Membrane desolvation for the analysis of organic solutions and liquid chromatographic samples with low power helium microwave induced plasma atomic emission detection

A flat sheet membrane desolvator (FSMD) was used to extend the applicability of a 120 W helium microwave induced plasma (He-MIP) to elemental analysis of organic-solvent-based samples and element selective liquid chromatographic detection. With the FSMD on-line, methanol could be nebulized with a sample flow rate of 1.5 ml/min and a carrier gas flow rate of 1.2 l/min without extinguishing the plasma. Under these conditions, applying desolvator countercurrent gas flows in the range 0–8 l/min restored of the original pink color of the pure helium MIP from the bluish-green caused by methanol. Significant reductions in the emission intensities of C₂ species at 436.5, 473.7, 512.9, and 563.6 nm were observed with the application of the FSMD. The intensities of chlorine analyte emission lines at 479.5, 481.0 and 481.9 nm increased with increasing countercurrent gas flow rates and reached a maximum intensity with a flow rate of 5.0 l/min. Detection limits for Cl and Pb were 2.1 and 0.1 ppm using a 1 m focal length monochromator. Other elements and solvent combinations were also examined. Element selective liquid chromatographic detection was preliminarily examined by monitoring 2,6-dichlorobenzene and 5,7-dichlorohydroxyquinoline at the 479.5 nm Cl atomic emission line. Chlorine detection limits in the 3–7 μg range (70–190 ng/s) were obtained.     

Non-trivial effects of high-frequency excitation for strongly damped mechanical systems

Some non-trivial effects are investigated, which can occur if strongly damped mechanical systems are subjected to strong high-frequency (HF) excitation. The main result is a theoretical prediction, supported by numerical simulation, that for such systems the (quasi-) equilibrium states can change substantially with the level of damping. For example, a strongly damped pendulum, with a hinge vibrated at high frequency along an elliptical path with horizontal or vertical axis, will line up along a line offset from the vertical; the offset vanishes for very light or very strong damping, attaining a maximum that can be substantial (depending on the strength of the HF excitation) for finite values of the damping. The analysis is focused on the differences between the classic results for weakly damped systems, and new effects for which the strong damping terms are responsible. The analysis is based on a slightly modified averaging technique, and includes an elementary example of an elliptically excited pendulum for illustration, alongside with a generalization to a broader class of strongly damped dynamical systems with HF excitation. As an application example, the non-trivial behavior of a classical optimally controlled non-linear system is investigated, illustrating how HF excitation may cause the controller to leave the system in an unexpected equilibrium state, quite different from the setpoint. The effects can be interesting for specialists in control of mechanical systems and structures. However the obtained results are more general. Similar effects could be expected first of all for microsystems where damping forces are typically dominating over inertia forces.     

The Effect of the Backward-Facing Step Height on Flow in a Channel with Rectangular Cross Section

The investigation of a channel flow with a backward-facing step on one wall is described. The height of the incoming channel H is adjustable as to allow alter the ratio of step height h over H; h/H = 1 : 10, 1 : 4, 1.02 : 1(h + H = 0.275m). Mutual correlations between the extremes of static pressure distributions, limits of the separation zone and of the corner vortex structures and Reynolds number are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solid state coordination chemistry: structural consequences of variations in tether length in the oxovanadium-copper-bisterpy-[O3P(CH2)nPO3]4- system, n= 1-6 (bisterpy = 2,2':4',4'':2'',2'''-quarterpyridyl-6',6''-di-2-pyridine)

Hydrothermal reactions of Na3VO4, an appropriate Cu(II) source, bisterpy and an organodiphosphonate, H2O3P(CH2)nPO3H2 (n = 1-6) yielded a family of materials of the type [Cu2(bisterpy)]4+/VxOy(n-)/[O3P(CH2)nPO3]4-. This family of bimetallic oxides is characterized by an unusual structural diversity. The oxides [[Cu2(bisterpy)]V2O4[O3PCH2PO3H]2] (1), [[Cu2(bisterpy)(H2O)]VO2[O3P(CH2)3PO3][HO3P(CH2)3PO3H2]] (4) and [[Cu2(bisterpy)]V2O4[O3P(CH2)6PO3H]2].2H2O (7.2H2O) are one-dimensional, while [[Cu2(bisterpy)(H2O)2]V2O4[O3P(CH2)2PO3][HO3P(CH2)2PO3H]2] (2), [[Cu2(bisterpy)]V4O8[O3P(CH23PO3]2].4H2O (3.4H2O) and [[Cu2(bisterpy)]V2O4(OH)2[O3P(CH2)4PO3]].4H2O (5.4H2O) are two-dimensional. The V(IV) oxide [[Cu2(bisterpy)]V4O4[O3P(CH2)5PO3H]4].7.3H2O (6.7.3H2O) provides a relatively unusual example of a three-dimensional bimetallic oxide phosphonate. The structures reveal a variety of V/P/O substructures as building blocks.     

Artificial ion channel formed by cucurbit[n]uril derivatives with a carbonyl group fringed portal reminiscent of the selectivity filter of K+ channels

Novel artificial ion channels (1 and 2) based on CB[n] (n = 6 and 5, respectively) synthetic receptors with carbonyl-fringed portals (diameter 3.9 and 2.4 A, respectively) can transport proton and alkali metal ions across a lipid membrane with ion selectivity. Fluorometric experiments using large unilamellar vesicles showed that 1 mediates proton transport across the membranes, which can be blocked by a neurotransmitter, acetylcholine, reminiscent of the blocking of the K+ channels by polyamines. The alkali metal ion transport activity of 1 follows the order of Li+ > Cs+ approximately Rb+ > K+ > Na+, which is opposite to the binding affinity of CB[6] toward alkali metal ions. On the other hand, the transport activity of 2 follows the order of Li+ > Na+, which is also opposite to the binding affinity of 2 toward these metal ions, but virtually no transport was observed for K+, Rb+, and Cs+. It is presumably because the carbonyl-fringed portal size of 2 (diameter 2.4 A) is smaller than the diameters of these alkali metal ions. To determine the transport mechanism, voltage-clamp experiments on planar bilayer lipid membranes were carried out. The experiments showed that a single-channel current of 1 for Cs+ transport is approximately 5 pA, which corresponds to an ion flux of approximately 3 x 107 ions/s. These results are consistent with an ion channel mechanism. Not only the structural resemblance to the selectivity filter of K+ channels but also the remarkable ion selectivity makes this model system unique.     

Thermodynamic Model of Inorganic Arsenic Species in Aqueous Solutions. Potentiometric Study of the Hydrolytic Equilibrium of Arsenious Acid

A potentiometric study of the hydrolysis of arsenious acid was carried out to define the thermodynamic model of the inorganic arsenic species in aqueous solutions. The protonation equilibrium of arsenious acid was determined at 25^°C. The variation of the stoichiometric formation constant with the ionic strength was also studied up to ionic strength 3.0 mol-dm^–3 in aqueous NaClO₄, NaCl, and KCl. The thermodynamic formation constant of arsenious acid (log K ^o = 9.22 ± 0.01) and the various interaction parameters were computed using the Modified Bromley Methodology (MBM), for both the molar and molal concentration scales at constant temperature (25^°C). The results showed the importance, not only of ionic strength, but also of the composition of the ionic medium on the distribution of the acid-base As(III) species as a function of pH in natural waters.