Capillary electrochromatography: effect of electrolyte concentration on electroosmotic flow and column efficiency

1. A study was made of conditions of formation of fine cobalt powder in a two-layer electrolytic bath. The optimum electrolysis parameters are: 200 g/liter CoCl2 · 6H2O electrolyte, pH 2–3, cathodic current density ic =40–50 A/dm2, bath temperature 20°C. 2. Very fine cobalt powder was produced for the first time from concentrated cobalt-chloride solutions (200–900 g/liter CoCl2 6H2O). 3. The influence of electrolyte concentration and acidity and cathodic current density on the appearance of the cobalt deposit and on its particle shape and size was studied by electron microscopy. 4. The ϕ vs i polarization curves recorded in the course of cobalt electrodeposition at various electrolyte concentrations confirmed the fact that the extent of dendrite formation decreases with increase in electrolyte concentration. 5. The effects of electrolyte concentration and acidity and cathodic current density on current yield were determined. The maximum current yield of fine metal powders (iron, cobalt, nickel) in a two-layer bath is 56–60% with dilute electrolyte solutions and 90–95% with a concentrated solution.

Effects of electrolyte type and concentration on the anodic oxidation of 4H-SiC (0001) in slurryless electrochemical mechanical polishing

Capillary electrochromatography (CEC) has been realised as a combination of high performance liquid chromatography (HPLC) and capillary electrophoresis (CE) allowing the separation of analytes based on their differing adsorption and migration behaviour. There is a considerable interest in developing new methodologies for CEC, which uses chromatographic beads or monoliths as stationary phases or alternatively employs open tubular (OT) capillaries relying on surface modifications. Besides the bulk flat flow profile of the mobile phase in CEC columns allowing an enhanced resolution, due to the influence of the applied electrical field there are other possibilities to provide a higher resolution with better detection. As an additional newly means for peak sharpening and sample enrichment isotachophoresis and a “sweeping mechanism” could be envisaged, which both take advantage of the inhomogeneous electric field pattern in the capillary by choosing appropriate leading and terminating background electrolytes (BGEs). Transient isotachophoresis would be another technique to provide an increased plate height in the separations, using an optimized sample matrix, e.g. containing a relatively high acetonitrile content, with the same leading and terminating BGEs. In this thesis, a new method to generate a “sharpening zone”, which is similar to the concept of transient isotachophoresis, was established using an aqueous sample matrix containing an organic solvent. Target analytes within this zone could be concentrated whilst they migrated through the capillary. A novel technique was developed that used the sharpening zone for sweeping and concentrating several unresolved analyte peaks allowing an enhanced peak resolution. As the aim was to concentrate only some part of the analyte zone containing compounds of interest, the position and width of the sharpening zone needed to be well controlled. Various techniques to tune the width and position of the sharpening zone were thus developed, involving modifying the organic modifier content in the BGE, applying pressure additionally to the electroosmotic flow (EOF) and modifying the inner surface of the capillaries. This work also critically evaluated some related existing knowledge and theoretical approaches in CEC including the concept of tuneable system eigenpeaks (noncomigrating or ghost peaks caused by waves of an electric field in the capillary). Although peak broadening caused by eigenpeaks (which often suppresses resolution in CEC) has been well described for aqueous or pure non-aqueous BGEs, a systematic study of eigenmobility in aqueous/acetonitrile BGEs had not been reported. The experiments related to the eigenmobility led to a new approach to tune the eigenpeak position in chromatograms whereby a selective sample peak sharpening mechanism was elaborated using the sharpening zone. The novel approach was demonstrated for the separation of various peptides in the CE mode and for the resolution of incompletely resolved chiral amino acids in CEC. These investigations furthermore led to the development of an appropriate stationary phase, which was produced using techniques for an in-column synthesis of a molecular imprinted polymer (MIP). Well prepared MIPs are capable of specifically enhancing the retention of target analytes, herein focusing on enantio-selective isolation of chiral molecules. Since such a MIP was rather rigid, which often caused capillary clogging when used as a conventional monolithic stationary phase, this MIP was incorporated into porous layer open tubular (PLOT) capillaries. Numerous experimental difficulties were overcome with respect to the vinylisation of long fused-silica capillaries and for the polymerisation of the MIP within using thermal- and photo-polymerisations. A method for the characterization of such MIP-PLOT capillaries was elaborated involving the Langmuir adsorption theory. The new columns were evaluated using chromatography, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and CEC analysis. All experiments were designed according to the principles of Green Chemistry. These concepts involved the use of small scale analysis, simulation studies reducing the number of performed experiments, systematic studies with low amounts of solvents and materials, and optimisation of synthesis methods to reduce time, energy and reagent consumption. The theories, methods and results presented in this thesis will, in the future, allow further targeted developments of novel analytical tools for a green, sensitive, selective and improved resolution analysis of chemical and biological compounds including chiral compounds, peptides and proteins.

Towards the ultimate minimum particle diameter of silica packings in capillary electrochromatography

The development of sol-gel open-tubular column technology in capillary electrochromatography (CEC) is reviewed. Sol-gel column technology offers a versatile means of creating organic-inorganic hybrid stationary phases. Sol-gel column technology provides a general approach to column fabrication for microseparation techniques including CEC, and is amenable to both open-tubular and monolithic columns. Direct chemical bonding of the stationary phase to the capillary inner walls provides enhanced thermal and solvent stability to sol-gel columns. Sol-gel stationary phases inherently possess higher surface area, and thus provide an effective one-step alternative to conventional open-tubular column technology. Sol-gel column technology is applicable to both silica-based and transition metal oxide-based hybrid stationary phases, and thus, provides a great opportunity to utilize advanced material properties of a wide range of nontraditional stationary phases to achieve enhanced selectivity in analytical microseparations. A wide variety of stationary phase ligands can be chemically immobilized on the capillary inner surface using a single-step sol-gel procedure. Sol-gel chemistry can be applied to design stationary phases with desired chromatographic characteristics, including the possibility of creating columns with either a positive or a negative charge on the stationary phase surface. This provides a new tool to control electroosmotic flow (EOF) in the column. Column efficiencies on the order of half a million theoretical plates per meter have been reported for sol-gel open-tubular CEC columns. The selectivity of sol-gel stationary phases can be easily fine-tuned by adjusting the composition of the coating sol solution. Open-tubular columns have significant advantages over their packed counterparts because of the simplicity in column making and hassle-free fritless operation. Open-tubular CEC columns possess low sample capacity and low detection sensitivity. Full utilization of the analytical potential of sol-gel open-tubular columns will require a concomitant development in the area of high-sensitivity detection technology.

Capillary columns with in situ formed porous monolithic packing for micro high-performance liquid chromatography and capillary electrochromatography

Adsorption of immunogamma globulin onto various synthetic calcium hydroxyapatite particles

The goal of the research reported in this dissertation is to develop packed and open-tubular capillary electrochromatographic methods for improved achiral and chiral separations of various classes of analytes. The first part of this research involves the separation of seven benzodiazepines by the use of the packed mode of capillary electrochromatography (CEC) and a 40 cm packed bed of Reliasil 3 μm C18 stationary phase. Optimal conditions were established by varying the mobile phase, the amount of organic modifier, the buffer concentration, the applied voltage, and the column temperature. The second part of this research focuses on the open-tubular mode of CEC and the polyelectrolyte multilayer (PEM) coating approach. In the first study of this part, poly (diallyldimethylammonium chloride), PDADMAC, was used as the cationic polymer and poly (sodium N-undecanoyl-L-glycinate), poly (L-SUG), was used as the anionic polymer for the construction of the PEM coating. The performance of the modified capillaries as a separation medium was evaluated by use of seven benzodiazepines as analytes. In the second study, the anionic polymeric surfactant poly (sodium N-undecanoyl-L-leucylvalinate), poly (L-SULV), was used as the chiral discriminator for the separations of several drug analytes. Reproducibility of the PEM coating was evaluated by computing the relative standard deviation (RSD) values of the electroosmotic flow (EOF). The PEM-coated capillaries were remarkably robust with excellent reproducibilities and high stabilities against extreme pH values. The stability of the capillary surface was further investigated after exposure to NaOH solutions. The structural changes of these coatings were monitored using laser scanning confocal microscopy (LSCM). These changes were discussed in terms of separations using open-tubular CEC (OT-CEC). In addition, the electropherograms obtained from the chiral separation of 1,1’-binaphthyl-2,2’-dihydrogenphosphate (BNP) in OT-CEC allowed the measurements of both selectivity and electroosmotic mobility changes after long exposure to NaOH.

The effects of electrolyte concentrations on calcium-sodium exchange equilibria in two soil samples of india

Ionic liquid-copolymerized monolith incorporated with zeolitic imidazolate framework-8 as stationary phases for enhancing reversed phase selectivity in capillary electrochromatography

Replacing pressure-driven flow with electroosmotic flow in chromatography with packed capillary columns results in a new and powerful analytical technique, combining the advantages of high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE): capillary electrochromatography (CEC). In essence, it involves packing CE capillaries with HPLC stationary phases and applying a voltage across the packed capillary, which generates an electroosmotic flow (EOF) that transports solutes along the capillary toward the detector; on the way, both differential partitioning and electrophoretic migration of the solutes occur, resulting in their separation. This dual separation mechanism can afford unique selectivities. Also, the plug-flow profile of EOF reduces flow-related band broadening, so that separation efficiencies of several hundred thousand plates per meter are often obtained (i.e., one or two orders of magnitude greater than those of present conventional chromatographic systems). There is no back pressure when EOF occurs, so small particle sizes (1–3 μm) and/or long columns can be used. Generally, carrier electrolytes containing high levels (40–80%) of organic solvents such as methanol or acetonitrile are employed, making it useful for water-insoluble compounds, which can be difficult to analyse by CE. CEC can be faster than HPLC, and gradient-elution CEC is being developed as an alternative to gradient-elution liquid chromatography of polymers.

The methods of C18 modification to silica gel are well described in the literature. Three C18 modification methods are known by which three different types of C18 stationary phases are obtained, respectively-a brush form, an oligomeric form, and a bulk form. The brush form is composed of separate monomeric ligands chemically attached to the silica surface, and is obtained by reaction with monochlorodimethyloctadecylsilane. The oligomeric form, where a C18 oligomer is bonded to each silanol site of silica surface, is obtained with dichloromethyloctadecylsilane. The bulk form composed of a 3 dimensional polymer-like network, is obtained with trichlorooctadecylsilane. In all cases, endcapping is generally required after C18 modification to prevent the tailing phenomenon in chromatographic separation. The oligomeric and bulk forms are not widely used in the commercial products because preparation of such phases demands drastic and time-consuming reactions at high temperatures. On the other hand, the brush form is easy to make under mild reaction conditions, and is widely used. Spherical porous silica gel is the most common material for the support of C18 modification that gives high separation efficiencies. Microwave techniques have been used in chemical synthesis and derivatization, preparation of nano materials, extraction, sample treatment and dissolution, etc. Microwave application has been expanded even to polymerization and immobilization of polymer coating on chromatographic stationary phases. Microwave heating is known to often cause fast and good reaction results owing to rapid and uniform heating. However, microwave application in preparation of monoliths or C18 ligand modification has not been reported so far. Recently, the monolithic column has raised a lot of interest in liquid chromatography. The monolithic column is composed of an one-body porous solid structure with nanometer-sized inner pores and micrometer-sized through channels. Particularly, preparation of monolith column is carried out in silica capillary and it is used in capillary electrochromatography (CEC). Open-tubular columns have significant advantages over their packed counterparts because of the simplicity in column preparation and hasslefree fritless operation. Column efficiencies of 100 000 theoretical plates per meter are common for open tubular CEC columns of 50 μ ID, and column efficiencies up to half a million theoretical plates per meter have been reported for sol-gel open-tubular CEC columns of 10-13 μ ID. In this study, the effects of microwave heating have been studied in preparation of open tubular monolithic silica capillary columns and C18 modification in comparison with thermal heating. Three different capillary columns have been prepared by different heating processes-1) microwave heating for monolith formation and C18 ligand immobilization; 2) microwave heating for monolith formation and thermal heating for C18 ligand immobilization; 3) thermal heating for monolith formation and C18 ligand immobilization. Their performances in CEC separation have been comparatively studied. The microwave heating method for OT (open tubular) monolith formation was much faster than thermal heating, and the thickness of the monolith layer by microwave heating was much thinner than that by thermal heating.

The need for clean energy as an alternative is inevitable. HHO gas has received much attention lately. In addition to electrolyte concentration, the breakthrough with a diverse electrode surface texture approach has not been extensively performed. Therefore, this study aims to determine the effects of NaOH concentration and plate surface texture on the performance of the HHO generator. In general, the increase in electrolyte concentration combined with surface texture caused an increase in output current, HHO gas production, and output temperature. As for the applied voltage variation with various surface textures, the increase in output current, HHO gas production, and output temperature also took place, similar to the case of increasing NaOH concentration. Either an increase in electrolyte concentration or an increase in applied voltage triggers faster ion movement, leading to an increase in conductivity, thus effectively assisting the electrolysis of water. Regarding the output current and HHO gas production, the textured surface had a much higher value than the plain surface in terms of increasing NaOH concentration or applied voltage variations. However, according to the R2 results, the linear surface has a stronger relationship with the output current and HHO gas production than the cross surface. In the case of the output temperature, the linear surface was slightly lower than the cross surface. It is possibly due to impurities in the electrolyte solution that contaminate the electrode surface, resulting in a lower output temperature on the linear surface.

The electrochemical oxide growth behaviour on titanium in acid and alkaline electrolytes

The viscosity of gastric juice and the concentrations of sodium, potassium, calcium, magnesium and chloride ions were measured before and after stimulation with pentagastrin in 10 children with cystic fibrosis and compared to those in 10 healthy children of corresponding ages. The viscosity values followed the same patterns as those for the sodium and calcium ion concentrations and were higher in the cystic fibrosis group. The electrolyte concentrations in the basal and different post-stimulation fractions of the gastric juice were higher in the cystic fibrosis group. Significant differences between both groups could only be found in the electrolyte concentrations. The total secretion of each of the electrolytes was the same in both groups because along with the increased electrolyte concentration in the cystic fibrosis group there was a reduced volume of gastric juice. The dependence of viscosity on the individual electrolyte concentration is discussed. The differences in the viscosity and the electrolyte concentrations in gastric juice from the cystic fibrosis children seems to be due to changes in the process of gastric secretion and not due to the influence of swallowed saliva.