African Journals Online
Bulletin of The Chemical Society of Ethiopia

Volume 17, Number 2, December 2003
ABSTRACTS

DETERMINATION OF BROMOXYNIL AND IOXYNIL IN THE PRESENCE OF CARBAMATES BY SUPPORTED LIQUID MEMBRANE-LIQUID CHROMATOGRAPHY IN RIVER WATERS

Titus Motswadi Maswabi¹ and Mathew M. Nindi^*

Department of Chemistry, University of Botswana, Private Bag UB 00704, Gaborone, Botswana

¹Now @ Botswana Bureau of Standards, Private Bag BO 48, Gaborone, Botswana

ABSTRACT.Sample pre-treatment and enrichment using the supported liquid membrane (SLM) technique for the determination of phenolic nitrile herbicides in presence of carbamates in river water samples was investigated. The uncharged herbicide molecules from the flowing aqueous solution diffuse through an immobilized water-immiscible organic solvent, supported by a porous polytetrafluoroethylene (PTFE) membrane, and trapped in a stagnant acidic acceptor phase in an ionic form. Using n-undecane as a membrane solvent, the SLM extraction methodology was successfully used for the enrichment and separation of phenolic nitrile herbicides in environmental waters with extraction efficiencies of 60% or better. A RDS (%) of 2.1 and 1.8 was obtained for the extraction of ioxynil and bromoxynil from river water, respectively.

Bull. Chem. Soc. Ethiop. 2003, 17(2), 119-128

DERIVATIVE SPECTROPHOTOMETRIC DETERMINATION OF TRACE LEAD IN ALLOYS AND BIOLOGICAL SAMPLES AFTER SEPARATION AND PRECONCENTRATION WITH THE ION PAIR OF 2-(5-BROMO-2-PYRIDYLAZO)-5-DIETHYLAMINOPHENOL AND AMMONIUM TETRAPHENYLBORATE ON MICROCRYSTALLINE NAPHTHALENE OR BY COLUMN METHOD

Mohammad Ali Taher^*

Department of Chemistry, Shahid Bahonar University of Kerman, Kerman, Iran

ABSTRACT. Lead is quantitatively retained on 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol-ammonium tetraphenylborate with microcrystalline naphthalene or by a column method in the pH range 4.0–6.0 from a large volume of aqueous solutions of various samples. After filtration, the solid mass consisting of the lead complex and naphthalene was dissolved with 5 mL of dimethylformamide and the metal was determined by third derivative spectrophotometry. Lead complex can alternatively be quantitatively adsorbed on ammonium tetraphenylborate-naphthalene adsorbent packed in a column and determined similarly. About 0.2 mg of lead can be concentrated in a column from 300 mL of aqueous sample, where its concentration is as low as 0.7 ng/mL. The interference of a large number of anions and cations has been studied and the optimized conditions developed have been utilized for the trace determination of lead in various samples.

Bull. Chem. Soc. Ethiop. 2003, 17(2), 129-138

CHEMICAL AND STRUCTURAL CHARACTERIZATION OF NATURAL PHOSPHATE OF HAHOTOE (TOGO)

Gado Tchangbeddji^1*, Gnande Djeteli¹, Koffi Ani Kili¹, Jean Michel Savariault² and

Jean Louis Lacout³

¹Laboratoire de Physico-Chimie des Matériaux, Faculté des Sciences Université de Lomé,

BP 1515, Lomé, Togo

²Centre d'Elaboration de Matériaux et d'Etudes Structurales, CNRS, BP 4247, F-31055 Toulouse Cedex 4, France

³CIRIMAT Equipe Physico-Chimie des Phosphates ENSIACET INP TOULOUSE,

118 route de Narbonne 31077 Toulouse Cedex 4, France

ABSTRACT.Chemical and structural characterizations of natural phosphates of Hahotoe (Togo) have been performed. From chemical analysis and FTIR study, it can be concluded that the material is carbonated fluoroapatite with poor substitution of calcium by cadmium and manganese. From these results, the molecular formula proposed is:

Ca_9.925Cd_0.004Mn_0.013[(PO₄)_5.886(CO₃)_0.113]F₂.

Powder X-ray diffraction fitting results confirm that compound belongs to the apatite family crystallising in the hexagonal system, space group P6₃/m. The cell parameters are: a = 9.3547(5) Å; c = 6.8929(4) Å.

Bull. Chem. Soc. Ethiop. 2003, 17(2), 139-146

CERAMIC PROPERTIES OF PUGU KAOLIN CLAYS. PART I: POROSITY AND MODULUS OF RUPTURE

Leonard D. Akwilapo^1* and Kjell Wiik²

¹Department of Chemistry, University of Dar es Salaam, P.O. Box 35061, Dar es Salaam, Tanzania

²Department of Chemistry, Norwegian University of Science and Technology, N-7491, Trondheim, Norway

ABSTRACT. The utilisation of Pugu kaolin clay as a raw material in porcelain has been tested by laboratory scale experiments. Physical characteristics of the clay have shown it to be of satisfactory quality and comparable to commercial clays found elsewhere. The chemical analysis has indicated the presence of high levels of iron oxide (~ 1.43%) which could adversely affect the translucency of whitewares. The “as mined” material could be suitable for ceramics that do not require high brightness specifications, such as stoneware and sanitary ware. The level of this oxide can, however, be reduced by appropriate means to give a relatively cleaner product that could be excellent for other types of whiteware products.

 Porcelain materials prepared using Pugu kaolin clay have shown to have similar properties as those prepared using other standard kaolin clays. The bulk density and flexural strength of the fired masses increase with firing temperature to a maximum at the soak temperature of 1200 ^oC. Beyond this soak temperature the flexural strength decreases. The decrease in strength is attributable to bloating which takes place as gasses are expelled from the matrix. Strictly firing procedures should be enforced in order to obtain a porcelain material of required strength.

Bull. Chem. Soc. Ethiop. 2003, 17(2), 147-154

COORDINATION OF CASSAVA STARCH TO METAL IONSAND THERMOLYSIS OF RESULTING COMPLEXES

Wojciech Ciesielski¹ and Piotr Tomasik^2,*

¹Institute of Chemistry and Environmental Protection, Pedagogical University, 42 201 Częstochowa, Poland

²Department of Chemistry, University of Agriculture, Mickiewicz Avenue, 21, 31 120 Cracow, Poland

ABSTRACT. Cassava starch formed Werner-type complexes with ions of metals from the transition groups. This was proven by conductivity and electron paramagnetic resonance measurements. The coordination of starch to central metal ions influenced the thermal decomposition of starch. As a rule complexes started to decompose at lower temperature than did starch. On the other hand, the decomposition proceeded at a lower rate than the decomposition of non-coordinated starch.