Organic solvent modifier and temperature effects in non-aqueous size-exclusion chromatography on reversed-phase columns.

Common reversed-phase columns (C18, C4, phenyl, and cyano) offer inert surfaces suitable for the analysis of polymers by size-exclusion chromatography (SEC). The effect of tetrahydrofuran (THF) solvent and the mixtures of THF with a variety of common solvents used in high performance liquid chromatography (acetonitrile, methanol, dimethylformamide, 2-propanol, ethanol, acetone and chloroform) on reversed-phase stationary phase characteristics relevant to size exclusion were studied. The effect of solvent on the elution of polystyrene (PS) and poly(methyl methacrylate) (PMMA) and the effect of column temperature (within a relatively narrow range corresponding to typical chromatographic conditions, i.e., 10°C-60°C) on the SEC partition coefficients KSEC of PS and PMMA polymers, were also investigated. The bonded phases show remarkable differences in size separations when binary mixtures of THF with other solvents are used as the mobile phase. The solvent impact can be two-fold: (i) change of the polymeric coil size, and possible shape, and (ii) change of the stationary phase pore volume. If the effect of this impact is properly moderated, then the greatest benefit of optimized solute resolution can be achieved. Additionally, this work provides an insight on solvent-stationary phase interactions and their effects on column pore volume. The only effect of temperature observed in our studies was a decreased elution volume of the polymers with increasing temperature. SEC partition coefficients were temperature-independent in the range of 10°C-60°C and therefore, over this temperature range elution of PS and PMMA polymers is by near-ideal SEC on reversed-phase columns. Non-ideal SEC appears to occur for high molar mass PMMA polymers on a cyano column when alcohols are used as mobile phase modifiers.

Aqueous size-exclusion chromatography of polyelectrolytes on reversed-phase and hydrophilic interaction chromatography columns.

The size-exclusion separation of a water-soluble polyelectrolyte polymer, sodium polystyrene sulfonate (NaPSS), was demonstrated on common reversed-phase (C18, C4, phenyl, and cyano) and hydrophilic interaction chromatography (HILIC) columns. The effect of common solvents - acetonitrile (ACN), tetrahydrofuran (THF), and methanol (MeOH), used as mobile phase modifiers - on the elution of NaPSS and the effect of column temperature (within a relatively narrow range corresponding to typical chromatographic conditions, i.e., 10 °C-60 °C) on the partition coefficient, KSEC, were also investigated. Non-size-exclusion chromatography (non-SEC) effects can be minimized by the addition of an electrolyte and an organic modifier to the mobile phase, and by increasing the column temperature (e.g., to 50 °C or 60 °C). Strong solvents such as THF and ACN are more successful in the reduction of such effects than is the weaker solvent MeOH. The best performance is seen on medium polarity and polar stationary phases, such as cyanopropyl- and diol-modified silica (HILIC), where the elution of the NaPSS polyelectrolyte is by a near-ideal SEC mechanism. Hydrophobic stationary phases, such as C18, C4, and phenyl, require a higher concentration of a strong solvent modifier (THF) in the mobile phase to reduce non-SEC interactions of the solute with the stationary phase.

Size exclusion chromatography of synthetic polymers and biopolymers on common reversed phase and hydrophilic interaction chromatography columns.

This work describes the applicability of common reversed phase and HILIC columns for size exclusion chromatography of synthetic and natural polymers. Depending on the nature of the solute and column stationary phase, a "non-retention" condition must be created with the aid of the mobile phase to achieve a unique size-based separation in isocratic mode. The various bonded phases show remarkable differences in size separations that are controlled by mobile phase conditions. Polymer-mobile phase and column-mobile phase solvation interactions determine polymer hydrodynamic volume (or solute bulkiness) and polymer-column steric interaction. Solvation interactions in turn depend on polymer, mobile phase and stationary phase polarities. Column-mobile phase solvation interactions determine the structural order of the bonded ligands that can vary from ordered (extended, aligned away from the silica substrate) to disordered (folded, pointing toward the silica substrate). Chain order increases with increased solvent penetration into the bonded phase. Increased chain order reduces pore volume, and therefore decreases the size-separation efficiency of a column. Conversely, decreased chain order increases pore volume and therefore increases the size-separation efficiency. The thermodynamic quality of the mobile phase also plays a significant role in the separation of polymers. "Poor" solvents can significantly reduce the hydrodynamic diameter of a solute and thus change their retention behavior. Medium polarity stationary phases, such as fluoro-phenyl and cyano, exhibit a unique retention behavior. With an appropriate polarity mobile phase, polar and non-polar synthetic polymers of the same molecular masses can be eluted at the same retention volumes.

Quantitation of sulfobutyl ether-ß-cyclodextrin (Captisol™) in Vestipitant IV solution by liquid chromatography with ultraviolet (UV) detection.

This work describes a simple, sensitive and fast liquid chromatographic method using ultraviolet (UV) detection for the quantitation of Captisol™ (sulfobutyl ether-ß-cyclodextrin, SBE-ß-CD) in Vestipitant (GW597599) IV formulation. The chromatographic system consists of a cyano-modified silica stationary phase column with 0.5mM copper(II) acetate in 50/50 (v/v) water/acetonitrile and 0.05% (v/v) of trifluoroacetic acid as the mobile phase. Due to the fact that SBE-ß-CD does not possess a chromophore suitable for UV detection, copper(II) acetate is used as a detection reagent. At low pH copper(II) acetate interacts with SBE-ß-CD and produces mixed copper(II) [Cu(2+)] chelate and copper(II) mono acetate [CuOAc(+)] complexes, while displacing sodium ions [Na(+)] from the sulfobutyl ether (SBE) group. The copper(II)-SBE-ß-CD interaction has optical properties that allow its detection by UV. This novel method is highly reproducible and reliable for accurate quantitation of SBE-ß-CD content in the Vestipitant IV solution, and in the solution without the Vestipitant matrix.