Einzelpartikel-ICP-MS : Möglichkeiten der Mikrosekunden-Zeitauflösung und der Kopplung an die Kapillarelektrophorese

Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) is a method that allows to obtain size, size distribution, and particle number concentration of nanoparticles (NPs) in suspensions only after few minutes of measurement. However, several challenges of commercially available SP-ICP-MS instruments currently exist that limit the analytical performance of the method. This thesis reports novel developments and improvements of SP-ICP-MS with the ultimate goal to be able to use it as a routine NP analysis method in the future. First, the state-of-the-art in SP-ICP-MS is reviewed on a step-by-step basis, from the sample introduction system to the detector. Applications of the method for the analysis of nanomaterials are critically discussed and current challenges are highlighted. Necessary improvements and directions for further developments are identified. Second, capillary electrophoresis (CE) is coupled to SP-ICP-MS and used for the first time with a data aquistion system (DAQ) that provides microsecond time resolution (5 µs dwell time, µsDAQ) for the separation and characterization of mixtures of Ag NPs. An online preconcentration approach is implemented to decrease the detection limits to the sub-microgram-per-liter range. In addition, it is demonstrated for the first time that the optimized CE-SP-ICP-MS method can be successfully used to separate NPs with similar sizes but different surface coatings. Each component in a complex mixture of 20 nm, 40 nm, 60 nm sized citrate-coated and 40 nm, 60 nm sized PVP-coated Ag NPs can be distinguished. Finally, a novel data processing algorithm for SP-ICP-MS with the µsDAQ is developed to extract NP signals from a continuous background signal. The method is based on Poisson statistics and allows to distinguish and quantify both NPs and dissolved elements. It is demonstrated that Ag NPs (20 nm – 100 nm) can be identified on a particle-by-particle level even in the presence of a significant concentration of ionic background (Ag+ up to 7.5 µg L-1, 107Ag+ up to 1 000 000 counts per second).Die Massenspektrometrie mit induktiv gekoppeltem Plasma im Einzelpartikel-Modus (SP-ICP-MS) ist eine Methode, mit der sich die Größe, die Größenverteilung und die Partikelkonzentration von Nanopartikeln (NP) in Suspensionen innerhalb von wenigen Minuten bestimmen lassen. Obwohl die SP-ICP-MS kommerziell erhältlich ist, gibt es zahlreiche Herausforderungen, die die analytischen Leistungskenndaten und die Anwendbarkeit der Methode für die Nanomaterialanalytik beschränken. Die vorliegende Arbeit beschäftigt sich mit der Entwicklung und Optimierung von neuen Ansätzen in der SP-ICP-MS, um diese in der Zukunft noch besser als Analysemethode für die Nanomaterialanalytik einsetzen zu können. Zunächst wird der Stand der Technik auf dem Gebiet der SP-ICP-MS schrittweise vom Probeneinführungssystem bis zum Detektor kritisch diskutiert. Wichtige Anwendungen werden rezensiert und notwendige methodische und apparative Verbesserungen werden identifiziert. Im Ergebnisteil der Arbeit wird eine neuartige Methode vorgestellt, die auf der Kopplung von Kapillarelektrophorese (CE) mit SP-ICP-MS beruht, mit einem kontinuierlichen Datenerfassungsystem mit Mikrosekundenzeitauflösung (5 µs Integrationszeit) arbeitet und erfolgreich für die Charakterisierung von Ag NP eingesetzt wird. Ebenso wird eine Methode zur Online-Aufkonzentration implementiert, um die Nachweisgrenzen zu verbessern (µg L-1 – Bereich). Schließlich wird die CE-SP-ICP-MS zur Trennung von NP mit ähnlichen Größen, jedoch unterschiedlichen Oberflächenbeschichtungen verwendet. Jede Komponente in einer komplexen Mischung, welche 20 nm, 40 nm und 60 nm große Citrat-beschichtete Ag NP, sowie 40 nm und 60 nm große PVP-beschichtete Ag NP enthielt, kann unterschieden werden. Zum Schluss wird ein Datenverarbeitungsalgorithmus für die SP-ICP-MS mit µsDAQ vorgestellt. Die entwickelte Methode basiert auf der Poisson-Statistik und ermöglicht die Unterscheidung und Quantifizierung von NP und gelösten Elementen. Das Verfahren ermöglicht den Nachweis von Ag NP (von 20 nm bis 100 nm) in Anwesenheit einer signifikanten Konzentration an ionischem Hintergrund (Ag+ bis zu 7.5 µg L-1, 107Ag+ bis zu 1 000 000 Anzahl von Impulsen pro Sekunde)

Separation of Silver Nanoparticles with Different Coatings by Capillary Electrophoresis Coupled to ICP-MS in Single Particle Mode

The possibility of separating mixtures of Ag nanoparticles (NPs) with similar sizes but different surface coatings using capillary electrophoresis coupled to single particle inductively coupled mass-spectrometry (CE-SP-ICP-MS) was investigated. In two-component mixtures, it was possible to separate 40 nm sized polyvinylpirrolidone (PVP)- and citrate-coated NPs, 40 nm sized polyethylene glycol (PEG)- and citrate-coated NPs, and 60 nm sized PVP- and citrate-coated NPs. The separation of a more complex mixture containing NPs with the different coatings and sizes was successful, and each component, namely, 20, 40, and 60 nm sized citrate-coated and 40 and 60 nm sized PVP-coated NPs, could be distinguished. The theoretically expected migration order was confirmed by experimental results with selected Ag NPs. On the basis of the experimental observations, a separation mechanism that considers the effect of stable vs displaceable coatings during NP migration in CE is suggested. The ICP-MS was equipped with a prototype data acquisition system (μsDAQ) that provided 5 μs time resolution

Implementation of Online Preconcentration and Microsecond Time Resolution to Capillary Electrophoresis Single Particle Inductively Coupled Plasma Mass Spectrometry (CE-SP-ICP-MS) and Its Application in Silver Nanoparticle Analysis

Capillary electrophoresis (CE) coupled to single particle inductively coupled plasma mass-spectrometry (SP-ICP-MS) was used for the first time with a prototype data acquisition (μsDAQ) system that features 5 μs time resolution (100% duty cycle) to separate and quantify mixtures of silver nanoparticles (Ag NPs). Additionally, an online preconcentration technique, reversed electrode polarity stacking mode (REPSM), was applied for Ag NPs analysis with CE-SP-ICP-MS for the first time. After optimization, best results were achieved using a injection time of 110 s and a constant pressure of 50 mbar in hydrodynamic injection mode. It was possible to detect 14.3 ± 1.5× more 20 nm sized, 21.0 ± 4.2× more 40 nm sized, and 27.7 ± 4.9× more 60 nm sized Ag NPs compared to the standard injection time of only 3 s. The effect of applied voltage on the NPs separation was studied, and a CE separation at 20 kV was found to be optimal for the present setup. The capability of CE-SP-ICP-MS for quantification of particle number concentration was investigated, and detection limits in the submicrogram-per-liter range were achieved. The possibility to separate 20, 40, and 60 nm sized Ag NPs simultaneously present in a mixture was demonstrated over a broad concentration range

New method for the discovery of adulterated cognacs and brandies based on solid-phase microextraction and gas chromatography - mass spectrometry

The article represents new method for discovery of adulterated cognacs and brandies based on solidphase microextraction (SPME) in combination with gas chromatography – mass spectrometry (GC-MS). The work comprised optimization of SPME parameters (extraction temperature and time, concentration of added salt) with subsequent analysis of authentic samples and comparison of the obtained chromatograms using principal component analysis (PCA). According to the obtained results, increase of extraction temperature resulted in an increase of response of the most volatile brandy constituents. To avoid chemical transformations and/or degradation of the samples, the extraction temperature must be limited to 30!C. Increase of the extraction time lead to higher total peak area, but longer extraction times (>10 min for 100 µm polydimethylsiloxane and >2 min for divinylbenzene/Carboxen/polydimethylsiloxane fibers) caused displacement of analytes. Salt addition increased total response of analytes, but caused problems with reproducibility. The developed method was successfully applied for discovery of adulterated samples of brandy, cognac, whisky and whiskey sold in Kazakhstan. The obtained data was analyzed applying principal component analysis (PCA). Five adulterated brandy and whisky samples were discovered and confirmed. The developed method is recommended for application in forensic laboratories

Defective defence in Daphnia daughters: silver nanoparticles inhibit anti-predator defence in offspring but not in maternal Daphnia magna

Finanziert aus dem Open-Access-Publikationsfonds der Universität Siegen für Zeitschriftenartikel.One major environmental problem of our time are emerging contaminants in the aquatic environment. While nanoparticles exhibit attractive features such as antimicrobial properties in the case of silver nanoparticles (AgNPs), earlier studies suggest that NPs are not completely filtered out at wastewater treatment plants and may therefore be continuously introduced into the aquatic environment. Although adverse effects of AgNPs on aquatic organisms have been extensively studied, there is still a lack of knowledge on how this chemical stressor interacts with natural cues on the maternal and subsequent generation of aquatic organisms. We tested whether AgNPs (NM-300K, 14.9 ± 2.4 nm, concentration range: 2.5 µg/L – 20 µg/L) affect the kairomone-induced adaptive anti-predator defence mechanism in maternal Daphnia and their offspring. While maternal Daphnia developed typical anti-predator defence mechanisms when exposed to kairomones and AgNPs, their offspring could not develop such adaptive defensive traits. The lack of this defence mechanism in offspring could have dramatic negative consequences (e.g. reduced Daphnia population) for the entire complex food web in the aquatic ecosystem. For a realistic risk assessment, it is extremely important to test combinations of chemical stressors because aquatic organisms are exposed to several natural and artificial chemical stressors at the same time

Impact of wastewater-borne nanoparticles of silver and titanium dioxide on the swimming behaviour and biochemical markers of Daphnia magna: An integrated approach

Due to their widespread use, silver (Ag) and titanium dioxide (TiO2) nanoparticles (NPs) are commonly discharged into aquatic environments via wastewater treatment plants. The study was aimed to assess the effects of wastewater-borne AgNPs (NM-300 K; 15.5 ± 2.4 nm; 25−125 μg L−1) and TiO2NPs (NM-105; 23.1 ± 6.2 nm; 12.5−100 μg L−1), from a laboratory-scale wastewater treatment plant, on Daphnia magna, at individual and subcellular level. For effect comparison, animals were also exposed to ASTM-dispersed NPs at the same nominal concentrations. The behaviour of D. magna was evaluated through monitoring of swimming height and allocation time for preferred zones after 0 h and 96 h of exposure. Biochemical markers of neurotransmission, anaerobic metabolism, biotransformation, and oxidative stress were subsequently determined. No 96-h EC50 (immobilization ≤ 4 %) could be obtained with wastewater-borne NPs and ASTM-dispersed TiO2NPs, whereas the ASTM-dispersed AgNPs resulted in an immobilization 96-h EC50 of 113.8 μg L−1. However, both wastewater-borne and ASTM-dispersed TiO2NPs, at 12.5 μg L−1, caused immediate (0 h) alterations on the swimming height. Allocation time analyses showed that animals exposed to ASTM-dispersed AgNPs spent more time on the surface and bottom at 0 h, and in the middle and bottom at 96 h. This pattern was not observed with ASTM-dispersed TiO2NPs nor with wastewater-borne AgNPs and wastewater-borne TiO2NPs. At the biochemical level, the more pronounced effects were observed with wastewater-borne AgNPs (e.g. induction of lactate dehydrogenase and glutathione S-transferase activities, and inhibition of catalase activity). This integrative approach showed that: (i) the behavioural and biochemical response-patterns were distinct in D. magna exposed to environmentally relevant concentrations of wastewater-borne and ASTM-dispersed NPs; (ii) the most pronounced effects on allocation time were induced by ASTM-dispersed AgNPs; and (iii) at the subcellular level, wastewater-borne AgNPs were more toxic than wastewater-borne TiO2NPs. This study highlights the need for the assessment of the effects of wastewater-borne NPs under realistic exposure scenarios, since processes in wastewater treatment plants may influence their toxicity