Determination of Ethanolic Concentration
Ethanol was extracted from samples by headspace solid-phase microextraction (HS-SPME) using a fibre coated with 85-μm polyacrylate film (Supelco, Bellefonte, PA, USA). Before use, the fibre was conditioned following the instructions of the manufacturer. An aliquot (500 mg) of each sanitising gel sample (1–7) and calibration standards was transferred to an 8-ml screw-capped amber vial with a PTFE-lined silicone septum. The vial was thermostated for 1 min at 30 °C before SPME extraction. The SPME fibre was inserted into the headspace of the vial through the septum on the screw cap, then it was exposed to the headspace of the vial for 20 s at 35 °C. After the extraction, SPME fibre was removed from the vial and inserted into the gas chromatograph (GC) injection system for the analysis.
A DANI 1000 DPC (Norwalk, CT, USA) GC provided with a split-splitless injector and a flame ionisation detector (FID) was used. The injector was set in splitless mode for 5 min and maintained at 250 °C. A fused silica capillary column, Supelcowax-10 (60 m × 0.25 mm i.d., 0.25 μm f.t.; Supelco, Bellefonte, PA, USA), was used for the chromatographic separation. The initial oven temperature, 65 °C, was raised at 6°C/min to 155 °C, and then at 20 °C/min to 250 °C. The detector temperature was 260 °C. The carrier gas was helium with a flow rate of 1 ml/min. The chromatograms were acquired and processed using Clarity integration software (DataApex Ltd., Prague, Czech Republic).
The external calibration curve for the quantification of ethanol was obtained by analysing standard gel samples at a different concentration of ethanol (40–70% w/w). These gels were prepared by dispersing Carbopol® 974 (1% w/w) to the corresponding hydro-alcoholic mixture under stirring. The dispersions were left under stirring for 24 h and, then pH was adjusted to 7.0 using triethanolamine.