Ion chromatography determination of trace level bromate by large volume injection with conductivity and spectrophotometric detection after post column derivatisation

Bromate is a well known by-product produced by the ozonisation of drinking water; the allowed concentration for human consumption has to be regulated to the low microg l(-1) range. A direct injection, ion chromatographic method was developed using a tetraborate eluent with serially connected conductivity and spectrophotometric detection. Bromate was detected after post-column reaction with fuchsin at 520 nm. Sample capacity was investigated by injecting large volumes (up to 6 ml) using a high total hardness and chloride tap water. Linear correlation of bromate response with volumes from 1 ml to 6 ml was demonstrated, the main limitation being the overlapping of the chloride peak with bromate. Up to 1.5 ml sample can be injected without any pre-treatment. With more than 1.5 ml injection volume, a sample pre-treatment with a cartridge in Ag and H form, followed by a 10 min degassing in an ultrasonic bath, was needed. This method was validated by analysing secondary reference materials and real samples from a drinking water treatment plant. The method was linear from the limit of quantification to 20 microg l(-1). Reproducibilities in tap water were 18% (5 microg l(-1), n=12) and 21% (1 microg l(-1), n=4) respectively for 1.5 and 6 ml injection volumes with conductivity detection, and 17% at 0.5 microg l(-1) (n=9) with spectrophotometric detection. Calculated detection limits were 0.5 microg l(-1) (6 ml) ahd 2 microg l(-1) (1.5 ml) for conductivity detection and 0.3 microg l(-1) (1.5 ml) for spectrophotometric detection.     

An example of a -minimal group which is not abelian-by-finite

In 1996 D. Macpherson and C. Steinhorn introduced -minimality as an analogue, for valued fields and some groups with a definable chain of normal subgroups with trivial intersection, of the notion of o-minimality. One of the open questions of that paper was the existence of a non abelian-by-finite -minimal group. We give here the first example of such a group.

     

Gas-phase hydrogen/deuterium exchange of adenine nucleotides

Gas-phase hydrogen/deuterium exchange reactions of (de)protonated (sodiated) adenosine-5'-mono-, di- and triphosphate ions with CD(3)OD, CD(3)CO(2)D and ND(3) were achieved using a combination of electrospray ionization and Fourier transform ion cyclotron resonance mass spectrometry. The reaction kinetics are dependent on factors such as the charge state, the phosphate chain length, the properties of the exchange reactants and the sodium content. The results indicate that the overall H/D exchange may involve specific sites even if endowed with high energetic barriers. The enhanced reactivity exhibited by adenosine polyphosphate ions compared with adenosine-5'-monophosphate suggests a critical role of the polyphosphate chain in rendering conformationally accessible remote H-donor sites. Low-energy collision-induced dissociation of (sodiated) adenine nucleotides anions supports the aptitude of the (poly)phosphate chain in probing distant sites via the intermediacy of a cyclic structure.     

A survey of product form queueing networks with blocking and their equivalences

Queueing network models have been extensively used to represent and analyze resource sharing systems, such as production, communication and information systems. Queueing networks with blocking are used to represent systems with finite capacity resources and with resource constraints. Different blocking mechanisms have been defined and analyzed in the literature to represent distinct behaviors of real systems with limited resources. Exact product form solutions of queueing networks with blocking have been derived, under special constraints, for different blocking mechanisms. In this paper we present a survey of product form solutions of queueing networks with blocking and equivalence properties among different blocking network models. By using such equivalences we can extend product form solutions to queueing network models with different blocking mechanisms. The equivalence properties include relationships between open and closed product form queueing networks with different blocking mechanisms.This work has been partially supported by CNR Project Research Funds Progetto Finalizzato Sistemi Informatici e Calcolo Parallelo and by MURST Project Research Funds Performability hw/sw di sistemi distribuiti e paralleli.     

Post-adiabatic approach to atomic and molecular processes: The van der Waals interactions of some open shell systems

Summary Various properties of post-adiabatic representations of multichannel Schrödinger equations are described in the general context of adiabatic and classical path approximations as used in atomic and molecular physics. The van der Waals interactions of fluorine, chlorine, and oxygen atoms with rare gases, hydrogen, methane, and hydrogen halides are considered: it is found that in some of these systems, the first-order post-adiabatic scheme exhibits a smaller coupling than the adiabatic representation, thus providing an appropriate choice of the basis functions for a decoupling approximation.     

Behaviour of selenium and tellurium species and their determination by ion chromatography

Summary An ion chromatographic method has been developed for the separation of Te (IV) and Se(IV) in hydrochloric acid mobile phases; the method has been used to determine tellurium in a high-purity non-stoichiometric semiconducting ZnCdTe-based material. Different cation-exchange columns (IonPac CS2, CS3, CS10), a mixed bed ion-exchange column (IonPac CS5), a multi-mode cation-exchange column (OmniPac PCX-500), anion-exchange columns (IonPac AS4, AS4A, AS5, AS5A, AS10, AS11) and a multi-mode anion-exchange column (OmniPac PAX-500) were evaluated for ion chromatographic separation of Se and Te and to study the chemical forms in which the analytes were eluted. The chromatographic data obtained enabled the calculation of both the sign and the chaarge of the eluting species.     

Electrochemical Organic Synthesis of Electron-Rich Biaryl Scaffolds: An Update

Biaryl scaffolds are widely spread in biologically important natural products, in numerous therapeutic agents, but they are also considered a privileged class of ligands and (organo)catalysts; therefore, the development of efficient alternative methodologies to prepare such compounds is always attracting much attention. The present review discusses the organic electrosynthesis of biaryls starting from phenols, anilines, naphthols, and naphthylamines. The most significant examples of the works reported in the last decade are presented and classified according to the single class of molecules: after the introduction, the first three sections relate to the reactions of phenols, naphthols, and anilines, respectively; the other two sections refer to cross-coupling and miscellaneous reactions.     

Ion chromatography with inductively coupled plasma mass spectrometry,a powerful analytical tool for complex matrices estimation of Pt and Pd in environmental samples

A new method for palladium and platinum direct determination in environmental samples is proposed by coupling ion chromatography with quadrupole inductively coupled plasma MS. In order to optimise Pd and Pt separation and to minimise interference from matrix in real samples, several anionic and cationic stationary phases have been compared at different mobile phase compositions. In particular, the effect of acidity and of the addition of oxalic acid to the eluent on separation and detection performance has been studied, and the anion-exchange column AG11 turned out to be more suitable. After chromatographic and mass spectrometer parameter optimisation, several potential interferences and the main quality parameters of the method, according to the Eurachem-CITAC recommendations, were evaluated: the detection limit for Pt was 5 ng l(-1) while the value for Pd was 230 ng l(-1). The method was successfully employed in the determination of platinum group elements in urban road dust and atmospheric particulates and the complete absence of matrix spectral interferences was demonstrated.