Mª Teresa Sevilla

Spectroscopic and electrochemical properties of nickel(II), iron(III) and cobalt(II) complexes with benzilbisthiosemicarbazone — importance of working conditions and the metal salt used in the final complex

Abstract Reactions of benzilbisthiosemicarbazone (LH6) with nickel, cobalt and iron chloride and nitrate give different complexes depending on the salts used and the working conditions. Reactions from nickel chloride give three complexes, 1, 2 and 3 when the solvent or the pH is modified. Complex 1 is obtained in ethanol under reflux, and in methanol, independently of temperature and also with basic medium. Complex 2 is formed by working in ethanol at room temperature. The ligand acts as a dianion in both complexes. In the presence of hydrochloric acid, the new isolated complex 3 presents the neutral form of the ligand. Reaction from nitrate yields only complex 1. Reactions with iron chloride give two new complexes with different formulae and grade of deprotonation in the ligand. For complex 4, obtained at room temperature, LH6 acts as an anion with a ligand–iron ratio of 2:1 and in its neutral form with a 1:1 ratio in complex 5, working under reflux. Reactions with iron nitrate yield complex 6, with the ligand in an intermediate situation, as anion but a nitrate remains. Complexes 7 and 8, with a 1:1 cobalt–ligand molar ratio are isolated from reactions with cobalt nitrate; both contain nitrate and ethanol or water to complete the co-ordination sphere. Attempts to get a macrocyclic thiosemicarbazone from reaction of benzil and LH6 in the presence of nickel or iron salt gave the complexes obtained, in absence of the dicarbonyl molecule. Electrochemical behaviour of complexes studied by cyclic voltammetry show metal-centred reduction processes for all of them. The reduction/oxidation potential values depend on the structures of complexes. Nickel complexes exhibit waves corresponding to Ni(III)–Ni(II) process. Electrochemical response of iron complexes depends on the presence of chloride ions.

Simultaneous and direct determination of iron and nickel in biological solid samples by high-resolution continuum source graphite furnace atomic absorption spectrometry

The simultaneous and direct determination of nickel and iron in plants and lichens has been investigated using high-resolution continuum source graphite furnace atomic absorption spectrometry. The primary resonance line for nickel at 232.003 nm and the adjacent secondary line for iron at 232.036 nm have been used for this purpose. The optimization of the experimental conditions was performed using a pine needles certified reference material (SRM 1575a). The influence of pyrolysis and atomization temperatures, the amount of solid sample introduced into the graphite furnace and the use of aqueous or solid standard for calibration were studied. The spectral interferences caused by absorption of the concomitants of the solid sample were detected and corrected using a least square algorithm. Aliquots of 0.1-1mg of the solid samples were weighed onto the solid sampling platforms and analyzed directly, without addition of any reagents. The limits of detection were 25 µg kg(-1) for nickel and 0.40 mg kg(-1) for iron and the precision, expressed as the relative standard deviation, ranged from 7% to 12%. The proposed method was used to determine both metals in different bioindicator samples with successful results.

Thiohydrazone copper(II) complexes. The relationship between redox properties and superoxide dismutase mimetic activity

The redox behaviour of copper(II) complexes with the open chain ligand, benzilbisthiosemicarbazone, and the macrocyclic one [3,4,10,11-tetraphenyl-1,2,5,8,9,12,13-octaazacyclotetradeca-7,14- dithione- 2,4,9,11-tetraene] has been explored by cyclic voltammetry. The half-wave potential values for the copper(II)/copper(I) redox couple and the spectral data obtained on dimethylsulfoxide (DMSO) solution agree with the superoxide dismutase (SOD)-mimetic activity of the complexes. The macrocyclic complexes show more positive reduction potential and more activity than the open chain derivatives. From our results it follows that the structure and conformation of ligand has influence on the redox potential of central atom in coordination compound. The changes in the coordination sphere are connected with the change of biological function of compounds represented by SOD-mimic activity. In addition, the L1H6 derivatives show quasireversible waves associated to Cu(II)/Cu(III) process.

Electrochemical sensor based on polystyrene sulfonate–carbon nanopowders composite for Cu (II) determination

A differential pulse anodic stripping voltammetric (DPASV) method, with an open circuit (OC) approach in the pre-concentration step has been developed for copper ion determination at very low concentration level using a sensor based on a polystyrene sulfonate-carbon nanopowders (PSS-CnP) composite. This composite material is easily prepared from ultrasonic assisted dispersions of CnP in aqueous solution of PSS. For preparation of sensor devices, a reproducible and inexpensive drop coating procedure of the surface of home-made pencil graphite electrodes (PGEs) using a CnP dispersion in PSS was performed. At the optimal conditions for accumulation (0.01molL(-1) KNO3 at pH 3) and measurement steps (a reduction potential of -0.5V for 60s and then, an anodic DPV scan) and using a pre-concentration time of 300s, the limit of detection was 0.11µgL(-1) (1.73nM). This OC-DPASV method using the PSS-CnP-PGE sensor was successfully employed for Cu(II) determination in mineral, river and sea water samples.

Fast sequential multi-element determination of major and minor elements in environmental samples and drinking waters by high-resolution continuum source flame atomic absorption spectrometry.

The fast sequential multi-element determination of 11 elements present at different concentration levels in environmental samples and drinking waters has been investigated using high-resolution continuum source flame atomic absorption spectrometry. The main lines for Cu (324.754 nm), Zn (213.857 nm), Cd (228.802 nm), Ni (232.003 nm) and Pb (217.001 nm), main and secondary absorption lines for Mn (279.482 and 279.827 nm), Fe (248.327, 248.514 and 302.064 nm) and Ca (422.673 and 239.856 nm), secondary lines with different sensitivities for Na (589.592 and 330.237 nm) and K (769.897 and 404.414 nm) and a secondary line for Mg (202.582 nm) have been chosen to perform the analysis. A flow injection system has been used for sample introduction so sample consumption has been reduced up to less than 1 mL per element, measured in triplicate. Furthermore, the use of multiplets for Fe and the side pixel registration approach for Mg have been studied in order to reduce sensitivity and extend the linear working range. The figures of merit have been calculated and the proposed method was applied to determine these elements in a pine needles reference material (SRM 1575a), drinking and natural waters and soil extracts. Recoveries of analytes added at different concentration levels to water samples and extracts of soils were within 88-115% interval. In this way, the fast sequential multi-element determination of major and minor elements can be carried out, in triplicate, with successful results without requiring additional dilutions of samples or several different strategies for sample preparation using about 8-9 mL of sample.

Chromium(III) determination without sample treatment by batch and flow injection potentiometry

A new and easy device for direct detection of chromium(III) in batch and flow analysis without previous oxidation/reduction or preconcentration steps of samples is designed and evaluated. For this purpose a potentiometric sensor with solid state membrane based on carbon paste matrix is developed. The sensor is modified with di(2-hydroxyphenylimino)ethane and the principal analytical parameters of the potentiometric response in batch and flow analysis are optimized and calculated. Optimal detection limits (1.4 x 10(-7)M in static mode and 5.4 x 10(-7)M in on-line analysis) and selectivity to trivalent chromium are obtained in both analysis modes. The use of this device to direct detection of chromium(III) in real samples is tested using a sediment Certified Reference Material. Chromium(III) determination is also carried out with successful results in environmental samples such as extracts from soils used as barriers in landfills and industrial samples such as waste waters from electroplating industries.

Flow and batch systems for copper(II) potentiometric sensing

A new carbon paste electrode modified with tetramethyl thiuram disulfide is prepared to use as copper potentiometric sensor in batch and flow analysis. The influence of pH and carbon paste composition on the potentiometric response is studied. The principal parameters of the flow system are optimized and the detection limits and the selectivity coefficients of the potentiometric sensor are calculated for static and flow mode. In both cases, the sensor shows high selectivity to copper ions but in flow analysis this selectivity is higher. The obtained detection limits are 4.6 x 10(-8) M for batch measurements and 2.0 x 10(-7) M for on-line analysis. The potentiometric sensor is applied to copper(II) determination in real samples in static and flow measurements. In both analysis modes, successful results are obtained.

Determination of essential elements in beverages, herbal infusions and dietary supplements using a new straightforward sequential approach based on flame atomic absorption spectrometry

A simple method based on FAAS was developed for the sequential multi-element determination of Cu, Zn, Mn, Mg and Si in beverages and food supplements with successful results. The main absorption lines for Cu, Zn and Si and secondary lines for Mn and Mg were selected to carry out the measurements. The sample introduction was performed using a flow injection system. Using the choice of the absorption line wings, the upper limit of the linear range increased up to 110mgL-1 for Mg, 200mgL-1 for Si and 13mgL-1 for Zn. The determination of the five elements was carried out, in triplicate, without the need of additional sample dilutions and/or re-measurements, using less than 3.5mL of sample to perform the complete analysis. The LODs were 0.008mgL-1 for Cu, 0.017mgL-1 for Zn, 0.011mgL-1 for Mn, 0.16mgL-1 for Si and 0.11mgL-1 for Mg.

Micro-sampling method based on high-resolution continuum source graphite furnace atomic absorption spectrometry for calcium determination in blood and mitochondrial suspensions

A micro-sampling and straightforward method based on high resolution continuum source atomic absorption spectrometry (HR-CS AAS) was developed to determine extracellular and intracellular Ca in samples of interest in clinical and biomedical analysis. Solid sampling platforms were used to introduce the micro-samples into the graphite furnace atomizer. The secondary absorption line for Ca, located at 239.856nm, was selected to carry out the measurements. Experimental parameters such as pyrolysis and atomization temperatures and the amount of sample introduced for the measurements were optimized. Calibration was performed using aqueous standards and the approach to measure at the wings of the absorption lines was employed for the expansion of the linear response range. The limit of detection was of 0.02mgL-1 Ca (0.39ng Ca) and the upper limit of linear range was increased up to 8.0mgL-1 Ca (160ng Ca). The proposed method was used to determine Ca in mitochondrial suspensions and whole blood samples with successful results. Adequate recoveries (within 91-107%) were obtained in the tests performed for validation purposes.