Selectivity in reversed-phase separations: general influence of solvent type and mobile phase pH

Area of Science:

• Analytical Chemistry
• Chromatography

Background:

• Optimizing chromatographic separations is critical for analyzing complex mixtures.
• Understanding mobile phase influences on retention and selectivity is key for effective method development.

Purpose of the Study:

• To investigate the impact of mobile phase pH and organic solvent composition on chromatographic retention and selectivity.
• To evaluate these effects across a diverse set of 15 stationary phases for over 70 compounds.
• To identify which mobile phase parameters, particularly pH, exert the most significant influence on separation selectivity.

Main Methods:

• Systematic variation of mobile phase pH (3, 7, 10) and organic modifiers (methanol, acetonitrile, tetrahydrofuran).
• Testing across 15 distinct stationary phases with a diverse analyte set (>70 compounds).
• Analysis of retention patterns and calculation of selectivity difference values to quantify variable impact.

Main Results:

• Mobile phase pH and organic solvent choice significantly alter compound retention and selectivity.
• Selectivity differences are highly dependent on the stationary phase and analyte properties.
• Changes in mobile phase pH were found to induce the largest selectivity differences, highlighting its critical role.

Conclusions:

• Mobile phase pH is the most influential variable for achieving significant selectivity changes in chromatography.
• Understanding analyte-specific responses to mobile phase composition is essential for robust method development.
• The findings provide practical guidance for optimizing chromatographic separations by controlling pH and solvent selection.