Total pore blocking as an alternative method for the on-column determination of the external porosity of packed and monolithic reversed-phase columns

An alternative method to determine the interstitial void volume and the external porosity inside a packed or a monolithic column was developed. The method is based on the total blocking of the mesopores of a porous support by filling them with a hydrophobic solvent. The strong interaction of the latter with the hydrophobic coating inside the pores keeps the solvent in position during the subsequent measurements. With the pores of the stationary phase material completely inaccessible for any type of polar molecules, the method allows to perform interstitial void measurements using small molecular weight (MW) molecules instead of the large MW molecules that need to be used in inverse size exclusion chromatography (ISEC). These small MW molecules are able to penetrate every corner of the interstitial volume and therefore lead to a very accurate determination of the external porosity. Since only one type of molecules needs to be injected, the often troublesome regression analysis needed in ISEC is omitted as well. In the present contribution, the method has been applied to a packed bed and a monolithic column to investigate the optimal conditions of flow velocity, liquid compositions, and unretained marker selection. The robustness and the repeatability of the method are discussed as well.     

Experiments with Organic Modifiers in Reversed-Flow MEKC

Reversed-flow MEKC, i.e. MEKC at low pHs to suppress the electroosmotic flow, was evaluated for the separation of some homologous series. At low pHs compared to MEKC, the elution order reverses and normal phase type migration is obtained. Moreover, the elution window is nearly infinite. Efficiencies are very high and reproducibilities in absolute migration times are acceptable (%RSD < 5). The influence of a series of alcohol modifiers was investigated.     

High performance liquid chromatography analysis of wine anthocyanins revisited: Effect of particle size and temperature

The complex anthocyanin fraction of red wines poses a demanding analytical challenge. We have found that anthocyanins are characterised by extremely low optimal chromatographic velocities, and as a consequence generic HPLC methods suffer from limited resolving power. Slow on-column inter-conversion reactions, particularly between carbinol and flavylium species, are shown to occur on the same time scale as chromatographic separation, leading to increased plate heights at normal chromatographic velocities. In order to improve current routine HPLC separations, the use of small (1.7 μm) particles and high temperature liquid chromatography (HTLC) were investigated. 1.7 μm particles provide better efficiency and higher optimal linear velocities, although column lengths of ∼20 cm should be used to avoid the detrimental effects of conversion reactions. More importantly, operation at temperatures up to 50 °C increases the kinetics of inter-conversion reactions, and implies significantly improved efficiency under relatively mild analysis conditions. It is further demonstrated using relevant kinetic data that no on-column thermal degradation of these thermally labile compounds is observed at 50 °C and analysis times of <2 h.     

Multiple Step Gradient Analysis in Stationary Phase Optimised Selectivity LC for the Analysis of Complex Mixtures

Stationary phase optimised selectivity liquid chromatography (SOSLC) is an approach to tune a given LC separation by combining different stationary phases in a multi- segment column set-up. The presently available SOSLC optimisation procedure and algorithm are, however, only applicable to isocratic conditions. This is a severe limitation for the analysis of mixtures composed of components covering a broad hydrophobicity range. A strategy is described to circumvent this limitation. The components of a mixture are divided into different groups according to hydrophobicity as elucidated by a gradient analysis on a C₁₈ reversed-phase column. Each group separation is then individually optimised with a specific isocratic mobile phase composition using the original SOSLC strategy. The mobile phase composition thereby only differs in the percentage of organic modifier between the various groups. Finally, a combination of stationary phases that guarantees sufficient selectivity for all the groups is selected and the separation is performed by a multiple step gradient, whereby each level consists of the mobile phase composition applied for the SOSLC optimisation of the individual groups. The multi step gradient approach is demonstrated through the analysis of a mixture of 27 steroids covering a wide range of hydrophobicity.     

A Polynomial Bound for Untangling Geometric Planar Graphs

To untangle a geometric graph means to move some of the vertices so that the resulting geometric graph has no crossings. Pach and Tardos (Discrete Comput. Geom. 28(4): 585–592, 2002) asked if every n-vertex geometric planar graph can be untangled while keeping at least n ^ε vertices fixed. We answer this question in the affirmative with ε=1/4. The previous best known bound was \(\Omega(\sqrt{\log n/\log\log n})\). We also consider untangling geometric trees. It is known that every n-vertex geometric tree can be untangled while keeping at least \(\Omega(\sqrt{n})\) vertices fixed, while the best upper bound was \(\mathcal{O}((n\log n)^{2/3})\). We answer a question of Spillner and Wolff (http://arxiv.org/abs/0709.0170) by closing this gap for untangling trees. In particular, we show that for infinitely many values of n, there is an n-vertex geometric tree that cannot be untangled while keeping more than \(3(\sqrt{n}-1)\) vertices fixed.     

ColliderBit: a GAMBIT module for the calculation of high-energy collider observables and likelihoods

We describe ColliderBit, a new code for the calculation of high energy collider observables in theories of physics beyond the Standard Model (BSM). ColliderBit features a generic interface to BSM models, a unique parallelised Monte Carlo event generation scheme suitable for large-scale supercomputer applications, and a number of LHC analyses, covering a reasonable range of the BSM signatures currently sought by ATLAS and CMS. ColliderBit also calculates likelihoods for Higgs sector observables, and LEP searches for BSM particles. These features are provided by a combination of new code unique to ColliderBit, and interfaces to existing state-of-the-art public codes. ColliderBit is both an important part of the GAMBIT framework for BSM inference, and a standalone tool for efficiently applying collider constraints to theories of new physics.     

A one-pot double C-H activation palladium catalyzed route to a unique class of highly functionalized thienoisoquinolines

The synthesis of a unique class of highly functionalized 3,4-thienoisoquinolines via an efficient palladium-catalyzed one-pot, regioselective double C-H activation is presented. This class of biologically relevant compounds has been prepared in five steps from commercially available starting materials with overall yields ranging from 27 to 62%. A masked carboxylic acid was used to direct C-H activation to the typically less reactive C4 position. Additionally, the carboxylic acid provides a synthetically useful handle for further functionalization.