Development of a capillary electrophoresis system coupled to sequential injection analysis and evaluation by the analysis of nitrophenols

A combination of a laboratory-made capillary electrophoresis system and a sequential injection analysis equipment is described. For characterization, the system was successfully applied to the separation and quantification of nitrophenols. A blue LED was used as light source, and hydrodynamic injection was carried out by using a pressure-stable solenoid valve and an inflatable pressure reservoir. A good reproducibility of migration time (0.5%) and peak heights (5%) were obtained. The calibration by using peak heights was found to be linear up to 776?µmol?L^?1 for all three compounds. The system was robust and reliable for autonomous analysis without observation. All maintenance requirements including the conditioning of the capillary and flushing of both buffer reservoirs were carried out automatically. Instrumentation aspects of the capillary electrophoresis part are compared with former described hyphenated flow systems showing maximal operation versatility. Instrumental control and data evaluation were carried out using the software package AutoAnalysis.     

Alumina Catalysed Knoevenagel Condensations of Ferrocene-1,1′-Dicarboxaldehyde

Several symmetrically and unsymmetrically bifunctionalised solvatochromic ferrocene derivatives have been synthesised via alumina catalysed Knoevenagel reactions of ferrrocene-1,1′-dicarboxaldehyde.     

A convenient and economic approach to achieve SI-traceable reference values to be used in drinking-water interlaboratory comparisons

Metrologically traceable reference values add an essential benefit to interlaboratory comparisons: unlike consensus values, they can be used to establish national and international comparability. Furthermore, the participating laboratories obtain a reliable and unbiased benchmark to check their results for accuracy. Usually, metrologically traceable reference values are obtained by so-called primary methods which demand excessive efforts at great expense. Within the framework of two national drinking-water interlaboratory comparisons (proficiency testing rounds), a new approach to provide metrologically traceable reference values was applied. It is solely based on existing data which were collected during the comparison itself. Lead (Pb) measurements serve as an example to show how metrologically traceable reference values were derived from the lead amount added during sample preparation and the amount of lead already present in the drinking-water matrix used to prepare these samples. Within this approach, the matrix content is calculated in a way similar to a standard addition experiment. An uncertainty budget for the reference value was set up which describes the link to the corresponding SI units. Isotope dilution mass spectrometry (IDMS) as a primary method was used to validate this approach in the case of cadmium, chromium, copper, lead, and nickel.     

The Cauchy problem of Lorentzian minimal surfaces in globally hyperbolic manifolds

In this note a proof is given for global existence and uniqueness of minimal Lorentzian surface maps from a cylinder into a large class of globally hyperbolic Lorentzian manifolds for given initial values up to the first derivatives. The results of this article are part of my PhD thesis written at the Max-Planck institute for Mathematics in the Sciences in Leipzig under the supervision of Prof. Jürgen Jost to whom I want to express my gratitude.     

Sequential injection analyzer for glycerol monitoring in yeast cultivation medium

A smart and versatile flow system for the at-line monitoring of glycerol based on sequential injection analysis is proposed. Formaldehyde, generated by oxidation of glycerol with sodium periodate, is transformed into 2,4-diacetyl-1,4-dihydrolutidine applying the Hantzsch condensation reaction with acetylacetone and ammonium. Dual-wavelength detection was carried out to minimize the contribution of the schlieren effect using a single blue LED. In-line sample dilution is accomplished applying the concept of zone-penetration and a new concept of sample splitting. Under optimized physical and chemical variables, regression curves over two dynamic working ranges of 0.1-4 and 1-40 g l⁻¹ were attained. The injection throughputs were 14 and 12 h⁻¹, respectively. Applying on-line data evaluation and conditional inquiries, the smart and independent selection of the adequate analytical procedure for the required working range was accomplished. The system was successfully applied to the at-line monitoring of glycerol in a continuous, cell-free medium flow from a yeast cultivation process during batch and fed-batch phase with glycerol as the only carbon source.     

A Zn4L6 Capsule with Enhanced Catalytic C−C Bond Formation Activity upon C60 Binding

A redox‐switchable self‐assembled Zn^II₄L₆ cage was synthesized that contains naphthalenediimide (NDI) motifs. Its reduction lent these NDI panels persistent radical anion character. The redox activity of this cage allows it to act as a catalyst for the oxidative coupling of different tetraaryl borates to give biaryls. The catalytic activity of the cage was enhanced following its binding of C₆₀, which implies a mechanism that does not involve encapsulation of the substrate.