Stadi preliminari nello sviluppo di un metodo voltammetrico di screening per il rilevamento di inquinanti farmaceutici nelle acque

Various active pharmaceutical ingredients (APIs) have been detected in all environmental compartments, at concentrations in the range of sub-ng/l to more than the mg/l. Even at such low concentrations, these compounds could be responsible for toxic effects in wildlife. In addition, the monitoring of pharmaceutical pollutants in the environment is limited by the heterogeneity of these substances and their metabolites, as well as their low concentrations, which make quantification difficult and expensive. For these reasons, studying analytical methods that can provide fast and simple monitoring has become crucial. Hence, the aim of this thesis work was to investigate the applicability of voltammetry for on-site screening of waters to detect the presence of pharmaceuticals. All the measurements were carried out with a portable potentiostat, using differential pulse voltammetry (DPV) as analytical technique and home-made carbon paste electrodes (CPEs) as working electrodes. This study focused on two of the most used analgesics and antipyretics: acetaminophen (APAP) and diclofenac (DCF), though the final purpose is to obtain a fingerprint of different APIs in waters. Both APAP and DCF were tested at pH values ranging from 2 to 10, to investigate the effects of pH on redox behaviour, sensibility and stability. The most suitable operating conditions were identified. Then, HLB (Hydrophilic Lipophilic Balance, a sorbent material)-based solid phase extraction (SPE) cartridges were used to reproduce on a small scale the use of polar organic chemical integrative samplers (POCIS), frequently adopted to collect samples for APIs determination. Aqueous solutions of APAP and/or DCF were driven through the SPE cartridge and the eluate was collected and analysed. The voltammetric analysis proved optimal retention of the analytes into the solid phase, as they could not be detected in the eluate. By eluting the pharmaceuticals retained by the sorbent, it was possible to develop two methods. The former involved the preparation of the carbon paste inside a Petri dish, where the eluate from the HLB solid phase was collected and dried. By doing this, the compounds eluted from the cartridge were incorporated into the CPE, allowing their qualitative detection. The latter exploited the re-dissolution of the dried extract in a small quantity of aqueous solution, to be analysed. Both the methods just described were applied to acetaminophen and diclofenac, singularly or in a mixture of the two. The procedures were repeated in four different aqueous media spiked with the target analytes, to highlight differences due to the matrix and to simulate real aqueous samples. However, the concentrations used for these simulations are decidedly higher than those found in the various environmental compartments. Evaporation of methanol is still a limiting step to be improved for the applicability of the method for field analysis. However, it is expected that the elution step will allow using the method to detect even very low amounts of contaminants, once the sensitivity of the method is improved. Indeed, further investigations are required to determine the limits of detection, to improve sensitivity, repeatability and accuracy of the methods. At the same time, the electrochemical behaviour of other APIs and their metabolites and the applicability of the methods to real samples and more complex and large-scale systems are yet to be studied.