Research and Thesis Projects

Trace element analytics in forensic science by means of Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Keywords: LA-ICPMS, Forensics, Single-shot analysis, micro-sampling, fast washout LA cell, TOF-MS, glass fragments

When a piece of evidence is found at a crime scene, it requires different analytical methods to determine the origin of that sample. For example, if a window is broken during a burglary, glass fragments will stick to the criminal’s skin and clothing. Being able to determine if the glass fragments found within a suspect’s clothes are from the same source as the fragments from the broken window at the crime scene, allows the linking of that suspect with the crime scene. This requires the sample to have a property, that is unique to that source. The concentrations of trace elements within the sample, introduced during production as impurities of the raw materials, can be used as one of these properties. With LA-ICPMS the trace elements in two samples can be determined and using different statistical models, it is possible to determine whether the two samples were from the same source. Due to the nature of forensic samples, sample size is limited and instrumental methods and statistics need to be developed in order to accurately match samples.
This project focuses on these developments with the goal of analysing the smallest possible samples reproducibly through instrumental changes and statistical treatment. This is accomplished by changing from continuous laser ablation to single shot analysis with a low-dispersion ablation cell and ToF-MS, allowing for quantification of every ablation pulse and thus vastly increasing the sample size.

Doctoral Student: Pascal Becker

Funding: ETH Zurich

Collaboration: Sabine Hess & Dr. Christian Bogdal (Forensic Institute Zurich), Dr. Peter Weis (BKA Wiesbaden)
 

Characterization and Evaluation of a Nitrogen based Microwave Inductively Coupled Atmospheric-Pressure Plasma as Ion Source for Inorganic Mass Spectrometry

Keywords: nitrogen plasma, microwave-induced plasma, mass spectrometry, characterization

Nitrogen based plasmas gained a lot of attention as alternative ion source for ICPMS due to the environmental-friendly nitrogen gas and its lower operating cost to sustain the plasma. However, initial plasma generation approaches were limited by their low operating power. In this project a recently developed high-power microwave inductively coupled atmospheric-pressure plasma (MICAP) is investigated as ion source for mass spectrometry (MS). The studies focus on fundamental properties of the MICAP ion source and its performance in element and isotope analyses. The combination of the new source with different sample introduction systems such as pneumatic nebulization and laser ablation is evaluated with respect to analyte sensitivity, molecular ion formation as well as attenuation of plasma background ions using a dynamic reaction cell. Additionally, the influence of the plasma solvent load and the matrix tolerance of the ion source are investigated. Furthermore, the abundances and impact of nitrogen based spectral interferences in the N₂ MICAP are analysed.

Doctoral Student: Monique Kuonen

Funding: SNSF project number 200021_197224

Coupling laser ablation to a nitrogen microwave inductively coupled atmospheric-pressure plasma mass spectrometer (MICAP-MS) for elemental analysis

Keywords: Laser ablation, nitrogen plasma, mass spectrometry

Laser ablation (LA) as a solid sampling technique has been established over the years for direct analysis while remaining micro-invasive. This enabled a broad range of applications in material sciences, forensics, geology, medicine and among others. More recently, a high-power microwave inductively coupled atmospheric-pressure plasma (MICAP) using nitrogen proved to be competitive with the traditional argon plasma source for elemental mass spectrometry. Unlike the argon ICP, the MICAP has proven to be stable towards introduction of direct air. Furthermore, nitrogen remains an unexplored ablation environment and the ablation behavior as well as the aerosol transport under nitrogen will be studied as a cheaper alternative to helium and argon. Combining LA with such a versatile plasma source as the N2-MICAP opens new possibilities in terms of analytical procedures or hardware compatibility. Ultimately, the reduction of the measurement costs by replacing argon with nitrogen will increase the accessibility of elemental analysis for all types of proven applications.

Doctoral Student: Dylan Käser

Funding: Radom™ Corporation, USA