracy and recovery of particle concentration. Relative standard deviation (RSD) and pooled RSD were used to verify precision. Stability during storage was evaluated at zero, one, four, seven and fourteen days after storage. Before characterizing the nanoparticles in consumer products, six different kinds of pretreatment methods were compared to select appropriate pretreatment methods (water, ethanol, and ethanol evaporation) on the basis of accuracy and precision. A total of ten consumer products (three of them were labelled as containing Ag NPs, three of them were labelled as containing TiO2 NPs, and four of them were not labelled as containing NPs) were analyzed with SP-ICP-MS using the optimal pretreatment method, transmission electron microscopy equipped with an energy-dispersive X-ray spectrometer (TEM-EDS), and field emission scanning electron microscope with an energy-dispersive X-ray spectrometer (FE-SEM-EDS). Results: Accuracy and precision were in the acceptable range according to the NIOSH guidelines for air sampling and analytical method development and evaluation. Size accuracy was higher than 95% (96–115%), with the exception of 30 and 50 nm TiO2 NPs (121–237%). Calibration lines of particle concentrations were linear and showed correlation coefficients of >0.99. Recovery of particle concentration was 91-109% with the exception of 30 nm TiO2 NPs. The RSD value to evaluate precision was 0.01–6.21, with the exception that the most frequent size data of TiO2 was 0.18–106.88. The accuracy and precision differences between Ag and TiO2 were due to the stability and characteristics of the reagents. It is recommended that samples are analyzed as quickly as possible for accurate size and particle concentration analysis

the time should not exceed one day. When samples contained a mixture of sizes, the recovery of bigger sized particles was over 100%, and the recovery of smaller sized particles was under 50%. The best treatment method was the Tween 80 method, wherein 0.1% of Tween 80 was added to the solution

this was not the optimal method for TiO2 analysis with a water base. According to SP-ICP-MS analysis, all of the consumer spray products contained Ag NPs and eight of the consumer spray products contained TiO2 NPs. The sizes of Ag NPs in the consumer spray products ranged from 27 to 81 nm, and particle concentrations ranged from 4.7 × 105 to 3.9 × 107 particles/mL. The sizes of TiO2 NPs in the consumer spray products ranged from 35 to 65 nm, and particle concentrations ranged from 7.7 × 107 to 9.2 × 108 particles/mL. SEM and TEM analyses also yielded similar sizes and concentrations. Conclusion: SP-ICP-MS is an analytical method for analyzing metallic NPs and has a number of unidentified technical issues. Analyses of Ag NPs and larger sized TiO2 NPs provided reliable data

however, analyses of smaller sized (<50 nm) TiO2 NPs and mixtures of different sized NPs were unreliable. Ten of the consumer products contained nanosized Ag particles, and eight of the consumer products contained nanosized TiO2 particles. The number of Ag NPs and TiO2 NPs in consumer products was over a hundred thousand. The results obtained from the analyses of consumer spray products could be applied to exposure assessments of consumer products. With further method validation, the SP-ICP-MS method could characterize the particle size and particle number concentration of diverse samples.