Advanced ultrasonic ambient ionisation sources for mass spectrometry and microdroplet accelerated reactions

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Taylor, HJ, 2022. Advanced ultrasonic ambient ionisation sources for mass spectrometry and microdroplet accelerated reactions. PhD, Nottingham Trent University.

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Abstract

This PhD thesis presents two related projects, linked because both benefit from the use of a specific kind of ultrasonic nebulizer.

The first project describes the development and subsequent application of a novel droplet-on-demand ionisation source which provides a solution to some of the limitations currently associated with performing mass calibration for mass spectrometry. After an initial development phase using a commercially available piezoelectric droplet-on-demand device, the system chosen for use was a Porous Ultrasonic Piezoelectric Plate (PUPP) device coupled to a conventional micro/nano-electrospray system.

The PUPP system was used in the analysis of a highly complex organic matter sample, Suwannee River Fulvic Acid, and used encoded internal recalibration to generate high confidence automated peak assignment. Due to the droplet-on-demand nature of the PUPP device, calibrant could be introduced whenever needed during analysis, and the intensity of the calibrant peak relative to sample peaks could be adjusted through the system’s ability to modulate the volume of calibrant sprayed, in real time.

Although the analysis of the samples using encoded internal recalibration showed no improvement in the peak assignment as expected, the workflow to get to the same stage is significantly simplified. The system is entirely automated, meaning that large batches of samples could be analysed, calibrated, and processed without the need for manual input by a user for each individual spectrum.

Further beneficial applications of the PUPP ionisation source are also presented, including the capability to perform rapid analysis of samples, component confirmation analysis and real-time adduct modification.

Additional tasks which were undertaken to support the development process of each project are presented, including the development of a 3D printed fused silica capillary grinding system to make custom electrospray needles and the software written to process the complex data generated for the ionisation source. Finally, recommendations for further development and other potential applications of the ionisation source are presented, which were beyond the scope of this project.

The second project, aimed to use the PUPP system to perform chemical synthesis in microdroplets, by taking advantage of the significantly enhanced chemical reaction rates observed inside microdroplets reported in the literature. The Hydrazone reaction is shown to proceed offline using the PUPP system. However, the reaction is shown to preferentially form the E isomer when performed inside a microdroplet, whilst during bulk synthesis the Z isomer is preferentially formed. Evidence for this is given, including the subsequent photorelaxation of the E isomer to form the more stable Z isomer.

Results indicated that the Pechmann condensation would be a new and suitable reaction which undergoes this reaction rate enhancement. However, this same success could not be achieved away from the mass spectrometer, and this was later discovered to be because of the difference in ionisation efficiencies of the reactants and products, which masked the true picture of the acceleration effect. Therefore, the decision was taken to shift the focus of the project towards establishing a robust screening method for microdroplet accelerated reactions which could be suitable for scale-up investigations, which is presented within this thesis.

Item Type:	Thesis
Creators:	Taylor, H.J.
Date:	September 2022
Rights:	The copyright in this work is held by the author. You may copy up to 5% of this work for private study, or personal, non-commercial research. Any re-use of the information contained within this document should be fully referenced, quoting the author, title, university, degree level and pagination. Queries or requests for any other use, or if a more substantial copy is required, should be directed to the author
Divisions:	Schools > School of Science and Technology
Record created by:	Linda Sullivan
Date Added:	14 Feb 2023 13:40
Last Modified:	14 Feb 2023 13:40
URI:	https://irep.ntu.ac.uk/id/eprint/48288