Scielo RSS <![CDATA[South African Journal of Chemistry]]> http://www.scielo.org.za/rss.php?pid=0379-435020160001&lang=es vol. 69 num. lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za <![CDATA[<b>Partial oxidation of <em>n</em>-pentane over vanadium phosphorus oxide supported on hydroxyapatites</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100001&lng=es&nrm=iso&tlng=es The selective oxidation of M-pentane to value-added products, maleic anhydride or phthallic anhydride by vanadium phosphorus oxide loaded on hydroxyapatites as catalysts and oxygen as oxidant was investigated. Hydroxyapatite (HAp) and cobalt-hydroxyapatite (Co-HAp) were prepared by the co-precipitation method and VPO with varying weight percentages (2.5-15.0 %) were loaded on the hydroxyapatite supports by the wet impregnation technique. The catalyst materials were characterized by surface area measurements, elemental analysis, powder X-ray diffraction (XRD), infrared spectroscopy (IR) and temperature-programmed reduction (TPR). VPO is present in two phases, viz.( VO)2P2O7 and VOPO4. With increase in the VPO loading on the hydroxyapatites, the (VO)2P2O7 phase also increased. From catalytic results, a conversion of 75 % of n-pentane and selectivity towards maleic anhydride, about 50 % and phthalic anhydride, about 25 %, were consistently achieved with loadings of 5.0 and 7.5 wt. % VPO at 360 °C for GHSVs of 1900 and 2300 h-1. Under optimum conditions, product yields of up to 40 % maleic anhydride and 20 % phthalic anhydride were obtained. It is proposed that the products formed through the diene intermediate. <![CDATA[<b>A preliminary investigation into the stability of inorganic arsenic species in laboratory solutions simulating sediment pore water</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100002&lng=es&nrm=iso&tlng=es A simple method to preserve arsenic species in simulated pore water was investigated. Synthetic pore water containing high levels of Fe, Mn and S (as sulfide, S2-) were synthesized and spiked with different arsenic species. Arsenite [As(III)], arsenate [As(V)], dimethylarsinate [(CH3)2AsO2-, DMA], monomethylarsonate [(CH3)AsO3²", MMA], monothioarsenate(V) species (AsO3S3-, MTA) and tetrathioarsenate(v) species (AsS4(3-), TTA) in different combinations were used. Disodium ethylenediamine tetraacetate (EDTA) and temperature was used to preserve speciation. Solutions were analyzed at intervals of one day, week, month and 2 months after preparation. Samples were analyzed by HPLC-ICP-MS using an ion exchange column and ammonium carbonate buffer. Samples containing Fe and Mn spiked with As(III), As(V), DMA, MMA showed adequate species preservation for two months when EDTA was added. The total As in samples containing Fe, Mn and S2- was preserved over 60 days however, speciation was not preserved. Samples spiked with synthesized mono- and feira-thioarsenate(V) species showed immediate degradation of the mono- and tetra-thioarsenic species into unidentified As-S species. The results show that while EDTA may be adequate to preserve As species containing high Fe and Mn concentrations, the combination of EDTA and temperature was not successful in preserving As speciation in samples containing sulfides. <![CDATA[<b>The synthesis of carbon nanomaterials using chlorinated hydrocarbons over a Fe-Co/CaCO<sub>3</sub> catalyst</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100003&lng=es&nrm=iso&tlng=es The effect of chlorine on the morphology of carbon nanotubes (CNTs) prepared from a Fe-Co/CaCO3 catalyst was investigated using chlorobenzene (CB), dichlorobenzene (DCB), trichlorobenzene (TCB), dichloroethane (DCE), trichloroethane (TCE) and tetrachloroethane (TTCE) as chlorine sources using a catalytic chemical vapour deposition (CCVD) method. Toluene was used as a chlorine-free carbon source for comparison. Multi-walled carbon nanotubes (MWCNTs) were successfully synthesized. The physicochemical properties of the CNTs were studied using transmission electron microscopy (TEM), Raman spectroscopy, thermal gravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (PXRD) spectroscopy, and X-ray photoelectron spectroscopy (XPS) techniques. The inner and outer diameters of the MWCNTs increased with an increase in the number of chlorine atoms contained in the reactant. Chlorine incorporation into the MWCNTs was observed by EDS analysis for all reactants. Formation of'bamboo-like' structures for the MWCNTs generated from TCE and TTCE was also observed, facilitated by the presence of the high percentage of chlorine in these reactants. Numerous MWCNTs revealed the presence of small carbon nanostructures that grew on top of the dominant CNTs, suggesting an unexpected secondary carbon growth mechanism. <![CDATA[<b>Oxyhalogen-sulfur chemistry: Kinetics and mechanism of oxidation of n-acetylthiourea by aqueous bromate and acidified bromate</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100004&lng=es&nrm=iso&tlng=es The oxidation of N-acetylthiourea (ACTU) by acidic bromate has been studied by observing formation of bromine in excess bromate conditions. The reaction displays an induction period before formation of bromine. The stoichiometry of the reaction was determined to be 4:3:4BrO3- + 3(CH3CO)NH(NH2)C=S + 3H2O ―> 4Br- + 3(CH3CO)NH(NH2)C=O + 3SO4(2-) + 6H+ (A) witha complete desulfurization of ACTU to its urea analogue. In excess bromate conditions the stoichiometry was 8:5: 8BrO3- + 5(CH3CO)NH(NH2)C=S + H2O ―> 4Br2 + 5(CH3CO)NH(NH2)C=O + 5SO4(2-) + 2H+ (B). Bromine is derived from an extraneous reaction in which bromide from stoichiometry (A) reacts with excess acidic bromate. The oxidation of ACTU by aqueous bromine gave stoichiometry (C):4Br2(aq) + (CH3CO)NH(NH2)C=S + 5H2O ―> 8Br- + (CH3CO)NH(NH2)C=O + SO4(2-) + 10H+. Reaction (C) is much faster than reactions (A) and (B), with a lower limit bimolecular rate constant of 2.1 X10(5) M-1 s-1 such that appearance of bromine signals complete consumption of ACTU. We were unable to trap any intermediate sulfur oxo-acids of ACTU on its oxidation pathway to N-acetylurea. As opposed to other substituted thioureas, none of its intermediates were stable enough to be isolated and detected. <![CDATA[<b>Lack of Co-crystal Formation with Cyclotriphosphazenes: A Cautionary Tale</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100005&lng=es&nrm=iso&tlng=es The attempted formation of co-crystals with a series of cyclotriphosphazene derivatives has been investigated. Despite numerous attempts, only one co-crystal was obtained. The crystal structure of this material, [hexakis(4-pyridyloxy)-cyclotriphos-phazene][terephthalic acid]2y is presented here. The crystal structures of 2,2-bis(4-formylphenoxy)-4,4,6,6-bis[spiro(2',2"-dioxy-1',1"-biphenylyl]cyclo-triphosphazene and hexakis(4-cyanophenoxy)cyclotriphosphazene are also reported for the first time. The extremely low rate of co-crystal occurrence in these materials cannot be explained, despite the consideration of several possibilities. This serves as a cautionary tale - co-crystal formation is not necessarily straightforward. <![CDATA[<b><i>In vitro </i></b><b>investigation of the antimicrobial activity of a series of lipophilic phenols and naphthols</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100006&lng=es&nrm=iso&tlng=es Five groups of phenols/naphthols (42 compounds in total) were synthesized and screened against Gram-positive Staphylococcus aureus and Bacillus subtilis, Gram-negative Escherichia coli and Klebsiella pneumoniae, and the fungus Candida albicans. Whereas compounds were found inactive against Gram-negative bacteria, potent activities against Gram-positive bacteria were observed. The activities correlate with the ability of molecules to form quinone methides, suggesting potential new modes of action. <![CDATA[<b>Synthesis, physical and antimicrobial studies of ferrocenyl-<i>N</i>-(pyridinylmethylene)anilines and ferrocenyl-<i>N</i>-(pyridinylmethyl)anilines</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100007&lng=es&nrm=iso&tlng=es Ferrocenyl-N-(pyridinylmethylene)anilines Schiff bases were synthesized by reaction of 3- or 4-ferrocenylaniline with either 2-, 3-, or 4-pyridinecarboxaldehyde under solvent-free conditions via mechanochemistry technique. Products were obtained in excellent yields within 10 min of grinding. The reactions afforded a melt or gummy semi-solid that solidified to the desired Schiff bases within a short time. These Schiff bases were reduced to their corresponding amines, ferrocenyl-N-(pyridinylmethyl)ani-lines, with NaBH4 over neutral Al2O3 solid support via grinding. Amines were obtained in excellent yields after intermittent grinding for approximately 1 h. Herein, five novel ferrocenyl-N-(pyridinylmethylene)anilines (compounds 3, 4, 6-8) and six ferrocenyl-N-(pyridinylmethyl)anilines (compounds 9-14) are reported. Compounds were characterized through FT-IR, ¹H-NMR, 13C-NMR, HRMS and SC-XRD techniques. These compounds show visible solvatochromism, when UV-Vis absorption was measured in polar and nonpolar solvents. In changing solvent from polar to non-polar, the Schiff bases exhibited a blue shift while the amines portrayed a red shift. Electrochemical studies on these compounds reveal that redox behaviour of the iron centre is influenced by the position imine or amine groups. Antimicrobial properties of these compounds were studied for Escherichia coli, Staphylococcus aureus, Salmonella typhimirium and Candida albicans. Highest activity was recorded against Gram-positive bacteria and fungi. <![CDATA[<b>Speciation of chromium and vanadium in medicinal plants</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100008&lng=es&nrm=iso&tlng=es In this study, Cr(VI) and V(V) were determined in medicinal plants collected from the farm located between two smelters. Chromium(VI) and vanadium(V) were leached from medicinal plants with 0.1 M Na2CO3 prior their determination by ETAAS. The concentration of Cr(VI) in medicinal plants varied between 3.1 ± 0.5 g-1 and 9.4 ± 0.2 μg g-1 and that of V(V) ranged from 1.1 ± 0.08μgg-1 to 17 ± 1.7μ.gg-1. It was established that element species taken up by plants do not depend on metal content in soil but is a function of plant properties. Results of the determination of water-soluble (hot water) Cr(VI) and V(V) concentrations showed that consumption of three cups of tea prepared from medicinal plants from Zizameleni farm is safe since recommended maximum limits is not exceeded through normal consumption of tea infusion. <![CDATA[<b>Organocatalyzed Mannich reactions on minocycline: Towards novel tetracycline antibiotics</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100009&lng=es&nrm=iso&tlng=es Herein, we report the development of a mild synthetic route towards novel minocycline derivatives using the proline-catalyzed three-component Mannich reaction. The reaction conditions were optimized and was then screened for its tolerance to the other popular organocatalysts as well as variation of the ketone and aldehyde substrates. The Mannich adducts were evaluated for their in vitro antibacterial efficacies against Gram-negative and Gram-positive bacteria. <![CDATA[<b>Anodized Edge-plane pyrolytic graphite for electroanalysis of pantoprazole in tablet dosage forms and human urine samples</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100010&lng=es&nrm=iso&tlng=es Electroanalytical parameters of different graphitic carbon-based electrode materials were compared to select the best one for the pantoprazole electroanalysis. Such parameters include sensitivity, repeatability, residual background current, and signal-to-background current ratio of the analytical response and such electrodes include conventional carbon-based electrodes such as glassy carbon (GC), carbon paste, edge-plane pyrolytic graphite (EPPG), and basal-plane pyrolytic graphite electrodes and film-coated modified GC electrodes with graphitic carbon-based materials such as carbon nanotube, nanographene, carbon black and graphite powder. The EPPG electrode, after applying a simple electrochemical anodization, showed more acceptable analytical performances compared with the other electrodes. Raman spectroscopy was employed to study the surface structural changes that occurred dring the anodic activation. Calibration plot with a good linearity was obtained in the concentration range of 0.2-25 and 0.02-8.5 μΜ, and the detection limit was estimated to be 0.055 and 0.0041 μΜ using cyclic voltammetry and differential pulse voltammetry techniques, respectively. Finally, the electrochemically activated EPPG electrode was used successfully for the determination of pantoprazole in tablet dosage forms and human urine samples with satisfactory results. <![CDATA[<b>Application of quaternized activated carbon derived from <i>Macadamia </i>nutshells for the removal of hexavalent chromium from aqueous solutions</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100011&lng=es&nrm=iso&tlng=es In this paper, the feasibility of quaternized activated carbon derived from Macadamia nutshells was explored in the removal of hexavalent chromium (Cr(VI)) from aqueous solutions. The amino-modified activated carbon was achieved by cross-linking native Macadamia activated carbon (MAC) with epichlorohydrin and grafting diethylenetriamine and triethylamine (EDT) on the surface and the product was labelled as MAC-EDT. The adsorbent was characterized by Fourier transform infrared spectros-copy (FTIR), Bruemer-Emmett-Teller (BET), scanning electron microscope (SEM) and the CHNS analyzer. The optimum parameters for Cr(VI) removal found were pH (5), contact time (120 min) and sorbent mass (0.10 g) where removal efficiencies were &gt;90 % in all cases. Langmuir model fitted the data best and the adsorption capacity was 145.5 mg g-1 after surface modification with EDT. The Cr(VI) ion was found to be adsorbed more as compared to other anions, and the sorption order was: SO4(2-) <PO4(3-) ≈ NO3- < Cr2O7². The removal mechanism involved adsorption of Cr(VI) and/or subsequent reduction of Cr(VI) to Cr(III). <![CDATA[<b>QuEChERS method development for bio-monitoring of low molecular weight polycyclic aromatic hydrocarbons in South African carp fish using hplc-fluorescence: An initial assessment</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100012&lng=es&nrm=iso&tlng=es Matrix components in the analysis of polycyclic aromatic hydrocarbons (PAHs) in fish require analytical methods with high selectivity and sensitivity. A quick, easy, cheap, effective, rugged and safe (QuEChERS) sample treatment method was optimized and applied, using HPLC-fluorescence for quantification of five low molecular weight PAHs: naphthalene (Nap), acenaphthene (Ace), phenathrene (Phe), fluoranthene (Flu) and pyrene (Pyr) in muscle of carp fish. Important in this study was the testing of different sorbents for clean-up in QuEChERS and comparison with Soxhlet extraction. Polymers and magnetite modified with γ-methacryloxypropyltrimethoxysilane (γ-MPS) were equally as selective towards PAHs as primary secondary amine (PSA) and multiwalled carbon nanotubes were the least selective. The concentration of PAHs in carp fish from Hartebeespoort Dam using QuEChERS extraction method was comparable to Soxhlet extraction and ranged from 0.8-739 μg kg-1. In this study, the minimum concentration of PAHs in carp fish was 0.8 μg kg-1 for fluoranthene and the maximum was 739 μg kg-1 for Ace using QuEChERS method. The study revealed that polymers and magnetite modified with γ-MPS could be used as alternative clean-up sorbent in QuEChERs and that the concentration of PAHs in carp fish in the dam are a source of concern. <![CDATA[<b>Towards a mechanistic understanding of rheological behaviour of water-in-oil emulsion: Roles of nanoparticles, water volume fraction and aging time</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100013&lng=es&nrm=iso&tlng=es The viscosity of water-oil emulsions plays an important role in oil production and transportation. The objective of this study was to improve the basic understanding of the influence of nanoparticles on the viscosity of water-in-oil emulsions. Using crude oil and different industrial nanomaterials, the droplet size distribution, droplet mean size, and rheological models of emulsions were investigated. Experimental results show that the addition of nanoparticles increases the crude oil viscosity; however, the Newtonian flow behaviour of oil is not affected by nanoparticles. It is observed that the viscosity of crude oil increased from 36.5 to 49 cP when the nanoparticle concentration was elevated from 0 to 0.1 wt%. From the results of rheological experiments, it can be concluded that the influence of nanoparticles on the emulsion viscosity is mainly affected by the type and amount of nanoparticles, water/oil-ratio and aging time. Mean droplet diameter decreased from 5.68 to 4.11 micrometre when 0.1 wt% nanoparticles were added to emulsion. The results also suggest that the properties of stabilized water-in-oil emulsions are significantly time-dependent, and the droplet size and viscosity of emulsions is reduced by time. Most of previously published correlations have huge errors and could not precisely predict the apparent viscosities of non-solid stabilized and solid-stabilized emulsions. None of the previously utilized equations did ever consider the effect of added solids to the emulsion. <![CDATA[<b>Graphene oxide/zinc oxide nanocomposite: A superior adsorbent for removal of methylene blue - statistical analysis by response surface methodology (RSM)</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100014&lng=es&nrm=iso&tlng=es Graphene oxide (GO) was synthesized from natural graphite using the Hummers method. Graphene oxide/zinc oxide nano composite were synthesized by mixing of GO and ZnO solutions and then freeze drying. The adsorptive performance of the nano composite was investigated in the removal of methylene blue. The statistical study of the adsorption process was carried out by response surface methodology (RSM). Experimental variables such as sample pH, adsorption time, dye concentration and adsorbent dosage were considered for the optimization process. The process was optimized by response surface methodology (RSM) through Box-Benhken method. The optimum conditions, predicted by the RSM were obtained at pH, contact time, initial dye concentration and adsorbent dosage of 6,8.5 min, 5 ppm, 0.02 g, respectively. The removal of methylene blue under optimum conditions was predicted to be 98.17 % and resulted in 97 % in practice. The Pareto analysis suggested that order of relative importance of the factors were as follows: adsorbent dosage > dye concentration > adsorption time > pH. Under optimized conditions, GO/ZnO nano composite showed a higher capacity than GO, carbon nanotube (CNT), ZnO and ZnO/CNT for adsorption of methylene blue. The study revealed that GO/ZnO could be a promising adsorbent for removal of industrial dyes from wastewaters. <![CDATA[<b>Determination of mercury in selected polluted sediments using HPLC-ICP-MS in Westbank area, Western Cape, South Africa</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100015&lng=es&nrm=iso&tlng=es High selectivity, excellent linearity and reproducibility were achieved using HPLC-ICP-MS method for mercury in sediments. The HPLC-ICP-MS method reported previously for mercury in biota analysis was adapted in terms of operational consumables and optimized for the efficient mercury determination in riverbed sediments; a first for South Africa. Results obtained for real environmental samples, were verified by Direct Mercury Analysis (DMA) by an accredited laboratory. The determination of inorganic and organic mercury compounds in sediments was based on the complexation of mercury compounds with cysteine. The separation was achieved on a reversed-phase C18 column (15 cm x 4.6 mm id) using aqueous 0.1 % w/v L-cysteine-HCl + 0.1 % w/v L-cysteine mobile phase at a flow rate of 0.8 mL min-1 at ambient temperature. The method was found to be suitable for the routine analysis of Hg compounds in sediments as well as aqueous media and was developed to determine the influence of humic substances on the bioavailability of mercury species. The results were comparable and consistent with those determined with a Direct Mercury Analyzer. The detection limit for methylmercury, ethylmercury and inorganic mercury were lower than 10 ng L-1 and recoveries for spiked samples was >90 % . The accuracy of the method was assessed by the analysis of certified reference material (European Reference Material ERMCC580 and Tort-2) and found to be in good agreement. Mercury concentration was determined in sediments collected from the Eerste Kuils River, Westbank area, Kuilsriver, Western Cape, South Africa. Mercury concentration was determined to vary from 2-14 ng g-1 (w.wt). <![CDATA[<b>Determination of metformin at metal-organic framework (Cu-BTC) nanocrystals/multi-walled carbon nanotubes modified glassy carbon electrode</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100016&lng=es&nrm=iso&tlng=es Glassy carbon (GC) electrode modified with Cu-based metal-organic frameworks (Cu-BTC, BTC = 2,3,5-benzenetricarboxylate) and multi-walled carbon nanotubes (CNTs) composites was developed. The Cu-BTCs were synthesized by two methods, traditional hydrothermal and ultrasonic irradiation methods. It was found that the Cu-BTC that was synthesized by the latter method, with mean crystallite sizes in the nanometers range, showed a higher impact on enhancing the electrocatalytic activity of the modified electrode toward the electro-oxidation of metformin compared to that synthesized with the former method with a larger crystallite size of micrometer-scale. The morphological characteristics of Cu-BTCs and Cu-BTC nanocrystals/CNTs modified GC electrode surface were characterized by scanning electron microscopy. The modified electrode showed excellent response of oxidation current for the determination of metformin. Under optimum conditions, the peak current showed good linearity with concentrations in the range of 0.5 μΜ to 25 μΜ and a detection limit of 0.12 μΜ, as well as good repeatability. The Cu-BTC nanocrystals/CNTs modified GC electrode was applied successfully to determine metformin in pharmaceutical samples with good accuracy. <![CDATA[<b>Characterization and speciation modelling of cyanide in effluent from an active slimes dam</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100017&lng=es&nrm=iso&tlng=es The utilization of cyanide in the process of gold extraction is an environmental concern as this pollutant is discharged with the tailings. The distribution and fate of cyanide in the environment upon release from the tailings dumps depends on its physical-chemical speciation. The present study was conducted to assess the presence of cyanide species in drainage water from an active slimes dam that receives effluent from a gold reprocessing plant in the Central Rand goldfield (south of Johannesburg, South Africa). Water samples were collected from decant pipes draining water from the top of the slimes dam as well as from a solution trench constructed around the dam. Efflorescent salt crusts and algae were also sampled along the solution trench to assess the extent of cyanide contamination and its promulgation from the slimes. Water samples presented varying chemistry with samples collected from the pipes recording low pH (between 2 and 4) with concentrations of weak acid dissociable cyanide (CN WAD) varying between 5.635 mg L-1 and 8.525 mg L-1. Water samples from the trench were less acidic (pH ranged between 5 and 7) with an average concentration of CN WAD of 21.72 mg L-1. These values are far greater than the limit of 0.50 mg L-1 set by the authorities through the 'Best Practice guidelines' for any effluent exiting a metallurgical treatment facility. Copper and iron cyanide complexes were the most abundant cyanide complexes in the water samples. The pH and conductivity of the solution prepared by the dissolution of the salt crusts (10 g in 50 mL of deionized water) were 3.44 and 1.611 mScm-1, respectively. High concentrations (198.4 mg kg-1)ofCN T were obtained in the crusts and these were predominantly strong acid dissociable cyanides (CN SAD)of Fe and Co. The presence of iron cyanides was evident from the bluish-green crusts (Prussian blue) observed around the site, indicating the extent of cyanide contamination. A very low pH (2.39) was recorded for the algae, with elevated concentrations of SCN- and OCN- that are byproducts of chemical conversion of cyanide. The Visual MINTEQ geochemical modelling code was used to complement the analytical methods in characterizing the speciation of cyanide. The simulations predicted the presence of the following metal-cyanide complexes in water samples as well as in the solid materials: Fe(CN)6(3-), Fe(CN)6(aq), NaFe(CN)6(2-), KFe(CN)6(2-), Ni(CN)4(2-), Zn(CN)4(2-), CaFe(CN)6-, NiH(CN)4- and NiH3(CN)4+. This study revealed that cyanide remains persistent in its immediate environment following its release from slimes dams, an issue of concern as some residential areas have developed in the proximity of such facilities. The major highlight of this work has been the comprehensive characterization of cyanide speciation by using geochemical modelling to complement analytical techniques. This is important in understanding the potential risk posed by this pollutant. <![CDATA[<b>Subsequent separation and selective extraction of thorium (IV), iron (III), zirconium (IV) and cerium (III) from aqueous sulfate medium</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100018&lng=es&nrm=iso&tlng=es <![CDATA[<b>Regression analysis in analytical chemistry. Determination and validation of linear and quadratic regression dependencies</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100019&lng=es&nrm=iso&tlng=es The theory and practice of the extended statistical evaluation for linear and quadratic regression models used for calibration were presented. Two complete examples, solved step by step were presented as a short guide. The validation of regression dependences was based on classic F-Snedecor, Lack of Fit, F IUPAC and Mandel tests. <![CDATA[<b>Development and validation of an ecofriendly HPLC-UV method for determination of capecitabine in human plasma: Application to pharmacokinetic studies</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100020&lng=es&nrm=iso&tlng=es A simple, rapid, cost-effective and green high-performance liquid chromatographic assay for determination of capecitabine in human plasma using a C18 reversed-phase analytical column was developed and validated. The separation was conducted by means of a mobile phase composed of formic acid solution (pH = 3): ethanol (55:45) running at a flow-rate of 1.0 mL min-1 with UV detection at 310 nm. The column temperature was set at 50 °C. Sample preparation involved protein precipitation by zinc sulfate-ethanol solution. This method is consistent with a high recovery of capecitabine in human plasma ranging from 95.98 to102.50 %.The calibration curves were linear over concentration range of 0.05-10.00 mL-1(r²> 0.9999). Between- and within-day variability was less than 15 % and the bias was within ±15 %. This validated method was successfully applied to a pharmacokinetic study enrolling seven Iranian cancer patients after administration of a morning oral dose of 1500 mg. <![CDATA[<b>A review of using spray pyrolysis through sol-gel materials in the synthesis of cathode materials for lithium-ion batteries</b>]]> http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502016000100021&lng=es&nrm=iso&tlng=es Over the years, new synthesis routes of the cathode electrochemical active material for lithium-ion batteries have improved remarkably to optimize their capacity and cycle life performance. This review study focused on the use of some techniques to synthesize the common cathode materials (LiCoO2, LiMn2O4, LiFePO4). The most common and simplest synthesis method was the mixing of powders in their solid-state form and heating them at relatively high temperatures over long periods. Other methods included the formation of sol-gel products that could be either heat-treated more or could be used directly by means of a spray pyrolysis method producing the desired active material. The spray pyrolysis method showed that suitable cathode oxide materials formed in shorter periods, resulting in small homogenous particles with narrow particle size distribution. The spray pyrolysis method allowed for making doped or coated cathode materials easily of the various base forms LiCoO2, LiMn2O4 and LiFePO4, with doping elements such as Zr, Mn, Ni, Co, B or Mg. Coating of the particles could also be done with materials such as glassy lithium boride oxide, TiO2 or carbon. These additives to the cathode material improved the active material's physical morphology and electrochemical properties.