Three spectra of each sample (one for the CPLOR) were recorded, using a PerkinElmer Spectrum One spectrometer equipped with a DTGS detector, an Ever-Glo source, and a KBr/germanium beam splitter. Samples were deposited without any preparation on an ATR cell equipped with a diamond crystal. Spectra were recorded between 4000 cm-1 and 650 cm-1 with a nominal resolution of 4 cm-1 and 16 co-added accumulations. Air was taken as reference for the background spectrum before each sample. Between spectra, the ATR plate was cleaned in situ by scrubbing with ethanol solution. A background spectrum was regularly collected and compared to the previous background spectrum to verify cleanliness. This procedure was also used as instrument qualification.