2.3.6. Fourier Transform Infrared Spectroscopy (FTIR)

FTIR was used to confirm the presence of cutin during the optimization of UAE experimental conditions. In this sense, the extraction yield obtained during the second extraction step was only considered if obtaining a band around 1702 cm⁻¹ in the FTIR spectrum. In any other case, the value given in the experimental design was 0. The cutin obtained using optimal extraction conditions was also analyzed by FTIR for all of the wastes. FTIR spectra of all of the samples were recorded with an infrared spectrophotometer Bruker Analitik IFS 66/S (Ettlingen, Germany) equipped with a KBr beam splitter, a deuterated triglycine sulphate (DTGS) detector and Bruker OPUS software (Version 3.1), also developed by Bruker Analitik. The analysis was performed, in triplicate, in the attenuated total reflectance (ATR) mode by using a Golden Gate accessory with a diamond crystal. The absorption spectra were obtained in the 4000–500 cm⁻¹ range using 64 scans and a resolution of 4 cm⁻¹.