Development of advanced laser processes for multiscale surface modifications of functional electrodes in Liquid Chromatography Mass Spectrometer (LC-MS) instrumentation

Abstract

LC-MS is a critical instrumentation technique for identifying components of mixtures containing both organic and inorganic substances. Because of this, the internal components of the mass spectrometer are susceptible to contamination during instrument operation. Direct contact between the instrument electrodes and the gas-phase ion particles is particularly problematic as it affects the sensitivity of the system. Therefore, there is a need for ion contamination resistant electrode surfaces. Surface modification methods using lasers are widely used for functionalisation applications such as self-cleaning surfaces, antibacterial surfaces, friction reduction and surface enhancement. This research hypothesises that laser surface modification can be controlled and used to create tailored surfaces to reduce surface contamination of critical components during the operation of LC-MS systems. An aperture plate electrode was used to test the hypothesis. As it is used as an ion beam collimator in the mass spectrometer, the aperture plate is susceptible to contamination. The aperture plate electrode is made of stainless steel 316L and has a lapped surface. The bovine insulin protein was used as a surface contaminant in our tests. Surface texturing on stainless steel 316L surfaces using short and ultrashort pulse lasers was studied to understand the generation of nanoscale surface structures. Selected cases of surface texturing were tested for their impact on the protein contamination behaviour of the aperture plate. A 532 nm nanosecond laser was used to create LIPSS with an extremely low aspect ratio and surfaces with significantly reduced roughness. Both LSFL and HSFL were created using a 355 nm picosecond laser. A novel method for generating HSFL features was identified that uses the laser plasma plume as one of the influencing parameters. The novel method showed finer control in the generation of HSFL features. A 800 nm femtosecond laser was used to experiment with modalities of structured laser vector fields and demonstrated the possibilities of creating complex surfaces with different beam types. The protein contamination behaviour tests show a reduction in contamination build-up rate on laser-textured aperture plates compared to non-laser-machined aperture plates. In addition, the results demonstrate some level of control over surface topography and surface chemistry. These improvements support our hypothesis that laser processing can be used to mitigate surface contamination. The promising results pave the way for further investigation to control and reduce contamination behaviour. In addition, the results of this study can be applied to other electrodes that are susceptible to surface degradation by analyte ions in the gas phase.

Date of Award	31 Dec 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Zhu Liu (Supervisor) & Olivier Allegre (Supervisor)