Electrochemical determination of trace amounts of environmentally important dyes

A number of dyes exhibit genotoxic or ecotoxic properties leading to the need for sensitive and selective methods for their determination. Because of the easy reducibility of dyes, modern polarographic and voltammetric methods (differential pulse polarography on classical dropping mercury electrode, differential pulse voltammetry on hanging mercury drop electrode or adsorptive stripping voltammetry) are suitable for the determination of trace amounts of these substances in the general environment in the vicinity of production plants. The scope and limitations of these methods is reviewed and optimum conditions for recently developed methods are summarized. It is shown that the sensitivity of newly developed polarographic and voltammetric methods is sufficient even for the most demanding applications and their selectivity can be increased by their combination with preliminary separation using thin layer chromatography or liquid extraction.     

Chemical heterogeneity in poly [styrene-co-(butyl methacrylate)] copolymer latexes prepared using different monomer addition modes. A study by isopycnic centrifugation in density gradient

 Three different styrene-butyl methacrylate copolymer latexes were prepared by a uniform procedure but introducing styrene (S), butyl methacrylate (BMA), and minor amounts of acrylic acid (AA), in three different orders: i) simultaneous monomers addition, which yielded {P(SBMA)}; ii) addition of S (and half of the AA) followed by BMA (and the remaining AA), yielding {PS/PBMA} and iii) the inverse order, {PBMA/ PS}. Product characterization was done by centrifugation in density gradients coupled to scattered light scanning photometry of the centrifugation tubes. IR and NMR spectra were obtained from bulk polymer as well as from isopycnic centrifugation fractions. In agreement with findings of other authors, the particles produced by simultaneous monomer addition {P(SBMA)} are made out of the statistical copolymer, whereas sequential monomer addition leads to the formation of latex with homopolymer domains. IR and NMR spectra of {PS/PBMA} and {PBMA/PS} are identical but isopycnic density band profiles of all three samples are distinct. Acrylic acid residues are not detected in the dialyzed latex, using both IR and NMR. Spectra of latex isopycnic fractions do also show significant differences arising from their monomer chemical compositions, but isopycnic centrifugation and spectral data do not reveal any correlation between particle density and monomer composition. Isopycnic centrifugation can thus solve two problems on latex characterization: first, it is a high-resolution preparative technique, unmatched by any other separation method. Second, it yields latex particle fingerprints, which are dependent on particle chemical characteristics, rather than on particle diameters. Received: 19 March 1996 Accepted: 29 August 1996     

Determination of radionuclides in the environment using gamma-spectrometry

Summary Seventy nine samples, including soil and rock, were collected from the agrestic region of the State of Pernambuco, Brazil. The activity concentrations of ²³⁸U and ²²⁶Ra in the samples were determined by gamma-spectrometry using an HPGe detector. The concentrations of ²³⁸U were 22 Bq ^. kg^-1 to 22 kBq ^. kg^-1. The concentrations of ²²⁶Ra were 14 Bq ^. kg^-1 to 17 kBq ^. kg^-1. The ²³⁸U/²²⁶Ra ratios in the soil were 0.7 to 3.4 (arithmetic mean 1.7). The radiometric data were evaluated to explain ²³⁸U and ²²⁶Ra migration in the soil and the possible consequences to the environment.     

Solid-state structure and solution behavior of eight-coordinate Sm(III) poly(pyrazolyl)borate compounds

[Sm(Tp(Me2)(2)(kappa(2)-S(2)CNR(2))] compounds (R = Et (1), Me (2); Tp(Me2) = HB(3,5-Me2pz)(3)) have been isolated from reaction of (R(2)NC(S)S)(2) with 2 equiv of [Sm(Tp(Me2)(2)]. Reductive cleavage of 2,2'-dipyridyl disulfide or 2,2'-dipyridyl diselenide by [Sm(Tp(Me2)(2)] afforded good yields of [Sm(Tp(Me2)(2)(kappa(2)-Y)] compounds (Y = 2-SC(5)H(4)N (3), 2-SeC(5)H(4)N (4)). 4 is the first selenopyridine complex of an f-block element. Sm(Tp(Me2)(2)(2-OC(5)H(4)N) (5) has been synthesized by salt metathesis of [Sm(Tp(Me2)(2)Cl] with the sodium salt of the 2-hydroxypyridine. The solid-state structures of 1, 3, 4, and 5 were determined by single-crystal X-ray diffraction analysis and revealed that the compounds are all eight-coordinate with dodecahedral geometry. The samarium atoms are bound in tridentate fashion to two pyrazolylborate ligands and in bidentate fashion by the third ligand. The solution behavior of the compounds was studied by (1)H NMR techniques. (1)H-(1)H exchange spectroscopy experiments give evidence for two distinct dynamic regimes occurring in solution.     

On-Line Preconcentration and Determination of Cadmium, Cobalt and Nickel in Food Samples by Flame Atomic Absorption Spectrometry Using a New Functionalized Resin

A new chelating sorbent has been developed using Amberlite XAD-2 resin anchored with pyrocatechol through the –CH₂– group. This sorbent, characterised by elemental analysis and infrared (IR) spectra, was used as a packing material for a minicolumn in an on-line preconcentration system for cadmium, cobalt and nickel determination. Metal ions were sorbed in the minicolumn, from which it could be eluted directly to the nebulizer-burner system of the flame atomic absorption spectrometer (FAAS). Metals can be eluted from the minicolumn with 0.50 mol L⁻¹ HCl or HNO₃. The enrichment factors were 22 (Cd), 23 (Co) and 25 (Ni), for 60 s preconcentration time, and 44 (Cd), 40 (Co) and 48 (Ni), if 180 s preconcentration time was used. Under the optimum conditions, the procedure allowed the determination of cadmium, cobalt and nickel with detection limits of 0.27, 0.59 and 1.29 μg L⁻¹, respectively, when preconcentration periods of 180 s were used. The accuracy of the procedure was sufficient and evaluated by analysing certified reference materials. The method was applied to the analysis of food samples (black tea and rice flour).     

Asymmetric line shape in the emission spectra of conjugated polymer thin films: an experimental signature of one-dimensional electronic states

The photoluminescence (PL) properties of thin films of the conjugated polymer [poly(2,5-bis(2(')-ethyl-hexyl)-1,4-phenylenevinylene] have been investigated. At low temperatures the PL spectra show a narrow peak for the electronic transition and a series of well defined vibronic sidebands, which clearly reveal the electron coupling with two different vibronic modes. The purely electronic transition peak is observed to be very asymmetric so that it cannot be adjusted by a single Lorentzian or Gaussian function. In order to understand and explain this asymmetry we have considered a model where the purely electronic transition line shape is partially generated by a broadened square-root singularity representing one-dimensional electron states, and partially by localized (zero-dimensional) states. The localized states are assumed to be those very close to the band edges and are represented in our model by a single Gaussian function. Numerical Franck-Condon analysis was performed, resulting in a very good agreement between the theoretical and the experimental emission spectra. This procedure has confirmed the one-dimensional character of the electron states as the basis for the understanding of the purely electronic line shape asymmetry in the PL spectra of conjugated polymers at low temperatures.     

Liquid chromatographic determination of cetirizine in oral formulations

The development and validation of a reversed-phase liquid chromatographic (LC) method for the determination of cetirizine dihydrochloride in oral formulations are described. An isocratic LC analysis was performed on a reversed-phase C18 column (250 x 4.6 mm id, 5 microm particle size). The mobile phase was 1% orthophosphoric acid solution, pH 3.0-acetonitrile (60 + 40, v/v), pumped at a constant flow rate of 1.0 mL/min. Measurements were made at a wavelength of 232 nm. The calibration curves were linear over the range of 10-30 microg/mL (r2 = 0.9999). The relative standard deviation (RSD) values for intraday precision were 0.94 and 1.43% for tablets and compounded capsules, respectively. The RSD values for interday precision were 0.13 and 0.82% for tablets and compounded capsules, respectively. Recoveries ranged from 97.7 to 101.8% for tablets and from 98.4 to 102% for compounded capsules. No interferences from the excipients were observed. Because of its simplicity and accuracy, the method is suitable for routine quality-control analysis for cetirizine in tablets and compounded capsules.