Analytical methods for investigating the presence, photoisomerisation-, and degradation kinetics of the UV-A filter avobenzone under aqueous conditions to ensure a more realistic environmental measurement

•Presence, photoisomerisation, and degradation of avobenzone (AV) were investigated.•The exact concentration of AV in (environmental) samples is the summed concentration of both tautomeric forms.•Photodegradation and/or photoisomerisation may occur in aqueous solutions depending on the conditions.•AV shows a strong freeze–thaw instability.