Research and Thesis Projects

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Optimization of sample introduction for nanoparticle analysis

Keywords: nanoparticle, diffusion, transport efficiency, plasma

The fluid dynamics inside the plasma torch of an ICPMS are complex and the efficiency of ion transmission is severely affected by diffusion. Additionally, the radial point of injection of particles or droplets into the ICP can strongly affect the relative abundance of ions detected by the mass spectrometer. These phenomena are especially problematic for analysis of individual nanoparticles because they can introduce artefacts about the elemental composition and usually reduce instrumental sensitivity. Hence it is crucial for their characterization that analyte loss by diffusion is reduced and thus the detection efficiency and accuracy of the ICPMS improved. The aim of this project is thus to study the effect of operating conditions on gas dynamics inside the ICP torch and thereby be able to optimize gas dynamics and lateral diffusion.

Doctoral Student: Lyndsey Hendriks

Funding: SNF Project 200021_162870/1

Fundamental studies of fs-LA ICPMS

Keywords: fs-LA, homogenized beam delivery, high resolution depth profiling

In this project we compare femtosecond and nanosecond laser ablation sampling for inductively coupled plasma mass spectrometry, with a focus on non-matrix matched quantification: Is femtosecond laser ablation really a non-thermal ablation process and what is the influence of different wavelengths on accuracy and reproducibility of an analysis?

Furthermore, a spatially homogenized energy profile of the femtosecond laser radiation delivered to the sample surface shall be realized. This would open up new possibilities for high resolution elemental depth profiling. We use Fourier optical transformations to homogenize the femtosecond laser intensity profile, which shall result in ablation craters with steep walls and flat bottoms. Thereby co-ablation of material from different depths is minimized and the elemental concentration should be determinable within a unique layer of about 50 nm.

Doctoral Student: Debora Käser

Funding: ETH Zurich

Laser Ablation Ion Funnel Mass Spectrometer (LAFUMA)

Keywords: Laser Ablation , Ion Funnel, RF, TOFMS.

The aim of this project is the characterization of newly developed ion extraction system in combination with laser ablation for the direct analysis of solid materials. The anticipated feature of this system is high ion transmission efficiency after generation at moderately low pressure (100 mbar) into a mass spectrometer operating at pressures < 10-4 mbar. A new ion funnel configuration consisting of a series of ring electrodes of progressively smaller internal diameter to which only RF-potential of alternating polarity is applied. The electric field creates a pseudo-static radial potential gradient causing the ions to be effectively focused and transmitted as a collimated ion beam with low energy spread. Ion detection is favorably carried out using a TOF MS system, which allows simultaneous detection of all isotopes of interest at high spectral frequency and reasonable mass resolution. The great advantage of this technique is given by its potential application of laser ablation mass spectrometry in many different fields such as elemental, isotopic and molecular analyses.

Doctoral Student: Lorenzo Querci

Funding: ETH Grant 29 15-2

High-Speed, High-Resolution, Multi-Elemental LA-ICP-TOFMS Imaging

Keywords: LA-ICP-TOFMS, simultaneous, multi-elemental, two- and three-dimensional imaging

Elemental imaging is becoming increasingly important for example in geology, biology and materials sciences, where characterizing micro-structures and determining elemental distributions across heterogeneous samples are of major relevance.

Until now, most instrumental approaches applied in either two or three dimensional imaging studies were done using laser ablation sampling coupled to a mass spectrometer with sequential isotope detection (quadrupole or magnetic sector). The fundamental principle of those systems did however not allow comprehensive multi-element detection – a requirement that can be met by time-of-flight mass spectrometry (TOFMS).

This project aims to establish LA-ICP-TOFMS for the fast acquisition of highly resolved quantitative multi-elemental images of solid samples. In the course of this work we investigate experimental approaches to optimize signal/noise by lowering dispersion of the LA-generated aerosol and reduce matrix dependency during calibration.

Doctoral Student: Marcel Burger

Funding: SNF Project 200020_141292

Quantification of Trace Elements by Portable Laser Ablation Sampling and Subsequent Inductively Coupled Plasma Mass Spectrometry

Keywords: Laser Ablation; Portable Analytical Methods; Elemental and Isotopic Fingerprinting; Archaeometry; Inductively Coupled Plasma Mass Spectrometry

A wide range of objects cannot be moved into the laboratory for chemical characterization because of their physical properties or regulatory restrictions. Thus, in order to be able to do quantitative trace-element and isotope analyses, an off-line portable laser ablation (pLA) sampling method is employed here. It comprises a field-deployable diode-pumped solid state laser with fiber optics for quasi non-destructive sampling, while the aerosol can be collected on filters. Subsequent analysis by ICPMS in the laboratory then allows the sensitive analysis of the material for its element and / or isotope composition.

In the scope of this project the applicability of the method is investigated e.g in archaeometric research to characterize objects regarding their provenance, age, and authenticity based on the elemental and isotopic fingerprints. Furthermore hardware modifications of the pLA device are studied to further broaden the range of objects that can be analyzed.

Doctoral Student: Stefan Kradolfer (ab 1. Nov. 2016)

Funding: ETH Zurich

Collaborations: Curt-Engelhorn-Centre Archaeometry gGmbH, Mannheim, Germany, University of Heidelberg, Institute for Geosciences, Heidelberg, Germany, Museum for Pre- and Early History, State Museums of Berlin, Berlin, German

Imaging Mass Cytometry

Keywords: fast washout LA cell, high spatial resolution, imaging

Laser ablation ICPMS imaging is able to reveal the spatial elemental distribution within a variety of sample types. In combination with isotopically labeled antibodies it is now used for imaging mass cytometry studies, exploiting the quasi simultaneously multi-elemental capabilities of ICP-TOFMS. Of special interest is the interplay of particular cells, their regulatory circuits and how processes in the tumor microenvironment are induced and maintained. Our major focus is further instrumental development.  This includes compact instrumental setups in conjunction with small laser spot diameters in the low and sub µm range for high lateral resolution imaging and low dispersion ablation cells for high throughput analyses. Additionally, we are working on alternative calibration strategies for quantitative imaging of biomaterials.

Doctoral Student:  Jovana Teofilovic

Postdoc: Gunnar Schwarz

Funding: ETH Zurich

Collaboration: System Biology Group of Bernd Bodenmiller, Institute of Molecular Life Sciences (Universität Zürich, Switzerland)


Sr isotope ratios and Rb-Sr ages by LA-ICPMS with isobar separation by
online electrothermal vaporization

Keywords: ETV, LA-ETV-MCICPMS, Rb-Sr Geochronology, Sr-isotope ratios, Isobaric Interference Suppression

High-precision Sr isotope ratio determination of solids by laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MCICPMS) is of importance for a variety of applications. The accuracy of the 87Sr/86Sr determination is however limited by the isobaric interference of 87Rb on 87Sr, which cannot be separated with the mass resolving power offered by today’s ICPMS. Unlike in solution based methods, where the separation of Rb and Sr can be achieved, in LA, all elements in the aerosol reach the plasma, leading to the mentioned interference. By heating the aerosol in an electrothermal vaporization (ETV) unit, changes in its chemical composition can be initiated and a selective suppression of the Rb-signal can be obtained due to the different vaporization temperatures of Rb (< 1’000° C) and Sr (SrO ≈ 3’000° C). The aim of this work is to develop and optimize a standalone ETV system with highest Rb-suppression and to improve the stability and the reproducibility of the set-up. Ultimately the system shall be employed in Sr-isotope analyses of geological materials in combination with LA –MCICPMS.

Doctoral Student: Ceren Yilmaz

Funding: SNF Project 200021_153583


Femtosecond Laser Ablation ICPMS for Depth Profiling of Thin Films

Keywords: fsLA-ICP-MS, PLD, perovskites, depth profiling

The perovskite-structured compound La1-xCaxMnO3 exhibits interesting magnetoresistant properties, depending on what exact stoichiometry it has when formed into thin films via pulsed laser deposition (PLD).

The aim of this project is the utilization of femtosecond laser ablation inductively coupled plasma mass spectrometry (fs-LA-ICPMS) as a depth profiling method for aforementioned materials in the sub-100 nm range, making use of the lower optical penetration depth and smaller heat affected zone when compared to ns-LA. Such characteristics can allow for the increase in depth resolution. Different laser wavelengths from near infrared (NIR) to ultraviolet (UV) are tested, as are different methods of ICPMS for ion detection, in particular; time of flight- and quadrupole mass spectrometers. Scanning electron microscopy, white light interferometry and confocal microscopy is applied to study fs-LA crater morphologies, thus providing insight on the laser-matter interaction.

Doctoral Student: Kevin Guex

Funding: SNF Project 200021-143665

Collaboration: Prof. Thomas Lippert, PSI (Switzerland)


Laser Ablation for Radiocarbon Analysis by Accelerator Mass Spectrometry

Keywords: LA-AMS, Radiocarbon, Spatial Record

A novel laser ablation based sampling system for radiocarbon (14C) measurements using accelerator mass spectrometry (AMS) is used for spatially resolved analyses of carbonate material. In this project we want to further improve the performance of the laser ablation sampling in terms of conversion of carbonates into gaseous CO2 by improving the beam delivery optics. Also we aim at modifications of the gas ion source of the AMS instrument to minimize leakage of CO2 and improve the C- generation. Thereby we aim at a spatial resolution of less than 100 mm and / or detection of lower 14C concentrations. Furthermore we employ the instrument for detection of radiocarbon profiles in natural carbonates as stalagmites, corals and otoliths.

Doctoral Student: Christiane Yenan (D-PHYS)

Funding: SNF Project 200021_160064/1

Collaboration: M. Christl (PI), A. Synal, L. Wacker, (D-PHYS)

AMS Homepage

Micro-scale radiocarbon analyses for cultural heritage

Keywords: 14C dating, Artworks, micro-sampling

In combination with material identification and stylistic assessment, radiocarbon (14C) dating can provide a time window of when a work of art was first created. Hereby 14C dating may play a key role in the puzzle of artwork authentication when considering items suspected to be fakes or when reattributing artworks to its painter. Nevertheless, its application as routine dating method is still rather limited due to the destructive nature of sample collection and prevents sampling of many valuable objects. However, over the past years the interest in radiocarbon measurements using accelerator mass spectrometry (AMS) in the microgram level has drastically increased and has driven the development of interfaces enabling the direct measurement of carbon dioxide. Thanks to these progresses, radiocarbon dating now has a greater potential to support the research and understanding of cultural heritage materials, ranging from rock art of the early modern humans to the most recent creation of art with reduced invasiveness to its integrity.

This project aims at the development of a micro-scale sampling strategy for artworks before radiocarbon measurements. The knowledge gained in other research field regarding 14C dating techniques on micrograms of carbon will be applied to cultural heritage objects. The problem of limited access to sample material in works of art will be addressed by downscaling the sample size, adjusting preparative steps and further avoiding handling of the sample after combustion with the new interface of the MICADAS gas ion source (GIS) that allows the direct transfer of CO2 from an elemental analyzer (EA) to the ion source. The possibility of dating new materials, such as the organic based binding medium, natural organic pigment or anthropogenic carbonates, will also be explored. This aspect requires the combination of additional analytical techniques, such as XRF, FTIR and Raman analyses, to fully characterize the composition of paint and assess sample’s suitability for 14C analysis prior sampling.

Doctoral student: Laura Hendriks

Funding: ETH Grant 21 15-1

Collaboration: Dr. I. Hajdas (D-PHYS), Prof. Dr. H.-A. Synal (D-PHYS), Prof. Dr. E. Ferreira (Cologne Institute of Conservation Sciences, TH Köln, University of Applied Sciences, Germany), M. Küffner (Swiss Institute for Art Research, SIK-ISEA Zurich, Switzerland), Bern University of the Arts, Bern, Zürich

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