Emerging contaminants represent newly identified organic chemical pollutants that are not yet covered by routine monitoring and regulatory programs. Current research on these contaminants is greatly hindered by the shortage of analytical methods due to the complex matrices, extremely low concentration and their “emerging” nature. In this study the innovative analytical and monitoring methods have been developed and validated for determination of emerging pollutants in water (including pharmaceutical and personal care products, pesticides and artificial sweeteners) based on graphene-silica composite as the solid-phase extraction (SPE) sorbent and as the receiving phase in passive sampler.
Graphene, a new allotropic member in the carbon family, has been considered to be a promising candidate for sorption material with high loading capacity because of its ultra-high specific surface area and large delocalized π-electron-rich structure. The composite employed in this work was synthesized by using the cross-link agent to covalently combine carboxylic acid groups of graphene-oxide with the amino groups of the modified silica gel. Afterwards, graphene-silica composite was obtained after treated with hydrothermal reaction in the microwave autoclave, which was demonstrated by X-ray diffraction (XRD).
The analytical procedure entails SPE followed by high performance liquid chromatography equipped with tandem mass spectrometers (HPLC-MS/MS). Several crucial parameters were optimized to improve recovery of the analytes, including the amount of sorbents, the ratio of graphene oxide/amino-silica and pH value of water samples. The best recovery results were achieved with 100 mg 10 % (w/w) graphene-silica composite, which were over 70 % except four artificial sweeteners, ranitidine and triclosan. Compared with its commercial counterpart Oasis HLB, pH value variation of water samples has less effect on the recoveries, making graphene composite to be a potential receiving phase of monitoring tool. The batch-to-batch reproducibility was verified on six independently SPE cartridges with graphene-silica composites from two repeatable synthetic batches, showing relative standard deviations (RSDs) in the range of 8.3 % to 19.1 %, except ibuprofen and saccharin. The cartridges proved to be reusable for at least 10 times consecutive extractions, with RSD < 14.9 %, except ibuprofen and diclofenac.
The Chemcatcher® passive sampler is frequently used for monitoring polar organic chemicals in surface water. Uptake kinetics is necessary to be quantified to calculate time-weighted average (TWA) concentration. A series of calibration experiments were conducted in the beaker renewal experiments as well as in the flow-through system with styrenedivinylbenzene-cross connect (SDB-XC) disks and graphene-silica composite as the receiving phase.
The results obtained from the beaker renewal experiments showed that the uptake kinetics of accumulated compounds with all Chemcatcher® configurations can keep linear within 2 weeks. The innovative configuration using graphene-silica composite powder placed between two PES membranes was able to accumulate eleven of the selected compounds with uptake rate (Rs) from 0.01 L/day (acesulfame K and sucralose) to 0.08 L/day (chlothianidin), while its commercial counterpart SDB-XC disks with polyethersulfone (PES) membranes can accumulate seven substances with Rs from 0.02 L/day (sucralose and chlothianidin) to 0.15 L/day (carbamazepine). In the flow-through system, when Chemcatchers® were equipped with SDB-XC disks without PES membranes, the linear uptake range for the majority of compounds was only in one week, except atrazine. The Rs of accumulated compounds were from 0.16 L/day (chloramphenicol) to 1.04 L/day (metoprolol) that are higher than the same substances in the beaker renewal experiments, in which the Rs of chloramphenicol and metoprolol were 0.09 L/day and 0.56 L/day respectively. However, if the PES membranes were employed, the uptake kinetics in both calibration experimental designs were comparable: the Rs of accumulated compounds from the configuration with SDB-XC disks covered by PES membranes were from 0.035 L/day (sucralose) to 0.17 L/day (carbamazepine) and from the configuration with graphene-silica composite were from 0.01 L/day (gemfibrozil) to 0.08 L/day (chlothianidin). Moreover, the uptake range can keep linear within two weeks. The developed Chemcatcher® method was successfully applied in real surface waters. 1-H benzontriazole, tolyltriazole and caffeine were the main contaminants in Elbe River and the Saidenbach drinking water reservoir. The investigated results between summer and autumn monitoring period were not significantly different.:Acknowledgement I
Abstract III
Zusammenfassung V
Content IX
List of Figures XIII
List of Tables XVII
Table of Abbreviations XIX
1. Motivation 1
2. Introduction 3
2.1 Emerging contaminants 3
2.1.1 Definition 3
2.1.2 Sources 3
2.1.3 Concern about the adverse impacts 5
2.2 Analysis of the emerging contaminants 7
2.2.1 General analytical process 7
2.2.2 Enrichment techniques 8
2.2.2.1 Liquid-liquid extraction (LLE) 8
2.2.2.2 Solid-phase extraction (SPE) 9
2.2.2.3 Innovative type of solid-phase extraction 13
2.2.3 Analytical methods 15
2.3 Graphene and its application in analytical chemistry 19
2.3.1 Introduction 19
2.3.2 Synthesis methods of graphene 20
2.3.3 Application in sample pre-treatment 21
2.3.3.1 Graphene-based material as SPE sorbent 21
2.3.3.2 Graphene-coated fibers as SPME sorbent 22
2.3.3.3 Magnetic graphene as MSPE sorbent 23
2.3.3.4 Graphene-based MIPs 24
2.4 Chemcatcher®—a passive sampling technique 25
2.4.1 Introduction 25
2.4.2 Theory 26
2.4.2.1 Equilibrium passive sampling 27
2.4.2.2 Kinetic passive sampling 28
2.4.3 Concept of Chemcatcher® 28
2.4.4 Calibration of Chemcatcher® 33
2.4.5 Performance and reference compounds 36
3. Study objectives and hypotheses 39
3.1 Study objectives 39
3.2 Hypotheses 41
4. Material and methods 43
4.1 Materials 43
4.1.1 Chemicals and solutions 43
4.1.2 Consumable materials and instruments 44
4.2 Synthesis of graphene-silica composite 46
4.3 SPE experiments 49
4.3.1 Packing method 49
4.3.2 SPE procedure 49
4.3.3 Optimization of SPE procedures 51
4.3.4 Repeatability and reusability test 52
4.4 Chemcatcher® experiments 53
4.4.1 Preparation and precondition 53
4.4.2 Calibration of Chemcatcher® 55
4.4.2.1 Preliminary test 55
4.4.2.2 Experimental design of the beaker batch tests 56
4.4.2.3 Experimental design of the flow-through system 57
4.4.3 Monitoring application of Chemcatcher® in surface water 59
4.4.4 Elution process 60
4.4.5 Statistic data evaluation 61
4.5 HPLC-MS/MS analysis 62
5. Results and discussion 63
5.1 Preparation and characterization of graphene-silica composite 63
5.2 SPE performance of the graphene-silica composite 67
5.2.1 Preliminary test of packing methods 67
5.2.2 Optimization of SPE procedures 68
5.2.2.1 The amount of sorbent 68
5.2.2.2 Graphene ratio in the composites 68
5.2.2.3 pH value of the water sample 69
5.2.3 Repeatability and reusability test 72
5.2.3.1 Performance of the off-line SPE 72
5.2.3.2 Repeatability and reusability test results 75
5.2.4 Summarized discussion of the SPE performance 76
5.3 Calibrating results of Chemcatcher® 86
5.3.1 Pre-test results 86
5.3.1.1 Feasibility test of commercial disks as receiving phase 86
5.3.1.2 Stability test 88
5.3.1.3 Elution optimization. 88
5.3.1.4 Recovery of the filters 92
5.3.2 Calibration results of renewal experiments 93
5.3.2.1 SDB-XC disks without and with membranes 93
5.3.2.2 Graphene-silica composite as receiving phase 97
5.3.3 Calibration results of the flow-through system experiments 101
5.3.3.1 Determination of experimental parameters 101
5.3.3.2 Concentration control 103
5.3.3.3 Calibration results 105
5.3.3.4 Preliminary evaluation of performance and reference compounds 112
5.4 Application of Chemcatcher® in surface water 114
5.5 Discussion about problems of commercial disks as receiving phase in Chemcatcher® 118
5.5.1 Deformation of commercial disks 118
5.5.2 The particles in the solution after elution 119
6. Conclusion and perspective 121
7. Annex 125
7.1 Material and methods 125
7.1.1 Chemicals 125
7.1.2 Silica gel and graphene oxide 144
7.1.3 Microwave reduction program 144
7.1.4 Working schedule of the calibration experiments in flow-through system 144
7.1.5 HPLC-MS/MS conditions 146
7.2 Experimental results 149
7.2.1 Stability of the colloid solution of graphene oxide 149
7.2.2 EDX analysis results 149
7.2.3 HPLC-MS/MS results 152
7.2.4 Calibrating results of the beaker renewal experiment 153
7.2.5 Calibrating results of the flow-through system experiments 157
7.2.6 Monitoring results in the Elbe River 161
Reference 163
Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:38809 |
Date | 24 March 2020 |
Creators | Liu, Yang |
Contributors | Worch, Eckhard, Stolte, Stefan, Song, Yonghui, Technische Universität Dresden |
Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
Language | English |
Detected Language | English |
Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
Rights | info:eu-repo/semantics/openAccess |
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