Semi-analytical study of transient electroosmotic flow of Maxwell fluids in nanochannels grafted with a strong polyelectrolyte layer having layered distribution of charges

We theoretically study transient electroosmotic flow of general Maxwell fluids through polyelectrolyte grafted nanochannel with a layered distribution of charges. By applying the method of Laplace transform, we semi-analytically obtain transient electroosmotic flow from Cauchy momentum equation and Maxwell constitutive equation. For nanochannels grafted with polyelectrolyte layers having different layered distribution of charges, we study the influence of dimensionless relaxation time, dimensionless polyelectrolyte layer thickness and dimensionless drag coefficient on transient electroosmotic flow. We verify that adjusting charge distributions of the layer can control intentionally the direction of the flows as well as strength of electroosmotic flow

The development of a method to determine felinine in body fluids by capillary electrophoresis : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Chemistry at Massey University

Ion-exchange, paper-chromatography and high performance liquid chromatography were used in earlier studies for the determination of felinine in biological fluids. These methods were either inadequate and/or need laborious sample pre-treatments. A new method for the determination of felinine by capillary zone electrophoresis has been developed. Preliminary investigations were carried out to address the conditions required for the separation of felinine. The separation of felinine can be performed on a fused-silica capillary with a 20 mM phosphate buffer (pH 2.0) and detection wavelength 200 nm. The separation principle was based on the different migration times due to the different molecular weights, molecular sizes and charges under an applied potential field. The quantitative determination of felinine levels in cat urine has been achieved. The cat urine analysis was performed directly on the capillary electrophoresis without making any felinine derivative(s). The levels of felinine in different cat genders are reported. The results were compared with the results of an HPLC felinine derivatization method. Felinine levels in entire male cat urine were much higher than those in female and castrated male cat urine. A synthetic felinine was employed as standard felinine. Linear relationships between peak area and concentration of synthetic felinine calibrations are reported. Mean felinine recovery in cat urine was 95.9%. Taurine, urea, creatine and creatinine, which exist in large amounts in cat urine, showed no interference with the analysis of felinine by this method. The new capillary zone electrophoresis method was then applied to the study of felinine stability. Conditions reported to influence the stability of felinine were investigated. These conditions included oxidation, storage temperatures and times, heating, acidic and alkaline solutions. Both synthetic felinine and felinine in cat urine were investigated. Storage temperature (-20°C to 20°C) had no significant influence on the stability of felinine while higher temperatures increased the decomposition of felinine. Felinine degraded at strong acid and base conditions but was relatively stable under mild acid and base conditions. A similar stability of felinine in human urine is also reported. The capillary zone electrophoresis method was also employed to study felinine in plasma and serum. Plasma and serum as well as urine can be analysed directly on the capillary electrophoresis after sufficient dilution. Conditions (eg. protein clean up, changing of injection time, 37°C heating) that might influence of felinine behaviour in plasma and serum are discussed. This study indicated that no traces felinine be found in cat plasma, within the detection limits of this new capillary electrophoresis method

Optimal control-based inverse determination of electrode distribution for electroosmotic micromixer

This paper presents an optimal control-based inverse method used to determine the distribution of the electrodes for the electroosmotic micromixers with external driven flow from the inlet. Based on the optimal control method, one Dirichlet boundary control problem is constructed to inversely find the optimal distribution of the electrodes on the sidewalls of electroosmotic micromixers and achieve the acceptable mixing performance. After solving the boundary control problem, the step-shaped distribution of the external electric potential imposed on the sidewalls can be obtained and the distribution of electrodes can be inversely determined according to the obtained external electric potential. Numerical results are also provided to demonstrate the effectivity of the proposed method

A microfluidic device for array patterning by perpendicular electrokinetic focusing

This paper describes a microfluidic chip in which two perpendicular laminar-flow streams can be operated to sequentially address the surface of a flow-chamber with semi-parallel sample streams. The sample streams can be controlled in position and width by the method of electrokinetic focusing. For this purpose, each of the two streams is sandwiched by two parallel sheath flow streams containing just a buffer solution. The streams are being electroosmotically pumped, allowing a simple chip design and a setup with no moving parts. Positioning of the streams was adjusted in real-time by controlling the applied voltages according to an analytical model. The perpendicular focusing gives rise to overlapping regions, which, by combinatorial (bio) chemistry, might be used for fabrication of spot arrays of immobilized proteins and other biomolecules. Since the patterning procedure is done in a closed, liquid filled flow-structure, array spots will never be exposed to air and are prevented from drying. With this device configuration, it was possible to visualize an array of 49 spots on a surface area of 1 mm2. This article describes the principle, fabrication, experimental results, analytical modeling and numerical simulations of the microfluidic chip.\ud \ud \ud \u

Determination of creatinine and creatine by capillary electrophoresis : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University

The assessment of creatinine and creatine in biological fluids is important in the evaluation of renal and muscular functions. For routine creatinine determinations in the clinical laboratory, the most frequently used method is the spectrophotometric one based on the Jaffé reaction. However, this reaction is not specific for creatinine. For this reason, several methods have been proposed, but the elimination of interferences in the determination of creatinine has still not been achieved in some of these methods; others solved this problem either with expensive equipment that does not suit routine analysis or necessitates time-waste procedures. In this thesis capillary electrophoresis was the new tool investigated. It was applied in an attempt to achieve both the separation of creatinine from the non-creatinine 'Jaffé- reacting' chromogens and the determination of creatine in serum. Capillary zone electrophoresis was performed with detection at wavelength 480 nm to separate creatinine from the non-creatinine 'Jaffé-reacting' chromogens in urine. The principle was based upon the different migration times due to the different molecule weights, molecular sizes and charges under the applied high voltage. The picric acid was employed as part of the running buffer to allow reaction of creatinine and picrate to take place after the sample injection. This procedure eliminated the negative influence of the reaction time that is controlled manually in the common Jaffé reaction method. Therefore, compared to the Jaffé reaction method, the new method achieved more accuracy and precision in the determination of creatinine. Determination of creatinine in serum and urine were studied at a new wavelength 417 nm, which gave a higher sensitivity of detection than at 480 nm. This wavelength shift made the determination of creatinine in serum possible by capillary zone electrophoresis without the non-creatinine 'Jaffé-reacting' chromogens interfering. In this method, serum only needed a simple filtration before the analysis. Creatine was discovered to have absorption at 417 nm in alkaline medium. Moreover, specific sample stacking was introduced in this method. The sample was dissolved in a mixture of two-volumes acetonitrile and one-volume 3 % ammonium chloride to give a 10-fold enhancement of detection sensitivity

Molecular Dynamics simulations of concentrated aqueous electrolyte solutions

Transport properties of concentrated electrolytes have been analyzed using classical molecular dynamics simulations with the algorithms and parameters typical of simulations describing complex electrokinetic phenomena. The electrical conductivity and transport numbers of electrolytes containing monovalent (KCl), divalent (MgCl$_2$), a mixture of both (KCl + MgCl$_2$), and trivalent (LaCl$_3$) cations have been obtained from simulations of the electrolytes in electric fields of different magnitude. The results obtained for different simulation parameters have been discussed and compared with experimental measurements of our own and from the literature. The electroosmotic flow of water molecules induced by the ionic current in the different cases has been calculated and interpreted with the help of the hydration properties extracted from the simulations