Structure Driven Prediction of Chromatographic Retention Times: Applications to Pharmaceutical Analysis.

Pharmaceutical drug development relies heavily on the use of Reversed-Phase Liquid Chromatography methods. These methods are used to characterize active pharmaceutical ingredients and drug products by separating the main component from related substances such as process related impurities or main component degradation products. The results presented here indicate that retention models based on Quantitative Structure Retention Relationships can be used for de-risking methods used in pharmaceutical analysis and for the identification of optimal conditions for separation of known sample constituents from postulated/hypothetical components.

Retention characteristics of some antibiotic and anti-retroviral compounds in hydrophilic interaction chromatography using isocratic elution, and gradient elution with repeatable partial equilibration.

The separation of some zwitterionic, basic and neutral antibiotic and antiretroviral compounds was studied using hydrophilic interaction chromatography (HILIC) on bare silica, bonded amide and urea superficially porous phases. The differences in the selectivity and retentivity of these stationary phases were evaluated for compounds with widely different physicochemical properties (logD -3.43 to 2.

Integrated Analytical and Statistical Two-Dimensional Spectroscopy Strategy for Metabolite Identification: Application to Dietary Biomarkers.

A major purpose of exploratory metabolic profiling is for the identification of molecular species that are statistically associated with specific biological or medical outcomes; unfortunately, the structure elucidation process of unknowns is often a major bottleneck in this process. We present here new holistic strategies that combine different statistical spectroscopic and analytical techniques to improve and simplify the process of metabolite identification. We exemplify these strategies using study data collected as part of a dietary intervention to improve health and which elicits a relatively subtle suite of changes from complex molecular profiles.

Some factors that can lead to poor peak shape in hydrophilic interaction chromatography, and possibilities for their remediation.

Some factors which present difficulties for obtaining good peak shape in hydrophilic interaction chromatography (HILIC) were studied. The effect of injection solvent composition and volume was systematically investigated using a selection of weak and stronger basic compounds on a hybrid bare silica phase. Increasing the mismatch between the injection solvent (range 95-0% ACNv/v) and the mobile phase (maintained at 95% ACNv/v) gave increasing deterioration in peak shape.

Performance of charged aerosol detection with hydrophilic interaction chromatography.

The performance of the charged aerosol detector (CAD) was investigated using a diverse set of 29 solutes, including acids, bases and neutrals, over a range of mobile phase compositions, particularly with regard to its suitability for use in hydrophilic interaction chromatography (HILIC). Flow injection analysis was employed as a rapid method to study detector performance. CAD response was 'quasi-universal', strong signals were observed for compounds that have low volatility at typical operating (room) temperature.

Comparison of the kinetic performance and retentivity of sub-2 μm core–shell, hybrid and conventional bare silica phases in hydrophilic interaction.

The separation performance and retention properties of four sub-2μm underivatised silica materials were evaluated in the hydrophilic interaction chromatography (HILIC) mode. These included an organic/inorganic hybrid silica, conventional silica, narrow particle size distribution silica and a core-shell silica. Van Deemter characterisation was performed using conditions to give high retention factors (k=5.

Comparison of peak shape in hydrophilic interaction chromatography using acidic salt buffers and simple acid solutions.

The retention and peak shape of neutral, basic and acidic solutes was studied on hydrophilic interaction chromatography (HILIC) stationary phases that showed both strong and weak ionic retention characteristics, using aqueous-acetonitrile mobile phases containing either formic acid (FA), ammonium formate (AF) or phosphoric acid (PA). The effect of organic solvent concentration on the results was also studied. Peak shape was good for neutrals under most mobile phase conditions.

Practical observations on the performance of bare silica in hydrophilic interaction compared with C18 reversed-phase liquid chromatography.

The kinetic performance of a bare silica and C18 phase prepared from the same sub-2μm and 3.5μm base materials were compared in the HILIC and RP mode using both charged and neutral solutes. The HILIC column was characterised using the neutral solute 5-hydroxymethyluridine, the weak base cytosine, and the strong base nortriptyline, the latter having sufficient retention also in the RP mode to allow comparison of performance.

Practical investigation of the factors that affect the selectivity in hydrophilic interaction chromatography.

Retention data for a series of 29 compounds comprising acids, bases and neutrals were obtained on six different hydrophilic interaction (HILIC) columns including bare silica, zwitterionic and those bonded with neutral bonded ligands. The principal aim of the work was to evaluate the effect of various experimental variables such as the nature of the stationary phase, buffer pH, buffer concentration, organic solvent and its concentration, and temperature, in order to determine which factors gave the most effect on the selectivity of the separation. The influence of solute properties on the separation, such as logD values, was also considered.