Quantification of DNT isomers by capillary liquid chromatography using at‐line SERS detection or multivariate analysis of SERS spectra of DNT isomer mixtures

With the global surge of terrorism and the increased use of bombs in terrorist attacks, national defence and security departments now demand techniques for quick and reliable analysis, in particular, for detection of toxic and explosive substances. One approach is to separate different analytes and matrix material before detection. In this work microliquid chromatography was used to separate two dinitrotoluene (DNT) isomers prior to detection via online UV–Vis spectroscopy. For identification, retention times were compared with reference samples and quantification was done by integration of UV–Vis absorption. Because UV detection is not particularly selective, Raman microscopic analysis was coupled to the liquid chromatography using a flow‐through microdispenser. Because DNT is difficult to detect with conventional Raman spectroscopy, the sensitivity was increased via surface‐enhanced Raman scattering (SERS) using silver‐quantum dots. Different analytical approaches to identify and quantify mixtures of two DNT isomers were evaluated. Good quantitative results were obtained using UV detection after microchromatographic separation (Limit of Detection: 0.11 and 0.06 for 2,4‐DNT and 2,6‐DNT). Coupling with SERS allowed for more confident differentiation between the highly structurally similar DNT isomers because of the additional spectral information provided by SERS. The application of a partial least squares algorithm also allowed direct SERS detection of DNT mixtures (root mean square error of prediction: 0.82 and 0.79 mg·L^–1 for 2,4‐DNT and 2,6‐DNT), circumventing the time‐consuming separation step completely. Copyright © 2012 John Wiley & Sons, Ltd.     

New supported liquid membrane-capillary electrophoresis in-line arrangement for direct selective analysis of complex samples

An in-line coupling of a micro-membrane extraction unit, based on supported liquid membrane, with commercially available capillary electrophoresis equipment is described. A main characteristic of this micro-membrane device, made from a simple Eppendorf tube, is that it permits the application of voltage in the acceptor solution to be applied during the extraction process. This has been shown as an alternative to enhance sensitivity, as the analytical signal achieved by applying 10 kV for 20 min was similar to that obtained without the application of voltage and with extraction time of 60 min. In addition, the design has been made permitting both in-line hydrodynamic and electrokinetic sample introduction into the electrophoretic capillary. The analytical potential of the proposed system has been demonstrated by the direct determination of nitroimidazoles from pig liver tissue. The high efficiency of the proposed system allowed the extraction and the determination of the analytes to be performed from a simple tissue homogenate obtained in water. The precision of the analysis of spiked samples, expressed in terms of relative standard deviation, was better than 4.8%.     

Vial position in the determination of chlorophenols in water by solid phase microextraction

The extraction of chlorophenol from water by headspace solid phase microextraction (HS-SPME) in vials located both vertically and horizontally is compared. The results obtained show that kinetic parameters are clearly affected by how the vial is placed in the analysis of semivolatile compounds. Extraction time for reach the equilibrium was three times lower in the horizontal configuration. An on-line extraction unit coupled to a continuous flow system is used to analyse unmodified ground water samples. In order to increase the high throughput, the analysis time is reduced and the sensitivity increased by making the extraction simultaneously with two fibres. The proposed method is applied to the analysis of spiked river water samples. The precision expressed as relative standard deviation ranges from 3.5 to 4.8%, and the recoveries from 94 to 105%.     

Cleavage of aryl iodides at carbon cathodes in organic carbonates. Surfaces doped by transition metals at the nanometric scale: Electro or redox catalysis?

The cathodic reduction of aryl iodides ArIs at carbon electrodes was achieved in cyclic carbonates (e.g., propylene carbonate PC). The novelty of the present method simply lies in the ability of title compounds to create aromatic carbanions that may act as nucleophiles towards carbonates. Consequently, several aromatic esters ArC(O)OR are generated as side products that play the role of redox mediators for indirectly cleaving C–X bond at solid inert electrodes. This procedure surprisingly allows one to obtain, through this self-induced redox catalysis, Ar–Ar dimers sometimes in high yield. Meanwhile, the triggering of such processes could be boosted by doping inert electrodes by electro-deposition of metals such as palladium, nickel, or silver. Extremely thin layers of metals are well shown to be very efficient (even at average thickness < 0.1 nm) to induce catalytic steps presenting quite large potential shifts compared to bare carbon electrodes when employed in inert solvents. The probable concomitance of electrocatalytic and redox catalytic processes is discussed and argued.     

Working group report: Heavy-ion physics and quark-gluon plasma

This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported.     

Enzymatic determination of pyrophosphate in urine by flow methods.

Two flow methods for the enzymatic determination of pyrophosphate are described that are used to diminish the consumption of reagents. One method is based on the use of an open-close circuit with manual injection using a syringe. The other is a sequential injection method. The analytical features of both methods are: a linear range of 0.4 - 20 mg L(-1), an LOD of 0.38 mg L(-1), and a CV of 2.0% for the sequential injection method, and a linear range of 0.3 - 15 mg L(-1), an LOD of 0.29 mg L(-1), and CV of 2.2% for the open-close circuit method. The methods were applied to the determination of pyrophosphate in urine. The pyrophosphate concentration determined in urine samples varied from 1.26 to 6.67 mg L(-1).     

A General Label Search to investigate classical graph search algorithms

Many graph search algorithms use a labeling of the vertices to compute an ordering of the vertices. We generalize this idea by devising a general vertex labeling algorithmic process called General Label Search (GLS), which uses a labeling structure which, when specified, defines specific algorithms.We characterize the vertex orderings computable by the basic types of searches in terms of properties of their associated labeling structures. We then consider performing graph searches in the complement without computing it, and provide characterizations for some searches, but show that for some searches such as the basic Depth-First Search, no algorithm of the GLS family can exactly find all the orderings of the complement. Finally, we present some implementations and complexity results of GLS on a graph and on its complement.     

Domain-wall spin dynamics in kagome antiferromagnets

We report magnetization and neutron scattering measurements down to 60 mK on a new family of Fe based kagome antiferromagnets, in which a strong local spin anisotropy combined with a low exchange path network connectivity lead to domain walls intersecting the kagome planes through strings of free spins. These produce unfamiliar slow spin dynamics in the ordered phase, evolving from exchange-released spin flips towards a cooperative behavior on decreasing the temperature, probably due to the onset of long-range dipolar interaction. A domain structure of independent magnetic grains is obtained that could be generic to other frustrated magnets.