Phototransformation of Amlodipine: Degradation Kinetics and Identification of Its Photoproducts

Nowadays, monitoring focuses on the primary compounds and does not include degradation products formed during various biological and chemical processes. Transformation products may have the same effects to human health and the environment or sometimes they can be more toxic than the parent compound. Unfortunately, knowledge about the formation of degradation products is still limited, however, can be very important for the environmental risk assessment. Firstly, the photodegradation kinetic of amlodipine was investigated in two experimental conditions: during the exposure to solar radiation and during the exposure to the light emitted by the xenon lamp. In all cases degradation of amlodipine followed a pseudo-first-order kinetics. In the next step, identification of transformation products of amlodipine formed during the exposure to xenon lamp irradiation was performed using ultra high performance liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS). As a result sixteen photoproducts were identified, their structures were elucidated and ultimately the transformation pathway was proposed. Fifteen compounds (out of 16 photoproducts) were newly identified and reported here for the first time; some of those compounds were formed from the first photoproduct, amlodipine pyridine derivative. Several analytes were formed only in acidic or basic conditions. Furthermore, the occurrence of amlodipine and its identified degradation products was investigated in environmental waters. Only one out of 16 compounds was found in wastewater effluent. The possibility of the sorption of examined analytes to sewage sludge particles was discussed based on QSAR.

当前环境监测工作多聚焦于母本化合物，未涵盖各类生物与化学过程中生成的降解产物。转化产物（transformation products）对人体健康与生态环境的影响可能与母本化合物相当，部分情况下其毒性甚至高于母本化合物。遗憾的是，目前学界对降解产物生成机制的认知仍较为有限，但其对环境风险评估却具有极高的重要性。
首先，本研究针对氨氯地平在两种实验条件下的光降解动力学行为展开探究：分别暴露于太阳辐射与氙灯辐照环境中。所有实验条件下，氨氯地平的降解均遵循准一级动力学规律。
随后，本研究采用超高效液相色谱-四极杆飞行时间质谱（ultra high performance liquid chromatography quadrupole time-of-flight mass spectrometry，UHPLC-QTOF-MS），对氙灯辐照过程中氨氯地平生成的转化产物进行鉴定。最终共鉴定出16种光解产物，完成了其结构解析，并推导得出对应的转化路径。16种光解产物中有15种为本次研究首次鉴定并报道的全新化合物；其中部分产物由第一种光解产物——氨氯地平吡啶衍生物转化生成。部分被测物仅在酸性或碱性条件下生成。
此外，本研究还针对环境水体中氨氯地平及其已鉴定降解产物的赋存水平展开了调查。16种产物中仅1种在污水处理厂出水中被检出。本研究基于定量结构-活性关系（Quantitative Structure-Activity Relationship，QSAR），探讨了被测物在污水污泥颗粒上的吸附潜力。