VISUALIZING AROMA: SPATIALLY RESOLVED, HIGH-THROUGHPUT, AND AUTOMATED DETECTION OF ODORANTS IN GRAPES USING AMBIENT IONIZATION MASS SPECTROMETRY

Abstract

This dissertation describes the development and validation of a novel headspace extraction approach for high-throughput analyses of trace-level volatiles. Solid phase mesh enhanced sorption from headspace, or “SPMESH”, consists of a sorbent coated mesh that simultaneously extracts and pre-concentrates volatiles from the headspace of a sample. By laser-etching thin films of polydimethylsiloxane, SPMESH Sheets could be made to fit on multi-well plates. This allowed for extraction and pre-concentration of 24 samples in parallel, followed by automated analysis by Direct Analysis in Real Time mass spectrometry, or DART-MS. Extraction and desorption conditions for SPMESH Sheet-DART-MS were optimized to increase sensitivity, using a response surface methodology experimental design. Gaskets and clamps were created for the extraction setup to reduce headspace cross-contamination between wells, which would artificially increase signal due to volatiles drifting between neighboring wells. Two analytes of interest were profiled in grapes, as markers of final wine flavor: 2-isobutyl-3-methoxypyrazine and linalool. Limits of detection were further improved with the use of high resolution MS for linalool (48 μg/L) and tandem MS for IBMP (4 ng/L). Using these optimized conditions, a multi-vineyard validation was performed using grapes harvested from June – September of 2019. Good correlations were found for both compounds using SPMESH Sheet-DART-MS compared to the standard industry method: SPME-GC-MS. In a separate study, SPMESH Sheets were used for liquid desorption, using only 2 μL droplets to extract the headspace volatiles. This approach expands the range of compounds that can be detected, beyond those compatible with DART-MS. It also improves the spatial resolution of the SPMESH Sheet, previously limited to 4 mm by the DART source, to the size of a 2 μL drop, approximately 0.1 mm. Droplet desorption SPMESH has the possibility to be used in the future for mass spectral imaging studies of volatile and semi-volatile compounds.