Contributions to reversed-phase column selectivity: III. Column hydrogen-bond basicity.

Area of Science:

• Analytical Chemistry
• Chromatography

Background:

• Reversed-phase chromatography (RPC) selectivity is governed by five interactions: hydrophobic, steric, and three types of hydrogen bonding.
• Hydrogen bonding between donor solutes (acids) and stationary-phase acceptor groups is poorly understood.

Purpose of the Study:

• To elucidate the mechanisms of hydrogen bonding between carboxylic acids and stationary-phase acceptor groups in RPC.
• To resolve uncertainties regarding column basicity in RPC.

Main Methods:

• Investigated three distinct stationary-phase sites (column basicity I, II, and III) influencing carboxylic acid retention.
• Analyzed interactions involving vicinal silanols, metal contamination, and embedded polar groups (EPG).

Main Results:

• Column basicity I, involving vicinal silanols, universally affects carboxylic acid retention in RPC columns.
• Column basicity II, linked to metal contamination, also impacts carboxylic acid retention in some type-A columns.
• Column basicity III, specific to EPG columns, involves the polar group acting as a proton acceptor for acidic solutes.

Conclusions:

• The study identifies and characterizes three distinct column basicity sites in RPC, crucial for understanding and predicting carboxylic acid retention.
• This work provides a clearer mechanistic understanding of hydrogen bonding in RPC, aiding in method optimization and column selection.