Molecularly-imprinted polymers for compound-specific isotope analysis of polar organic micropollutants in aquatic environments

The widespread occurrence of polar organic micropollutants in the environment such as pesticides and pharmaceuticals raises major concerns about their fate. Demonstrating their degradation under field conditions is difficult because changes in compound concentration can be subscribed to concurrent processes . In contrast, changes of the isotope ratios, which is monitored by compound-specific isotope analysis (CSIA), offers conclusive evidence of (bio)degradation of the contaminant. Unfortunately, due to the high detection limits for analysis by gas- or liquid chromatography / isotope-ratio mass spectrometry (GC/IRMS or LC/IRMS) and the low occurrence of these contaminants in environmental waters, ng/L to µg/L1, large volumes of water need to be processed to obtain the required analyte masses for analysis. While enrichment of the required analyte masses is often possible using conventional solid-phase extraction (SPE) methods, the lack of selectivity towards the target analytes leads to inevitable co-enrichment of organic matrices, which compromises the acquired isotopic signatures. Synthetic polymers with selective binding sites can be obtained by molecular-imprinting techniques that are engineered to specifically enrich certain target analytes, but their application to stable-isotope analysis has not been studied. Therefore, it was the goal of this dissertation to investigate the effectiveness of increasing the overall selectivity of sample preparation workflows for GC/IRMS and LC/IRMS using molecularly-imprinted polymers (MIP). Carbon- and nitrogen isotope analysis of 1H-benzotriazole, a typical corrosion inhibitor in dishwashing detergents, was investigated in different environmental samples as an example of a ubiquitous polar organic micropollutant. Procedures for the treatment of > 10 L water samples were developed in this work. The synthesis of MIP enabled the selective cleanup of the analyte in organic solvent, which was obtained by previous enrichment by conventional SPE. Through an assessment of imprinting factors, interaction enthalpies, and δ15N isotope effects, it was determined hydrogen bonding between the traziole ring of 1H-benzotriazole and the produced MIP were responsible for the selective interactions. The procedure was applied successfully without inducing isotope fractionation of the analyte to river water samples, as well as influent and effluent samples of a wastewater treatment plant containing 4 µg/L 1H-benzotriazole and dissolved organic carbon (DOC) loads of up to 28 mg C/L. Interferences caused by organic matter from surface waters on the GC/IRMS measurements were investigated for varying loads of DOC compared to constant amount of atrazine. A DOC:micropollutant ratio of 10 in the extracted sample was the maximum limit of GC/IRMS for accurate and precise δ13C, which corresponds to river water containing 7 µg/L atrazine and 0.3 mg C/L DOC. A cleanup procedure of the river water extracts using MIP allowed accurate and precise δ13C in samples with an initial DOC:micropollutant ratio up to 100. Presence of traces of protic solvents in the environmental extract prior to the cleanup with MIP caused complete loss of atrazine, desethyl-atrazine, and desisopropyl-atrazine. The DOC:micropollutant ratio was found to be a useful apriori indicator for assessing effectiveness of GC/IRMS measurements of contaminants in environmental waters. Direct extraction of the herbicide glyphosate and its transformation product AMPA was performed without chemical derivatization from different environmental waters using a MIP based on ionic interactions. A method for quantification of the analytes was successfully developed and optimized using ion chromatography-electrospray ionization tandem mass spectrometry. Method quantification limits ranged from 17 to 82 ng/L for glyphosate and from 37 to 54 ng/L for AMPA with recoveries from 26 to 97% and from 63 to 105%, respectively. Complexation of glyphosate with leaching organic carbon from the MIP was initially responsible for loss of 80% of the analyte, for which sodium hydroxide was used to break the complex and recover the analyte. Natural organic matter in water that bound to the investigated MIP was efficiently removed by percolation of the MIP extract over reversed-phase cartridge with no loss of the analytes. δ13C measurements of the analytes on LC/IRMS at different steps of the sample preparation showed no isotope fractionation. The results from this work demonstrate that molecular-imprinting techniques prior to CSIA are an e ective tool for the selective extraction/cleanup of polar organic micropollutants from different environmental waters. Two approaches for the implementation of MIP in sample preparation are possible: (i) Organic extracts of aquatic samples after reversed-phase SPE can be used for a further selective cleanup step with MIP, whereas, (ii) water-compatible MIP can be used for the direct extraction of ionized organic contaminants from water samples. The coupling of MIP with either of these two approaches to GC/IRMS and LC/IRMS broadens the reach of CSIA by enabling the measurement of environmental samples. For future work on CSIA, the developed approaches can be used and expanded to many other polar organic micropollutants to investigate their sources and fate in the field- and catchment-scale studies, offering thereby new perspectives to CSIA