On-line coupling of size-exclusion chromatography and capillary zone electrophoresis via a reversed-phase C18 trapping column for the determination of peptides in biological samples

Since biologically active peptides usually exhibit their effects in low concentrations, the development of sensitive analytical methods has become a challenge. In this paper, a multidimensional system is presented, consisting of a size-exclusion chromatographic (SEC) separation followed by a trapping procedure on a 4 mm x 3 mm ID reversed-phase C18 (RP18) column with subsequent elution of the trapped fraction and separation by capillary zone electrophoresis (CZE). The system has been tested with mixtures of six enkephalins and albumin, mimicking biological matrices such as plasma and cerebrospinal fluid. After separation of albumin from the enkephalins in the SEC dimension a heart-cut of 200 micro L, containing the enkephalin peak, is taken, concentrated on the RP18 microcolumn and, after elution with a 20 micro L plug of 80% acetonitrile, electrokinetically injected into the CZE system, where stacking and separation is achieved. While validation shows generally good linearity and reproducibility, the quantitation limit with UV detection is acceptable (2.5 micro g/ mL with an injection volume of 50 micro L).     

The Passive Polymer Problem

In this article, we introduce a generalization of the diffusive motion of point-particles in a turbulent convective flow with given correlations to a polymer or membrane. In analogy to the passive scalar problem we call this the passive polymer or membrane problem. We shall focus on the expansion about the marginal limit of velocity–velocity correlations which are uncorrelated in time and grow with the distance x as |x| , and small. This relation gets modified in the case of polymers and membranes (the marginal advecting flow has correlations which are shorter ringed.) The construction is done in three steps: First, we reconsider the treatment of the passive scalar problem using the most convenient treatment via field theory and renormalization group. We explicitly show why IR-divergences and thus the system-size appear in physical observables, which is rather unusual in the context of ordinary field-theories, like the ⁴-model. We also discuss, why the renormalization group can nevertheless be used to sum these divergences and leads to anomalous scaling of 2n-point correlation functions as e.g., S ²ⁿ (x)[(x, t)–(0, t)]²ⁿ . In a second step, we reformulate the problem in terms of a Langevin equation. This is interesting in its own, since it allows for a distinction between single-particle and multi-particle contributions, which is not obvious in the Focker–Planck treatment. It also gives an efficient algorithm to determine S ²ⁿ numerically, by measuring the diffusion of particles in a random velocity field. In a third and final step, we generalize the Langevin treatment of a particle to polymers and membranes, or more generally to an elastic object of inner dimension D with 0D2. These objects can intersect each other. We also analyze what happens when self-intersections are no longer allowed.     

Measuring functional renormalization group fixed-point functions for pinned manifolds

Exact numerical minimization of interface energies is used to test the functional renormalization group analysis for interfaces pinned by quenched disorder. The fixed-point function R(u) (the correlator of the coarse-grained disorder) is computed. In dimensions D=d+1, a linear cusp in R'(u) is confirmed for random bond (d=1, 2, 3), random field (d=0, 2, 3), and periodic (d=2, 3) disorders. The functional shocks that lead to this cusp are seen. Small, but significant, deviations from the 1-loop calculation are compared to 2-loop corrections and chaos is measured.     

Haltbare L?sungen von Eriochromschwarz T

Zusammenfassung Wäßrige Eriochromschwarzlösungen lassen sich durch Zugabe von Hydroxylammoniumsulfat und Isopropanol stabilisieren. Nach der angegebenen Vorschrift hergestellte Lösungen sind je nach Aufbewahrung 4 Wochen bis 1 Jahr beständig. Auch bei der Titration von Calcium und Magnesium in Gegenwart von Schwermetallen tritt keine Zersetzung des Indicators mehr ein.

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Summary Aqueous solutions of Eriochrome Black indicator can be stabilized by the addition of hydroxyl ammonium sulphate and isopropanol. Solutions prepared according to the instructions given in this paper are stable for four weeks to one year depending on type of storage. There is no longer any degradation of the indicator when titrating calcium and magnesium in the presence of heavy metals.

     

Multistability and chaos by parametric excitation of longwave modes in a YIG sphere

Spin-wave instabilities in spheres of yttrium iron garnet have been studied by ferromagnetic resonance within the coincidence regime of the first-order Suhl instability (1.8–3.4 GHz), i.e. both the uniform mode and pairs of spin-waves were simultaneously excited on resonance. From the characteristic behaviour above the threshold, three different regimes of resonance fields (and frequencies) could be distinguished: For low fields (640–680 Oe) and for high fields (950–1210 Oe) the amplitude of magnetization remains time independent and only at high input power becomes suddenly chaotic. In the intermediate regime (680–950 Oe) a very complex multistable behaviour occurs and a variety of oscillations and sequences of bifurcations are observed. We discuss our experimental results in terms of a multi-mode model which, beyond spin-waves, considers the excitation of longwave modes with wavelengths in the order of sample dimension. Magnetostatic modes and spin-waves can be described within a unified picture by introducing spherical spin-waves which are classified by symmetry. A new mechanism based on the indirect excitation of the magnetostatic (4,3,0) mode is introduced. Numerical simulations show that this mechanism can explain both the multistability and the complex dynamic behaviour of the system.     

Über die dilatometrisch indizierten Titrationen

Dilatometrical indication can be applied to oxidation-reduction reactions; this is demonstrated by the following oxidation-reduction couples: K₂Cr₂O₇/FeSO₄, K₂Cr₂O₇/Na₃AsO₃, Ce(SO₄)₂/FeSO₄, Ce(SO₄)₂/Na₃AsO₃. Amounts between 1 and 12 m Val show a deviation of less than 0.2%. With the couple KMnO₄/FeSO₄, especially with KMnO₄/Na₃AsO₃ the point of equivalence cannot be figured out so exactly as in the above cases. However, from the titration courves a conclusion may be drawn as to the course of the reaction. The changes in volume occurring under the oxidation-reduction reactions are determined and compared with those theoretically excepted.     

Selective and sensitive on-line flow extraction,preconcentration and normal-phase liquid chromatography

The on-line coupling of flow extraction with normal-phase liquid chromatography (LC) was studied. The aqueous sample was introduced into the extraction unit and the organic phase of this unit was fed to the LC system, via a precolumn. This column preconcentrated the sample, thereby diminishing band broadening and improving the sensitivity. Caffeine and zidovudine were used as test compounds; the limits of detection in standard solutions were 2 × 10^?9 and 1.2 × 10^?8 M, respectively. The applicability of the method to real samples (beverages and urine) was investigated. The correlation coefficient of the calibration graphs was ? 0.99.