Combustion generated nanomaterials: online characterization via an ICP-MS based technique. Part I: calibration strategy with a TGA

Abstract

The coupling between a scanning mobility particle sizer (SMPS) and an inductively coupled mass spectrometry (ICP-MS) was in the past shown to obtain simultaneous size-resolved and elemental information on nanoparticles, using a rotating disc diluter (RDD) as conditioning and dilution system. A calibration strategy for the hyphenated RDD-SMPS-ICP-MS setup is presented here. Evaporation experiments of ZnCl₂ powder were performed at four different temperatures, using a TGA as an aerosol source to correlate linearly the weight in loss of the TGA with the averaged ICP-MS intensities measured in transient mode. The calibration curve of Zn showed a good correlation factor (R² = 0.9985) and a sensitivity of 20.95 × 10³ counts ng⁻¹. The LoD (limit of detection) of the method was estimated to be ∼32 ng cm⁻³, once the total dilution of the whole setup is considered. A second set of experiments was performed, where ZnO and CaCl₂·2H₂O powders were used as reactants to generate ZnCl₂ particles. The output data of the two instruments were treated and appropriately converted, to allow a direct and quantitative comparison between the performances of SMPS and ICP-MS. The ICP-MS signal of Zn was quantified by using the external calibration performed with the coupling of a TGA with an ICP-MS, while the SMPS volume data used two general assumptions, namely spherical morphology and bulk density of ZnCl₂. Additional TEM analysis performed on the size-selected ZnCl₂ particles allowed to check their morphology. The proposed calibration strategy of the ICP-MS signals enables to evaluate the SMPS quantification procedure.