Evaluation and application of bismuth as an internal standard for the determination of lead in wines by simultaneous electrothermal atomic absorption spectrometry

A method for the direct determination of Pb in wines by simultaneous multi-element atomic absorption spectrometry (SIMAAS) using a transversely heated graphite atomizer, Zeeman-effect background corrector and internal standardization is proposed. Bismuth was used as an internal standard and Pd(NO3)2 plus Mg(NO3)2 as chemical modifier to stabilize both the analyte and the internal standard. The implementation of two pyrolysis steps avoided any build-up of carbonaceous residues on the graphite platform. All diluted samples (1 + 1 v/v) in 0.2% v/v HNO3 and reference solutions (5.0-50 microg l(-1) Pb in 0.2% v/v HNO3) were spiked with 25 microg l(-1) Bi. For a 20 microl aliquot dispensed into the graphite tube, a good correlation (r = 0.9997) was obtained between the ratio of the analyte signal to the internal standard signal and the analyte concentration of the reference solutions. The electrothermal behaviour of Pb and Bi in red, white and rosé wines were compared. In addition, absorbance variations due to changes in experimental conditions, such as atomizer temperature, integration time, injected sample volume, radiation beam intensity, graphite tube surface, dilution and sample composition, were minimized by using Bi as internal standard. Relative standard deviations of measurements based on integrated absorbance varied from 0.1 to 3.4% and from 0.5 to 7.3% (n = 12) with and without internal standard correction, respectively. Good recoveries (91-104%) for Pb spikes were obtained. The characteristic mass was 45 pg Pb and the limit of detection based on integrated absorbance was 0.9 microg l(-1) Pb. Internal standardization increased the lifetime of the tube by 25%. Direct determinations of Pb in wines with and without internal standardization approaches were in agreement at the 95% confidence level. The repeatability and the tube lifetime were improved when using Bi as internal standard. The improvement in accuracy using an internal standard was only observed when the analytical results were affected by errors.     

Template synthesis in the nickel(II)–thiocarbohydrazide–propanone triple system

The complexing process proceeding in the Ni^II–thiocarbohydrazide (H₂N–H–NC(=S)–NH–NH₂)–propanone triple system in EtOH solution and nickel(II)hexacyanoferrate(II) gelatin-immobilized matrix has been studied. It has been found that in the first case, template synthesis leading, as a minimum, to formation of three coordination compounds of Ni^II with (N,N,S,S)-donor tetradentate ligands having NiL¹, NiL² and NiL³compositions where L¹ is 4,6,6-trimethyl-2,3,7,8-tetraazanonen-3-di(thiohydrazide)-1,9, L² is 4,6,6,12-tetrametyl-1,9-dithio-2,3,7,8,10,11-hexaazatridekadien-3,11-hydrazide-1 and L³ is 2,8,10,10,16-pentamethyl-5,13-dithio-3,4,6,7,11,12,14,15-octaazaheptadekatrien-2,7,15 is observed, whereas in the gelatin-immobilized matrix, a complexing process in the system considered does not occur.     

Intramolecular "Aryl-metal chelate ring" pi,pi-interactions as structural evidence for metalloaromaticity in (aromatic alpha,alpha'-diimine)-copper(II) chelates: molecular and crystal structure of aqua(1,10-phenanthroline)(2-benzylmalonato)copper(II) three-hydrate

By reaction of Cu(2)CO(3)(OH)(2), 2-benzylmalonic acid (H(2)Bzmal), and 1,10-phenanthroline (phen), [Cu(Bzmal)(phen)(H(2)O)] x 3H(2)O (compound 1) has been obtained and characterized by thermal, spectral, magnetic, and X-ray diffraction methods. The molecular structure of 1 is remarkably similar to that of [Cu(Bzmal)(bipy)(H(2)O)] x 2H(2)O (compound 2, bipy = 2,2'-bipyridine). In both complexes, the aryl(Bzmal) ring produces an unexpected pi,pi-stacking interaction with the Cu(II)-(aromatic alpha,alpha'-diimine) chelate ring, at an average distance d(pi)(-)(pi) of 3.40 A, involving roughly parallel and smoothly slipped rings. This insight is discussed as new structural evidence for metalloaromaticity of Cu(II)-(aromatic alpha,alpha'-diimine) chelate rings. Interestingly, 1 recognizes itself by a weak intermolecular pi,pi-stacking interaction between aryl(Bzmal) ligands to give pairs of complex molecules. In contrast, there is an intermolecular pyridyl-pyridyl pi,pi-stacking interaction also forming pairs of complex molecules in 2.     

Application of ultra-low level liquid scintillation to the determination of 222Rn in groundwater

A procedure for the determination of ²²²Rn in environmental water samples using liquid scintillation counting (LSC) was applied. The extractive scintillator RADONS^Ò and an ultra-low background 1220 QuantulusÔ were used. A minimum detectable activity of 0.1 Bq·l^?1 in 20 ml was found with low-diffusion polyethylene vials and 200 minute measurement time. Quenching effects and possible interferences due to the existence of other radionuclides in the extraction process were studied. The procedure was controlled by gamma-ray spectrometry of the ²²²Rn daughters. Applications to environmental samples collected from spas, wells, and public springs in Extremadura (Spain) are presented.     

Modeling of temperature-programmed desorption thermograms for the determination of adsorption heat considering pore and surface diffusion

In this work, two partial differential equation-based models have been proposed for the quantitative analysis of temperature-programmed desorption (TPD) thermograms when the adsorption cell can be modeled as a well-mixed reactor, using the Langmuir equation as the adsorption isotherm and including the effect of diffusional resistance. One model considers pore diffusion, and the other considers surface diffusion. For both models, the rate of adsorption is proportional to the gas pressure. By nondimensionalizing these models, the range of design parameters for which the accumulation in the gas cell, diffusional resistance, and readsorption have an important effect on the TPD signal is proposed. An important conclusion is that the dimensionless numbers accounting for the diffusional resistance and the corresponding range of parameters are quite different for both mechanisms. The models have been validated with two systems where surface and pore diffusion are the relevant mechanisms: (i) CO2-Na-mordenite and (ii) CO2-Na-mordenite pellets.     

Setting up of recovery profiles: A tool to perform the compliance with recovery requirements for residue analysis

The use of the recovery term has presented some confusion in Analytical Chemistry. Recent IUPAC recommendations propose to distinguish between two terms: recovery or recovery factor, ℜ, and apparent recovery, ℜ*. Apparent recovery includes recovery factor and a new recovery term proposed in this paper, named calibration recovery, ℜ^C, which depends of the type of systematic error due to the matrix effect (constant and/or proportional) and is related to the applied calibration methodology. This paper highlights the dependence of the calibration recovery on the sample analyte concentration and, for extension, of the apparent recovery, defines the recovery profile, and makes evident the need to determine a “fit for purpose” analyte concentration interval to comply with a regulated recovery requirements. An approach to estimate the calibration recovery and its associated uncertainty in relation to the above-mentioned dependence is presented. The usefulness of the proposed methodology has been shown in the quantification of a pesticide by GC-ECD for assessing dermal exposure.     

Direct electrochemistry and enzymatic activity of hemoglobin in positively charged colloid Au nanoparticles and hemoglobin layer-by-layer self-assembly films

Alternate adsorption of positively charged colloid-Au nanoparticles (nano-Au⊕) and negatively charged hemoglobin (Hb) on L-cysteine (L-cys) modified gold electrode resulted in the assembly of {Hb/nano-Au⊕}n layer-by-layer films/L-cys modified gold electrode. The nano-Au⊕ was characterized by transmission electron micrograph (TEM) and microelectrophoresis. The modified electrode interface morphology was characterized by electrochemical impedance spectroscopy (EIS), atomic force mi- croscopy (AFM), cyclic voltammograms (CV) and chronoamperometry. Direct electron transfer between hemoglobin and gold electrodes was studied, and the apparent Michaelis-Menten constant ( km app) of the modified electrode was evaluated to be 0.10 mmol·L?1. Moreover, the higher activity of proteins in the nano-Au⊕ films could be retained compared with the electropolymerization membrane, since the pro- teins in nano-Au⊕ films retained their near-native structure. Direct electron transfer between hemoglo- bin and electrode and electrochemically catalyzed reduction of hydrogen peroxide on a modified elec- trode was studied, and the linear range was from 2.1×10-8 to 1.2 ×10?3 mol·L-1 (r = 0.994) with a detection limit of 1.1×10-8 mol·L-1 H2O2.     

Enantiomers of sterically hindered n-aryl-4-pyridones: Chromatographic enrichment and thermal interconversion

N-Aryl-4-pyridones 1–6 were synthesized by condensation of the corresponding 4-pyrone with anilines. The enrichment of the enantiomers was achieved by liquid chromatography on triacctylcellulose, enantiomeric purities of(+)-1 and (+ )-2 being measured by ¹H-NMR in the presence of an optically active auxiliary. Barriers to partial rotation about the C-N bond in 1-4 were determined and compared with corresponding biphenyls.     

Thiocarbonyl rhodium complexes with tricyclohexylphosphine and other nitrogen and phosphorus donor ligands

Summary The preparation of the covalent Rh(OCIO₃)(CS)(PCy₃)₂ and Rh(OClO₃)(CS)(PPh₃)(PCy₃) perchlorato complexes is described, These complexes react with mono- or bidentate nitrogen donor ligands to give new cationic complexes of the [Rh(CS)(PCY₃)₂L]ClO4 and [Rh(CS)(PPh,)(PCy₃)L]ClO₄ types,