Determination of polynuclear aromatic hydrocarbons in water samples using large volume on-column injection capillary gas chromatography

An automated large volume on-column injection technique for capillary gas chromatography (GC) with solvent divert and heated retention gap technology has been utilized to determine polynuclear aromatic hydrocarbons (PAHs) in samples of industrial plant process water. Injecting large sample volumes on-column enabled the sample preparation procedure to be simplified and provided a fast, labor-saving technique for screening water samples. Diverting approximately 95% of the solvent away from the analytical column and the detector enabled chromatography to reflect classical capillary loading and detector conditions. Simplifications include significant reduction of sample and eluent volumes used during extraction and the elimination of Kuderna-Danish evaporative concentration. System performance, such as linearity and limit of detection, were evaluated for selected PAHs. Spiked water samples were prepared in the lower μ/L range to determine extraction efficiency. Results are compared with those obtained by a reputable contract laboratory following EPA Method 625.     

Alternatives for the reduction of Cu(II) ion levels in hemodialysis membranes produced from sugar-cane bagasse

The objective of the present study was to seek alternatives for the reduction of Cu(II) ion levels in hemodialysis membranes produced by the cuprammonium process. The alternatives used were: (a) replacement of the solvent Cu(NH₃)₄(OH)₂, used in the original process, with Cu(EDA)₂(OH)₂, and (b) increasing the reflux time of the bagasse purification process from 1.5 to 3.0 h. The experimental results were obtained by analysis of Cu(II) content in the membranes by atomic absorption, by complexometry via UV/Vis spectroscopy of the solutions of filter paper, bagasse and lignin, and by monitoring the various stages of the purification process (by FTIR and by loss of mass), i.e. pretreatment with 0.25 M NaOH followed by treatment with 4.2 M EDA and reflux with EtOH/HNO₃ (20%, v/v). The results showed that the Cu(II) content in the membranes decreased with the use of the Cu(EDA)₂(OH)₂ solvent, that the purification process could not be improved further since cellulose degradation was observed, and that the Cu(II) content in the membranes produced was still to high for their use for hemodialysis treatment.     

Differential pulse polarographic determination of arsenic, selenium and tellurium at mug levels

An analytical method, based on differential pulse polarography, for determination of arsenic, selenium and tellurium in solid matrices, is described. The method involves decomposition of the matrix with a mixture of nitric, perchloric and hydrofluoric acid, isolation of tellurium from the other analytes by liquid-liquid extraction (from 4M hydrochloric acid with methyl isobutyl ketone), and determination of the analytes. Tellurium is determined separately, and arsenic is determined in the same solution as selenium after determination and oxidation of the selenium and addition of catechol. Graphitized carbon black and chelating resin were used to eliminate the organic solvent in the aqueous solution and avoid interferences due to the other metals of the matrix. The decomposition, the influence of each analyte on the determination of the others, and the extraction process were given particular attention. The method is characterized by>96% recovery, with a relative standard deviation ranging from 2 to 10% at ppm levels.     

MIP models for production lot sizing problems with distribution costs and cargo arrangement

This study presents mixed integer programming (MIP) models for production lot sizing problems with distribution costs using unit load devices such as pallets and containers. Problems that integrate production lot sizing decisions and loading of the products in vehicles (bins) are also modelled, in which constraints such as weight limits, volume restrictions or the value of the cargo loaded in the bins are considered. In general, these problems involve a trade-off between production, inventory and distribution costs. Lot sizing decisions should take into account production capacity and product demand constraints. Distribution decisions are related to the loading and transport of products in unit load devices. The MIP models are solved by the branch-and-cut method of an optimization package and the results show that these approaches have the potential to address different practical situations.     

Multielement analysis of lichen samples using XRF methods. Comparison with ICP‐AES and FAAS

This research presents the contents of Ca, Fe, Zn, Br, Rb, Sr and Pb in lichen samples used as biomonitors of air pollution collected in Havana. Statistical comparisons were made among the results obtained in three campaigns during three years. Two X‐Ray Fluorescence (XRF) methods were used, employing for excitation an annular ¹⁰⁹Cd source and a Mo X‐ray tube with a molybdenum secondary target. In both cases, matrix effects were corrected by the use of normalization for the Compton scattered peak; in this way the determination is more efficient. For quality control of the results, biological Certified Reference Materials were analyzed and were made comparisons between XRF, Inductively Coupled Plasma‐Atomic Emission Spectrometry and Flame Atomic Absorption Spectrophotometry. No significant differences were found between the different techniques. The elemental distribution patterns obtained for each metal were associated with different pollution sources, thus contributing to the assessment of air pollution in Havana. Copyright © 2015 John Wiley & Sons, Ltd.     

Non-chromatographic speciation of toxic arsenic in vegetables by hydride generation-atomic fluorescence spectrometry after ultrasound-assisted extraction

A non-chromatographic, sensitive and simple analytical method has been developed for the determination of toxic arsenic species in vegetable samples by hydride generation-atomic fluorescence spectrometry (HG-AFS). As(III), As(V), dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA) were determined by hydride generation-atomic fluorescence spectrometry using a series of proportional equations. The method is based on a single extraction of the arsenic species considered from vegetables through sonication at room temperature with H(3)PO(4) 1 mol L(-1) in the presence of 0.1% (w/v) Triton XT-114 and washing of the solid phase with 0.1% (w/v) EDTA, followed by direct measurement of the corresponding hydrides in four different experimental conditions. The limit of detection of the method was 3.1 ng g(-1) for As(III), 3.0 ng g(-1) for As(V), 1.5 ng g(-1) for DMA and 1.9 ng g(-1) for MMA, in all cases expressed in terms of sample dry weight. Recovery studies provided percentages greater than 91% for all considered species in spiked samples of chards and aubergines. Total toxic As found in the aforementioned samples was at the level of 90 ng g(-1); As(III) is followed by As(V), DMA and MMA which are the main species of As in chards being As(V) the main As compound in aubergines.     

Characterization of a reduced molybdenum-oxo compound derived from an oxo-transfer process under stoichiometric conditions

The stoichiometric oxidation of phosphanes or alcohols by a Mo(VI)-dioxo complex (1) followed both by UV spectroscopy results in the formation of a Mo(V) dimer with two μ-oxo bridges and two terminal oxo functions (3). Its structure is determined by an X-ray analysis depicting a Mo–Mo bond well in accord with the diamagnetic character of the complex. The spectroscopic follow up of the oxygen atom transfer process shows clearly that complex 3 is the end product of a series of intermediates among which one (2) is postulated as being a geometrical isomer of 3.     

Synthesis and Characterization of Halo, Cyanato, Thiocyanato and Selenocyanato Molybdenum(VI) Dioxo and Dioxo-μ-oxo Complexes

Ten new 4,4′-bipyridyl molybdenum(VI) dioxo and dioxo-μ-oxo complexes have been synthesized and fully characterized. The substituents on the bipyridyl moiety are: t-butyl, benzyl, carbomethoxy, nitro and methoxy groups, whereas the functional ligands on molybdenum are: chloro, bromo, thiocyanato, cyanato and selenocyanato groups. The molecular structure of three of them have been determined by single crystal X-ray crystallography and showed distortions from an octahedral geometry in accord with the nature of the various substituents.