Comparison of sp-ICP-MS and MDG-ICP-MS for the determination of particle number concentration

Abstract

In 2011, the European Commission introduced new regulations on how nanomaterials are defined. Since then, researchers have emphasized that more complete characterization of nanoparticles (NPs) includes not just mass and size determinations, but also the determination of the particle number concentrations. In this study, two different sample introduction approaches for the analysis of NP suspensions with inductively coupled plasma mass spectrometry (ICP-MS) were investigated: pneumatic nebulization (sp-ICP-MS) and microdroplet generation (MDG-ICP-MS). These approaches were compared for the determination of particle number concentrations (PNCs) of gold and silver NP suspensions diluted in either ultra-pure water or citrate solution. For accurate sp-ICP-MS analysis, it is crucial to know the transport efficiency of nebulized sample into the plasma. Here, transport efficiencies, measured by the waste collection method, were 11-14 % for Ag suspensions and 9-11 % for Au. In contrast, the droplet transport efficiency of MDG-ICP-MS was 100 %. Analysis by sp-ICP-MS yielded a lower particle number concentration than expected (only 20-40 % of the expected value), whereas MDG-ICP-MS had NP recoveries up to 80 %. This study indicates that NP reference materials are of major importance for particle number determination and detailed results on particle number concentrations for different suspensions with respect to storage time are discussed.

The accurate determination of number concentration of inorganic nanoparticles using spICP-MS with the dynamic mass flow approach

“…Diluting the particles in a citrate solution was reported 15 to achieve better recoveries of the expected nanoparticle number concentration than those obtained for 60 nm Ag NP using water as the diluent. The same paper 15 reported that the citrate-based suspensions for the 80 and 100 nm NP showed lower recoveries. This paper, however, does not provide further evidence for NP destabilisation (e.g.…”

Monodisperse microdroplets: a tool that advances single-particle ICP-MS measurements

“…Basic understanding of the accuracy of sp-ICP-MS measurement and data analysis approaches is hampered by a lack of NP reference materials certied for both element mass and number concentration. This lack of standards has led to inconsistent measurement practices among researchers, which may cause confusion for new practitioners of sp-ICP-MS. For example, there is little consensus on signicant measurement conditions such as optimal dwell time, most accurate method to determine transport efficiency and absolute elemental sensitivities, [55][56][57][58] or robust signal-thresholding criteria for NP identication. 59 There are, indeed, many researchers working to harmonize and standardize sp-ICP-MS measurements, [60][61][62][63] but, without a suite of well-characterized reference NPs, this process remains a challenge.…”

Nanoparticles in analytical laser and plasma spectroscopy – a review of recent developments in methodology and applications

“…323,324 Another possibility to achieve the highest possible transport efficiency is represented by microdroplet generator (MDG) sample introduction systems which can produce monodisperse droplets with a controlled volume and speed. 325,326 Unfortunately, MDGs are more prone to contamination and clogging compared to pneumatic nebulizers, hence, several papers demonstrated the advantageous utilization of the combination of pneumatic nebulizers and MDGs. [327][328][329][330] In these setups, MDG provided well-dened droplets of known dissolved ion concentration for calibration purposes and NPs were introduced by a pneumatic nebulizer via a dual-inlet system.…”