Comparison of Direct and Indirect Measures of Transport Efficiency in Single Particle ICP-MS

Published

December 16, 2023

Author(s)

Karen Murphy, Antonio Montoro Bustos, Lee L. Yu, Monique Johnson, Michael R. Winchester

Abstract

Accurate calibration of the fraction of introduced sample that is transported to the plasma, termed "transport efficiency" (TE), is required for spICP-MS measurement of particle number concentration (PNC) and for measurement of particle size (diameter, PS) when using ionic standards to obtain the mass of analyte per particle event. TE is strongly influenced by the type and operating conditions of the sample introduction system. In this study we systematically compare three methods for measurement of TE, the particle frequency (TEF), particle size (TES) and dynamic mass flow (DMF) methods. TEF and TES provide a direct measure of TE but require a single nanoparticle reference material accurately value-assigned for PNC and PS. The DMF method provides an indirect measure of TE, requiring only measurement of the mass difference between the amount of sample solution introduced to the instrument and the amount of effluent exiting the spray chamber (SC), but assumes that the measured difference represents the fraction of sample transported to the plasma. Three different SC types, Scott double pass, impact bead and baffled cyclonic SCs operated at cooled and ambient temperature conditions and using different nebulizers and ICP-MS platforms are studied. When operating the SC at ambient temperature, the DMF method yielded systematically higher measures of TE than the TEF and TES methods regardless of nebulizer type, SC type or ICP-MS platform. While better agreement between the three measures of TE was achieved when operating the SC at 2 °C, results were not consistent. Results for spICP-MS measurement of gold nanoparticle (AuNP) PNC computed using either the TEF or DMF measures of TE and PS computed using either the TES or DMF measures of TE expressed as the median percent difference from the known value for various value-assigned AuNP suspensions ranged from – 18 % to + 8 % (TEF) and from – 1 % to – 70 % (DMF) for PNC whereas results for PS ranged from – 3 % to + 1 % (TES) and from – 4 % to + 44 % (DMF) across all conditions. The large negative bias in results for PNC and positive bias in results for PS by the DMF method indicates an overestimation of TE which was traced to low recovery of the SC waste effluent. Results for ionic Au concentration measured in the waste flow versus the sample flow for the baffled cyclonic SC indicate analyte partitioning at both temperatures but partitioning at 2 °C was observed to be greater than at ambient temperature (≈21 °C). While the indirect measure of TE (DMF method) could yield unbiased and precise results in some cases (baffled cyclonic SC/Meinhard nebulizer at 2 °C), only the direct measures of TE (TEF and TES) could yield unbiased results across all use conditions.

Citation

Spectrochimica Acta Part B: Atomic Spectroscopy

Pub Type

Journals

Download Paper

https://doi.org/10.1016/j.sab.2023.106841

Local Download

Keywords

transport efficiency, calibration, single particle ICP-MS (spICP-MS), nanoparticle, number concentration, particle size, spray chamber

Citation

Murphy, K. , Montoro Bustos, A. , Yu, L. , Johnson, M. and Winchester, M. (2023), Comparison of Direct and Indirect Measures of Transport Efficiency in Single Particle ICP-MS, Spectrochimica Acta Part B: Atomic Spectroscopy, [online], https://doi.org/10.1016/j.sab.2023.106841, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=936032 (Accessed September 11, 2024)