An improved ion-selective electrode for perchlorate

A new liquid-membrane ion-selective electrode for perchlorate ion based on tetrakistri-phenylphosphine silver(I) perchlorate in nitrobenzene is described. Its dynamic range and selectivities relative to most common anions are comparable to those of the Orion model 92-81 perchlorate sensor. However, it suffers much less hydroxide-ion interference than the Orion product.     

An improved potential surface for formaldehyde

A potential energy surface for the ground X? ¹A₁ state of H₂CO has been derived, which reproduces the position of a recently calculated H₂ + CO transition state. The variational method for the determination of frequencies of potential energy surfaces has been extended to tetra-atomics, thus enabling the surface to be refined.     

An improved algorithm for satellite-derived UV radiations

The improved algorithm surface irradiance derived from a range of satellite-based sensors (SIDES) is presented in this article. It calculates various types of surface UV intensities, such as biologically weighted or unweighted UV spectra, integrated doses or irradiance at specific wavelengths, using data from satellite instruments. These surface UV data are mainly useful for environmental impact or process studies where high accuracy or a high temporal resolution is required. In contrast to several previous studies, SIDES has been validated with spectral measurements. By this method an averaging of positive or negative deviations over the complete wavelength range is avoided. This is especially important for UV wavelengths around 300 nm where biological effectiveness is highest. The results of SIDES deviate less than 7% from ground-based observations for wavelengths between 295 and 400 nm. In contrast, the corresponding deviations of the joint research center algorithm escalate for shorter wavelengths, reaching 35% at 295 nm. This large deviation is due to an inaccurate interpolation procedure that has been detected by spectral analysis. Thus, spectral validation is demonstrated to be an appropriate tool to detect weaknesses in such an algorithm and provides information essential for improvement.     

An improved mercury control for capillary burettes

Summary A mechanically superior mercury control for capillary burettes has been developed which holds a high column of mercury without leakage and still affords a minute control over the rise of the mercury in the capillary.

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Zusammenfassung Es wurde eine infolge ihrer mechanischen Bauart vorzügliche Kontrollvorrichtung für Kapillarbüretten entwickelt, die eine hohe Quecksilbersäule ohne Quecksilberverlust (durch Leckwerden) festhält und eine äußerst genaue Beobachtung der Höhe der Quecksilbersäule in der Kapillarröhre gestattet.

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Résumé On a développé un contrôle, méchaniquement supérieur, à mercure pour des burettes capillaires, lequel tient une haute colonne de mercure sans fuite et qui donne un contrôle très précis de l'élévation du mercure dans le tube capillaire.

     

An improved cell for in-situ electrochemical ESR

An improved cell for simultaneous electrochemical ESR based on a coaxial cylindrical cavity is described and shown to have high sensitivity whilst behaving as a satisfactory hydrodynamic electrode as evidenced by Tafel analysis, by Levich analysis and comparison with theory for the dependence of the ESR signal on electrode currents and electrolyte flow rate.     

An improved model potential for liquid lithium

An improvement in the computed structure of liquid lithium was obtained by adding the Xα Slater exchange energy to the electron pseudopotential of Ashcroft, Singwi, Sjölander et al. The remaining discrepancies can only be corrected by using a fully non-local pseudopotential for lithium, and perhaps by improving experimental accuracies of structure factors.     

An improved OPLS-AA force field for carbohydrates

This work describes an improved version of the original OPLS-all atom (OPLS-AA) force field for carbohydrates (Damm et al., J Comp Chem 1997, 18, 1955). The improvement is achieved by applying additional scaling factors for the electrostatic interactions between 1,5- and 1,6-interactions. This new model is tested first for improving the conformational energetics of 1,2-ethanediol, the smallest polyol. With a 1,5-scaling factor of 1.25 the force field calculated relative energies are in excellent agreement with the ab initio-derived data. Applying the new 1,5-scaling makes it also necessary to use a 1,6-scaling factor for the interactions between the C4 and C6 atoms in hexopyranoses. After torsional parameter fitting, this improves the conformational energetics in comparison to the OPLS-AA force field. The set of hexopyranoses included in the torsional parameter derivation consists of the two anomers of D-glucose, D-mannose, and D-galactose, as well as of the methyl-pyranosides of D-glucose, D-mannose. Rotational profiles for the rotation of the exocyclic group and of different hydroxyl groups are also compared for the two force fields and at the ab initio level of theory. The new force field reduces the overly high barriers calculated using the OPLS-AA force field. This leads to better sampling, which was shown to produce more realistic conformational behavior for hexopyranoses in liquid simulation. From 10-ns molecular dynamics (MD) simulations of alpha-D-glucose and alpha-D-galactose the ratios for the three different conformations of the hydroxymethylene group and the average (3)J(H,H) coupling constants are derived and compared to experimental values. The results obtained for OPLS-AA-SEI force field are in good agreement with experiment whereas the properties derived for the OPLS-AA force field suffer from sampling problems. The undertaken investigations show that the newly derived OPLS-AA-SEI force field will allow simulating larger carbohydrates or polysaccharides with improved sampling of the hydroxyl groups.     

An improved empirical force field for saturated hydrocarbons

A new molecular mechanics force field for alkanes is presented. The force field aims to eliminate some identified failures of the well-known MM2 force field. The new energy function gives an improved prediction of the rotational barriers of highly congested molecules, a better calculation of short nonbonded contacts, and the correct reproduction of bond elongation in small torsion angles. The calculation of sublimation enthalpies is also improved. The standard deviation of the formation enthalpies for a set of 54 compounds is 0.63 kcal/mol; this compares with the reported value of 0.42 calculated with MM2 and MM3 for different sets. The force field parameters were obtained using a least squares method.     

An improved microwave plasma torch for atomic spectrometry

The analytical performance of a microwave plasma torch was improved through mechanical alterations. Several problems reported in earlier designs were addressed: the ignition and stabilization of a helium plasma in the MPT was difficult; high powers were required to both ignite and operate the plasma; otherwise, the plasma would erratically change from an annular to a filament type discharge. In the new torch, the helium discharge was stabilized by replacing the copper central tube with one made of quartz. In addition, air entrainment was alleviated through use of a sheathing gas. This modification simplified the background mass spectrum and raised the effective ionization temperature of the discharge. A detailed schematic diagram of the new microwave plasma torch is presented.     

An improved set of mndo parameters for sulfur

The MNDO parameters for sulfur have been reoptimized. Calculations for a number of sulfur compounds indicate a very significant improvement. Inclusion of d AOs failed to correct the errors for compounds of sulfur in its higher valence states. Since d AOs are not included, the calculations are still confined to compounds of divalent sulfur.     

An improved reaction valve for flow injection analysis

Summary A new type reaction valve for flow injection analysis has been developed. In a FIA system with this valve the injected sample is once passed into a loop of the valve, thereafter the valve is rotated to the next position. Therefore, the sample is retained in the loop in a stop-state for a long time and the next sample is introduced into another loop in the next position. When the valve is rotated for one round, the stopped sample in the fist loop is again passed into the detector flow cell. Thus, an analysis, which needs a long reaction time, can be performed with this valve with high precision.

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Verbessertes Reaktionsventil für die Flie\injektionsanalyse

     

An improved actinide separation method for environmental samples

This paper presents a rapid method of separation of five actinide elements (Th, U, Np, Pu, and Am) for aqueous media samples. This separation method utilizes the unique chemistries of the actinides at low concentrations^1,2 and the properties of the EIChroM TRU-Resin^TM extraction resin. In order to cleanly recover the five actinides from aqueous samples or solubilized soil samples, the sample is passed through the column twice. The sample is first loaded in an HCl solution with hydrogen peroxide. This allows the Am and most matrix ions to pass through the column. Then the Th is eluted using dilute HCl followed by the Np and Pu which are eluted together with oxalic acid in dilute HCl solution. Finally, the U is eluted with ammonium oxalate solution. A calcium-oxalate coprecipitation is performed on the original load solution containing the Am ions and the dissolved precipitate is then reloaded onto the TRU-Resin^TM column in HNO₃ with ascorbic acid. The procedure requires approximately 1.5 working days for experienced technicians, greatly reduces waste, and generally results in actinide recoveries of 80–100%.     

An improved residue analytical method for phenylurea herbicides

Summary An improved HPLC method with electrochemical detection is applied to the determination of phenyl urea herbicide residues in crops. The analysis includes extraction and hydrolysis with NaOH, clean-up by steam distillation and partition into methanol/HCl and quantitation of the aniline by HPLC with 2-column switching technique and amperometric detection.     

An improved general harmonic force field for ethylene

The recent availability of certain critical experimental data, both from this and other laboratories, for isotopic species of the ethylene molecule, has enabled the previously published GHFF to be redetermined with much greater precision. Several significant changes in the force constants occur, bringing the empirical values into better overall agreement with ab initio values. Calculated data using the new force field are considered to be sufficiently reliable to be used with confidence in spectroscopic and structural applications and are listed.