Thesis (MTech. degree in Chemistry)--Tshwane University of Technology, 2010.

published_or_final_version / abstract / toc / Chemistry / Master / Master of Philosophy

High-pressure homogenization using a new flat valve homogenizer in combination with enzymatic digestion with a crude protease was investigated as a means of releasing Se compounds from zoological and botanical matrices prior to slurry introduction GF-AAS. Timed trials with four zoological certified reference materials (CRMs), three botanical reference materials (RMs), and a food crop indicated that Se release was quantitative after homogenization or became quantitative within 1 h of digestion at 60°C. / The same technique was employed on five animal feed samples. / A new model of homogenizer equipped with ceramic homogenizing valve was evaluated in terms of analyte metal contamination levels within the final sample dispersion. / Five animal feed samples and four wood pulp samples, were investigated for their content of Cu, Fe and Mn using high-pressure homogenization as the sample preparation technique prior to GF-AAS. Dispersions of dried animal feeds were sub-sampled reliably after 7 days of storage at 4°C. Trials on pulp samples indicated that pulps could be sub-sampled reliably after 1 day of storage. (Abstract shortened by UMI.)

Three direct interfaces for coupling high performance liquid chromatography (HPLC) with atomic absorption spectrometry (AAS) were developed and optimized for the determination of ionic organolead, organoselenium and organoarsenic compounds. The first all-quartz interface consisted of a thermospray nebulizer and a flame microatomizer in which ionic alkyllead analytes (R$ sb{ rm n}$Pb$ sp{ rm (4-n)+};$ R = CH$ sb3,$ C$ sb2$H$ sb5)$ were atomized by a methanol (from HPLC eluent)-oxygen kinetic flame, and channeled in a quartz tube (atom keeper) mounted into the AAS optical beam. Alternately, the classical electrothermal atomization technique for organolead species (quartz furnace under hydrogen atmosphere) was coupled with a post-column derivatization-volatilization apparatus based on the ethylation of ionic alkylleads by sodium tetraethylborate. The limits of detection provided by these two approaches were 1.0-3.4 ng and 0.10-0.15 ng, respectively. Arsonium ((CH$ sb3) sb3$RAs$ sp+;$ R = CH$ sb3,$ CH$ sb2$CH$ sb2$OH, CH$ sb2$COOH) and selenonium ((CH$ sb3) sb2$RSe$ sp+;$ R = CH$ sb3,$ CH$ sb2$CH$ sb2$OH) species were quantified using a novel HPLC-AAS approach based on a direct coupling of three processes: thermospray nebulization, thermochemical hydride generation using hydrogen gas, and diffuse flame atomization. Direct evidences for the thermochemical hydride generation process was obtained by injecting (CH$ sb3) sb3$SeI and SeO$ sb2$ into the interface and capturing the gaseous end products in liquid chemical traps specific for SeH$ sb2$ and Se(IV). Both analytes were derivatized to SeH$ sb2$ only in the presence of hydrogen in the interface. Reverse- and normal-phase high pressure liquid chromatographic methods were also developed and adapted for the HPLC-AAS analyses of alkyllead, arsonium and selenonium compounds in real samples. The limit of detection of the arsonium and selenonium cations were 7.6-13.3 ng and 31.0-43.9 ng, respectively.

The scope of these studies was two-fold: to evaluate high pressure homogenized slurries as a rapid means of screening wood pulps for their Cu, Mn and Fe content and to evaluate the high pressure homogenization in combination with chelating agents or enzymatic digestion for the liberation/extraction of metal ions from this matrix. / Cu, Mn and Fe were determined successfully in pulp samples using high-pressure homogenization prior to slurry introduction-GF-AAS. The analysis time of the method from sample acquisition to determination was of the order of a few minutes per sample. / Different cellulose swelling/dissolution agents were evaluated for the generation of quasi-stable pulp suspensions, rich in cellulose. High-pressure homogenization alone or in combination with chelating agents or enzymatic digestion was also investigated as a means of quantitatively releasing these metal ions into the liquid phases. / A new model of homogenizer equipped with ceramic homogenizing valve with a few modifications was evaluated in terms of metal contamination levels within the final sample dispersion. (Abstract shortened by UMI.)

Several biologically important arsenic compounds including methylarsonate, trimethylarsine oxide, tetramethylarsonium ion, arsenobetaine and arsenocholine were prepared, in good yields, from sodium arsenite, or dimethylarsinic acid. These organoarsenic compounds together with arsenite, arsenate and dimethylarsinic acid were used as standards for the development of analytical methods for determining the levels of individual arsenic compounds (arsenic speciation) present in natural matrices. / Arsenobetaine, arsenocholine and tetramethylarsonium ion were separated by high performance liquid chromatography (HPLC) with on-line detection by thermochemical hydride generation (THG)-AAS. The analytes were eluted from the cyanopropyl bonded phase HPLC column with a 1% acetic acid methanolic mobile phase which also contained diethyl ether triethylamine, and trimethylsulfonium iodide or picrylsulfonic acid. A surface response methodology and a univariate optimization procedure were used to determine the optimum concentration of solvent modifiers in the methanolic mobile phase. Limits of detection in the range 4-5 ng (as As) were obtained for the arsonium analytes under optimum chromatographic conditions. / A simple phenol extraction procedure was developed to isolate arsonium analytes from edible marine tissues (lobster tail muscle, peeled and deveined shrimp, and cod fillet), cod liver oil and human urine. The crude extracts were separated on the cyanopropyl column using a methanolic mobile phase and detected on-line by THG-AAS. Recoveries from tissues or from urine which had been spiked at 0.1-3.4 $ mu$g of As cation/g of fresh weight were 80% or greater for each of five sample types. / An improved HPLC-AAS interface which was compatible with either aqueous or organic mobile phases was also developed. The interface provided approximately equivalent responses to different arsenic oxidation states which resulted in low to subnanogram chromatographic limits of detection for arsenic oxyanions and arsonium cations in an aqueous or methanolic mobile phase. Nascent As anions and As cations were conveniently coextracted from aqueous solution or from fish muscle by phenol extraction and quantified in the same chromatographic run. This method has been applied to a standard reference sample of dogfish muscle (DORM-1), a marine reference sediment sample (PACS-1) and to sediment porewaters (SAG-15) from the Saguenay Fjord.

ABSTRACT Toxicological studies have shown that the degree of toxicity of some elements depends on the chemical form in which the element is present. Chromium (III) is considered as an essential micronutrient for human whereas chromium (VI) is a potentially carcinogenic agent. So the speciation of inorganic chromium in environmental samples is required for accurate assessment of pollution levels. The chromium content in natural water is usually very low, and a preconcentration is often necessary prior to the determination. A sensitive and selective preconcentration and speciation procedure is developed for the determination of trace and ultra trace amounts of chromium species by utilizing chemiluminescence (CL) and flame atomic absorption spectrometric (FAAS) techniques. The performances of amino silica-gel, amino sol-gel, mercapto silica-gel beads and metal oxides for solid phase extraction of chromium are examined either in column or batch type studies. Considering the advantage of concentrating Cr(III) and Cr(VI) ions separately simply by adjusting the pH of the medium, amino silica-gel resin is chosen in this study. The influences of different experimental parameters on the separation and preconcentration of chromium species such as pH, eluent concentration, flow rate, particle size of the resin are investigated. Chemiluminescence detection studies are performed by using the catalytic effect of Cr (III) on the reaction between luminol and hydrogen-peroxide and Cr (VI) is detected after reduction to Cr (III). Luminol and H2O2 concentrations and the pH of the medium are optimized to increase the sensitivity of the system. Chemiluminescence is inherently a very sensitive technique. When a preconcentration step is included in the CL mesurement of very low concentrations of chromium is possible to determine. Indeed, a 25-fold enhancement in sensitivity of chromium ions is achieved after incorporating amino silane&ndash / gel colums in the system and 0.2 &amp / #61549 / g/L of chromium (corresponds to the concentration of chromium in natural waters) was measured. A fully automated FI-CL system is designed that allows all necessary operations to be performed on-line. This system allows the pre-conditioning of micro-columns with different buffer solutions / adsorption of chromium species in micro-columns / washing these columns to remove interfering matrix components / elution of the species with minimum volume / transporting the species and chemiluminescence reagents to the cell / and, finally, cleaning of all pertinent conduits in the FIA-system in order to prevent carry-over between individual samples.

ABSTRACT ELECTROCHEMICAL HYDRIDE GENERATION AND ATOM TRAPPING ATOMIC ABSORPTION SPECTROMETRY FOR DETERMINATION OF ANTIMONY Menemenlioglu, ipek M.S., Department of Chemistry Supervisor: Prof. Dr. O. Yavuz Ataman June 2004, 82 pages Electrochemical hydride generation is a suitable alternative to common hydride generation by NaBH4 which is widely used for the detection of volatile elements such as As, Se, Sb, Sn, Bi, Ge, Te and Pb. In this study, a thin-layer flow through electrochemical cell was designed. Lead and platinum foils were employed as cathode and anode materials, respectively, for the generation of antimony hydride. Argon was used as the carrier gas. The inlet arm of the conventional quartz tube atomizer was used for on-line preconcentration of generated hydrides. A portion of the inlet arm was heated externally to the collection temperature for trapping the analyte species which were generated electrochemically. For the revolatilization of the trapped species, the trap was further heated to the revolatilization temperature and hydrogen gas was introduced into the system 10 seconds afterwards. The experimental operation conditions for electrochemical hydride generation which include the acidities and flow rates of catholyte and anolyte solutions, carrier gas flow rate and the applied electric current, were optimized. For trapping, collection and revolatilization temperatures and hydrogen flow rates were optimized. Analyses of standard reference materials were performed to check the accuracy of the proposed method. 3&amp / #963 / limit of detections were found as 1.03 ng ml-1 and 0.053 ng ml-1 with and without employing the trap, respectively. The trap has provided 20 fold sensitivity improvement.

Trace amounts of germanium is determined by flame atomic absorption spectrometry by utilizing the vaporization of germanium tetrachloride. Using a continuous flow reactor, sample solution is mixed with concentrated hydrochloric acid and heated to 80&ordm / C to form volatile germanium tetrachloride which can be subsequently sent to N2O-C2H2 flame AAS. The necessary conditions for the volatilization of germanium tetrachloride are investigated in detail and the applicability of the method for the determination of trace amounts of germanium in real samples and standard reference materials are presented. Detection limit of the method, based on 3s, was 0.034 ng mL-1 using a sample of 1 mL. The precision was 0.3 %, expressed as the relative standard deviation for a germanium concentration of 1 ng mL-1. Owing to the high selectivity of the proposed method, no interference effect was observed.

Thesis (Ph. D.)--McMaster University (Canada), 1989. / Source: Dissertation Abstracts International, Volume: 62-13, Section: A, page: 0000.