Esme Candish

A simplified approach to direct SPE-MS

Microextraction by packed sorbent (MEPS) has been directly hyphenated with ESI-MS for the rapid screening of opiates and codeine metabolites in urine. This study introduces a novel format of MEPS that incorporates a two-way valve in the barrel of the syringe enabling the direction of liquid flow to be manipulated. Controlled directional flow (CDF) MEPS allows sharp, concentrated sample bands to be delivered directly to the MS in small volumes and effectively eliminates the need to optimize elution. The method optimization assessed the recovery, matrix effects, and the speed of infusion, all critical variables for optimum ESI performance. Matching extraction workflows demonstrated a reduction in carryover from 65% for conventional MEPS to only 1% for CDF MEPS. The recovery (<89% for 50 μL sample), matrix effects (<42%), linearity (r(2) > 0.99), and LODs (<5 ng/mL) were determined to demonstrate method performance. The optimized approach was employed for the screening of codeine metabolites in urine. The ion trace revealed sharp sample bands corresponding to the codeine metabolites. At-line MEPS-ESI-MS allowed both sample preparation and analysis to be completed in only 5 min facilitating high throughput and alleviating the burden of method development.

Characterization of large surface area polymer monoliths and their utility for rapid, selective solid phase extraction for improved sample clean up

While polymer monoliths are widely described for solid phase extraction (SPE), appropriate characterization is rarely provided to unravel the links between physical characteristics and observed advantages and disadvantages. Two known approaches to fabricate large surface area polymer monoliths with a bimodal pore structure were investigated. The first incorporated a high percentage of divinyl benzene (PDVB) and the second explored hypercrosslinking of pre-formed monoliths. Adsorption of probe analytes; anisole, benzoic acid, cinnamic acid, ibuprofen and cortisone were investigated using frontal analysis and the SPE performance was compared with particulate adsorbents. Frontal analysis of anisole described maximum adsorption capacities of 164mgg(-1) and 298mgg(-1) for hypercrosslinked and PDVB adsorbents, respectively. The solvated state specific surface area was calculated to be 341 and 518m(2)g(-1) respectively. BET revealed a hypercrosslinked surface area of 817m(2)g(-1), 2.5 times greater than in the solvated state. The PDVB BET surface area was 531m(2)g(-1), similar to the solvated state. Micropores of 1nm provided the enhanced surface area for hypercrosslinked adsorbents. PDVB displayed a pore size distribution of 1-6nm. Frontal analysis demonstrated the micropores present size exclusion for the larger probes. Recovery of anisole was determined by SPE using 0.4 and 1.0mLmin(-1). Recovery for PDVB remained constant at 90%±0.103 regardless of the extraction flow rate suggesting extraction performance is independent of flow rate. A more efficient sample purification of saccharin in urine was yielded by PDVB due to selective permeation of the small pores.

Dry film microchips for miniaturised separations

In this work microfluidic devices were made from the dry film photoresist Ordyl SY330, characterised by optical and electron microscopy and used for electrophoretic separations. A simple and fast microfabrication process was developed for the fabrication of channels that are 50 μm wide and 30 μm in height, requiring only the use of an office laminator, a hot plate, an exposure source and mask and an electric drill to make four microdevices in less than 1 h. The optical properties of the photoresist were studied and the resist showed significant absorbance below 370 nm and 570–630 nm, and had an optical transmission of 80% between 400 and 550 nm. Fluorescence emission over the region of maximum transmission was low allowing these devices to be used for fluorescence detection at 488/512 nm. Electrophoretic separation of APTS and three derivatised sugars was performed in 20 mM phosphate buffer, pH 2.5 with efficiencies of the three sugars of 40 000 plates (2 100 000 plates/m) within 30 s at a field strength of 500 V/cm. The simple fabrication process also allowed microchannels to be easily filled with chromatography particles before sealing, avoiding the challenging task of slurry packing, and the potential of these devices for liquid chromatography was demonstrated by the extraction of fluorescein onto anion exchange particles.