Ethanol Content Determination
A simple and rapid analytical method, HS-SPME in combination with GC/FID, has been used for the extraction and quantification of ethanol in commercial hand sanitiser gels. The quantification of ethanol has been successfully performed by external standard method, with good precision and linearity. Values of inter-assay coefficients of variation lower than 7.8% indicate that the technique is reproducible, while the calibration curve prepared by analysing standard gels with known content of ethanol shows linear relationship with highly significant (p < 0.01) correlation (r = 0.9971) (Fig. 1a). The concentration of ethanol (% w/w) in the tested hand sanitiser gels ranges from 37.1 ± 1.9% w/w (gel 6) to 66.1 ± 2.0% w/w (gel 5). Three gels (gels 3, 4 and 6) have an average ethanolic content below the lower limit (60% v/v, i.e. 52.1% w/w) of the WHO recommended range (5), while four are within the recommended range. The highest ethanol concentration (≥ 60% w/w) was determined for gels 1, 2 and 5. Among these, gel 2 and gel 5 are those authorised as biocides (Table I). No methanol was detected in any of the analysed gels (data not shown).
Fig. 1 GC/FID analysis of ethanolic content in the gels. a Calibration curve for the quantification of ethanol. The calibration curve was prepared by analysing Carbopol® gels with a standard concentration (40–70% w/w) of ethanol. b The concentration of ethanol (% w/w) determined by GC/FID in the analysed hand sanitiser gels (1–7). The red line indicates the lower limit of the range of concentration of ethanol recommended by the WHO for hand sanitisers. “*” indicates products that are biocides