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On-Line Concentration Techniques in Capillary Electrophoresis and the Experimental Investigation of Electroextraction

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On-Line Concentration Techniques in Capillary Electrophoresis and the Experimental Investigation of Electroextraction ON-LINE CONCENTRATION TECHNIQUES IN CAPILLARY ELECTROPHORESIS AND THE EXPERIMENTAL INVESTIGATION OF ELECTROEXTRACTION Riikka-Mari Haara Master's thesis 4.8.2016 University of Helsinki Laboratory of Analytical Chemistry Tiedekunta/Osasto Fakultet/Sektion – Faculty Laitos/Institution– Department Faculty of science Chemistry Tekijä/Författare – Author Riikka-Mari Haara Työn nimi / Arbetets titel – Title On-line concentration techniques in capillary electrophoresis and the experimental investigation of electroextraction Oppiaine /Läroämne – Subject Analytical chemistry Työn laji/Arbetets art – Level Aika/Datum – Month and year Sivumäärä/ Sidoantal – Number of pages Master's thesis 08/2016 94 Tiivistelmä/Referat – Abstract Capillary electrophoresis is a great option for analyzing metabolomics compounds since the analytes are often charged. The technique is simple and cost-efficient but it is not the most popular equipment because it lacks high concentration sensitivity. Therefore, on-line concentration techniques have been developed for capillary electrophoresis. The aim of this thesis is to give an introduction to the most common on-line concentration methods in capillary electrophoresis, and to demonstrate a novel on-line concentration technique termed electroextraction. Until now, the research of on-line concentration techniques in capillary electrophoresis is mainly focused on methods based on field amplification, transient isotachophoresis, titration incorporated methods or sweeping, which are presented in the literature section. In a two-phase electroextraction, the electrodes are placed in an aqueous acceptor phase and in an organic donor phase, in which the analytes are dissolved. When the voltage is applied, the conductivity difference in the two phases cause high local field strength on organic phase leading to fast migration of the cationic analytes towards the cathode. As soon as the analytes cross the solvent interface, their migration speed decrease and they are concentrated at the phase boundary. In these experiments, a normal capillary electrophoresis analyzer was used with a hanging aqueous phase droplet at the tip of the capillary inlet. The experimental part was carried out at Leiden University, Division of Analytical BioSciences in the Netherlands. An electroextraction-capillary electrophoresis system was built for the analysis of biological acylcarnitine compounds. After the method parameters were assessed with ultraviolet detection, the method was coupled with mass spectrometric detection, and the selectivity and repeatability were briefly tested. Sensitivity was enhanced with the electroextraction procedure but the extraction factors were not satisfactory yet. Selectivity of electroextraction was discovered when the extraction of acylcarnitines was performed using different solvents. All parameters affecting the electroextraction procedure were not tested, and therefore the instability of the method was not completely understood. Thus, the method should be further investigated and optimized. In fact, all on-line concentration methods ought to be optimized for the target analytes in their existing matrix. Avainsanat – Nyckelord – Keywords On-line concentration, capillary electrophoresis, electroextraction Säilytyspaikka – Förvaringställe – Where deposited Laboratory of Analytical Chemistry and Helsinki University Library Muita tietoja – Övriga uppgifter – Additional information Table of contents Page 1. ABBREVIATIONS 3 2. INTRODUCTION 6 I THEORY 7 3. CAPILLARY ELECTROPHORESIS 7 3.1. Electro-osmotic flow 8 3.2. Separation of compounds 9 3.3. Injection 10 3.4. Detection 11 4. ON-LINE CONCENTRATION TECHNIQUES 13 4.1. Field amplified sample stacking 14 4.2. Field amplified sample injection 18 4.3. Pressure assisted electrokinetic injection 20 4.4. Large volume sample stacking 21 4.5. Transient isotachophoresis 26 4.6. Electrokinetic supercharging 34 4.7. Titration incorporated methods 36 4.7.1. Dynamic pH junction 37 4.7.2. pH-mediated stacking 40 4.8. Sweeping 46 4.8.1. Sweeping in electrokinetic chromatography 46 4.8.1.1 Pseudostationary phases 46 4.8.1.1.1 Charged pseudostationary phases in a homogeneous electric field 49 4.8.1.1.2 Charged pseudostationary phases in a heterogeneous electric field 50 4.8.1.2 Parameters for optimal sweeping 53 4.8.2. Sweeping in capillary zone electrophoresis 54 1 4.9. Electroextraction 58 4.10. Combination of on-line concentration techniques 59 II EXPERIMENTAL 64 5. BACKGROUND 64 5.1. Electroextraction procedure 64 5.2. Chemicals 66 5.2.1. Crystal violet 66 5.2.2. Acylcarnitines 67 5.2.3. Solvents 69 6. EXPERIMENTS 70 6.1. Preparation of solutions 70 6.1.1. Background electrolyte solution 70 6.1.2. Crystal violet samples 70 6.1.3. Acylcarnitine samples 71 6.2. Analytical conditions 71 7. RESULTS AND DISCUSSION 73 7.1. Samples 73 7.2. Electroextraction 73 7.3. Visual monitoring of the stability of a droplet 75 7.4. Electroextraction-capillary electrophoresis-ultraviolet detection 77 7.5. Capillary zone electrophoresis-mass spectrometry 79 7.5.1. Electroextraction parameters 79 7.5.2. Different solvents 81 7.5.3. Repeatability 83 8. CONCLUSIONS 84 9. ATTACHMENTS 86 10. REFERENCES 86 2 1. ABBREVIATIONS 5-FAM 5-carboxyfluorescein Ab antibody AD amperometric detection APFO ammonium perfluorooctanoate ARG phenylthiohydratoin arginine ASEI anion selective exhaustive injection BGE background electrolyte, running buffer BPDE benzo(a)pyrene diol epoxide Brij 35 polyoxyethylene (23) lauryl ether Brij 58 polyoxyethylene (20) cetyl ether C4D capacitively coupled contactless conductivity detector CAPS 3-(Cyclohexylamino)1-propanesulphonic acid CE capillary electrophoresis CEC capillary electrochromatography CGE capillary gel electrophoresis CIEF capillary isoelectric focusing CITP capillary isotachophoresis CMC critical micelle concentration CSEI cation selective exhaustive injection CTAB cetyltrimethylammonium bromide CTAC cetyltrimethylammonium chloride CV crystal violet CZE capillary zone electrophoresis DETA diethylenetriamine DG deoxyguanosine DLLME dispersive liquid-liquid microextraction DTAB dodecyltrimethylammonium bromide EDTA ethylenediaminetetraacetic acid EF extraction factor EKC electrokinetic chromatography EKI electrokinetic injection 3 EKS electrokinetic supercharging EKSI electrokinetic stacking injection EOF electroosmotic flow ESI electrospray ionization EtOAc ethyl acetate FA formic acid FASS field amplified sample stacking FASI field amplified sample injection FESI field enhanced sample injection FL fluorescein disodium salt GSH glutathione GSSG glutathione disulfide HDI hydrodynamic injection HCB high conductivity buffer HIS phenylthiohydratoin histidine HPLC high performance liquid chromatography HV high voltage ICP inductively coupled plasma ID internal diameter IDP indapamide IEF isoelectric focusing ITP isotachophoresis L length LE leading electrolyte LIF laser-induced fluorescence LLE liquid-liquid extraction LOD limit of detection LVSS large volume sample stacking MEEKC microemulsion electrokinetic chromatography MEKC micellar electrokinetic chromatography MeOAc methyl acetate MeOH methanol MES 2-(N-morpholino)ethanesulfonic acid miRNA microRNA MS mass spectrometry 4 MSPE magnetic solid-phase extraction MW molecular weight n-BuOH n-butanol NACE non-aqueous capillary electrophoresis NaDC sodium deoxychlolate NPS neutral pseudostationary phase NRB neutralization reaction boundary PAEKI pressure assisted electrokinetic injection PEI-Mal maltose-modified hyperbranched poly(ethylene imine) PDA photodiode array detector Poly-SUS poly(sodium 10-undecenyl sulfate) proFACE protein-facilitated affinity capillary electrophoresis PS pseudostationary phase pSAm-f poly(sodium 2-acrylamido 2-methyl 1-propane sulfonate-co-stearyl acrylamide) SB-12 N-dodecyl-N,N-dimethylammonium-3-propane-1-sulfonic acid SDME single drop microextraction SDS sodium dodecyl sulfate SOT sotalol SPE solid phase extraction SVZ sample vacancy zone TE terminating electrolyte TFA trifluoroacetic acid TG tris-glycine tITP transient isotachophoresis Tris tris(hydroxymethyl)aminomethane TTAB tetradecyltrimethylammonium bromide UV ultraviolet 5 2. INTRODUCTION Capillary electrophoresis (CE) has a long history as a separation technique and it is applied to pharmaceutical, environmental, biological, food, forensic and toxicological samples. Power of the technique is in high separation efficiency, simplicity, low cost and the small need for sample and solvent volume. However, CE has never gained similar popularity as high performance liquid chromatography (HPLC) because CE suffers from low concentration sensitivity due to small sample injection volume (nL). Addition of an on-line preconcentration technique to CE analysis has given rise to better sensitivity. New preconcentration methods are being developed and recently the combination of more than one technique has become popular. Many metabolomics compounds are charged making CE a potential instrument for analyses. In metabolomics studies, often analytes in low concentrations are the most significant. To understand metabolic processes, the number of samples to be analyzed is large. Fast and sensitive analytical techniques are needed to keep up with the high sample throughput. None of the existing analytical methods is capable of measuring all the desired analytes in one run. Sample preparation will always result in loss of some compounds. Analytical devices have also limitations with sample matrices and analyte characteristics. Combination of analytical
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