Electrokinetic molecular separation in nanoscale fluidic channels

This report presents a study of electrokinetic transport in a series of integrated macro- to nano-fluidic chips that allow for controlled injection of molecular mixtures into high-density arrays of nanochannels. The high-aspect-ratio nanochannels were fabricated on a Si wafer using interferometric lithography and standard semiconductor industry processes, and are capped with a transparent Pyrex cover slip to allow for experimental observations. Confocal laser scanning microscopy was used to examine the electrokinetic transport of a negatively charged dye (Alexa 488) and a neutral dye (rhodamine B) within nanochannels that varied in width from 35 to 200 nm with electric field strengths equal to or below 2000 V m-1. In the negatively charged channels, nanoconfinement and interactions between the respective solutes and channel walls give rise to higher electroosmotic velocities for the negatively charged dye than for the neutral dye, towards the negative electrode, resulting in an anomalous separation that occurs over a relatively short distance (<1 mm). Increasing the channel widths leads to a switch in the electroosmotic transport behavior observed in microscale channels, where neutral molecules move faster because the negatively charged molecules are slowed by the electrophoretic drag. Thus a clear distinction between "nano-" and "microfluidic" regimes is established. We present an analytical model that accounts for the electrokinetic transport and adsorption (of the neutral dye) at the channel walls, and is in good agreement with the experimental data. The observed effects have potential for use in new nano-separation technologies.     

High-performance liquid chromatography with post-column derivatisation and fluorescence detection for sensitive determination of aflatoxin M1 in milk and cheese

A new HPLC method with fluorescence detection using pyridinium hydrobromide perbromide as a post-column derivatising agent has been developed to determine aflatoxin M1 in milk and cheese. The detection limits were 1 ng/kg for milk and 5 ng/kg for cheese. The calibration curve was linear from 0.001 to 0.1 ng injected. The method includes a preliminary C18-SPE clean-up and the average recoveries of Aflatoxin M1 from milk and cheese, spiked at levels of 25-75 ng/kg and 100-300 ng/kg, respectively, were 90 and 76%; the precision (RSDr) ranged from 1.7 to 2.6% for milk and from 3.5 to 6.5% for cheese. The method is rapid, easily automatable and therefore useful for accurate and precise screening of aflatoxin M1 in milk and cheese.     

(2‐Hydroxy isobutyric) acid containing poly(glycolic acid): Structure–properties relationship

Poly(glycolic acid) (PGA) and a series of novel random copolymers of PGA containing 2‐hydroxyisobutyrric acid (PGAPHIB) (HIB unit content from 1.5 to 7.4 mol %) were synthesized and characterized in terms of chemical structure and molecular weight. Afterward, the polyesters were examined by thermogravimetric analysis, differential scanning calorimetry, and X‐ray diffraction techniques. The copolymers, which displayed a better thermal stability than PGA, at room temperature appeared as semicrystalline materials: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of the melting temperature with respect to homopolymer PGA. Baur's equation described well the T_m‐composition data. X‐ray diffraction measurements allowed the identification of the PGA crystalline structure in all cases. After melt quenching, semicrystalline samples were obtained with the exception of PGAPHIB7.4 copolymer. The introduction of HIB units decreased the crystallization rate compared with pure PGA. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1901–1910, 2010     

The Peter principle revisited: A computational study

In the late sixties the Canadian psychologist Laurence J. Peter advanced an apparently paradoxical principle, named since then after him, which can be summarized as follows: ‘Every new member in a hierarchical organization climbs the hierarchy until he/she reaches his/her level of maximum incompetence’. Despite its apparent unreasonableness, such a principle would realistically act in any organization where the mechanism of promotion rewards the best members and where the competence at their new level in the hierarchical structure does not depend on the competence they had at the previous level, usually because the tasks of the levels are very different to each other. Here we show, by means of agent based simulations, that if the latter two features actually hold in a given model of an organization with a hierarchical structure, then not only is the Peter principle unavoidable, but also it yields in turn a significant reduction of the global efficiency of the organization. Within a game theory-like approach, we explore different promotion strategies and we find, counterintuitively, that in order to avoid such an effect the best ways for improving the efficiency of a given organization are either to promote each time an agent at random or to promote randomly the best and the worst members in terms of competence.     

Density and Volume Properties of Ethane-1,2-diol + 1,2-Dimethoxyethane + Water Ternary Mixtures from −10° to 80°

Thermodynamic interactions in the ethane-1,2-diol (1) + 1,2-dimethoxyethane(2) + water (3) ternary system have been investigated in terms of the excessmolar volume, derived from density measurements at 19 different temperaturesfrom –10;dg to 80;dgC. Fourteen three-component mixtures have been considered,covering the entire composition range. The excess molar volumes are discussedin terms of conformational changes induced in each component by the presenceof another one. The results obtained support the hypothesis of the absence of anythree-component complex adducts under all experimental conditions investigated.     

A multiresidue method with mobile on-site sampling based on SPE for ultratrace analysis of plant protectants in environmental waters

A new multiclass/multiresidue method for monitoring plant protectant residues in raw- and drinking waters with on-site sampling using a mobile, self-contained sampling unit based on SPE was developed and validated. 38 active compounds with widely varying chemical and physicochemical properties (acid-base properties, polarities, vapor pressures, solubilities) are measured from just one sample and work-up. 100 mL water, acidified with acetic acid, are drawn through a cartridge filled with Amberchrom resins by means of a calibrated 100 mL syringe driven by servo motors, control circuit and rechargeable battery. Volumetric flow is high, quantitative extraction of acidic, neutral and weak basic substances is accomplished in a few minutes and loaded cartridges are transported into the laboratory. Further work-up, i.e. elution, drying, concentration and solvent change, is designed strictly non-selectively and produces 250 μL of an “extract”, which is the starting point of two GC measurement lines, GC-NPD and GC-ECD. Chlorinated herbicide acids are derivatised into perfluorinated benzyl esters employing reaction conditions so smooth that the organochlorine hydrocarbons are not destroyed at all and both substance classes can be chromatographed in one GC run. ECD-chromatograms from derivatised solutions are rather complex, therefore the flow is split after injection onto two columns with different polarities and two EC-detectors in order to resolve all analytes and matrix interferents. Short-chain carbonic acids added to the water prior to preconcentration are adsorbed on the hydrophobic surface in a reversible process and impart the Amberchrom resins with a partially hydrophilic character. Method performance was ascertained using tap water fortified at the 0.2 μg L^–1 level: Mean recoveries were between 70 and 115% and method detection limits (MDLs) below 0.08 μg L^–1. Waters from different sources did not affect the recoveries, loaded cartridges are stable for two weeks’ storage when cooled. Received: 28 December 1998 / Revised: 20 April 1999 / Accepted: 13 May 1999     

The Bisymplectomorphism Group of a Bounded Symmetric Domain

We determine the group of diffeomorphisms of a bounded symmetric domain, which preserve simultaneously the hyperbolic and the at symplectic form. *Research partially supported by GNSAGA (INdAM) and MIUR of Italy; MIUR Project “Geometric Properties of Real and Complex Manifolds” (PRIN05). **Research partially supported by GNSAGA (INdAM) and MIUR of Italy; MIUR Project “Geometric Properties of Real and Complex Manifolds” (PRIN05). ***Part of this work was done in July 2007 during a visit of G. Roos at Politecnico di Torino; visit supported by GNSAGA (INdAM) and MIUR of Italy; MIUR Project “Geometric Properties of Real and Complex Manifolds: (PRIN05).