Simultaneous Mass Quantification of Nanoparticles of Different Composition in a Mixture by Microdroplet Generator-ICPTOFMS

Abstract

This work investigated the potential of a high temporal resolution inductively coupled plasma time-of-flight mass spectrometer (ICPTOFMS) in combination with a microdroplet generator (MDG) for simultaneous mass quantification of different nanoparticles (NPs) in a mixture. For this purpose, a test system containing certified Au NPs, well characterized Ag NPs, and core-shell NPs composed of an Au core and an Ag shell was employed. Thanks to the full spectra coverage and rapid simultaneous detection of the TOFMS, the element composition of individual particles can be determined. The pure Ag NPs and the core-shell NPs could be differentiated despite the same mass of Ag they contain. Calibration with monodisperse droplets consisting of standard solutions allowed for the mass quantification of NPs without the use of NP certified materials. On the basis of this mass quantification, the sizes of NPs originating from the same aqueous suspension were simultaneously determined with an accuracy of 7-12%. The size-equivalent limits of detection estimated with the 3*σ criterion were 13 nm for Au and 16 nm for Ag. Estimation of the LODs using Poisson statistics resulted in 19 and 27 nm, respectively. In addition, the 30 μs temporal resolution of the ICPTOFMS allowed studying interactions of NPs with the ICP based on their transient MS signals. The results demonstrated a difference in vaporization behavior of the core-shell NPs and solutions and indicated that vaporization of the Ag shell takes place prior to the Au core.

Single Particle ICP-MS: Advances toward routine analysis of nanomaterials

“…In principal, if the solution concentration and droplet size are accurately known, the analyte mass entering the plasma is known and can be used to compute the relationship between analyte mass and instrument response (counts/element mass) for any element [33,34]. Recently, these MDGs have been applied to the analysis of nanomaterials by ICP-OES [35], ICP-MS [36], and ICP-TOFMS [37]. The signal generated from droplets containing analyte elements show considerable precision, with relative standard deviations below 5 % in most cases.…”

“…3B) [37,74]. By using a time-of-flight mass analyzer, nearly all elements can be detected quasisimultaneously on a particle-by-particle basis and with short detection dwell times (~33 μs).…”

Drop-on-demand microdroplet generation: a very stable platform for single-droplet experimentation

“…Another example strategy injects single microdroplets into an inductively coupled plasma source for elemental analysis. 18,20 Highprecision generation of microdroplets has also been exploited for calibration of water-vapor isotope spectrometry, 21 ionic liquid deposition, 22 the study of coalescence dynamics and mixing 23 and the isolation of single biological cells. 24 The production of metal droplet in an on-demand fashion is also well studied.…”

Mass spectrometry for the characterization and quantification of engineered inorganic nanoparticles

“…Although quadrupole instruments provide NP size detection limits of around 20 nm, a microdroplet generator installed in a time-offlight or a sector-field mass analyzer have enabled measuring metal NPs with around 10 nm size detection limit [27]. The improvement of the few types of commercially available ICP-MS instruments is mandatory in order to get better information about NPs chemical composition, number and mass concentrations, multi-element capabilities for heterogeneous engineered NPs, size and sizedistributions of the NPs at mass concentration levels down to ng L −1 [23,28].…”