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.