title: Evaluation of number concentration quantification by single-particle inductively coupled plasma mass spectrometry: microsecond vs. millisecond dwell times.
abstract: The quality of the quantitative information in single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS) depends directly on the number concentration of the nanoparticles in the sample analyzed, which is proportional to the flux of nanoparticles through the plasma. Particle number concentrations must be selected in accordance with the data acquisition frequency, to control the precision from counting statistics and the bias, which is produced by the occurrence of multiple-particle events recorded as single-particle events. With quadrupole mass spectrometers, the frequency of data acquisition is directly controlled by the dwell time. The effect of dwell times from milli- to microseconds (10 ms, 5 ms, 100 μs, and 50 μs) on the quality of the quantitative data has been studied. Working with dwell times in the millisecond range, precision figures about 5 % were achieved, whereas using microsecond dwell times, the suitable fluxes of nanoparticles are higher and precision was reduced down to 1 %; this was independent of the dwell time selected. Moreover, due to the lower occurrence of multiple-nanoparticle events, linear ranges are wider when dwell times equal to or shorter than 100 μs are used. A calculation tool is provided to determine the optimal concentration for any instrument or experimental conditions selected. On the other hand, the use of dwell times in the microsecond range reduces significantly the contribution of the background and/or the presence of dissolved species, in comparison with the use of millisecond dwell times. Although the use of dwell times equal to or shorter than 100 μs offers improved performance working in single-particle mode, the use of conventional dwell times (3-10 ms) should not be discarded, once their limitations are known.
authors.affiliation: Group of Analytical Spectroscopy and Sensors (GEAS), Institute of Environmental Sciences (IUCA), University of Zaragoza, Pedro Cerbuna 12, 50009, Zaragoza, Spain.|Group of Trace Elements, Spectroscopy and Speciation (GETEE), Department of Analytical Chemistry, Nutrition and Bromatology, University of Santiago de Compostela, Avda. Das Ciencias, s/n, 15782, Santiago de Compostela, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Abad-Álvaro
authors.affiliation: Group of Trace Elements, Spectroscopy and Speciation (GETEE), Department of Analytical Chemistry, Nutrition and Bromatology, University of Santiago de Compostela, Avda. Das Ciencias, s/n, 15782, Santiago de Compostela, Spain.
authors.forename: Elena
authors.initials: E
authors.lastname: Peña-Vázquez
authors.affiliation: Group of Analytical Spectroscopy and Sensors (GEAS), Institute of Environmental Sciences (IUCA), University of Zaragoza, Pedro Cerbuna 12, 50009, Zaragoza, Spain.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Bolea
authors.affiliation: Group of Trace Elements, Spectroscopy and Speciation (GETEE), Department of Analytical Chemistry, Nutrition and Bromatology, University of Santiago de Compostela, Avda. Das Ciencias, s/n, 15782, Santiago de Compostela, Spain.
authors.forename: Pilar
authors.initials: P
authors.lastname: Bermejo-Barrera
authors.affiliation: Group of Analytical Spectroscopy and Sensors (GEAS), Institute of Environmental Sciences (IUCA), University of Zaragoza, Pedro Cerbuna 12, 50009, Zaragoza, Spain.
authors.forename: Juan R
authors.initials: JR
authors.lastname: Castillo
authors.affiliation: Group of Analytical Spectroscopy and Sensors (GEAS), Institute of Environmental Sciences (IUCA), University of Zaragoza, Pedro Cerbuna 12, 50009, Zaragoza, Spain. flaborda@unizar.es.
authors.forename: Francisco
authors.initials: F
authors.lastname: Laborda
keywords: Nanoparticle; Number concentration; Quantification; SP-ICP-MS; Single particle