Chiral separations by host-guest complexation with cyclodextrin and crown ether in capillary zone electrophoresis

Summary Capillary zone electrophoresis using cyclodextrins and a chiral crown ether as buffer constituents was studied for the enantiomeric separation of drugs and amino acids. Based on results obtained from separation of racemic -amino acids both chiral selectors are compared with respect to resolution, efficiency and retention time. For (±)-Quinagolide effects of buffer composition and temperature are examined using -cyclodextrin as chiral agent. Optimum conditions were pH 2.5 at 30 mmol L^–1 -cyclodextrin. A linear dependence of retention on -cyclodextrin concentration allowed calculation of formation constants of the host-guest complexes. Buffer concentration and temperature also influence resolution. The application of a chiral crown ether to the separation of optical isomers in capillary zone electrophoresis is described for the first time. Chiral recognition of solutes depends on the formation of protonated alkyl amines and separation is attributed to the formation of diastereomeric host-guest complexes with different interactions for each enantiomer. The effects of crown ether concentration on resolution are presented.     

Preparation,Characterisation, and Structure of N-Methylated Derivatives of 1,3,5-Triamino-1,3,5-trideoxy-cis-inositol: Polyalcohols with Unusual Acidity

1,3,5-Trideoxy-1,3,5-tris(dimethylamino)-cis-inositol (TDCI) and 1,3,5-trideoxy-1,3,5-tris(trimethylammonio)-cis-inositol (TTCI) were prepared by methylation of 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (TACI). The ability of TDCI to form both intermolecular and intramolecular H-bonds, as demonstrated by X-ray diffraction, is probably responsible for the good solubility of TDCI in almost every common solvent. TTCI was found to be a polyol of unusual high acidity (pK₁ = 8.14 ± 0.02, pK₂ = 13.0 ± 0.2). This phenomenon could be explained by electrostatic interactions between the charged substituents of the cyclohexane residue.     

Optimization of a wet chemical continuous flow analysis method exemplified by the determinations of kjeldahl nitrogen and total phosphorus

The optimization of a rather complex wet chemical analysis method, such as the measurement of Kjeldahl nitrogen or total phosphorus with the Technicon AutoAnalyzer, is extremely tedious when purely empirical approaches are used. A mathematical model of the different stages of the measuring method (digestion, neutralization and color reaction) is described. The system can then be optimized for maximum measuring sensitivity. Optimization is done by solving numerically the non-linear optimization problem with constraints. The starting values for the optimization algorithm were found by varying these values systematically within the tolerated range, with checks that none of the constraints were violated. The theoretical results predict an increase in sensitivity by a factor of 15 compared to the method used previously. In practice, the sensitivity was increased by a factor of 10 for the total phosphorus method. For the simultaneous low-level determinations of Kjeldahl nitrogen and total phosphorus some problems of stability remain.     

2D time-domain nuclear magnetic resonance (2D TD-NMR) characterization of cell wall water of Fagus sylvatica and Pinus taeda L.

Cellulose - Water dominates the wood cell wall in the hygroscopic range. The state and amount of cell wall water influence the physical and mechanical properties of wood. 2D time-domain nuclear...     

Temperature-Responsive Electrocatalysis Based on Poly(N-Isopropylacrylamide)-Modified Graphene Oxide (PNIPAm-GO)

Poly(N-isopropylacrylamide)-modified graphene oxide (PNIPAm-GO), which is a type of thermally responsive GO, was designed and synthesized through a covalent “grafting-from” strategy. The as-prepared modified nanosheets integrated the individual advantages of two components, such as the thermal sensitivity of the PNIPAm terminal as well as the conductivity and the open 2D structure of the GO substrate. PNIPAm-GO was able to perform the reversible regulation of hydrophilicity/hydrophobicity in aqueous solution upon variations in the temperature. Such a unique property might also lead to the utilization of PNIPAm-GO as an intelligent electrode material to achieve a switchable electrochemical response toward a [Fe(CN)₆]^3−/4− probe. The PNIPAm-GO modified glassy carbon electrode (PNIPAm-GO/GC electrode) was able to exhibit better electrochemical performance in an ON/OFF switching effect than the PNIPAm-modified glassy carbon electrode (PNIPAm/GC electrode) without GO owing to the intrinsic properties and large surface area of the introduced GO. Moreover, it was found that the PNIPAm-GO/GC electrode also displayed excellent thermally responsive electrocatalysis toward the detection of 1,4-dihydro-β-nicotinamide adenine dinucleotide (NADH) and dopamine (DA), which resulted in two different catalytic statuses on the same electrode. This kind of switchable catalytic performance of the PNIPAm-GO/GC electrode might greatly enhance the flexibility of its application, and thus it is expected to have wide potential for applications in the fields of biosensors and biocatalysis.     

Über einen neuen aromatischen Kohlenwasserstoff C24H18 aus Erdölen

Ohne Zusammenfassung     

Adjustment of a GC automatic liquid sampler for high-performance liquid chromatography

Summary An automatic liquid sampler for high-performance liquid chromatography is described.The sampler is based on a GC-injection system from Hewlett-Packard. The HPLC sampler has a unique cleaning system, excellent reproducibility and a plug-in compatibility for sample identification and computer control for Hewlett-Packard integrators and Laboratory Data Systems.     

Injection of large volumes of aqueous solutions in capillary supercritical fluid chromatography and sample preconcentration by multiple injections

The possibility of using water or aqueous solutions as the solvent in capillary supercritical fluid chromatography was successfully demonstrated. Large volumes (up to 1 μl) of aqueous sample solutions were injected. Sample preconcentration was performed by means of multiple injections of aqueous sample solutions. The solutes were trapped at the beginning of the column at low density (high temperature and low pressure) and eluted using a density programme. The method can be applied to trace analysis. It proved to be linear in the range examined. Flame ionization detection was used for the studies. As this technique is not sensitive to water, no solvent peak appears, which may be an advantage for certain applications. The influence of water injections on the column performance and the reproducibility of injection was investigated.