The role of stationary phases in reversed-phase liquid chromatography in the application of solvent optimization procedures

The development of liquid chromatographic separation procedures, which meet high standards of reliability and ruggedness, is of increasing importance. A number of software programs are available to make method development in laboratory practice less time consuming and also less dependent on the degree of knowledge of the analyst. Method development, as well as the subsequent routine analysis, generally start from the assumption of a constant column quality (that is, selectivity). In this study the role of the column in method development in reversed-phase liquid chromatography was investigated. It is shown that the influence of nominally identical stationary phases from different manufacturers on the results of method development procedures is significant. This also implies that the transferability of chromatographic separation conditions between "identical" columns is poor

Climate related shifts in the NCP ecosystem, and consequences for future spatial planning

Een uitgebreide meetinspanning op de Noordzee, in combinatie met wiskundige en statistische modellering, laat zien dat de klimaatveranderingen in de vorm van een verandering in de overheersende windrichting, een toename van de windsnelheid, een toename van de zeewatertemperatuur, als wel als een toenemende CO2 concentratie van de atmosfeer, niet alleen leidt tot een verandering van de samenstelling van het zeewater in de vorm van bijvoorbeeld opgelost anorganisch koolstof en zuurgraad, maar ook tot een, zei het beperkte, verlaging van de productiviteit van op en in de zeebodem levende filterende organismen, die op hun beurt het voedsel zijn van bodembewonende vissen

The International Pulsar Timing Array: First data release

International audienceThe highly stable spin of neutron stars can be exploited for a variety of (astro)physical investigations. In particular, arrays of pulsars with rotational periods of the order of milliseconds can be used to detect correlated signals such as those caused by gravitational waves. Three such 'pulsar timing arrays' (PTAs) have been set up around the world over the past decades and collectively form the 'International' PTA (IPTA). In this paper, we describe the first joint analysis of the data from the three regional PTAs, i.e. of the first IPTA data set. We describe the available PTA data, the approach presently followed for its combination and suggest improvements for future PTA research. Particular attention is paid to subtle details (such as underestimation of measurement uncertainty and long-period noise) that have often been ignored but which become important in this unprecedentedly large and inhomogeneous data set. We identify and describe in detail several factors that complicate IPTA research and provide recommendations for future pulsar timing efforts. The first IPTA data release presented here (and available on-line) is used to demonstrate the IPTA's potential of improving upon gravitational-wave limit

Review on the chemical and thermal stability of stationary phases for reversed-phase liquid chromatography

is the separation mode of choice. Faster method development procedures using aggressive eluents under elevated temperature conditions, the need for improved selectivities, efficiencies and resolution, the reduction of solvent consumption and also the decrease of analysis times require reversed-phase (RP) columns of high chemical and thermal stability. Until now, the majority of columns for RPLC separations are manufactured from silica substrates. Silica has many favorable properties making this material nearly ideal as a support for RP columns. However, its solubility, that increases considerably in eluents of pH above ±7, is a drawback preventing its widespread use over the entire pH range. In addition, also the thermal stability of silica is limited. Recently, however, substantial progress has been made in the synthesis of RPLC silica-based stationary phases showing satisfactory thermal and chemical stability under many different experimental conditions. Also, new substrates mainly based on other inorganic substrates like, e.g. alumina and zirconia have been developed now as a starting material for the preparation of RPLC stationary phases of improved chemical and thermal stability. In addition, for the same reasons, many efforts have also been made to synthesize polymer and also polymer-coated phases. These latter phases, more particularly those based on zirconia, but also polymer phases show a high degree of chemical and thermal stability compared to silica counterparts. In this paper, an overview will be given of the state-of-the-art of the thermal and chemical stability of the different available stationary phases for RPLC

Effect of buffers on silica-based column stability in reversed-phase high-performance liquid chromatography

Previous studies have shown that bonded-phase packing degradation at pH 9–10 mainly is due to silica support dissolution, and does not primarily result from the hydrolysis of covalently attaching siloxane bonds. Column stability also is significantly affected by the type and concentration of organic mobile-phase modifier. We now find that silica-based bonded-phase packings variably degrade with buffers containing different anions and cations. This effect is especially apparent with intermediate- and high-pH buffers. Under the same conditions, pH 10 aqueous carbonate and phosphate buffers with 50% methanol degraded bonded-phase packings much faster than borate and glycine buffers. The nature of the buffer cation also influences bonded-phase packing stability, with column lifetime a function of sodium> potassium> ammonium cations. The rate of bonded-phase packing degradation at pH 7–10 increases with higher concentrations of certain buffers, but especially phosphate. Column degradation is very strongly influenced by temperature. Certain mobile phase-buffer conditions can lead to increased column lifetime, so that practical operation up to pH 10 appears possible for some silica-based columns

High pH mobile phase effects on silica-based reversed-phase high-performance liquid chromatographic columns

Aqueous mobile phases above pH 8 often cause premature column failure, limiting the utility of silica-based columns for applications requiring high pH. Previous studies suggest that covalently bound silane ligands are hydrolyzed and removed by high-pH mobile phases. However, we found that the siloxane bonds for certain monomeric silanes are hydrolyzed very slowly from silica supports at pH 9–10. Therefore, bonded-phase packing degradation at high pH is a result mainly of silica support dissolution. The rate of column degradation for C18 columns is influenced not only by the type and purity of silica support, but also by the nature of the silane stationary phase. We found different rates of degradation for several commercial C18 columns. The relative rates of silica dissolution for these packings were determined by chemically measuring the silicate formed during column purging at high pH. The type and concentration of mobile phase organic modifier also significantly influences column degradation at high pH. Certain silica-based C18 packings can be used for long periods at pH 9 without significant changes in chromatographic properties. Results of this study better define the practical utility and limitations of silica-based columns in high pH environments

A first step towards miniaturized HPLC systems in analytical routine laboratories

This article shows that the first step towards the miniaturization of HPLC systems can be made without any, or only slight, modification to conventional equipment. Minor (less expensive) equipment modifications, particularly the use of micro-detector cells, allow the routine use of 3.2- and 2.1-mm i.d. small-bore columns in isocratic as well as gradient mode. This work encourages analysts to take a step towards the introduction of miniaturized HPLC systems in their laboratories, resulting in a considerable reduction in the use and costs of organic solvents and the establishment of "greener" laboratories