Pure Eluent Research Articles

Consequences of on-line dialysis on polyelectrolyte molar masses determined by size-exclusion chromatography with light scattering detection.

Size-exclusion chromatography with light scattering detection experiments conducted on poly(acrylic acid) neutralized to different degrees or using hydroxides with different counterions suggest that the same counterion and degree of neutralization is observed at the detector, irrespective of salt concentration, degree of neutralization and counterion at the time of injection. This strongly supports that during the chromatographic experiment the counterions of the polyelectrolyte are exchanged with those of the eluent, resulting in an effective dialysis of the polyelectrolyte solution during the size-exclusion chromatography experiment. Consequently, the refractive index increment determined by a refractive index detector equals the refractive index increment obtained after excessive dialysis against the pure eluent. Therefore, the species detected and characterized by light scattering coupled to size-exclusion chromatography are not identical to the species injected into the chromatographic system. Despite this structural change during the chromatographic experiments, the correct molar mass for the injected species is obtained by size-exclusion chromatography with light scattering detection.

Radical Chain End Chemical Transformation of SG1-Based Polystyrenes

Radical chain end functionalization of polystyrene previously prepared by NMP using the SG1 nitroxide was investigated. Hydroxy-functional polystyrenes were easily prepared by two different pathways: via an exchange with TEMPO nitroxide followed by a Zn/AcOH reduction or via a radical hydroxylation using the in situ preparation/reduction of the corresponding hydroperoxide. The introduction of a bromine end group was performed by radical bromination under mild conditions using ethyl 2-bromoisobutyrate as bromine transfer agent. The latter polymer was further reacted with NaN3 and also used as a macroinitiator to prepare PS-b-PMMA by ATRP to confirm the chemical post-transformation. Azide-functional polystyrenes were also prepared by a one-step radical azidation reaction using ethanesulfonyl azide. In all cases, the chemical transformations were followed by both liquid chromatography at the critical condition in pure eluent and Maldi-Tof MS.

Liquid chromatography at the critical conditions in pure eluent: An efficient tool for the characterization of functional polystyrenes

Functional polymers are usually separated by liquid chromatography at critical conditions (LC-CC) using a desorli/adsorli mixture as eluent. In this paper, we describe LC-CC using dimethylformamide (DMF) as pure eluent at 72 °C and its application to the analysis of functional polystyrenes. The critical adsorption point is reached by tuning the temperature so that the lack of repeatability is no longer a problem. We analysed several batches of polystyrenes, exhibiting different molecular weights and functionalities. We were able to differentiate di-, mono- and non-functional polystyrenes, bearing carboxylic acid, hydroxyl or nitroxide moieties. The behaviour of these polystyrenes expressed by the experimental results was compared with their behaviour described by the LC-CC theory through the calculation of the effective interaction parameter of each end group. The technique also makes it possible to quantify the fractions of different functional polymers in a blend.

Separation of simple ions by gel chromatography : I. simple model of separation for single-salt systems

The chromatographic separation of simple ions by a polymer gel in water was modelled as a liquid—liquid partition process. The model consists of two “homogeneous” phases, a mobile phase of pure eluent and a stationary (gel) phase of a structureless concentrated polymer solution with a few electric charges fixed within it. Thermodynamic considerations and a simplifying approximation yielded a simple description of single-salt systems, which accounted for the chromatographic behaviour of simple ions at low and high concentrations in a systematic fashion. The intoduced notion of “intrinsic distribution coefficients” of ions proved to be useful. The main mechanism of the separation ions is suggested to be the difference in the thermodynamic stabilities of individual ions in the two phases, rather than involving size-exclusion and adsorption effects.

Influence of temperature, pressure and eluent composition on the behaviour of binary eluents under sub- and supercritical conditions : Pentane and 1,4-dioxane

In supercritical fluid chromatography, the temperature- and pressure-dependent behaviour of the chromatographic parameters for binary eluent mixtures, containing pentane as the primary component and 1,4-dioxane as a secondary component, is similar to that or pure eluents. The isobars show maxima above the critical temperature for capacity factors and for resolution. With increasing content of the secondary component in the mixture, the critical temperatures rise and the maxima move to higher temperatures. The maxima are more pronounced at lower coloumn pressures. Maxima appear also when plotting versus eluent composition at constant temperature and pressure. All maxima occur at both sub- and supercritical pressure. Temperature—pressure—composition triple points can be found where the capacity factors or the resolution reach maximum values. This can be used for optimizing separations.

Some physical characteristics of corning porous glass packing in gel permeation chromatographic separations

The nature of the interactions between the main gel permeation chromatography (GPC) components. viz., the solute, eluent and gel, was examined. Corning controlled porosity glass (CPG) was chosen as the column packing and the separation of low-molecular-mass organic molecules, polystyrene standards and narrow-molecular-mass-distribution poly-2-vinylpyridine samples was carried out. Pure eluents (methyl ethyl ketone and dimethylformamide) and mixed eluents (methyl ethyl ketone-ethanol, methyl ethyl ketone-acetone and dimethylformamide-methanol) were used. The results showed that the attractive physical forces between solutes and CPG also contribute to the mechanism of separation. These forces could be suppressed or avoided by changing the nature of the solvent.