74900 series

Samples were dissolved in acetonitrile:water:glacial acetic acid (50:50:0.1% v/v) to provide ~50 µM concentrations. The Bruker Apollo ESI source operating conditions in the atmospheric pressure region of the source were: nitrogen concurrent gas 160 °C, 10 PSI, nitrogen countercurrent gas 160 °C, 30 flow rate (arbitrary units). Samples were delivered at 2–3 µL/min by use of a Cole Parmer 74,900 Series syringe pump to the single sheath needle assembly positioned 45° off-axis from the entrance capillary. The ESI needle was held at ground, while the endcap and capillary voltages were set at −3500 V and −4000 V, respectively. Nozzle or skimmer voltages in the 10⁻⁶ torr region of the source were held at 110 V, and 15.2 V, respectively. Ions were collected in the accumulation hexapole for approximately 0.5 s. The ion population was transferred to the Bruker ICR Infinity™ cell for analysis. In addition, 512 K data points were broadband detected at a Nyquist Frequency of 625 MHz (~m/z 200) yielding 0.42 s of acquisition time. Sixteen transients were co-added followed by Gaussian apodization and one zero fill prior to Fourier transformation. Accurate mass measurements were obtained by external calibration with polypropylene glycol of average mass 425 (Aldrich, Milwaukee, WI, USA).

The electrospinning solution was prepared by dissolving 20 wt% PS and 0.3% (w/v) TBAB into DMF and was stirred with magnetic stirrer at room temperature for 24 h until a transparent solution was obtained. The electrospinning apparatus consisted of a high-voltage power supply (Series EL, Glassman High Voltage Inc.), a syringe pump (74900 series, Cole-Parmer Instrument Company), a stainless steel needle (O.D. = 0.7 mm) and a grounded aluminum foil plate. The electrospinning solution was placed in the syringe and injected through a stainless steel needle with the flow rate of 0.38 mL/h by a syringe pump. The tip-to-collector distance was set about 10 cm. A high voltage of 15 kV was applied to the needle tip, resulting in a continuous jetting stream. The electrospinning process was performed at room temperature with the relative humidity of about 50%. The collection time of the nanofibrous membrane was 2 h. Finally, the collected PS electrospun nanofibrous membrane was dried in an oven at 80 °C for 4 h. A PS nanofibrous membrane was cut into a regular disk-sized pieces (d = 5 mm).

To investigate the effect of potassium phosphate during a wet spinning process, buffers containing 50 mM HEPES pH 8.0, or 50 mM sodium acetate pH 5.0 were prepared with the addition of 0 to 500 mM potassium phosphate, prepared from KH₂PO₄ and K₂HPO₄ at the relevant pH. N-R₇-C at 100 mg/mL was extruded at 0.5 mL/h using a syringe pump (Cole-Palmer 74,900 series) with a 1 mL syringe, through a blunted 16G needle.

Isoflurane and hexachloroethane were purchased from Sigma Aldrich (UK), both with stated purities of 99%. Enflurane was purchased from Fluorchem Ltd. (UK) with a stated purity of 97%. All chemicals were used without further purification. At room temperature Isoflurane and enflurane are liquids and hexachloroethane is a white granulated solid. For the liquid samples, typically 50 μL were spotted onto cotton placed inside a glass syringe (Weber Scientific, UK), which was inserted through a septum into the forward flow. A syringe driver (Cole Palmer 74900 series; IL, USA) was used to introduce the compound into the forward flow at a constant rate. For hexachloroethane, a few mg were deposited into a glass vial sealed with a PTFE septum (Thames Restek, Bellefonte, PA, USA) through which the forward gas flowed.
Zero air grade and pure nitrogen (oxygen free and 99.998% minimum nitrogen) carrier gases used for this experiment were purchased from BOC Gases (UK). Prior to entering the reaction region, all carrier gases were passed through moisture and hydrocarbon traps (Supelco 23991 and Agilent BHT-4, respectively).

A syringe pump (74,900 series, Cole-Parmer
Instruments, Illinois, USA) was used to infuse the dopants. The compounds
were added post-column using a PEEK T-piece. The dopant flow rate
was typically 20 μL/min, representing ca. 10% of the LC effluent.