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Investigations into the effects of electrospray deposition sample preparation parameters on analyte signal in MALDI MS imaging samples & correcting mass accuracy and signal intensity errors in a MALDI TOF mass spectrometer
Dissertation   Open access

Investigations into the effects of electrospray deposition sample preparation parameters on analyte signal in MALDI MS imaging samples & correcting mass accuracy and signal intensity errors in a MALDI TOF mass spectrometer

Brian Malys
Doctor of Philosophy (Ph.D.), Drexel University
Mar 2024
DOI:
https://doi.org/10.17918/00010433
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Abstract

Electrospray deposition Matrix-assisted laser desorption-ionization Mass spectrometry imaging Time-of-flight mass spectrometry Analytical Chemistry Mass Spectrometry
The thesis consists of three sections. In the first, depth profiles are collected and used to investigate the effects of electrospray deposition (ESD) parameters on matrix deposition for matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging (MSI) samples. Various matrix deposition parameters including spray time, spray height and matrix identity were varied and the resulting signal of three analytes was collected in sequential spectra using a small number of laser shots. It was found that the spray parameters have a significant effect on the resulting analyte signal and its distribution throughout the matrix overlayer, with homogeneous and heterogeneous distributions of analyte signal observed. The differences in analyte distributions are explained using the fundamental principles of ESD. By identifying the sections of the matrix overlayer with the most analyte signal present, much higher quality MALDI MS images can be collected. In the second section, the use of ESD to apply matrix with an additional solvent spray to incorporate and homogenize analyte within the matrix overlayer was demonstrated. Prior to this incorporation spray, samples prepared using alpha-cyano-4-hydroxycinnamic acid (CHCA) and 2,5-dihydroxybenzoic acid (DHB) as the matrix showed low signal while the sample using sinapinic acid (SA) initially exhibited good signal. Following the incorporation spray, the sample using SA did not show an increase in signal, the sample using DHB showed moderate gains, while CHCA samples saw large increases in signal. The use of an incorporation spray to apply solvent by ESD to a matrix layer already deposited by ESD provides an increase in signal by both promoting incorporation of the analyte within and homogenizing the distribution of the incorporated analyte throughout the matrix layer. In the final section, ESD samples were used to determine the source of error in both mass accuracy and signal intensity in a MALDI time-of-flight (TOF) mass spectrometer (MS). This source of error was found to be due to small differences in the initial position of ions formed in the source region of the TOF MS. These differences arise largely from misalignment of the instrument sample stage, with a smaller contribution arising from the non-ideal shape of the target plates used. By physically measuring the target plates used and comparing TOF data collected from three different instruments, an estimate of the magnitude and direction of the sample stage misalignment was determined for each of the instruments. A correction method was developed to correct the TOFs and peak areas obtained for a given combination of target plate and instrument, significantly decreased the error observed.

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