Complexation of buffer constituents with neutral complexation agents: part I. Impact on common buffer properties

Area of Science:

• Analytical Chemistry
• Physical Chemistry

Background:

• Buffer properties like pH, ionic strength, and conductivity are critical for separation techniques such as capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC).
• Complexation between buffer constituents and complexing agents can significantly alter these crucial buffer properties, affecting separation outcomes.

Purpose of the Study:

• To theoretically and experimentally investigate the impact of complexation between buffer constituents and neutral complexing agents on buffer properties.
• To demonstrate how cyclodextrins, as model complexing agents, influence the pH and complexation characteristics of various buffer systems.

Main Methods:

• Theoretical modeling of buffer systems.
• Experimental analysis using model buffer systems (benzoic acid/LiOH, CHES/LiOH, TAPS/LiOH, Tricine/LiOH, MOPS/LiOH, MES/LiOH, acetic acid/LiOH) with cyclodextrins as complexing agents.
• Nuclear Magnetic Resonance (NMR) spectroscopy and affinity capillary electrophoresis (ACE) to determine complexation constants.

Main Results:

• Demonstrated substantial changes in pH due to complexation.
• Showed that charged forms of zwitterionic buffer constituents complex more strongly with cyclodextrins than neutral forms, confirmed by NMR.
• Determined complexation constants for both forms of selected compounds using NMR and ACE, showing good agreement.
• Used obtained data for theoretical descriptions of pH variations based on buffer composition and concentration.

Conclusions:

• Complexation significantly influences buffer properties, necessitating careful consideration in analytical method development.
• Theoretical predictions are valuable for understanding complexing systems and deriving general rules for buffer behavior.
• The study provides a framework for predicting and controlling buffer properties in complexation scenarios relevant to separation science.