Thermo scientific nicolet 380 spectrometer

The analyses on the effect of the HEas on the skin was assessed using the total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), similarly to that reported in our previous study (Nowak et al., 2021b (link)). In brief, the pure skin was cut into 1 cm² piece and applied to the HEas for 24 h. Then the skin samples were washed with isopropanol, blotted dry, and air-dried for 2 h. An ATR unit obtained the spectra using Thermo Scientific Nicolet 380 spectrometer (Thermo Fisher Scientific, Waltham, MA, United States). The recorded spectrum represented an average of 32 scans obtained with a 4 cm⁻¹. The spectra were collected in the wavenumber range of 4,000–400 cm⁻¹. The internal reflectance element (IRE) used in this study was an ATR diamond plate. The skin was carefully mounted on the IRE. For comparison, the analysis was also performed for clean skin, not treated with a hydrogel.

The pig skin samples were analyzed by FTIR-ATR technique according to the modified method of Ahad et al., Chen et al. [16 (link),66 (link)]. The skin was prepared according to the procedure described in Section 4.6. The 0.1 g EOEa was applied to the skin, the study was conducted for 24 h (equivalent to the duration of permeation studies). After the test, each skin disc was washed, blotted dry, and air-dried for 2 h. The pure skin, without essential oil, was the control. The functional groups occurring in the tested skin samples were analyzed using the Fourier transformed infrared (FTIR) spectra. The spectra were obtained using Thermo Scientific Nicolet 380 spectrometer (Thermo Fisher Scientific, Waltham, MA, USA) equipped with an ATR diamond plate. Thirty-two scans were acquired in the 4000–400 cm⁻¹ range.