Ion-selective electrodes in potentiometric titrations; a new method for processing and evaluating titration data

A new method to convert the potential of an ion-selective electrode to concentration or activity in potentiometric titration is proposed. The advantage of this method is that the electrode standard potential and the slope of the calibration curve do not have to be known. Instead two activities on the titration curve have to be estimated e.g. the starting activity before the titration begins and the activity at the end of the titration in the presence of large excess of titrant. This new method is beneficial when the analyte is in a complexed matrix or in a harsh environment which affects the properties of the electrode and the traditional calibration procedure with standard solutions cannot be used. The new method was implemented both in a method of linearization based on the Grans's plot and in determination of the stability constant of a complex and the concentration of the complexing ligand in the sample. The new method gave accurate results when using titrations data from experiments with samples of known composition and with real industrial harsh black liquor sample. A complexometric titration model was also developed.     

On Energy-Optimal and Time-Optimal Precise Displacement of Rigid Body with Friction

Minimal time optimality and minimal energy optimality are usually considered as competing approaches for the trajectory planning for the precise movement of a rigid body. Theoretical and simulation results show that, with appropriate choice of constraints, these approaches are equivalent in the sense that they produce the same trajectory. This trajectory is globally optimal for both objectives. Constraints for velocity, driving force and jerk are taken into account. The model includes Coulomb and viscous friction. The optimal control solver was used as a numerical tool.     

Comparison of triple quadrupole,hybrid linear ion trap triple quadrupole,time‐of‐flight and LTQ‐Orbitrap mass spectrometers in drug discovery phase metabolite screening and identification in vitro – amitriptyline and verapamil as model compounds

Liquid chromatography in combination with mass spectrometry (LC/MS) is a superior analytical technique for metabolite profiling and identification studies performed in drug discovery and development laboratories. In the early phase of drug discovery the analytical approach should be both time‐ and cost‐effective, thus providing as much data as possible with only one visit to the laboratory, without the need for further experiments. Recent developments in mass spectrometers have created a situation where many different mass spectrometers are available for the task, each with their specific strengths and drawbacks. We compared the metabolite screening properties of four main types of mass spectrometers used in analytical laboratories, considering both the ability to detect the metabolites and provide structural information, as well as the issues related to time consumption in laboratory and thereafter in data processing. Human liver microsomal incubations with amitriptyline and verapamil were used as test samples, and early‐phase ‘one lab visit only’ approaches were used with all instruments. In total, 28 amitriptyline and 69 verapamil metabolites were found and tentatively identified. Time‐of‐flight mass spectrometry (TOFMS) was the only approach detecting all of them, shown to be the most suitable instrument for elucidating as comprehensive metabolite profile as possible leading also to lowest overall time consumption together with the LTQ‐Orbitrap approach. The latter however suffered from lower detection sensitivity and false negatives, and due to slow data acquisition rate required slower chromatography. Approaches with triple quadrupole mass spectrometry (QqQ) and hybrid linear ion trap triple quadrupole mass spectrometry (Q‐Trap) provided the highest amount of fragment ion data for structural elucidation, but, in addition to being unable to produce very high‐important accurate mass data, they suffered from many false negatives, and especially with the QqQ, from very high overall time consumption. Copyright © 2010 John Wiley & Sons, Ltd.     

Uranyl(VI) complexes of [O,N,O,N′]-type diaminobis(phenolate) ligands: Syntheses,structures and extraction studies

The syntheses and crystal structures of four new uranyl complexes with [O,N,O,N′]-type ligands are described. The reaction between uranyl nitrate hexahydrate and the phenolic ligand [(N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-N′,N′-dimethylethylenediamine)], H₂L1 in a 1:2 molar ratio (M to L), yields a uranyl complex with the formula [UO₂(HL1)(NO₃)] · CH₃CN (1). In the presence of a base (triethylamine, one mole per ligand mole) with the same molar ratio, the uranyl complex [UO₂(HL1)₂] (2) is formed. The reaction between uranyl nitrate hexahydrate and the ligand [(N,N-bis(2-hydroxy-3,5-di-t-butylbenzyl)-N′,N′-dimethylethylenediamine)], H₂L2, yields a uranyl complex with the formula [UO₂(HL2)(NO₃)] · 2CH₃CN (3) and the ligand [N-(2-pyridylmethyl)-N,N-bis(2-hydroxy-3,5-dimethylbenzyl)amine], H₂L3, in the presence of a base yields a uranyl complex with the formula [UO₂(HL3)₂] · 2CH₃CN (4). The molecular structures of 1–4 were verified by X-ray crystallography. The complexes 1–4 are zwitter ions with a neutral net charge. Compounds 1 and 3 are rare neutral mononuclear [UO₂(HLn)(NO₃)] complexes with the nitrate bonded in η²-fashion to the uranyl ion. Furthermore, the ability of the ligands H₂L1–H₂L4 to extract the uranyl ion from water to dichloromethane, and the selectivity of extraction with ligands H₂L1, H₃L5 (N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-3-amino-1-propanol), H₂L6 · HCl (N,N-bis(2-hydroxy-5-tert-butyl-3-methylbenzyl)-1-aminobutane · HCl) and H₃L7 · HCl (N,N-bis(2-hydroxy-5-tert-butyl-3-methylbenzyl)-6-amino-1-hexanol · HCl) under varied chemical conditions were studied. As a result, the most efficient and selective ligand for uranyl ion extraction proved to be H₃L7 · HCl.     

Onp-groups as loop groups

Archiv der Mathematik -     

The effect of additives on the speed of the crystallization front of xylitol with various degrees of supercooling

Some liquids can be kept in a supercooled or supersaturated metastable state for substantially long periods. Such liquids can be applied as long-term heat storage where the latent heat can be released when needed. As xylitol possesses a relatively high value of latent heat and as it can be easily supercooled, it has promising properties for this application. However, the speed of the crystallization of xylitol is low, leading to a low release rate of latent heat.Several additives have been experimentally tested for the purpose of accelerating the crystallization speed. The effect of the additives on the latent heat, on the melting temperatures, and on the long-term durability of the supercooled state was also measured.The highest speeds of the crystallization front, at a temperature of 22 °C, were achieved with methanol as an additive leading to speeds 33 times higher in vertical experiments and in 170 times higher in horizontal ones than with pure xylitol. The improved speed of the crystallization front is mostly caused by the methanol flow currents generated as a result of the separation of methanol during crystallization, and to a lesser extent, as a result of the increase in the speed of the growth of the crystals.     

Implementation of a chemical equilibrium constraint in the multivariate curve resolution of voltammograms from systems with successive metal complexes

A multivariate curve resolution (MCR) method, using a constrained alternating least squares (ALS) procedure with a new chemical equilibrium constraint, was applied to differential-pulse polarograms of successive metal complexes. This new restriction imposes the fulfillment of a chemical model defined by a set of stability constants that are optimised along the iterative ALS procedure. The reliability of the method was tested with simulated data and with polarograms measured for the systems Zn(II) + glutathione and Cd(II) + 1,10-phenanthroline. These systems respectively yield two and three successive and electroactive complexes, which are inert from the electrochemical point of view, that is, the complexes virtually do not dissociate during the measurement. Although the presence of electrode adsorption could induce overestimation of some concentrations and losses of linearity between concentrations and signals, the results showed that the proposed method can yield satisfactory estimations of the stability constants in this kind of system. The performance of the new method is compared with the performances obtained using MCR-ALS without the equilibrium constraint and using traditional curve fitting least-squares approaches.     

Influence of anionic additive on Hg(2+) interference on Ag(+)-ISEs based on [2.2.2]p,p,p-cyclophane as neutral carrier

The influence of the anionic additive on the Hg²⁺ interference on Ag⁺-ion-selective electrodes (Ag⁺-ISEs) based on [2.2.2]p,p,p-cyclophane as π-coordinating neutral carrier was studied by potentiometric measurements. The weakly coordinating carborane anion (7,8,9,10,11,12-hexabromocarborane, CB₁₁H₆Br₆⁻) was compared with the commonly used tetrakis(4-chlorophenyl borate) (TpClPB⁻) as the anionic additive in plasticized PVC membrane-based Ag⁺-ISEs. The Hg²⁺ interference was reduced by six orders of magnitude when replacing TpClPB⁻ with CB₁₁H₆Br₆⁻ as the anionic additive, resulting in determined by the matched potential method (MPM). This indicates that weakly coordinating carboranes may be particularly useful as anionic additives in ISEs for soft cations.