Influence of UV Irradiation Source and of Carboxylic Acid Additives on the Kinetics of Photodegradation of Five Tricyclic Antidepressant Drugs in Aqueous Medium

Use of antidepressant medication has increased substantially nowadays. Investigations of their photostability in aqueous environment are therefore needed both for shelf life assessment of liquid pharmaceutical formulations and for development of wastewater remediation technologies. In this work, the comparative kinetics of photodegradation of five tricyclic antidepressants (TCAs) in aqueous solution was studied under direct photolysis using UVA, UVB, and UVC sources, respectively. A gas chromatography–mass spectrometry (GC-MS) method was developed and validated intra-laboratory for accurate quantification of the five TCAs (amitriptyline hydrochloride AMI, doxepin hydrochloride DOX, imipramine hydrochloride IMI, clomipramine hydrochloride CLO, trimipramine maleate TRI) in the course of photodegradation. UVC photolysis yielded the highest rates of photodegradation, followed by UVB and then UVA. The molecular structure and UV absorption characteristics of individual TCAs were shown to influence photodegradation rates as well. Specifically, heteroatoms (N, O, Cl) present in the molecule and redshifted UV absorption bands increased photosensitivity typically in the order: AMI < IMI < TRI < CLO < DOX. The effect that some mono- and polycarboxylic acids dissolved in the aqueous solutions had on TCA photodegradation kinetics under UVC was also investigated and, for most TCAs, rates were faster and durations required for their complete photodegradation decreased generally in the order: citric > oxalic > maleic > benzoic acid. Furthermore, citric acid was reused for a second round of TCA photodegradation and showed rate enhancement effects very close to those exhibited in the first round.