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No description available.

A rapid scanning square wave voltammetric detector has been developed for use with high performance liquid chromatography.The electrochemical cell used in the detector was designed so that the HPLC effluent flows through the center of a large diameter platinum disk electrode and is then forced to flow radially across the electrode surface. The arrangement of the electrodes in the cell was intended to result in large analytical currents while minimizing electrical resistance and analyte band spreading in the detection zone. The detector was evaluated in terms of its minimum detectable quantity, linear dynamic range, electrochemical efficiency, and analyte band spreading. The MDQ was found to be in the low parts per billion range for hydroquinone. The detector was shown to provide data that is qualitatively superior to data obtained by amperometric detection and was shown to be compatible with gradient elution HPLC over a broad range of solvent compositions. A sensor based on the quartz crystal microbalance was also developed for use in flowing solvent streams. Quartz crystals were treated with various compounds to produce close - packed monolayer coatings which could interact with solutes entering the flow cell. The solute capacity was determined for one of the monolayer coatings and various factors that influence the magnitude of the OCM signal were investigated. These factors include the solvent flow rate, the solvent strength, solute molecular structure, and bonded phase molecular structure. The QCM sensor was found to be a convenient probe for conducting surface adsorption studies and the molar free energy of adsorption was determined for some chemically related solutes on an amine modified crystal. / Ph. D.

Carbon tetrachloride (CCl₄ ) was closely evaluated as a carrier solvent in high-performance liquid chromatography (HPLC). The separation and retention trends of ninety-two selected compounds from eleven chemical classes (furans, thiophenes, aromatic hydrocarbons, ethers, esters, ketones, aldehydes, aromatic amines, azaarenes, alcohols and phenols) on three analytical silica-bonded phase (amino (NH₂), cyano (CN) and polar amino-cyano (PAC)) columns were investigated with CCl₄ and refractive index (RI) detection. The sample capacity and column efficiency of each of the NH₂ and PAC columns were measured and compared. Besides, a method of determining unmeasurable capacity factors (k' values) was found and illustrated. / M.S.

The extraction of fifteen (15) polymer additives with supercritical carbon dioxide which are used as antioxidants, uv stabilizers, process lubes, flame retardants and antistats from eight formulations of polystyrene is demonstrated and compared to traditional dissolution/precipitation extractions. The purpose of the study was twofold: 1) the development of a high performance liquid chromatography (HPLC) method(s) for the additives and 2) the determination of the viability of supercritical fluid extraction (SFE) for the additives from polystyrene. Separation of some of the additives was achieved using reversed phase liquid chromatography. Nine of the additives were assayed in this manner while, the remaining six additives could not be assayed using reversed phase liquid chromatography. In order to develop an extraction method for the additives, the effects of static extraction time, CO2 density, and temperature were first investigated. These preliminary extractions revealed that a static extraction period which afforded an opportunity for the polymer to swell combined with a high CO2 density and extraction temperature above the glass transition (Tg) yielded quantitative recoveries of the additives. Triplicate extractions of the various polystyrene formulations matched additive recoveries obtained by the traditional dissolution/precipitation method. / Master of Science

Small diameter LC columns provide rapid thermal equilibration and are ideal candidates for temperature programmed LC. Special instrumentation requirements are presented and details of column assembly are given to permit the preparation of highly efficient, stable microbore columns. Three LC temperature control systems are described and their individual strengths and weaknesses are discussed. Problems encountered in raising the temperature of an LC column are addressed and solutions are described. Experimental results of column and instrumentation evaluation are given and the effects of temperature on speed, efficiency, stability and retention of a broad range of samples is reported. Temperature and solvent programming are compared directly. / Ph. D.

Yes / Microemulsion is a stable, isotropic clear solution consisting of oil based substance, water surfactant and cosurfactant. There are two types of microemulsion which are used as a mobile phase; water in oil (w/o) and oil in water (o/w).Microemulsion has a strong ability to solubilize both hydrophobic and hydrophilic analytes, therefore reducing the pre-treatment of the sample which is needed for the complex sample. Recent reports found that separating the analytes by using microemulsion high performance liquid chromatography can be achieved with superior speed and efficiency compared to conventional HPLC modes. In this work, Oil in water (o/w) microemulsion has been used for the determination of nifedipine in pharmaceutical preparation. The effect of each parameter on the separation process was examined. The samples were injected into C18, analytical columns maintained at 30°C with a flow rate 1 ml/min. The mobile phase was 87.1% aqueous orthophosphate buffer 15 mM (adjusted to pH 3 with orthophosphoric acid), 0.8% of octane as oil, 4.5 SDS, and 7.6% 1-butanol, all w/w. The nifedipine and internal standard peaks were detected by UV detection at λ max 237 nm The calibration curve was linear (r2=0.9995) over nifedipine concentrations ranging from 1 to 60 μg/ml (n=6). The method has good sensitivity with limit of detection (LOD) of 0.33 μg/ml and limit of quantitation (LOQ) of 1.005 μg/ ml. Also it has an excellent accuracy ranging from 99.11 to 101.64%. The intra-day and inter-day precisions (RSD %) were <0.45% and <0.9%, respectively.

M. Tech (Department of Chemistry, Faculty of Applied and Computer Sciences) Vaal University of Technology. / A simple and rapid method for determination of estrone (E1) and β-estradiol (E2) was developed and validated using high performance liquid chromatography (HPLC). The solutions of standards and sample were prepared with distilled water. HPLC separation was performed in isocratic method 50/50 (water/methanol) using 4.6 mm x 250 mm id film thickness 5 µm) XDB-C18 capillary column, detector DAD, UV on 254 nm, temperature 20 ºC with flow rate of 2 mL/min, sample volume 20 µL and run time of 10 min. Calibration curves were linear between concentration range 1.0 - 15.0 ppm. The method was validated for limit of detection and quantification, linearity, precision, trueness and specificity. Also the method was applied to directly and easily to the analysis of the E1 and E2. Adsorption experiments were carried out in batch mode using multistirrer in a series of Erlenmeyer flasks of 50 ml capacity covered to prevent contamination having concentration ranges of E1 and E2 from 1 to 10 mg/L with adsorbent dose range 0.01 to 1 g at pH range 1 to 10 and temperature range 15°C to 35°C, placed on multistirrer. The results of the batch studies showed that simultaneous adsorption shows the maximum percent (91%) removal of E1 and (86 %) E2 at optimum temperature 25 °C of adsorbent dose 0.1 g, and pH 7. The mechanism, isotherms and kinetics of removal of two endocrine disrupting chemicals, estrone (E1) and β-estradiol (E2) by activated carbon adsorption were investigated in an agitated non-flow batch adsorption studies. Mathematical models were used to describe the adsorption phenomenon with the kinetic and thermodynamic parameters evaluated using the adsorption equilibrium data at varying temperatures. Higher adsorption rates were achieved at acidic to neutral pH ranges, with the sorption kinetic data showing a good fit to the pseudo second order rate equation and the Langmuir adsorption isotherm model for both E1 and E2. The Gibbs free energy were –16.68 kJ/mol and –17.34 kJ/mol for E1 and E2 respectively. The values of enthalpy for both E1 (84.50 kJ/mol) and E2 (90 kJ/mol) indicated a chemical nature of the sorption process. Both the isotherm and thermodynamic data obtained all supported the mechanism of adsorption of E1 and E2 to be mainly chemisorption’s supported by some physical attractions.

M. Tech (Department of Chemistry, Faculty of Applied and Computer Sciences) Vaal University of Technology. / In this study, analytical method for determining the chlorinated phenols in water was developed using High Performance Liquid Chromatography. The following four compounds which are 2, 4, 6- Trichlorophenol (2, 4, 6 TCP), 3-chlorophenol (3CP), 2, 4- Dichlorophenol (2, 4 DCP) and 4-chloro-3-methylphenol (4C3MP) were identified and quantified with a High Performance Liquid Chromatography (HPLC). The validation parameters tested were,: linearity, trueness, precision, detection limit of quantitation, sensitivity, specificity, selectivity. The linear calibration ranges of five standard solution from 1-10 ppm. The linearity ranges between 0.9298-0.9813. The activated carbon based on the waste macadamia nutshell activated carbon (MAC) was investigated for its potential uses as an adsorbent for chlorinated phenols removal and compared with grafted macadamia nutshell activated carbon (GMAC). The adsorbent was characterized with Fourier transform infrared spectrophotometer (FTIR), scanning electron microscope (SEM) and thermo gravimetric analysis (TGA). The parameters such as pH, temperature, contact time, concentration and adsorbent were investigated by adsorption technique. The strata C18E has been used before for the same reason and therefore the research was based on mimic the functional group of solid phase extraction (SPE) into macadamia activated carbon (MAC). The functional groups in SPE C18E are benzene and octadecyl. MAC was grafted with strata C18E functional groups to compare its potential with the SPE. The pseudo-first-order and pseudo-second-order kinetic models were applied to verify the experimental data. The pseudo-second order exhibited the best fit for the kinetic studies for MAC adsorption. Chemical removal of chlorinated phenols from wastewater is necessary to reduce harmful products on the environment and human health. Chlorinated phenols have been previously listed as some of the highest priority contaminants and as well as mainly important capability carcinogenic toxins released from chemical plants. Their availability in water supplies was perceived by their bad taste and smell. The acceptable chlorinated phenols concentration in portable water is 1 (mg/l) base on the approval of world health organization. The permanent checking of chlorinated phenols in environmental samples has a greater significance and stresses highly effectiveness, common selectively and great sensitively methods. The maximum uptake of Phenol using weighed mass of MAC was found to be 78 % and for GMAC was 84% for both 2,4,6TCP. t=250 min, pH=5, Co=1mg/l, T = 25 oC and m = 0.3 g/l were the optimum condition for Phenol-MAC system and GMAC system. Over all analysis of equilibrium model analysis indicates the fitness of Langmuir isotherm model to Phenol MAC adsorption system, suggesting a monolayer adsorption of phenol on the surface of MAC. Phenol adsorption capacity of MAC was found to be decreasing with increase in temperature suggesting that the adsorption process was exothermic in nature, which was further supported by the negative values of change in enthalpy. Characterization of MAC and GMAC confirmed the mesoporous texture, highly carbonaceous nature and a higher effective surface area of 912 m2/g. The highest phenol uptake capacity of GMAC was found to be 8.0049 mg/g. The optimal conditions for various process parameters are t = 250 min, pH=5, Co=1mg/l, T = 25 oC and m = 0.3 g/l were the optimum condition for Phenol-GMAC system. Like Phenol-MAC system, the kinetics studies confirmed that Phenol-GMAC adsorption system can be described by pseudo- second-order kinetics model. Equilibrium model analysis indicates the fitness of Langmuir isotherm model to Phenol-MAC adsorption system, suggesting a monolayer adsorption of phenol on the surface of GMAC. Phenol adsorption capacity of GMAC was found to be decreasing with increase in temperature suggesting that the adsorption process was exothermic in nature, which was further supported by the negative values of change in enthalpy. The negative values of Gibb’s free energy suggested that adsorption of phenol onto GMAC was a spontaneous process.

HPLC has been used and can quickly determine several ions simultaneously. The method of determination described for transition metals [Cr(III), Fe(III), Ni(II), Co(II), Cu(II), Zn(II), Cd(II), Mn(II)] and [Ca(II), Pb(II)] using HPLC with UV-VIS detection is better than the PAR complexation method commonly used. The effects of both eluent pH and detector wavelength were investigated. Results from using different pHs and wavelengths, optional analytical conditions for the separation of [Ni(II), Co(II), Cu(II)], [Cr(III), Fe(III), Ca(II), Ni(II), Cu(II)], and [Ca(II), Zn(II), Pb(II)] in one injection, respectively, are described. The influence of adding different concentrations of Na_2EDTA solvent to the sample is shown. Detection limits, linear range, and the comparisons between this study and a post-column PAR method are given.