M.S. El-Shahawi

Chemical speciation and recovery of gold(I, III) from wastewater and silver by liquid-liquid extraction with the ion-pair reagent amiloride mono hydrochloride and AAS determination.

A novel and low cost liquid-liquid extraction procedure for the separation of gold(III) at trace level from aqueous medium of pH 5-9 has been developed. The method has been based upon the formation of a yellow colored ternary complex ion associate of tetrachloro gold(III) complex anion, AuCl(4)(-) with the ion-pair reagent 1-(3,5-diamino-6-chloropyrazinecarboxyl) guanidine hydrochloride monohydrate, namely amiloride, DPG(+).Cl(-). The effect of various parameters, e.g. pH, organic solvent, shaking time, etc. on the preconcentration of gold(III) from the aqueous media by the DPG(+).Cl(-) reagent has been investigated. The colored gold species was quantitatively extracted into 4-methyl pentan-2-one. The chemical composition of the ion associate of DPG(+).Cl(-) with AuCl(4)(-) in the organic solvent has been determined by the Jobs method. The molar absorptivity (2.19x10(4)Lmol(-1)cm(-1)) of the associate DPG(+).AuCl(4)(-) at 362nm enabled a convenient application of the developed extraction procedure for the separation and AAS determination of traces of aurate ions. Mono-valence gold ions after oxidation to gold(III) with bromine water in HCl (1.0molL(-1)) media have been also extracted quantitatively from the aqueous media by the developed procedure. The chemical speciation of mono- and/or tri-valence gold species spiked to fresh and industrial wastewater samples has been achieved. The method has been also applied successfully from the separation of gold(I) and gold(III) species from metallic ions and silver. The developed method has also the advantage of freedom from most diverse ions.

Spectral, magnetic, thermal and electrochemical studies on new copper(II) thiosemicarbazone complexes

The chelation behavior of some =N(1) and NH(4) thiosemicarbazones towards copper(II) ions has been investigated. The isolated complexes are characterized by elemental analysis, magnetic moment, electronic, IR, ESR and ms spectra, and by thermal and voltammetric measurements. The substituents on =N(1) and/or NH(4) thiosemicarbazones and the log K values of the ligands play an important role in complex formation. The IR spectra showed that the reagents HAT, HAET, HAPT, HApClPT, H2ST and HBT are deprotonated in the complexes and act as mononegative SN donors; H2SET, H2SpClPT, H2HyMBPT and H2HyMBpClPT, as binegative NSO donors while H2SPT is a mononegative NSO donor. The ESR spectra of the complexes are quite similar and exhibit axially symmetric g-tensor parameters with g ‖ > g ⊥ > 2.0023. The loss of thiol and/or hydroxyl hydrogen was confirmed from potentiometric titrations of the ligands and their copper(II) complexes. The protonation constants of the ligands as well as the stability constants of their Cu(II) complexes were calculated. Thermogravimetric analysis of the complexes suggests different decomposition steps. The Coats–Redfern and Horowitz–Metzger equations have been used to calculate the kinetic and thermodynamic parameters for the different thermal decomposition steps of some complexes. The redox properties, nature of the electroactive species and the stability of the complexes towards oxidation are strongly dependent on the substituents on the precursor NH(4) thiosemicarbazone. The redox data are discussed in terms of the kinetic parameters and the reaction mechanism.

Synthesis, spectroscopic characterization, redox properties and catalytic activity of some ruthenium(II) complexes containing aromatic aldehyde and triphenylphosphine or triphenylarsine.

A series of new mixed ligand penta-coordinated square pyramidal ruthenium(II) complexes containing benzaldehyde or its substituents and triphenylphosphine or triphenylarsine have been synthesized and characterized. In the electronic spectra, three well-defined peaks in the visible region were observed and assigned to d-d transitions in D(4h) and low spin axially distortion from O(h) symmetry. The spectrochemical parameters of the complexes were calculated and placed the ligands in the middle of the spectrochemical series. The redox properties and stability of the complexes toward oxidation were related to the electron-withdrawing or releasing ability of the substituent in the phenyl ring of the benzaldehyde. The electron-withdrawing substituents stabilized Ru(2+) complexes, while electron-donating groups favored oxidation to Ru(3+). The mechanism and kinetics of the catalytic oxidation of benzyl alcohol by the complex [RuCl(2)(Pph(3))(C(6)H(5)CHO)(2)] in the presence of N-methylmorpholine-N-oxide have also been studied.

Post-Gulf-War assessment of nutrients, heavy metal ions, hydrocarbons, and bacterial pollution levels in the United Arab Emirates coastal waters

A post-Gulf War coastal sea water pollution assessment program was carried out through monitoring the concentrations of major nutrients, heavy metal ions, selected hydrocarbons, and selected bacterial communities counts at different sites along the coasts of the United Arab Emirates on the Arabian Gulf. Abu-Dhabi and Dubai coastal waters had occasional high nutrient levels with some fluctuations and wide spatial and temporal variations, suggesting the presence of anthropogenic sources of pollution creating these conditions near the sampling sites. Sharjah and Ajman Creeks had lower nutrient levels. Bacterial counts had distinct patterns peaking in spring and autumn, and diminishing during summer and winter. Total and faecal coliform counts fluctuated depending on the presence of nearby recreation and commercial areas, and were at no time consistently high. Bacillus, Pseudomonas, Staphylococcus, Micrococcus, and Alteromonas were the predominant bacterial genera in these waters. Slightly higher hydrocarbon concentrations were detected both in surface waters and sediments, most likely a result of the deliberate release of crude oil into the Gulf waters during the Gulf War.

Spectrophotometric determination of periodate or iodate ions by liquid-liquid extraction as an ion-pair using tetramethylammonium iodide

A simple and accurate extractive Spectrophotometric procedure was developed for the microdetermination of periodate and iodate in aqueous media. The determination of periodate was based upon the extraction of the ion-pair formed between the periodate and tetramethylammonium iodide at pH 4 in chloroform followed by direct Spectrophotometric measurements at 509, 358 and 288 nm. The optimum concentration range evaluated by Ringboms plot, the molar absorptivity, the Sandells sensitivity and the stoichiometry of the formed ion-pair were critically determined. Iodate could be determined quantitively by the proposed procedure after oxidation to periodate with potassium persulphate. The effect of the diverse ions on the determination of the periodate and/or iodate by the proposed procedures was also investigated. The application of the method for the analysis of iodate or periodate in the artificial fresh water was successfully carried out.

Ruthenium(II) 2-hydroxybenzophenone N(4)-substituted thiosemicarbazone complexes

New ruthenium(II) complexes with 2-hydroxybenzophenone N(4)-substituted (Me, Ph and/or piperidyl) thiosemicarbazones have been prepared and characterised by elemental analysis, molar conductivity, thermal analysis, spectroscopy (i.r., 1H-n.m.r. and u.v.–vis.) and by cyclic voltammetry. The thiosemicarbazones coordinate to ruthenium(II) as mononegative tridentate ligands via the deprotonated hydroxyl group, N1 nitrogen and thione sulphur centres. The redox properties, nature of the electrode processes and the stability of the complexes towards oxidation in CH2Cl2 are discussed. The change in the E1/2 values of the complexes can be related to the basicity of the N(4)-substituents. All the complexes display an irreversible one-electron charge-transfer couple in the potential range studied.

Preconcentration and separation of acaricides by polyether based polyurethane foam

This paper reports the preconcentration of some dissolved organic phosphorous and chlorinated acaricides in water by porous polyether based polyurethane foam. Preliminary screening tests on the retention of the tested compounds, i.e., dicofol and bromopropylate, by polyether foams indicated that a very high percent removal of the tested species was obtained. The retention rate was found fast and reaches equilibrium in a few minutes. The various parameters, e.g., pH, extraction media, shaking time, salt effect, temperature and sample volumes affecting the preconcentration of the tested species by the unloaded foam, trioctylamine and trimethylphosphate treated foam have been optimized via batch modes of separation. The unloaded foams were employed in column modes for the retention and recovery of the tested species. The sorption efficiency and recovery of the compounds by the unloaded foams column were found to be up to 97.5%. The height equivalent to a theoretical plate (HETP) obtained by the unloaded foam was found to be in the range 1.1-1.3 ± 0.2 mm. The sorption mechanism of the tested compounds by the foams was discussed.

Synthesis and spectroscopic characterization of cobalt(II) thiosemicarbazone complexes

Thiosemicarbazone derivatives are formed on reaction between acetophenone, salicylaldehyde, benzophenone and/or 2-hydroxy-4-methoxybenzophenone and thiosemicarbazide or its N4H substituents (ethyl-, phenyl-, and p-chlorophenyl-). The ligands were investigated by elemental analysis and spectral (IR, 1H NMR and MS) studies. The formulas of the prepared complexes have been suggested by elemental analyses and confirmed by mass spectra. The coordination sites of each ligand were elucidated using IR spectra revealing bidentate and tridentate coordination. Different geometries for the complexes were proposed on the basis of electronic spectra and magnetic measurements. The complexes have been analyzed thermally (TG and DTG) and the kinetic parameters for some of their degradation steps were calculated.

Sensitive detection and semiquantitative determination of mercury(II) and lead(II) in aqueous media using polyurethane foam immobilized 1,5-di-(2-fluorophenyl)-3-mercaptoformazan.

1,5-Di-(2-fluorophenyl)-3-mercaptoformazan (F(2)H(2)Dz) immobilized and plasticized with tri-n-butylphosphate (TBP) polyurethane foam (PUF) were found suitable for the detection of mercury(II) and lead(II) in extremely dilute aqueous solutions. In batch mode of extraction with immobilized F(2)H(2)Dz-foam as low as 0.05 and 0.15 mug ml(-1) of mercury(II) and lead(II), respectively were detected and the colored chelates were found more stable over 72 h. Lower concentrations of these metal ions (</=1 ppb) were detected by plasticized F(2)H(2)Dz-TBP foam packed in column extraction mode. Semiquantitative determination of these metals was also possible using a suitable standard color scale. The effect of diverse ions on the detection of 1 mug mercury(II) and lead(II) by the proposed F(2)H(2)Dz-foam test was critically investigated. The method was satisfactorily applied for the detection of mercury(II) or lead(II) in natural water samples.

Iodometric determination of gold and platinum by 168- and 126-fold chemical amplification reactions

Abstract A simple, low cost method is described for the determination of gold(I) and platinum(II) at the μg level with 8- and 6-fold amplification, respectively. The method is based on oxidation in a solution (pH 2.4–4.3) of gold(I) or platinum(II) with aqueous potassium periodate, masking the unreacted periodate with molybdate and iodometric determination of the produced iodate and gold(III) or platinum(IV). The sensitivity of the proposed method can be enhanced by separation of the liberated iodine on a polyurethane foam column, and oxidizing the collected iodine with an excess of periodate. The iodate produced in the effluent and washing solution is then titrated iodometrically after masking the excess periodate. This procedure offers a 168- and 126-fold amplification for gold(I) and platinum(II), respectively. Analysis of the binary mixtures of gold(I) and (III) or platinum(II) and (IV) in aqueous solution has been carried out successfully.