Development and performance evaluation of a high mass resolution time of flight laser ablation ionisation mass spectrometer

This thesis contributes to the field of analytical chemistry of solid samples by introducing a new instrument with unprecedented performance characteristics and analytical capabilities. The instrument is based on the laser ablation and ionisation time-of-flight (LI-TOF-MS) technique. This technique has the potential to provide standard free quantitative analysis with sensitivities in the ppm range and below over a wide mass range of several hundred amu and more. LI-TOF-MS was initially developed and commercialised in the 1980ies and 1990ies by a series of companies. However, the interest in the technique faded soon because the laser and computer technology at the time was not sufficient to meet the requirements of reliable quantitative analysis and alternative techniques were preferred. In this thesis, a new instrument, called LMS- GT, is presented. By using modern computer and laser- technology, this instrument achieves mass resolutions of m/Dm = 10000 and sensitivities in the ppm range and below. These performance characteristics open new perspectives for the LIMS technique to rival the dominant analytical techniques. At the beginning of this project was a miniature LIMS prototype, from which plenty of know-how on laser ablation/ionisation mass spectrometry was collected, an empty laboratory space and the vision that is possible to build a high performance LIMS instrument for element and isotope analysis of solid samples at the micrometre scale. This thesis documents the technology transfer from the miniature prototype to a reliable full-scale laboratory instrument that was designed from scratch. A series of pre-developments on the miniature prototype allowed to test the potential of a UHV compatible microscope, the application of a high speed switch to blank highly abundant species in the mass spectra and advanced data processing. All of these pre-developments were published in three first author papers and are included in the thesis. Also, a thorough literature research was conducted to find the best instrument layout for the new system and initial parameters for the subsequent modelling of the ion system. The extensive simulation was concurrently carried out in SIMION, ZEMAX and CATIA for ion optics, light optics and mechanical design respectively. After successful completion of the design phase, over 4000 parts and several hundreds of metres of cables were manufactured and assembled. The complete development phase is documented in this thesis. Now, the initially empty laboratory space hosts an instrument setup of more than 2x2x2.5 m3 size. The commissioning phase showed that the design and assembly was performed correctly: Mass spectra were recorded since the first laser shot. The thesis concludes with the presentation of the first mass spectra recorded with the new instrument and a detailed discussion of the performance parameters. It was also possible to show good agreement between the simulation and the measurement.

Shea, Herbert
Wurz, Peter
Lausanne, EPFL

Note: The status of this file is: EPFL only

 Record created 2019-07-29, last modified 2019-09-10

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