Article pubs.acs.org/ac
Investigation of a Combined Microdroplet Generator and Pneumatic Nebulization System for Quantitative Determination of MetalContaining Nanoparticles Using ICPMS Benita Ramkorun-Schmidt,†,‡ Spiros A. Pergantis,§ Diego Esteban-Fernández,†,‡ Norbert Jakubowski,‡ and Detlef Günther*,∥ †
School of Analytical Sciences Adlershof, Humboldt-Universitaet zu Berlin, Brook-Taylor Strasse 2, 12489, Berlin, Germany BAM Federal Institute for Materials Research and Testing, Richard-Willstätter Strasse 11, 12489, Berlin, Germany § Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Voutes Campus, Heraklion 71003, Greece ∥ ETH Zurich, Department of Chemistry and Applied Biosciences, Laboratory of Inorganic Chemistry, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland
Downloaded by UNIV OF CAMBRIDGE on September 4, 2015 | http://pubs.acs.org Publication Date (Web): August 13, 2015 | doi: 10.1021/acs.analchem.5b01604
‡
S Supporting Information *
ABSTRACT: In this work, a routinely applicable approach is presented to characterize metal NPs. Individual droplets generated from a microdroplet generator (MDG) were merged into an aerosol generated by a pneumatic nebulizer (PN) and introduced into an ICPMS. The MDG offers high transport efficiency of individual and discrete droplets and was therefore used to establish a calibration function for mass quantification of NPs which were introduced through the PN following the single particle procedure as described elsewhere. The major advantages of such a combined configuration include fast processing of large sample volumes, fast exchanges of different sample matrixes, and the calibration of the NP signal using traceable elemental standards, thus avoiding the need to use NP reference materials or other, not always thoroughly characterized, commercially available NPs. The transport efficiency of the sample introduction is calculated based on the fact that 100% of the calibrant reaches the plasma through the MDG, whereas for the PN a NP suspension containing a known number concentration is used. Alternatively, bulk analysis of the NP material allows transport efficiency determination without any additional information from reference NPs. With this method, we could determine the size of standard silver NPs at 60.4 ± 1.0 nm and 80.0 ± 1.4 nm, respectively, which agrees with the size ranges given by the supplier (60.8 ± 6.6 nm and 79.8 ± 5.4 nm). Furthermore, we were also able to determine the NPs number concentration of the sample (Ag/Au) with a deviation of 3.2% the expected value.
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information about the elemental composition of the NPs, cannot analyze particles in situ and sample preparation can be time-consuming. ICPMS is widely used for elemental analysis in the fields of biomedicine,6 geology,7 and environmental sciences.8 Because of the high sensitivity, wide linear dynamic range, multielemental capabilities, structure independent response, comparatively low requirement for sample preparation, and convenient hyphenation to different sample introduction and separation techniques, ICPMS has also been described as a promising technique for characterizing metal containing NPs at trace levels.9 Single particle mode ICPMS (sp-ICPMS) has
he commercial applications of nanoparticles (NPs) have seen a considerable increase in the past few years. The unique chemical and physical properties of certain types of NPs, which mainly originate as a result of their large surface area to volume ratio, set them apart from their corresponding micro- and macroparticles. Silver (Ag) and gold (Au) engineered NPs are among the most widely used.1,2 The antibacterial properties of Ag NPs and the optical properties of Au NPs are some of their attractive features. However, the fate of NPs is currently not well understood, especially at environmentally relevant concentrations and in complex matrixes. To describe NPs in terms of their morphology and size, scanning electron microscopy (SEM),3 transmission electron microscopy (TEM),4 and atomic force microscopy (AFM)5 are the most commonly used methods. The latter can provide high spatial resolution, however, and does not provide any © 2015 American Chemical Society
Received: April 9, 2015 Accepted: July 27, 2015 Published: July 27, 2015 8687
DOI: 10.1021/acs.analchem.5b01604 Anal. Chem. 2015, 87, 8687−8694
Article
Downloaded by UNIV OF CAMBRIDGE on September 4, 2015 | http://pubs.acs.org Publication Date (Web): August 13, 2015 | doi: 10.1021/acs.analchem.5b01604
Analytical Chemistry
The objective of this work was to develop a flexible and rapid method for NP analysis involving the use of a microdroplet generator (MDG) due to the rapid quantification capabilities and a sp-ICPMS for higher sample throughput. Therefore, a hybrid approach combining both existing techniques was established and studied in detail. The MDG served to introduce well-defined droplets of known dissolved metal concentration for response factor calculation. The NP-containing aqueous sample was introduced via the pneumatic nebulizer spray chamber system. On the basis of this approach, the metal mass fraction and thus size of the intact NPs can be readily determined. This novel sample introduction configuration was optimized in terms of the ICPMS parameters in order to obtain high signal sensitivity as well as high reproducibility. The applicability of this arrangement and the figures of merit are demonstrated and reported for the analysis of Ag and Au NPs. Furthermore, the NP number concentrations, at different concentration levels, were also determined.
been proposed for the analysis of engineered inorganic particles in liquids10 and involves the analysis of dilute particle solutions, measured using short dwell times. This allows for the recording of single element signals coming from one particle at a time.11−15 Therefore, sp-ICPMS has become an attractive approach for NP determination, since it can also accommodate a wide range of sample matrixes and allows for rapid sample switchover.11,15,16 However, to be able to quantify particles in terms of number concentration of particles and mass fraction of analyte, the transport efficiency of the sample introduction system must be determined precisely. With the use of a pneumatic nebulizer in combination with a spray chamber, the major challenge in sp-ICPMS is the determination of the sample introduction efficiency. The spray chamber removes droplets that are larger than 20 μm in diameter14,17 after nebulization to prevent unstable plasma. Depending on the type of nebulizer and spray chamber used for the experiments, transport efficiencies between 10 and 70%, as shown by Olesik et al.,18 can be achieved. However, most commonly applied nebulizers provide efficiencies in the order of
