Improved miniaturised solid phase extraction

The thesis focuses on the development of miniaturised solid phase extraction (SPE) technologies for the rapid and effective processing of complex biological samples prior to mass spectrometry (MS) analysis. The first section focuses on the format and operation of miniaturised solid phase extraction devices. The existing technology was queried and improved for a more efficient operation. The miniaturised SPE technology, microextraction by packed sorbent (MEPS), was explored as a representative format due to ease of operation. A superior format of MEPS was developed that incorporates a two-way valve in the syringe barrel for efficient sample and solvent introduction to the adsorbent bed. Controlled directional flow (CDF)-MEPS allows fluid to be introduced directly into the syringe barrel, bypassing the adsorbent bed entirely. Matching extraction workflows demonstrated a reduction in carryover from 65% for conventional MEPS to only 1% for CDF-MEPS. The developed technology was directly hyphenated with electrospray ionisation (ESI)-MS and sharp, concentrated sample bands were revealed. The second section of this thesis explores the concept of organic polymer monolith adsorbents for improved miniaturised SPE. Polymer monoliths are widely described as adsorbents for SPE but appropriate characterisation of physical characteristics is rarely explored to probe any observed advantages and disadvantages over alternative adsorbents. Fabrication of large surface area adsorbent involved a high percentage of the crosslinking monomer, divinyl benzene (DVB), or the hypercrosslinking of preformed polymer. Frontal analysis studied the adsorption of probes; anisole, phenol and cortisone. Extraction performance was compared with conventional polymer particulate adsorbents. The polymer monolith adsorbents demonstrated a clear advantage for the small probes, as a high extraction performance (high recovery) could be achieved independent of flow rate. Limited retention of cortisone was seen for both polymer monolith adsorbents as the surface area was predominantly provided by micropores inaccessible to the larger probe cortisone. The size exclusion mechanism of the microporous large surface area poly(DVB) was exploited as it presented a physical barrier restricting proteins from accessing the adsorbent's internal surface. A hydrophilic layer of poly(ethylene glycol) methacrylate (PEGMA) was grafted to the residual vinyl groups of the poly(DVB) and their suitability as restricted access materials was explored. PEGMA monomers with glycol chain lengths of Mn 360 and 950 were studied. The external hydrophilic layer was delicately balanced to prevent protein binding while preserving the hydrophobic capacity and rapid analyte mass transfer. Sharp breakthrough curves confirmed that both hydrophobic capacity and rapid analyte mass transfer were maintained for poly(DVB)-g-PEGMA950, while the adsorbent displayed a substantial reduction in protein binding. Ibuprofen was extracted from human plasma (diluted 20% v/v), using both poly(DVB) and poly(DVB)-g-PEGMA950. The extracts were analysed by at-line ESI-MS. The sample from prepared with the biocompatible poly(DVB)-g-PEGMA950 provided extracts with reduced protein content resulting in a more sensitive and improved at-line ESI-MS analyses.