Dilution versus fractionation: Separation technologies hyphenated with spICP-MS for characterizing metallic nanoparticles in aerosols

The presence of metal salts has become one of the major limitations for measuring metallic nanoparticles (NPs) in single particle inductively coupled plasma mass spectrometry (spICP-MS). Their presence generates a background signal in spICP-MS that can be overlapped with the signal intensity of small particles, leading to inaccurate NP size distributions. To overcome this analytical problem, sample pretreatment methods (e.g. dilution or fractionation) have been applied to liquid samples before spICP-MS measurements to minimize the ionic interference. However, the number of studies focused on reducing the presence of metal salts in aerosol characterization is limited. In this contribution, we investigated three different technologies coupled to an ICP-MS for online separating metallic NPs signals from ionic interference signals of metal salts in the aerosol. A rotating disk diluter (RDD) was used for the online dilution of the aerosol, while a differential mobility analyzer (DMA) and a centrifugal particle mass analyzer (CPMA) were used for the online fractionation of specific-sized NPs in the aerosol. The results from the analysis of 100 nm gold NPs (AuNPs) mixed with gold salts (Au3+, mass ratio 1:25) showed the particle size limit of detection decreased from 78 nm to 61, 50, and 33 nm by using RDD, CPMA, and DMA respectively. In addition, it was found that the separation performance of AuNPs was in the order of DMA > RDD > CPMA. The methods used in this study based on spICP-MS have the potential to characterize directly NPs in complex aerosols containing metal salts.