Size and isotopic ratio measurements of individual nanoparticles by a continuous ion-monitoring method using Faraday detectors equipped on a multi-collector-ICP-mass spectrometer

Abstract

We investigated the capability of high-gain Faraday detectors equipped on a multi-collector-ICP-mass spectrometer (MFC-ICP-MS) in performing both particle size and Ag isotopic ratio determination for individual silver nanoparticles (Ag NPs). Two high-gain Faraday detectors equipped with 10¹³ Ω resistors were used to detect transient signals emanating from individual NPs (particle events). A continuous ion-monitoring method (CIM) was adopted to obtain reliable isotopic ratio data from the particle events. The CIM measurements of the signal intensities obtained from Ag NPs (40, 60, 80, 100, and 200 nm) exhibited a good linearity with the sizes of the Ag NPs. The variations of the measured ¹⁰⁹Ag/¹⁰⁷Ag ratio for the particles of each size in the isotopic ratio measurements (about 100 particles sampled per size) were about: 12% for 40 nm, 4.9% for 60 nm, 1.9% for 80 nm, 1.2% for 100 nm, and 0.26% for 200 nm. The resulting precision of the ¹⁰⁹Ag/¹⁰⁷Ag ratio measurements can be basically attributed to both shot noise (counting statistics) and background fluctuation on amplifiers. The data obtained here demonstrated that the MFC-ICP-MS system combined with the CIM can be employed to determine both the NP size and isotopic ratio of constituent elements.