The top spectrum (yellow) shows new AESUB Yellow, examined via transmission spectroscopy in the form of a KBr pellet. AESUB Yellow was examined shortly after it was taken from the original bottle. In this figure, the top spectrum (yellow) is used as a reference. The bottom spectrum (purple) shows the residue of AESUB Yellow, examined with FTIR UATR. The bottom spectrum was adjusted with the help of a "ATR Correction" function, so the two spectra can more easily be compared.

On the two spectra, especially the bottom spectrum (purple), there are peaks that may indicate the presence of carboxylic acid: A wide peak at over 3000 cm^-1 (O-H), a peak between 1800-1630 cm^-1 (C=O) and a peak around (or near) 1300-1000 cm^-1 (C-O) (Gupta et al. 2023, Pavia et al. 2015).

The spectra was made using the raw data from Nielsen 2024, and were adjusted for the purposes of this abstract, by translating the text from Danish to English and changing the colors of the spectra.