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Abstract:

In this thesis the degradation by electrochemical oxidation via boron doped diamond (BDD) was assessed for the selected pharmaceutical compounds iopromide (IOP), sulfamethoxazole (SMX), 17α-ethinylestradiol (EE2) and diclofenac (DCF) in simulated wastewater (SWW) and real hospital effluent wastewater (RWW). The influence of the applied current, the flow rate through the electrochemical cell, the initial compound concentration and the wastewater matrix (SWW versus RWW) was evaluated. This study confirmed that the degradation has pseudo first-order reaction kinetics for all experimental conditions tested. It was shown that SMX, EE2 and DCF degraded readily in SWW and RWW, however, the degradation of IOP was considerably slower, which is in agreement with previously reported slow degradation kinetics using typical advanced oxidation processes. Activation energies for the degradation reactions were calculated and it was shown that the flow rate in the electrochemical cell only had a moderate effect on the degradation rate of EE2 and DCF. In contrast, the applied current had a major effect. The BDD electrochemical oxidation was shown to be an effective technique for removing pharmaceutical components from the effluent of a biological hospital wastewater treatment plant. However, the slower degradation of generally more hydrophilic transformation products should be taken into account when a full mineralization and a toxicity screening of the pharmaceuticals is pursued. This study sparked the interest for the analysis of samples with increasing complexity. Appropriate analytical methods to evaluate the presence, metabolism, degradation and removal efficiency of specific compounds were necessary for this purpose. Therefore, a generic methodology was developed to overcome the need for multiple analyses on complementary columns to cover the separation of all compounds due to large differences in polarity. A commercially available ultra-high performance liquid chromatography (UHPLC) system was equipped with two external switching valves to connect hydrophilic interaction liquid chromatography (HILIC) and reversed-phase liquid chromatography (RPLC) columns in series for the sequential analysis of polar and non-polar compounds. The principle relies on the isolation of unretained peaks eluting from a first dimension column in a sample loop, before directing them to a second column for separation. The setup was successfully applied for the separation of 32 pharmaceutical compounds with a wide range of polarities. Since the mobile phases employed in highly orthogonal separations were not directly compatible, a mixing unit was required to alter the mobile phase composition before executing the second dimension separation. To deal with the incompatibility of the HILIC eluate and the ensuing RPLC separation, in first instance commercially available mixers were included in the setup. Later, a novel mixing unit was proposed, based on the use of two restriction capillaries with different flow resistances to dilute the mobile phase eluting from the first dimension with a solvent appropriate for the second dimension separation. The restriction capillaries were implemented using three high-pressure switching valves and two T-pieces. It was demonstrated that the dilution ratio can be adequately predicted using the law of Hagen-Poiseuille and can be adjusted easily by changing the dimensions of the restriction capillaries. The dilution volume required to obtain acceptable recoveries was investigated and the use of different column diameters in the first and second dimension was proposed to increase the sensitivity of the analysis. Under optimum dilution conditions, recoveries ranging between 82% and 99% were always obtained, while repeatability values were excellent. The proof-of-concept of the different setups was demonstrated for the separation of 20 pharmaceuticals with log D-values ranging between –5.75 and 4.22. Since information about the occurrence of pharmaceuticals in water is scarce and pharmaceuticals are typically only present in the µg/L to ng/L range in European waterways, a solid-phase extraction (SPE) procedure combining hydrophilic lipophilic balanced and strong cation exchange sorbents allowing the simultaneous extraction of polar and non-polar pharmaceuticals from simulated wastewater was evaluated. Besides for metformin that could not be eluted from the SPE cartridge and ticlopidine that could not adequately be extracted, good recovery rates between 75% and 106% were obtained for all studied compounds. To demonstrate the applicability of the presented setup in routine water analysis, further research is required to validate the entire methodology.